Energy efficiency and building construction in India

Building and Environment 36 (2001) 1127–1135

www.elsevier.com/locate/buildenv

Energy e!ciency and building construction in India Piyush Tiwari Institute of Policy and Planning Sciences, University of Tsukuba, Tsukuba 305-8573, Japan Received 13 April 1999; received in revised form 22 May 2000; accepted 11 July 2000

Abstract The energy conservation has become an important issue in building design, it is logical to apply the principle of energy costing to building projects, and to look for ways to minimize the total energy consumed during their lifetime. Even though the total quantity of energy consumed in a building during its lifetime may be many times than that consumed in its construction, there are number of reasons why the energy use in the construction process, and in particular in the building materials used, should be treated as a matter of importance in looking for ways to minimize energy use in the built environment as a whole. In this paper the energy costs of alternative construction techniques using an optimization framework are assessed and compared. The techniques of construction evaluated in this paper are commonly used pucca techniques as well as low-cost construction techniques. Energy consumption and resource requirements due to the use of alternative techniques of construction for a representative room of size 3:5 m × 3:5 m × 3:14 m are evaluated. An assessment of the magnitude of energy consumption, if housing shortages have to be met, shows that a huge amount of energy would be consumed in housing sector alone. The associated levels of carbon dioxide emissions associated with this construction would also be prohibitively high. Finally the paper concludes with recommendations for structural changes in the energy c 2001 Elsevier Science Ltd. All rights and construction policy in India to minimize energy consumption in building construction.  reserved. Keywords: Energy e!ciency; Optimization; Building design

1. Introduction The link between the use of energy in buildings and the total energy use is well established. The link between energy production and use and local and global environment is causing increasing concern worldwide. There are thus good environmental reasons for seeