Review of energy efficient features in vernacular architecture for improving indoor thermal comfort conditions

Renewable and Sustainable Energy Reviews 65 (2016) 459–477

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Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser

Review of energy efficient features in vernacular architecture for improving indoor thermal comfort conditions S.S. Chandel a,n, Vandna Sharma b, Bhanu M. Marwah b a b

Centre for Energy and Environmental Engineering, National Institute of Technology Hamirpur, 177005, Himachal Pradesh, India Department of Architecture, National Institute of Technology, Hamirpur 177005, Himachal Pradesh, India

art ic l e i nf o

a b s t r a c t

Article history: Received 24 August 2015 Received in revised form 25 May 2016 Accepted 8 July 2016

In this study a comprehensive review of vernacular architecture research status is presented. The objective of the study is to identify energy efficient vernacular architecture features affecting indoor thermal comfort conditions for adaptation in modern architecture to suit present day lifestyles. The main features identified are: built mass design, orientation with respect to sun, space planning, openings, sunspace provision, construction techniques, and building and roof materials. Earth with its low compressive strength and durability is found to be prominently used vernacular building material due to its thermal insulation property. The current status and codal provisions regulating use of earth as a building material in different countries namely Australia, New Zealand, South Africa, France, New Mexico, Colombia, Spain and India, are reviewed so as to assess its suitability in modern context. Vernacular architecture features in different climatic zones of India including north-western Himalayan state of Himachal Pradesh are also studied along with a case study in composite climate of Hamirpur region, which identifies the relation of vernacular architectural features with thermal comfort conditions. The study identifies an emerging architectural style for this Himalayan region incorporating thermal comfort, energy efficient features, passive solar features, current design and construction techniques. Studies to develop this architecture style, improvement in the strength and durability of earth as building material and thermal comfort studies of vernacular houses are identified as follow up research areas. The study is of relevance for utilizing vernacular materials and architectural features for improving thermal comfort in modern buildings worldwide. & 2016 Elsevier Ltd. All rights reserved.

Keywords: Climate responsive features Energy efficient features India North-Western Himalayas Thermal comfort Vernacular architecture

Contents 1. 2.

3.

4.

5.

n

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Factors affecting vernacular architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Impact of climate and geographical conditions of region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Socio-economic and cultural factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Relation of energy efficiency with vernacular architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Shape and energy efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Materials and embodied energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Relation of thermal comfort with vernacular architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4. Thermal comfort and passive environmental control features in vernacular architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5. Climate specific energy efficient features in vernacular architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Use of earth as building material and codal provisions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Present status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Earth as an energy efficient vernacular material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Overview of codes and legal regulations for the use of earth as building material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4. Adaptation of vernacular architecture for improving energy efficiency in modern context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vernacular architecture of Indian state of Himachal Pradesh – a case study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Corresponding author. E-mail addresses: [email protected], [email protected] (S.S. Chandel).

http://dx.doi.org/10.1016/j.rser.2016.07.038 1364-0321/& 2016 Elsevier Ltd. All rights reserved.

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5.1. 5.2. 5.3.

Climatic zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468 Vernacular house design features in different climatic zones of the state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469 Case study of vernacular architecture in Climatic Zone1 of Himachal Pradesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470 5.3.1. Methodology followed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 5.3.2. Survey results of vernacular houses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 5.3.3. Energy efficient features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 6. Results and discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472 6.1. Analysis of survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472 6.2. Identification of factors influencing vernacular architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 6.3. New architectural style for the western Himalayan region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 6.3.1. Planning features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 6.3.2. Design features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 6.3.3. Materials and construction features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 Appendix I. Sample questionnaire for socio-economic survey carried out for sample vernacular houses in district Hamirpur, Himachal Pradesh 474 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476

1. Introduction Vernacular architecture is evolved from centuries of experience of people living under different climatic conditions worldwide [1,2]. It involves design and construction techniques using locally available resources based on the environmental, cultural and historical background of people [3]. This architectural style takes care of climatic and energy conserving features providing enhanced thermal comfort. In modern context vernacular architecture can provide solutions for a number of problems like degradation of environment quality, indiscriminate depletion of resources, green house gas emissions, high energy usage, deforestation etc. However, presently this architectural style is on the verge of extinction as it has been abandoned by people to follow the so called modern conventional architectural style [4]. The importance of energy efficient features in vernacular architecture has been highlighted by a number of authors. Liu et al. [5] and Chandel et al. [6–9] suggested that it is important to adopt indigenous design and construction styles or to opt for more flexible modern construction systems which incorporate features of traditional architecture and passive solar techniques. The adaption of these features can lead to better amalgamation of vernacular techniques in modern houses to improve energy efficiency, cost effectiveness and sustainability as shown by Chandel and Sarkar [10] and Foruzanmehr and Vellinga [11]. Priya et al. [12] suggested that by spatial organization, design/planning techniques, construction materials, inclusion of passive solar design features, comfortable indoor environment can be achieved in modern houses. Agugilaro et al. [13] discussed the bio-climatic features of traditional architecture worldwide. Different bio-climatic zones have different types of design, planning and spatial organization of dwellings. Use of these climate responsive design strategies, their incorporation in modern buildings by construction industry would promote the bio-climatic architecture in urban planning. The study also points out that the inclusion of bio-climatic guidelines would result in indoor comfortable environment and save energy consumed in buildings for heating and cooling. Dili et al. [14] studied passive features of vernacular architecture of Kerala and showed that prevalence of modular building concept, internal open courtyards as per ancient geometrical grids, proportions and scale, verandah, orientation of building, spatial organization of internal spaces, use of local materials and special methods of construction will lead to creation of comfortable indoor environment in houses without input of external energy equipments. The study showed that these passive bio-climatic features resulted in maintaining of higher indoor air temperatures

in winters and lower indoor air temperatures thereby creating comfortable indoors. Moreover, the features also maintain a continuous gentle flow of wind inside the building which resulted in a balanced level of temperature and humidity inside the building irrespective of outside conditions. Thus planning /design and material usage features of vernacular houses can be advantageously applied in modern houses. The main objective of the study is to identify energy efficient features in vernacular architecture affecting indoor thermal comfort conditions for adaptation in modern architecture to suit present day lifestyles. In this context a detailed literature review of relevant research studies carried out during the period 1975–2015, is presented with focus on thermal comfort and energy performance. The factors affecting vernacular architecture and their relation with climate, energy efficiency for built mass in terms of shape, materials, embodied energy, thermal comfort and passive heating or cooling techniques are identified. The current status of earth construction and codal provisions regulating use of earth and adaptations are discussed briefly in the study. The associated problems like low compressive strength and durability in the use of earth are also studied. Along with the review of worldwide study, the traditional architecture features in different climatic zones of north-western Himalayan Indian state of Himachal Pradesh are also studied followed by a specific case study of Hamirpur region, which identifies relation between vernacular architecture and thermal comfort conditions. The vernacular architecture features in design, construction and planning aspects which affect indoor thermal comfort in houses are identified. Consequently a new type of architecture called “Modern Himalayan Architecture Style” has been proposed for building construction for this region of India. Energy efficient features of this architectural style can be advantageously added for improving indoor thermal comfort in residences and commercial buildings alike. The paper is organized as follows: Section 2 gives parameters affecting vernacular architecture, Section 3identiies relation of energy efficiency with vernacular architecture focusing on shape, design, materials, embodied energy, thermal comfort and passive cooling features, Section 4 discusses current status of use of earth as building material, codal provisions and adaptations of vernacular architecture for improving energy efficiency in modern context in terms of improving traditional materials and designs, Section 5 presents case study of traditional architecture of an Indian state of Himachal Pradesh; Section 6 presents results and discussion followed by conclusion in Section 7.

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2. Factors affecting vernacular architecture

2.2. Socio-economic and cultural factors

The socio-economic, cultural and climatic conditions of different geographical locations govern the design, planning and material usage in vernacular architecture. Architectural features of different climatic zones like building form, orientation, envelope design, activity areas, shading, openings, and use of natural ventilation are important to be considered. These parameters are responsible for difference in energy performance of various vernacular styles worldwide and are discussed in this section.

The architecture of a region is also affected by socio-economic, cultural, and human factors. Hanita et al. [18] showed that these factors can dictate and surpass the advantages of vernacular systems and disadvantages of conventional systems. A comparative analysis of both these systems showed that human factor plays an important role in deciding the design, construction and architectural features of built mass. This is also reflected in the energy performance of the buildings. The study suggested improvements in contemporary house designs using vernacular architectural features in Oman. Surveys were conducted for selected architectural elements, spatial patterns representative of socio-cultural and climate aspects of Oman and the indoor environmental conditions. The research tried to amalgamate most appropriate features of both the styles. The study suggests that human factors along with climatic factors needs to be considered while designing houses in modern context and planning. The three main characteristics of vernacular architecture identified are: construction, design and planning. Each characteristic is developed as per climate, topography, and material availability, socio- cultural and economic factors. The construction aspects include features like massive or lightweight construction, type of structural and finishing walls, floor and roofing in building and type of structural system. The construction features of buildings are developed and affected by the climate, topography and availability of materials in the region. Similarly design characteristics are identified as positioning of internal spaces like rooms, corridors, other internal spaces, building shape, size and height of rooms, provision of central open spaces as courtyards, front activity spaces as verandahs, provision of openings in the form of doors and windows, sunspaces and external and internal aesthetics of building. These all are affected by the age group of occupants and family size, their requirements, socio-cultural factors like occasions, festivals, traditional values and economic factors i.e. economic ability to spend on façade decoration or internal aesthetical treatments. The planning features include layout of building which can be compact in case of cold climate and loose in case of warm-humid climate for decreased or increased natural cross-ventilation respectively. The presence or absence of shading devices over openings or at the entrance as roof overhangs over verandahs or courtyards for protection against harsh wind, sun or rain are also governed by climate of the area followed by sociocultural factors. The factors affecting characteristics and features of vernacular architecture are shown in Table 1.

2.1. Impact of climate and geographical conditions of region Various geographical regions have different climates which forms the basis for the use of particular type of construction material and housing designs. In a study on the traditional architecture of north-east India, Singh et al. [15] in a study carried out a survey of 42 old vernacular houses representative of different bio-climatic zones of North-East India and identified passive solar features in these houses which include layout strategies of house, spatial planning and designing of different spaces in accordance with sun and wind direction and usage of local materials like wood, cane, bamboo, stone, mud, jute, lime. It was found that people modified the houses to reduce the need for external energy inputs to fit in changing lifestyle patterns. This resulted in practical, cost-effective and energy efficient solutions which are more or less ignored in the modern architecture. This new form of regional architecture called “Assam type” has evolved over time based on amalgamation of climate, vernacular architecture and present lifestyle needs.. Author suggested that inclusion of bio-climatic features of vernacular houses should be considered i modern houses for better indoor thermal environments at minimal energy inputs. Canas et al. [16] in a study of Spanish vernacular houses showed that climate plays a significant role in the development of spatial and design features of houses. The case study of 212 vernacular houses in five different climatic zones of Spain led to the identification of bio-climatic strategies for different zones: for oceanic climatic zone, optimum use of solar radiation coupled with rain protection strategy; for continental climatic zone protection against winter low temperature and summer solar radiation by designing building with high thermal mass; for mountainous region, use of compact form of built mass and shutters for avoiding ingress of cold winds through openings, for Mediterranean climatic zone; protection against solar radiation and water conservation. These features can be followed in modern construction to avail their benefits. Nguyen et al. [17] studied the climate responsive design principles inherent in vernacular architecture of Vietnam which showed the design features, spatial organization and building physics of vernacular houses are very well adapted to prevailing climate resulting in maintenance of indoor thermal comfort naturally. Six traditional and vernacular houses from three different climatic regions were studied in terms of material use, orientation, spatial organization, construction techniques in relation with indoor environment. In total 17 bio-climatic strategies used in these dwellings were identified as: building orientation and shape, solar shading, natural ventilation, cross ventilation, stack ventilation and single-side ventilation, natural lighting techniques, light weight construction, high thermal mass, evaporative cooling, earth cooling, passive cooling by using color, thermal insulation of materials, passive solar energy use, storm prevention, flood prevention, rainwater discharge, moisture and condensation prevention. Analysis of these strategies using “description and image” approach showed that natural ventilation followed by building orientation; building shape and solar shading were most effective strategies to maintain indoor thermal comfort passively in climatic conditions of Vietnam.

3. Relation of energy efficiency with vernacular architecture Studies showed that in Indian residences nearly 48% of energy consumed is used only for maintaining indoor thermal comfort [19]. Saving the energy spent in maintaining comfortable indoor environment has gained momentum globally over the past years [20]. The study suggested that building temperature ranges should be based on real time empirical feedback of the respective occupant's requirements. This also forms the basis to study the relation of thermal comfort, energy efficiency and passive environmental control methods inherent in traditional vernacular architecture as discussed by Edward and Kurian [21] and Dili et al. [22,23]. 3.1. Shape and energy efficiency The shape of built mass, orientation and overall form governs the amount of energy consumed as such the decision for architectural style needs to be based on these factors. A study by Bostancioglu et al. [24] showed the relation between construction

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Table 1 Factors affecting aspects and features of vernacular architecture. S. No.

Characteristics of vernacular architecture

Features of characteristics

Factors affecting characteristics

1

Construction

Massive construction Lightweight construction

Climate, topography

Material type (structural and finish): walls, floor, roof Type of structural system: walls, floor, and roof

Climate, topography, availability of materials

Room structure: number and size Building shape Building storey Courtyard planning Windows

Demographic profile, Socio-cultural factors Socio-economic factors Climate, socio-cultural factors Climate

Grills Sun Spaces Earth air tunnels Aesthetics

Climate, socio-cultural factors

2

3

Design

Planning

Social, cultural and economic factors

Layout-compact or loose Shading devices- presence /absence

costs, heating energy costs, proper shaping and orientation of buildings of the same area for different shapes: square, rectangular, star, T-shape, H-shape. Different envelope alternatives with thermal insulation options and appropriate building materials for walls, floors and roofs were analyzed and determined. With the aim to reduce cost of residential buildings, decreasing operational costs and construction costs; correlation was derived between construction costs, heating energy costs, proper shape and orientation of the building. Investigation included calculation of construction costs and annual heating costs for different shapes using heat energy demand over variable periods, annual fuel demand for alternatives, and consumption of natural gas and surface solar gain of buildings. Assessment of life cycle costs was done using ratio of cost increase per each time slice within the period and interest rates which gave most appropriate shapes as square and rectangle than T, H-shapes with reduced construction costs, annual heating costs and life cycle costs. 3.2. Materials and embodied energy Modern materials consume energy in the form of embodied and operational energy in transportation, construction and maintenance. However, vernacular materials have low embodied energy and consume very less energy during usage as compared to conventional modern materials. Shukla et al. [25] studied the construction of a demonstration house using low energy materials like cow dung, soil and sand. The house was checked for the embodied energy related to construction of main structure, foundation, flooring, finishes, furniture, maintenance and electric work. It was found that the vernacular house not only saved a lot of energy but also led to reduced amount of CO2 (carbon dioxide) released into atmosphere per year as compared to conventional house. Praseeda et al. [26] studied the comparative energy consumption aspects in terms of embodied and operational energy for vernacular and modern materials. The investigation showed that change from vernacular to modern in wall materials leads to increase in embodied energy. The operational energy is found to significantly influence by climatic factors of the area. Extreme harsh climatic conditions influence the use of more operational energy for maintaining indoor thermal comfort. While vernacular buildings have inbuilt passive environmental control strategies; modern building materials lags behind on this aspect. Assessment of operational energy consumed in dwellings was done with the use of rubble stone masonry, burnt clay brick masonry and stabilized soil blocks as wall materials in two different climatic regions. The results showed that operational energy does not show significant

Climate, socio-cultural factors

variation for traditional houses in warm-humid and moderate climatic zones with different wall materials. However, significant variation is seen in operational energy for hot-dry climatic conditions for different walling materials used. This indicates that replacement of rubble stone masonry by burnt clay brick masonry and stabilized soil block masonry increases the embodied energy of houses significantly. Replacement of vernacular building materials by modern materials like cement, burnt clay bricks therefore not only have an adverse effect on indoor thermal comfort environment but also increase overall energy consumption of the house for maintaining indoor thermal comfort. The traditional building materials are very effective in maintaining indoor thermal comfort environment thereby reducing the external energy consumption [12]. Coupled with solar passive techniques vernacular materials are sustainable resources and provide comfortable interiors in a passive way. The study was carried out in coastal belts of Nagapatinam and discusses the features like courtyards with wind catchers, thick external walls, verandas, sloping roof are examples of bioclimatic architecture. Use of local materials like mud, mud-brick and brick with higher thermal resistance is found very effective in maintaining indoor temperatures. Arrangement of buildings in linear pattern separated by narrow shaded streets and orientation of streets in a way ensuring shading of building façade by overhangs, sloping roofs resulting in receiving of minimum building radiation and have reduced peak heat flux into the building. Design features like greater ceiling height, provision of verandas acting as buffer space between outside and interior environment, openings like ventilators and skylight providing cross-ventilation by stack effect along with appropriate use of local materials contribute towards creation of comfortable indoor thermal environment. The study suggests that incorporation of these principles would help in reducing the dependency on artificial means for achieving thermal comfort. Gupta [27] identified that the use of local materials reduces the transportation costs of construction materials and hence reduce greenhouse gas emissions associated with transportation. Use of rammed earth construction leads to considerable savings in energy consumption due to lower values of embodied and operational energy. The study pointed out that rammed earth construction technology is appropriate for future propagation provided mechanical properties of earth like compressive strength, bond strength and flexural strength are improved. The study suggests that locally available earth has good potential for construction purposes after being stabilized. A case study is presented where full scale walls are being constructed with rammed earth, structural performance of these walls in terms of compressive

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strength, flexural strength has been checked and found to be at par with building materials. The study pointed out that rammed earth construction technology is appropriate for future propagation provided mechanical properties of earth like compressive strength, bond strength and flexural strength are improved. The embodied energy in different types of masonry work is studied by Reddy et al. [28]. The comparative analysis of total embodied energy of buildings made using brickwork, soil-cement blocks showed that by using alternative building construction materials nearly 50% of energy can be saved. The study indicated that alternative building technologies like stabilized mud blocks, prefabricated roofing systems, masonry vaults, filler slab roofs, lime -pozzolana cement reduced the total embodied energy of the buildings. Embodied energy has been studied in terms of total energy involved during manufacturing process of building materials, their transportation and assembly at the construction site. The study showed that modern building construction materials like aluminum, steel, cement and lime shows very high consumption of energy while lime –pozzolana cement consumes less energy. Therefore when lime-pozzolana cement as an alternative building material replaces cement for construction purposes; lot of energy can be saved. Soil-cement blocks were found to be one of the most energy-efficient alternative materials which can be advantageously used for walling, roofing and flooring. Ramesh et al. [29] analyzed vernacular building materials and alternative technologies for roofing and terracing options in terms of total embodied energy in buildings and identified the use of blast furnace slag cement, fly ash cement, fiber reinforced composite cement as alternative to cement. The concrete, sisal based composite panels can be used for wall partitions and organic materials can be used as alternative to wood composites and tiles. The use of vernacular materials like mud phuska, mud layer and alternative materials like lime mortar terracing, flat terracing, lime concrete, pressed clay, cavity lime concrete reduce the total energy consumption of building thereby leading to energy savings. 3.3. Relation of thermal comfort with vernacular architecture Vernacular architecture has evolved with the need to create thermal comfort conditions. The thermal comfort performance of a vernacular house is found to be better than modern houses. Thermal comfort is dependent on a combination of four elements: indoor temperature, outdoor temperature, and relative humidity and clothing pattern of the people of the region as shown by Singh et al. [30–32]. The study discusses the thermal performance of vernacular architecture in North East regions of India using thermal comfort models developed by Nicol [33], Humphreys [34] and Auliciems [35]. A correlation is found between human thermal sensation, adaptations (combined effect of physiological, psychological, environmental and behavioral adaptations) and the local climate of the region. This study includes field measurements of indoor and outdoor temperatures of selected houses and survey based on questionnaire developed as per ASHRAE-55–2004. ASHRAE-55–2004 focuses on combined effect of indoor thermal environmental factors like temperature, thermal radiation, humidity and air speed and personal factors like human activity and clothing, which affect thermal environmental acceptance of people. The revised standard (ANSI/ASHRAE Standard 55–2010) includes addition of PMV/PPD (PMV: Predicted Mean Vote, PPD: Predicted Percentage of Dissatisfied) calculation methods and the concept of adaptation. It is frequently used for evaluating existing indoor thermal environment of the buildings. Singh et al. [30–32] determined the comfort temperatures from mean monthly temperatures. Other design parameters like external wall thickness, construction material, inter-room partition wall thickness, false ceiling height, doors and windows

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dimensions influencing indoor thermal comfort were measured. These parameters were compared for different climatic zones of the region. The neutral temperature and comfort temperatures were evaluated by using ASHRAE 7 point sensation scale and it was found that comfort temperatures are always associated with adaptations using Humphreys and Auliciens adaptive comfort models. Humphreys and Auliciems [33–35] reported that building occupants feel comfortable with respect to mean temperatures of the environments in which they were living by adapting themselves to their respective indoor climates. The concept of adaption states that in case of a change leading to discomfort of people, people act in a way that would restore back their comfort. This adaptation is in combined form of physiological adaptation (acclimatization) and behavioral adaptation (personal and environmental). In this homeostatic system proposed by them, thermal comfort is a “controlled variable”. Du et al. [36] studied building microclimate parameters like relative humidity, distribution of air temperature, solar radiation and wind characteristics which are closely related to summer thermal comfort to understand energy efficiency and role of vernacular elements in bioclimatic designs for achieving energy efficiency. The study was focused on relation of building microclimate and thermal comfort for a typical vernacular house situated in Chongqing in the hot and humid climate area of China. The study was performed through field measurements, dynamic thermal and CFD (Computational Fluid Dynamics) simulation model. Simulation model was developed for the microclimate of the building and was validated through actual field measurements. The study investigated thermal comfort conditions in a Chinese traditional vernacular house for summer season. Investigation showed that when in daytime operative temperature was higher than comfortable temperature for nearly one-third of summer season; wind velocity in semi-outdoor and outdoor spaces improved the thermal comfort. This study showed the effectiveness of vernacular design-planning elements like courtyards, placing of living and other important rooms around the courtyard, patios in front and rear etc. which maintain building microclimate and create thermally comfortable interiors both at day and night time in summers. Therefore proper orientation of aspects both outdoor and indoor, appropriate building form in terms of aesthetics, function and landscape all contribute towards building good microclimate which affects the thermal comfort condition inside the buildings. Singh et al. [37] studied thermo-physical features of a building along with socio- economic and cultural features which govern the thermal comfort pattern in the region. This further elaborates the adaptations involved by people in the built masses for their comfort. Indraganti et al. [38] and Yao et al. [39] have shown that a general thermal comfort model cannot be developed for all the climatic zones. Due to difference in climatic conditions and most importantly in socio-economic and cultural parameters of the area, different thermal comfort models are required to define comfortable temperatures of the area specific. These comfort models should be developed on the basis of indoor and outdoor temperature, relative humidity, and clothing pattern of people of the particular region. Indraganti et al. [38] aimed that investigation of thermal comfort aspects in residential buildings through survey of over 100 subjects in months of summer and monsoon. The investigation found a thermal comfort band of 26–32.5 °C with neutral temperature of 29.23 °C. The study emphasized that the use of design-planning application and adaptive controls play a significant role in thermal comfort of occupants and needs to be considered before construction of buildings. The study conducted by Yao et al. [39] emphasized on the use of “black box” theory to propose a theoretical adaptive model of thermal comfort and

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factors like culture, climate, social, psychological and behavioral adaptations which ultimately affect the thermal comfort of occupants. The study developed an adaptive predicted mean vote model and relation between adaptive predicted mean vote (aPMV) and the predicted mean vote (PMV) in free-running buildings. The model also explains the cause of result differences between field surveys and lab based studies. The adaptive predicted mean vote method takes into consideration of local climate, culture, social background and behavior habits and lifestyles and therefore differs for different geographical locations. Heidari et al. [40] found range of thermal comfort zone for Ilam, a city located in western Iran using thermal sensation scales and regression analysis. The study comprised of two thermal comfort field studies conducted in the form of short term surveys and long term surveys respectively. The field studies were conducted during climatically extreme periods of hot summer and cold winter in 1998 for naturally ventilated buildings. The study showed a good relationship between neutral temperature versus room temperatures and between indoor comfort and outdoor conditions. The study showed variability of acceptable conditions and revealed that people adapt themselves to comfort at high indoor air temperatures. Comparison of thermal performance of traditional architecture with conventional architecture in terms of materials and techniques yields important results regarding environmental behavior of vernacular style as studied by Algifri et al. [41]. The study gauged the thermal performance of traditional adobe houses and conventional houses of Yemen through transient heat transfer analysis. The quantitative results proved the thermal appropriateness of vernacular material (adobe) over the conventional concrete in terms of reduced energy costs. A number of thermal comfort studies of vernacular houses have been carried out by various authors. These studies are based on different thermal comfort models which are summarized in Table 2. Different studies have used different models [15–45] most appropriate in terms contextual variables with respect to respective geographical location. The analysis of vernacular architecture studies using adaptive thermal comfort model and ASHRAE Standard 55/ISO 7730, led to the identification of Adaptive thermal comfort model to be used in follow up research for thermal comfort study of vernacular houses in Hamirpur region of Himachal Pradesh with factors affecting it as climate context, human variables (in terms of building type, culture, socio-economic aspects), period of study (time). 3.4. Thermal comfort and passive environmental control features in vernacular architecture Passive environmental control techniques inherent in vernacular architecture have proven to be very effective in providing

comfortable indoor environment and savings on energy consumption of buildings [46–52]. Vernacular architectural designs which affect the energy consumption pattern of households [45] are quite effective for natural ventilation and cooling [53]. The traditional buildings in hot regions in countries like Iran incorporate a number of cooling features leading to thermal comfort conditions. Vernacular buildings in Iran show enhanced indoor thermal comfort and were found more energy efficient than modern conventional buildings. Foruzanmehr and Fergus [45] following a systematic scientific approach identified the extent of applicability of vernacular passive cooling systems in modern dwellings to lower energy consumption. A comparative analysis of vernacular and conventional households showed lower energy consumption pattern in vernacular houses as compared to modern houses in Iran. The study involved identification of the extent to which natural passive cooling systems are useable and their application would reduce air-conditioning in modern housing based on three aspects:

 Physical and cultural aspects: social order, forms, shape, space, style, type, and identification of prevalent architectural patterns,

 Thermal comfort aspects using various thermal comfort models relevant to the study

 Energy performance aspects: Energy audit, developing computer-simulated models Study by Shan et al. [54] shows that adoption of passive environmental control methods in northern rural China not only led to energy savings but also create comfortable indoor conditions without any input of external energy equipments or fuel requirements to heat the interiors. Passive energy saving retrofit measures adopted were addition of sunspaces outside, south window combined with overhanging cornice, utilization of passive solar energy, replacement of north window by double layered window for reducing heat loss in winters, use of local waste materials polystyrene granules in the form of insulation layer to the north and west wall surfaces, use of rock wool and expanded pearlite into regular blocks for interior of wall and roof insulation. In order to solve problem of low indoor temperature in houses in winter due to poor thermal insulation of building envelopes, concept of 'Zero coal village' coupled with practical demonstration was proposed. Study by Toe et al. [55] showed potential and effectiveness of vernacular passive cooling techniques in improving thermal comfort conditions in the modern brick terraced houses in Malaysia. The passive cooling techniques like night ventilation, roof insulation, window and wall shading devices, presence of courtyards were also found to be effective in maintaining indoor comfort temperature and humidity levels. The cross-ventilation is found to be effective in lowering indoor room temperatures. In traditional Chinese houses,

Table 2 Thermal comfort model based studies of naturally ventilated vernacular houses/buildings showing better indoor thermal comfort temperature. Model used

Study reference Country

Adaptive thermal comfort approach[19,20]

[36] [31,32]

[38] [22] [43] [55] [39] [12]

Context

Outdoor temperature (°C)

China

Vernacular houses

24.3–42

North -East India

Vernacular house in Tezpur, Imphal, Cherrapunjee regions

10–35 (Tezpur) 10–35 (Imphal) 5–25 (Cherrapunji) Hyderabad, India Naturally ventilated apartment houses 21–34 Tamil Nadu-India Vernacular buildings in coastal regions of 22–34 Nagapattinam China Vernacular dwellings 10.4–34 Malaysia Vernacular dwellings 24–36 Chongqing, (China) Naturally ventilated lecture building 4.8–39.2 Tamil Naidu Vernacular dwellings 24–42

Indoor temperature (°C)

28–31 26–26.3 24.2–28.9 22.2–24.2 28–32 28–32 8.3–27 26–29 8.8–38.10 24–32

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small courtyards were found to be quite effective to cool indoors through nocturnal ventilation and cooling. Microclimate modification and urban heat island mitigation were also identified as part of potential passive cooling techniques. Study of vernacular architecture in Tamil Naidu showed that natural and passive bio-climatic concepts were used to create comfortable indoor conditions [12]. The designing techniques like linear planning of houses, formation of dormant axis, connecting front entrance door to courtyards, corridors and ends in rear door, consideration of sun path and wind direction for orientation of rooms for day lighting and natural ventilation, wind catchers located at the top of the courtyards for ventilation, use of local materials like mud, lime mortar, brick, thatch roofing, country tiles, bamboo and timber for construction, high thermal mass of walls, provision of courtyards play a vital role in maintaining comfortable indoor temperature and humidity levels comparative with harsh outdoor microclimate. A study by Dili et al. [56,57] in warm-humid climate of Kerala in India showed that by properly arranging building blocks around central open courtyard built according to geometrical principles, provision of 10° roof slope towards north and south side for easy drainage of rainwater, more height of rooms than modern houses, shading of windows as protection against excessive sun, wind and rain are quite effective in controlling indoor temperature and humidity levels in rooms to a desirable extent. The indoor temperature of the rooms near courtyard was found to be 3° 8 °C lower than outdoor temperature whereas indoor humidity levels were found to range between 50–80% as against 32–95% outdoor humidity. The maximum indoor temperature in modern houses was found to be 2.5 °C higher than traditional houses. The study identified natural ventilation and building envelope as important parameters for regulating air temperature, relative humidity, air speed, controlling solar radiation and providing comfortable indoor environment without external energy equipments. The design features like dooryard, double-pitched roof and eaves which have large implications on temperature and wind velocity in internal spaces in vernacular dwellings in China were identified by Borong et al. [58].The sun-shade and insulation features were found to be of great importance. The effect of natural ventilation on quality of indoor environment and night ventilation in the form of thermal pressure natural ventilation were found to be more effective than daytime ventilation. The use of 300 mm thick mud brick wall pasted with white plasma, provision of overhead wooden floor in bedrooms for damp-proofing and dehumidification, roof designed as double-pitched raft, more ceiling height than modern house, compact layout, presence of vegetable garden, traditional door yard meant for providing shade from solar radiations, landscaping of dooryard help to lower indoor temperatures by 10 °C than ambient temperature. The study showed that design strategies like sun shading and insulation of building envelope through use of various materials and construction techniques can lead to create thermally comfortable interiors in modern houses as well followed by enhancement of night time ventilation in houses. Foruzanmehr and Vellinga [11] showed that vernacular buildings in Iran are more energy efficient with enhanced indoor thermal comfort than modern conventional buildings. Authors conducted thermal comfort survey in Yazd city of Iran characterized by hot summers in order to find out the comfort temperature zone in vernacular dwellings. The study identified the passive cooling features and systems prevalent in Iranian vernacular architecture. The representative dwellings were selected based on criteria of location, age, material condition, accessibility and existence of intact vernacular passive cooling strategies. The study showed that underground basement rooms in the building are used as summer rooms. The extensive use of wind catchers and

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earth tunnels are the measures adopted to lower extreme summer heat. These vernacular features identified can be incorporated to lower energy consumption in modern houses in Yazd in Iran. Bezemer [53] evaluates the characteristics of vernacular architecture namely features of built masses, shape, form, materials in tropical areas of West Indies, Malaysia and Pacific in assisting modern passive cooling systems for ventilation in domestic buildings and their application in modern context. The investigation involved study of Malay houses and showed that elements like location of building, its shape and form, use of materials all resulted in thermally comfortable interiors. Ventilated roof space helps to cool the houses, large eaves provides effective sun shading over window openings, open interior spaces with minimum of walls and partitions allow good ventilation inside the rooms, placing of house on stilts to catch wind of higher velocity have been identified as some of the effective measures which makes house appropriate to local tropical climate and thereby promoting comfortable interior environments. 3.5. Climate specific energy efficient features in vernacular architecture Zhai and Previtali [59] discussed vernacular architecture characteristics of different climatic zones around the globe and identified 114 vernacular regions. Each vernacular region is characterized by unique vernacular features like envelope construction, roof material, ceiling structure, room structure, building shape, building storey, window, infiltration, relationship to ground, and shading. The study analyzed these features in terms of energy implications to overall building energy consumption using a building energy simulation and optimization tool. The energy performance of vernacular buildings are compared with modern buildings and found that vernacular buildings with earth walls and thatched roof are more energy efficient than buildings which were built following energy conservation codes. The vernacular architecture of Kerala reflects the use of natural and passive thermal comfort methods for warm-humid climate [60]. The study shows that Vaastu shastra (Indian traditional architecture) forms the basis of climate responsive features in the region. Kerala is having heavy rainfall, high relative humidity and moderate temperatures. Owing to predominance of two seasons: rainy and non-rainy seasons, entire design and planning features have evolved accordingly. The presence of open courtyards, steep sloped roofs, provision of gables at the roof end to enhance ventilation, decorative jallis (nets) as ventilators for attic spaces formed by false wooden ceiling, strut comprising walls spaced by slats forming good fenestration design, use of local materials like mud, laterite, granite stone blocks, lime mortar, wood, bamboo, clay-roofing tiles, coconut palm leaves, vegetable juices in lime mortar for wall painting marks the prominent passive vernacular construction technology of Kerala. This bio-climatic passive technology addresses the problems of excessive moisture present in air, heavy rainfall, ingress of direct and intense solar radiation and subsequent high temperatures. Passive strategies like building orientation according to direction of sun and wind, arrangements of courtyards and internal spaces in such a way that would enhance air circulation and natural ventilation in all internal spaces, pitched roof guarding against heavy rains, placing of building blocks on high plinths to avoid dampness, large overhangs guarding against harsh effects of sun, wind and rain, use of insulation materials like laterite for external walls, wood for ceilings show the adaption of vernacular houses to the climate conditions in Kerala. These can be advantageously applied in modern houses to maintain indoor thermal comfort in houses. The vernacular architecture styles in different climatic and geographical locations is shown in Table 3. The difference in

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Table 3 Identified climate specific energy efficient features of vernacular architecture in different climatic zones [59]. Parameter

Climate Hot /warm

Cold

Composite

Construction aspects Lightweight construction

Massive construction

Materials Room structure

Roof- slates, thatch, bark, felt, wood, turf, palm leaves Single room structure with good ventilation

Adobe, cob, rammed earth, wood and earth, earth and stone, stone and wood Single room structure with fire pit

Building shape

East-west axes, circular, rectangular

Building storey Courtyard planning Windows

Single storey Present –average to very prominent Large window openings

South facing, rectangular, L-shaped, U-shaped with aspect ratio 1–1.5 Multi-storey Not in practice No large openings-minimal window area

Massive construction for walls and lightweight for roof Walls- adobe, stone, roof- wood, bamboo and slates, thatch Three-four rooms with /without fire pit with average provision of ventilation Generally South facing, Rectangular Double storied Not in practice Average window openings

Grills

Intricately carved in stone, wood, Translucent screens combined with heavy wooden panels Minimum entrance space as verandah and not facing sun Used for cooling air Large eaves project outside creating shaded area Loosely packed – to allow maximum ventilation and infiltration Very prominent to cut direct sun

Not used

Stone/ wooden carved jallis

Present as solarium or front verandah facing sun maximizing solar gain Not in practice

Present as front verandah

Sun Spaces Earth air tunnels Layout Shading devices Countries

Compact to reduce the effect of harsh sun and cold Very less/ negligible

Rajasthan, Sumatra, West, south India, China, New Mexico, Morocco, parts of North India, Egypt, Japan Indonesia, Nepal

vernacular architecture styles is due to different cultural and socio-economic factors combined with climatic and geographical factors as adopted by inhabitants of the region.

4. Use of earth as building material and codal provisions 4.1. Present status Use of earth as construction material in vernacular architecture is region specific. Rammed earth is most prominent material used in vernacular construction due to its thermal insulation properties, ease of work, low-cost maintenance and most significantly high energy efficiency. Elizabeth and Cassandera [61] have discussed a number of techniques for making strong constructions using earth as building material. Various aspects of such construction systems like eco-efficiency, economic and environmental advantages in comparison to non-renewable resource consumption pattern, waste generation, energy consumption, carbon-dioxide emissions and indoor air quality patterns are studied. In a similar study, Kennedy [62] has described the crude use of straw bale construction, adobe, rammed earth, and straw-clay construction or with a combination of stabilizers like aluminum cans, paper fibers, and earth binding agents. The use of vernacular architectural style in present day context has been shown through a number of case studies like development of sustainable ecovillage in rural South Africa, straw bale construction in Anapra, Mexico, Zopilote, traditional, colonial and ecological buildings in Mexico, plastered straw bale construction in China. The barriers in adopting traditional architecture are identified as follows:

 Social barrier: a person invests in a house to reflect his in

creased social status thus rejects traditional ways of house construction. Institutional barrier: government and financial institutions fail to acknowledge the validity of traditional building alternatives for new construction thereby capital investment is considered as risk or waste of financial resources.

Used for cooling air and winter heating. Partially compact and partially loose with building on ground Average /optimum for Protection against rain, wind Parts of north India,

4.2. Earth as an energy efficient vernacular material Earth construction systems have proven to be very efficient in maintenance of thermal comfort due to thermal insulation properties of earth as shown by Benardos et al. [63].These advantages become more prominent if construction is done under ground in comparison to above the ground construction. The study reports a case study of direct comparative assessment regarding energy consumption of a propped earth sheltered residence (underground) and an above-ground structure of similar characteristics. The earth shelter structure is equipped with state-of-art passive energy features. The study reveals that energy requirements are considerably lesser for sheltered structures than the above-ground structure with no apparent increase in construction cost. The study proposes a new type of design and building style in earth construction involving features of green engineering design. In another study, Gupta [27] highlights the advantages of using earth as local construction material over modern construction materials in terms of reduced greenhouse gas emissions associated with transportation of these materials, better thermal insulation properties over modern construction materials. However, mechanical properties of earth like compressive strength, bond strength, and flexural strength are not being studied in detail. The study provides a detailed account of the tests of earth regarding compressive strength, pull-out strength of different rebar diameters and out of plane bending on walls. Quiteria et al. [64] pointed out that although earth is an excellent thermal comfort performing material yet its mechanical properties like compressive strength and durability are not at par with those of modern materials like cement concrete. The study discusses soil based construction systems in walls with reference to the traditional bracing system that provide strength and durability to wall. The authors analyzed design of braced construction system with application of appropriate loads and showed that durability factor is improved by introduction of bracing pattern in traditional construction systems. The study also analyzed critically the collapse of earth constructions without bracings and with bracings. Use of non-linear static method revealed that bracing

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concept in traditional houses act as reinforcement and protects the walls, roof etc. from collapse thus providing stability and strength to the structure. Although use of alternative low-cost sustainable technologies for affordable housing on mass scale have been propagated worldwide yet, there are no serious attempts to incorporate the energy efficient features and use of traditional materials in modern construction practices which would lead to thermal comfort in modern architecture. 4.3. Overview of codes and legal regulations for the use of earth as building material Earth has been recognized as a standard building material and many countries have framed codes and regulations. These regulations describe its use in proper manner for construction, design and energy efficiency improvements as stated by Torgal and Jalali [65]. Germany passed certain technical recommendations as Earth building codes in 1998 which were revised in 2008 [66,67]. In Australia in 2002, Australian Earth building Handbook was prepared highlighting usage of earth construction [68]. New Mexico framed regulations for rammed earth and adobe based construction [69,70]. Regulation on earth construction in New Zealand were framed in three parts namely NZS4297:1998, NZS4298:1998 7& NZS4299: 1998 [71]. These regulations address the construction for building height up to 3.3 m and above without and with provisions of NZS 4297:1998. In 2001, Zimbabwe formulated regulations for earth construction as “code of practice for rammed earth structures” [72]. These regulations are addressed in six basic sections: materials, formwork, foundations, wall design according to compressive strength and water absorption, masonry structural stability and details and finishes. In India, various codes regulate the use of earth in various forms for different purposes [73] Table 4 shows guidelines and codal provisions of different countries regarding usage of earth for building construction purposes.

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Agenda 21 in “The 1992 Rio Earth Summit” [74] highlighted the importance of vernacular architecture in achieving energy efficiency and sustainability. It stressed on the use of indigenous building sources, regulation of energy-efficient design principles, use of labor-intensive techniques in place of energy-intensive construction techniques, incentives to promote the traditional techniques and self-help strategies, improving construction materials along with techniques. 4.4. Adaptation of vernacular architecture for improving energy efficiency in modern context Improvements in materials and construction techniques help to save a lot of energy and curb the need of HVAC systems in residences. Liu et al. [75] created new prototypes of earth houses that would improve the living conditions by having energy efficient features of traditional earth houses, are low cost, conserve natural environment of upper reaches of Yangtze River in China, curb reliance on HVAC (Heating Ventilation and Air-conditioning), and avoid degeneration of vernacular architecture. Questionnaire based surveys and field measurements were performed to study traditional houses and new environment conditions. The study involved practical demonstration of improved material (earth) with combination of modified designing and planning techniques in construction of over 40,000 m2 of new earth housing by involving local people. In the north Indian region, low cost passive solar adobe houses designed and built by a crusader of vernacular materials and architecture Didi Contractor [76] by using indigenous materials have come up as a sustainable solution. The technique is based on improving traditional materials and design to fit the modern day requirements also. Most important feature of this technology is that it involves local artisans, thereby addressing problems at grass-root level. The use of appropriate materials and passive solar features can lead to improvement in thermal comfort conditions. Passive solar features incorporated in buildings at construction stage play a major role in improving energy performance as shown by Chandel and

Table 4 Description of country specific guidelines/codes for earth construction [65–73]. S.no Country

Guideline/Code Name

Description of relevant code/guideline

1

United States ASTM International: 2010-Standard Guide for Design of ASTMD 559-57: Standard Test Methods for Wetting and Drying Compacted Soil-Cement Earthen Wall Building Systems Mixtures

2

New Zealand

SNZ: Standards New Zealand

3

New Mexico

4

Spain

5

Colombia

State Regulations “ Rammed Earth And Adobe Based Construction”-1999 AENOR: Spanish Association For Standardization And Certification 2008 ICONTEC, 2004

6

Australia

Australian regulations “Bulletin 5”-1952 by CSIRO Replaced by “Australian Earth Building Handbook” 2002

Earth wall construction

7

South Africa

ARSO: African regional standards: 1996

ARS 670: Compressed earth blocks, standards for terminology ARS 683: Compressed earth block- standards for classification of material identification test and mechanical tests KS 02-1070: Specification for stabilized soil blocks

8

Kenya

KEBS: Kenya bureau of standards

9

Tunisia

INNORPI: Tunisian standards:1996

10

France

AFNOR: 2001

11

India

IS 13,827:1993 IS 17,251,982(reaffirmed 2002)

NZS 4297:1998: Engineering design and earth buildings - establishes performance criteria for mechanical strength, shrinkage, durability, thermal insulation and fire resistance NZS 4298:1998: Materials and workmanship for earth building requirements NZS 4299:1998: Earth buildings not requiring specific design CID: NMAC 1474: New Mexico earthen building materials code: construction industries division:2009 UNE 41,410:2008-12-10: Compressed earth blocs for walls and partitions NTC 5324: Ground blocks cement for walls and divisions Definitions, specifications, test methods, conditions of delivery

INNORPI: NT 2133: Specifications techniques INNORPI: NT 2135: Definition, classification et. Designation AFNOR:XP P13-901: Compressed earth blocks for walls and partitions: definitions-specifications-test methods-delivery acceptance conditions Improving Earthquake Resistance Of Earthen Buildings-guidelines BIS: Specification For Soil Based Blocks Used In General Building Construction NBC Handbook (IS 17,251,982)

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Aggarwal [6]. The building studied is a modern bank office building which retains traditional heritage features and incorporates passive solar features namely orientation, air-lock lobby at the main entrance, provision of two sun spaces on south face, a 36 m2 roof top solar air heating system, solar wall on south face, double-glazed sealed windows, insulation of west wall using wood paneling and covering the exposed roof with thermally insulating resin bonded mineral wool. Monitoring of the building showed that passive solar features greatly enhanced the indoor thermal comfort at reduced energy costs resulting in saving of about 35% of energy in terms of reduced energy losses and lower electricity bills. The study shows that the modern buildings can result in energy savings with enhanced thermal comfort while retaining traditional architecture features and passive solar techniques. A number of buildings have been constructed in the state under a Solar House Action Plan for Himachal Pradesh which was coordinated by one of authors (SS Chandel). The objective of this plan is to incorporate passive solar features in houses for improving the comfortable living conditions while retaining the traditional hill architecture features [8,9]. Incorporation of passive solar features in modern houses for maximizing energy efficiency of the houses has been practically realized by retaining traditional hill architecture strategy in Shimla, Dharamshala, Chamba, Kinnaur and Lahul-Spiti hilly regions of the state.

5. Vernacular architecture of Indian state of Himachal Pradesh – a case study The vernacular houses in rural areas of Himachal Pradesh are found to incorporate a number of passive solar features. Most of

the houses are designed to capture maximum sun during winters and use biomass for cooking and space heating. Spaces like verandahs in front and south capture sun, side spaces act as buffers on north side to guard against cold winds, design principles like placing of living room, bedrooms, stores according to direction of sun to avail maximum sun, planning of cattle sheds on ground floor so that the cattle body heat is utilized for providing heat to living rooms above, designing of cooking spaces on ground floor so that entire family could sit around the biomass cooking and space heating stove, small sized openings on north side and wide glazing on south side, provision of solariums, construction of walls with double thickness are some of the varied energy efficient provisions inherent in vernacular architecture of the state. 5.1. Climatic zones Himachal Pradesh is located in north India between 30.38° and 33.2° North latitudes and 75.77° to 79.07° East longitudes in north-western Himalayas.The state has 12 districts and can be divided into three major climatic zones based on altitude and geography (Figs. 1–3) [77,78].

 Climatic Zone 1: Areas with altitude between 400 and 1500 m



having tropical to subtropical climate covering districts of Una, Bilaspur, Hamirpur, Kangra and some parts of Mandi, Solan and Sirmaur districts with temperature range 10–15 °C and predominantly heavy rainfall. Climatic Zone2: Areas with altitude between 1500 and 4500 m having subtropical to wet temperate climate covering Chamba, Shimla and some parts of Solan, Sirmaur, and Mandi districts with temperature range 5–10 °C with predominantly moderate rainfall.

Fig. 1. Administrative districts of Himachal Pradesh state in India [78,79].

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Fig. 2. Annual mean temperature zones of Himachal Pradesh.

 Climatic Zone 3: Areas with altitude between 4500 and 6000 m having dry-temperate, sub-alpine and alpine zones covering districts of Lahul-Spiti, Kullu, Kinnaur with temperature range of 0–5 °C and o0 °C with sparse and negligible rainfall. 5.2. Vernacular house design features in different climatic zones of the state Houses in three climatic zones of the state are different from each other in terms of design, planning, aesthetics and material usage as well as owing to different geographical, climatic features and availability of materials and flora-fauna. Houses in areas like Kangra, Hamirpur (Zone1) and also in Shimla (Zone2) generally have sloping roof owing to heavy to average rainfall. Houses in Kangra, Hamirpur are generally one to two storeyed high. Houses in Shimla are generally two to three storeyed high with sloping gable roofs of slate or wooden shingles. Lower storey is occupied by cattle, sheep and goats. Houses are made of mud and are detached in nature. Ground floor has no windows for thermal insulation purposes and is used for keeping cattle and storing food grains made in the form of food grain storage compartments approachable from first floor. First floor has granary and store room and second floor has all living rooms with central room having hearth for warming spaces. This layout is very

much thermally conducive since living rooms for people are kept warm by warmth from body heat of animals and further buffer of food grain storage which secludes them from immediate effect of cold from ground floor. In Kullu (Zone 3), houses are three to four storeyed high. These tower shaped houses have one room in each storey as open wooden verandah meant as sun space. Houses are greater in height than in length or breadth which are fixed and hence these plans are called standard plans. The walls are made of dry-stone masonry devoid of any mortar. The stones are kept in place by timbers placed upon one another at vertical intervals of two or three feet. Generally, a house is forty or fifty feet in height with ten, twenty or even thirty layers of beams in the walls. The intersections are filled with squared grey stones. Greater use of wood imparts more solidity and thermal conduciveness to the structure. Layout of houses of Zone 3 has similar features with difference in design owing to different climatic and cultural factors. However, houses in Lahul-Spiti (Zone 3) are quite different with average of three storeys with flat mud roofs. Lower storey comprises of house for cattle, horses, sheep and goats and upper floors are occupied by respective inhabitants. The rooms are made of rafters of blue pine, pencil or even birch depending upon the availability of the timber. The construction includes short crossrafters of birch wood tied tightly with coping of faggots. In

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Fig. 3. Classification of Himachal Pradesh as per altitude zones.

designing, upper floors consist of interior or winter room, an outer summer room, and a verandah room open on fourth side. Loom is generally located inside the verandah. Inner rooms are further marked by added feature of corn-chests made of slate set in wooden frames, large stone bowls, iron cauldrons, cooking pots, and iron pot stand, wooden and earthen pots. Houses in Spiti have occasionally different layout with a central courtyard or space around which all rooms are planned on three sides. Only exception is the flat roof at top of the houses since it is

required for sun drying of fuel wood, fodder, and food grains [78]. Table 5 summarizes vernacular architecture features of different climatic zones. 5.3. Case study of vernacular architecture in Climatic Zone1 of Himachal Pradesh The objective of the case study is to identify building materials which contribute towards thermal insulation and energy efficient

Table 5 Climatic and vernacular design features of three zones of Himachal Pradesh [77–80]. Features

Climatic Zone 1

Climatic Zone 2

Climatic Zone 3

Altitude

Areas with altitude between 400 and 1500 m

Climate

Recognized as lower Hills Tropical to subtropical climate

Areas with altitude between 1500 m and 4500 m Recognized as Inner Himalayas Subtropical to wet temperate climate

Areas with altitude between 4500 and 6000 m Recognized as Greater Himalayas Dry-temperate, subalpine and alpine zones

600–1600 mm Highest to medium rainfall areas 10–15 °C

600–1200 mm Medium rainfall areas 5–10 °C

300–900 mm Lowest rainfall areas 0–5 °C and o 0 °C

Parts of Una, Bilaspur, Hamirpur, Mandi, Kangra, Solan and Sirmaur East -west for hot (Una, Bilaspur, Mandi, Kangra) to Northsouth for composite regions (Hamirpur, Solan, Sirmaur)

Parts of Solan, Sirmaur, Mandi, Chamba and Shimla districts Preferable south being cold region

Districts of Lahul–Spiti, Kullu, Kinnaur Towards south being coldest region

Courtyard planning with all rooms around it for hot areas (Una, Mandi, Bilaspur), Verandah in front for composite regions (Hamirpur, Solan, Sirmaur). Less glazing

Verandah in front and occasionally similar sun spaces on all sides Compact structures Fully glazed partially closed opening for maximum sun.

Solarium and closed verandahs made of glass and wood at upper floors Compact structures Very less or negligible openings as windows.

Rainfall Annual Mean Temperature Areas Vernacular Planning features Vernacular Designing features

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features in the design and planning of the vernacular houses in Hamirpur district in Himachal Pradesh which lies in climatic zone1with sub-tropical climate and located (30°41′00″ North latitude and 76°31′00″ East Longitude), altitude 765 m above mean sea level with average yearly rainfall 124.8 cm [80]. 5.3.1. Methodology followed The study is based on field measurements and questionnaire based subjective surveys. The questionnaire (Appendix-I) was framed on the basis of exhaustive discussions with experts from Town and Country Planning (TCP) Department, Public Works Department of district Hamirpur and study by Teo and Lin [81]. TCP is the Himachal Pradesh state government nodal agency for formulating and implementing housing regulations in the state. Data were recorded and documented in the form of plans and sections supported by photographs. The whole district was studied using development plan of Hamirpur by selecting specific villages. Vernacular architecture of 60 houses in 82 villages was studied by recording spatial measurements, architectural features, and material usage. Households with family size varying from three to five were selected. 5.3.2. Survey results of vernacular houses The surveyed vernacular houses were 60–70 years old with passive solar features in some houses. The orientation of the houses is found to be along the contours towards south side to avail maximum sun because of prolongation of winter season than summer season. The analysis of vernacular houses reflects a typical living pattern with passive energy efficient features inherent in construction and design of the houses. Living pattern shows arrangement of different spaces influenced by architectural design principles practiced in the area owing to the subtropical warm humid climate. The design, planning, architectural features and materials used have thermal insulation properties which improve the indoor thermal comfort of the houses. This improves energy efficiency of the houses. Energy efficiency of these features will be verified through a thermal comfort study as follow up research. These two storeyed houses use local stone and adobe bricks for

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foundation, adobe bricks for walls, bamboo, wood and slates for roof and rammed earth and mud phuska for floors. Prominent use of adobe in walls and staircase results in better thermal comfort inside the house. Houses are generally two storeyed with average number of four rooms in all houses. Plan of houses is very compact in rectangular or square form with no courtyards or buffer spaces in between to reduce heat loss. Fig. 4 shows a typical section of a vernacular house located in Kot village; district Hamirpur, Himachal Pradesh, India. The stone is used in walls up to cill level and adobe from cill level to roof level with occasional wooden windows in-between. Floors are finished with layers of mix of cow-dung and mud which again has thermally insulating properties. The ground floor is made of stone finished with cow dung-mud plaster called mudphuska and first floor/upper floor is made of wooden/bamboo lengths finished with bamboo splits called 'bamboo chachra' topped by mud-phuska coating. First floor has same layout with small kitchen space in corner room adjoining staircase. Internal staircase is made of wood and adobe connects both the floors. However, the width of the flights is very less and sufficient only to allow one person to move at a time. Small windows flank walls of rooms with entrance door located on north side of the house. Toilets are not located inside the house but outside in close proximity due to cultural beliefs. Thermally this is an added advantage since it separates wet areas from the rest of the house thereby maintaining thermal insulation of the house Sloping roof is made up of wooden rafters topped by bamboo lengths and bamboo splits in the form of chachra (half bamboo culms) topped by slates. 5.3.3. Energy efficient features Questionnaire based survey showed that residents of vernacular houses do not use any equipment for heating or cooling in winters or summers. Both material and architectural design features result in better thermal performance of these houses. Owing to massive 18″ thick adobe walls, use of wood for roof and mud phuska (mix of mud and cow-dung) which are all thermally insulating materials, thermal insulation of house is excellent which curtails the need of

Fig. 4. Typical section of a vernacular house located in Kot village; district Hamirpur, Himachal Pradesh, India.

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external energy equipments either in winters or summers. Further compactness of the houses, orientation of the houses towards south, presence of sun spaces like verandah, small windows in north side etc. also accounts for better indoor thermal environment in these houses. This shows these houses are energy efficient which will further be studied by a thermal performance study of these houses as a follow-up research work. The energy efficient construction, planning and design characteristics identified in vernacular houses of Hamirpur district are shown in Table 6.

6. Results and discussion In this section the results identified from literature review and case study are presented and discussed. 6.1. Analysis of survey The regression analysis of the data collected from questionnaire based survey was carried out. The results are shown in Fig. 5. The analysis shows that occupants of vernacular house are very much satisfied with their houses with satisfaction level of 70%. The occasional problems like inflexibility of design for change of openings for alteration of space function, number of habitable rooms are less; only 3; building height is less – up to 2.4 m (each storey), structural and surface defects – occurrence of cracks, peeling of plaster, surface

erosion, Frequent maintenance and repair of structural systems is required and absence of building facilities like water supply, sewerage, solid waste management inside the building. Therefore it is seen through the analysis of survey that traditional vernacular styled houses have defects of deterioration, cracks (structural and surface defects), plaster peeling, infestation by rodents, termites, dampness problems requiring frequent repair and maintenance however there is no problem of excessive heat gain or loss in seasons of summers and winters. The case study therefore gives description about various constraints and problems faced by occupants of vernacular houses as analyzed through regression analysis and shown in Fig. 6. These constraints have been identified as: economic status, non-availability of masons, trends in construction (preference for modern and aesthetically appealing materials like marble), structure and design (inflexibility to undergo renovation and deterioration defects) restrict the use of vernacular construction techniques on wider scale. Vernacular techniques do not fit very well in present day lifestyle and context due to problems in its use. Moreover masses are ignorant on large scale about minor modifications needed for adaptability and therefore vernacular techniques not widely accepted by common masses. This paves the way for use of modern conventional architectural style by people for building houses. These reasons form the basis of decline of vernacular architecture style from housing scenario even from rural areas as well. In terms of structural defects; poor durability

Table 6 Energy efficient features in vernacular architecture of Hamirpur district. Building Characteristics a. Construction Walls: stone up to sill level; adobe bricks in ground /first floor Ground floor: rammed earth or stone flooring Upper floors: wood with bamboo and mud phuska Roof: wooden rafters, bamboo lengths, bamboo splits and slates b. Planning Layout Shading devices c. Design Room structure Building shape Building storey Courtyard planning Verandah Windows Grills

Features

Remarks

Adobe walls (18″ thick) plastered with mud–phuska

Thermally insulator due to large mass

Floor coated with mud–phuska and cow dung.

Cow dung and mud phuska both are thermally insulating materials Both wood and mud phuska are thermally insulating materials Thermal insulator

Floor coated with mud–phuska and cow dung. Lightweight sloping roofs with attic as insulation chamber

Compact- to reduce the effect of harsh sun and cold Average /optimum for protection against rain, wind

Helps to minimize heat loss Guard against weathering agents, reducing energy loss

Three to four rooms with drawing room and store/bedroom on ground floor, kitchen and bedroom on upper floor. Rectangular south facing buildings Double storey Absent Present facing sun maximizing solar gain. Small openings with size in general as 2′  3′ Intricately carved in wood also serving as railings in balconies.

– Maximize heat gain and minimize heat loss Helps to minimize heat loss Maximize heat gain Helps to minimize heat loss –

Fig. 5. Observations of satisfaction level of subjects with vernacular houses.

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Fig. 6. Problems and constraints in use of vernacular architecture.

and compressive strength of adobe require frequent repairs and maintenance which is becoming more difficult due to non-availability of trained masons, time constraint for repair works owing to change in lifestyles and modern day requirements of people. Thus, people refrain from using vernacular architecture although it is highly energy efficient. This forms the ground work for modification in vernacular materials especially earth; use of which improves thermal insulation properties. 6.2. Identification of factors influencing vernacular architecture

 Main factors affecting vernacular architecture are climate, to 

pography, social, economic and cultural aspects, material availability, seismic activity proneness. Most frequently used vernacular construction material is earth. However, earth lacks in durability and compressive strength and needs improvement. Energy performance results of the case study showed that vernacular architecture features are quite energy efficient and responsible for conducive indoor thermal environment in old traditional houses.

Identification of factors which influence vernacular architecture helps in understanding the development process of indigenous construction techniques and their relevance with respect to climate context of the area. These features are bioclimatic in nature and have proven to be very appropriate passive environmental control strategies in vernacular traditional houses. Owing to these bio-climatic features traditional houses maintain comfortable indoor environment without external energy equipment input. Important lessons can be adopted as guidelines from bioclimatic features of vernacular houses for design and planning of new modern houses both for creation of indoor thermal comfort and saving of energy which is consumed in maintaining thermal comfort of houses. This would also propagate economical use of natural resources for building construction purposes and hence promoting sustainability in housing sector. Present housing scenario of the state Himachal Pradesh shows that people are using certain features of traditional architecture like use of sloping roofs, provision of verandahs as sun spaces. However, adoption of these features are on a smaller scale and not in appropriate manner, for example verandahs are provided in houses but not according to the sun and wind orientation thereby leading to more disadvantages than benefits of the very bio-climatic feature. In this regard, results of present study would prove to be useful for understanding of passive environmental features of vernacular architecture for maximizing health and thermal comfort benefits in housing. 6.3. New architectural style for the western Himalayan region The present study results in suggesting a new architectural style for the western Himalayan region which is based on amalgamation of climatic factors, prevalent energy efficient features

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and passive solar characteristics of old traditional houses,current lifestyle requirements of people and modern architecture and construction techniques. Besides solar passive features are incorporated in modern houses in cold hilly regions of Himachal Pradesh based on traditional style and material availability as elaborated by Chandel [8,9]. Based on use of local materials like mud, wood; these construction techniques are an inherent part of vernacular hill architecture of Himachal Pradesh which are now being taken seriously by planning authorities of the state and incorporated in building regulations of the state also as reflected in the development plan [81]. This is resulting in the development of a new type of architectural style based on modern concepts of passive solar architecture and thermal comfort features of vernacular architecture which can be called as “Modern Himalayan Architecture”. The main features of this architecture style are summarized as follows: 6.3.1. Planning features House shall be planned as per contours; direction of sun and wind and facing south to avail maximum sun during winters, maximum vegetation or heavy mass on north side of the building to guard against winter winds, pacing of habitable rooms on south-western side and wet areas of house like toilets on southern side. 6.3.2. Design features Compact design of house, provision of sun spaces like solariums, verandahs on southern side to avail maximum sun and to guard against wreathing agents, provision of buffer spaces in areas directly opening to outside to act as heat and air locks, provision of adequate shading devices on openings, provision of cooking space or kitchen in house in a way that centrally radiates heat to all rooms and is central gathering space, less number of opening on north side and more on southern and western side, use of sloping roof serving dual purpose by providing attic spaces inside and maintaining insulation of roof. 6.3.3. Materials and construction features Use of weather proof materials like stone up to cill level to guard against ingress of moisture and cold, provision of sun space, Trombe wall on south side and double cavity wall on north side to guard against loss of heat, use of modified vernacular material wherever possible like slates on roof, and for flooring, adobe with stabilizers in the form of cement stabilized blocks or like, proper provision of drainage at roof level to guard against heat loss and weathering agents, use of dark colors on the surface of walls and roof to absorb more heat in daytime. Solar passive systems like solar water or air heating systems can also be integrated in the construction of modern buildings on roof. Energy efficient features of this style can be advantageously added in single storeyed residential units and double or triple storeyed commercial buildings for benefits of better indoor thermal environment.

7. Conclusions A comprehensive review of vernacular architecture studies worldwide is presented to identify energy efficient features which improve the indoor thermal comfort conditions. The current status of use of earth as building material, codal provisions and adaptations of vernacular architecture for improving energy efficiency in modern context are presented along with case study of vernacular architecture of a location in Himachal Pradesh, India. Based on the study following conclusions are drawn:

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 Main parameters affecting energy efficiency and thermal com-









fort in vernacular architecture are identified as: use of earth, stones, wood and bamboo as building material, built mass design, orientation with respect to sun, space planning, openings, sunspaces, construction techniques, and roof materials. Passive environmental controls like improvements in design, use of appropriate building materials and inclusion of passive solar features, of vernacular architecture can be used in the construction of modern buildings to enhance indoor thermal comfort conditions. Earth is prominently used as vernacular building material due to its availability and thermal insulation property. However, there is need to improve its durability and compressive strength to use it as modern building material. Codal provisions /guidelines are made for using earth as building material by a number of countries. However, these provisions can further be elaborated by providing detailed earth building engineering designs, improving mechanical strength, shrinkage, durability, thermal insulation and fire resistance etc which is being followed only in a few countries at present. Prominent vernacular architecture features in different climatic zones of India are found to be in harmony with nature which mainly follows traditional Indian architecture (Vaastu Shastra) principles. Orientation of houses is the main feature of most of these houses in southern states and in western Himalayan state to utilize Sun's energy in winters for space heating and shading in summers. In warm and humid climates prominent features are: court yard planning, natural ventilation through roof/ wind catchers, high thermal mass, earth as construction material, burnt earth roof tiles where as in cold climates main features are high thermal mass, sunspaces, attic for insulation, sloped roofs, covered verandah, compact



planning, less openings.Vernacular houses have solar passive features inherent in their design, planning, orientation and construction techniques. The case study in north-western Himalayan Indian state of Himachal Pradesh identifies the relation of vernacular architecture with thermal comfort conditions. The study brings out a new architecture style for north-western Himalayan region. However, the present day construction scenario shows fast replacement of vernacular architecture tradition with modern architecture. This new architecture style is unsustainable and provides less thermally comfortable indoor built environment due to use of modern construction materials and techniques ignoring planning, designing and orientation considerations.

However with the initiatives taken by the government of Himachal Pradesh like making passive solar housing technology mandatory for buildings, preserving heritage buildings and following hill architecture features a new type of traditional yet modern energy efficient architecture style is emerging which can be called as “Modern Himalayan Architecture”. The existing byelaws and building regulations of Himachal Pradesh allow this type of architecture however some modifications may be necessary. This architecture style can be followed in the entire Himalayan region with some modifications. This style is the requirement of the region leading to thermal comfort living conditions to suite modern life styles. Further follow up research studies can be undertaken to develop this architecture style along with improving the strength of earth with natural and vernacular stabilizers. Thermal comfort studies of vernacular houses along with identification of most appropriate adaptive thermal comfort model are other areas of research.

Appendix I. Sample questionnaire for socio-economic survey carried out for sample vernacular houses in district Hamirpur, Himachal Pradesh

1. Name, Address of person 2. Family structure: Number of family members

Tick (√)

0–5 6–10 11–15 Other…

Age group of family members 0–15 years 16–30 years 31–45 years Other…

Tick (√)

Occupation

Tick (√)

Service Agriculture Business Other…

3. Building Structure: Wall Material:

Tick (√)

Bamboo Mud Stone Wood Other…

Floor Material:

Tick (√)

Slates Mud Stone Wood Other…

Roof Material:

Tick (√)

Slates Mud Stone Wood Other …

4. Housing Obsolescence: 4.1 Physical Obsolescence Building Age

Tick (√)

Structural Defects

Tick (√)

Surface Defects

Tick (√)

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0–25 years 26–50 years 51–75 years 4 75 years

Beam Column Wall Slab/Roof Other

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Infestation Plaster Peeling Cracks Other

4.2 Economic Obsolescence Income Level

Tick (√) Repair Cost Tick (√) Construction Cost Tick (√) Repair Period Tick (√) Repair Ease Tick (√)

4 10 Lac Per Annum 5–9 Lac Per Annum 1–4 Lac Per Annum 50,000–99,000 Per Annum Any Other

Very High High Moderate Low Negligible

Very High High Moderate Low Negligible

0–6 Months 1–2 Years 3–5 Years 6–10 Years 46 Years

Very Good Good Moderate Fair Poor

4.3 Functional Obsolescence Design Flexibility

Tick (√) Room Height

Very High High Moderate Low Negligible

Tick (√) Stories Number

4 Required o Required Optimum No Opinion

4 Required o Required Optimum No Opinion

Tick (√) Maximum Size

Room Tick (√) Max. Room No. Tick (√)

4Required oRequired Optimum No Opinion

0–2 3–5 6–8 48

4.4 Social Obsolescence Visual Appeal

Tick (√)

Very Pleasing Pleasing Average Less Pleasing Negligible

5. Site Obsolescence: Transport Link Connectivity

Tick (√)

National Highway State Highway District Roads Link Roads None

Condition Of Roads

Tick (√)

Very Good Good Moderate Fair Poor

6. Sustainability: Indoor Environment Quality Tick (√) Inside Comfortable Temperature Tick (√) External Heating/Cooling Equipment Use Tick (√) Very Good Good Moderate Fair Poor

Very Good Good Moderate Fair Poor

Very Often Often Sometimes Less Required Seldom Required

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7. Design Aspects/Visual Character Of Building: Shape

Tick (√)

Building Projections/Recesses

Square Rectangular L-Shape Circular /Semi-Circular

Tick (√)

Verandah Arcades Porch Any Other

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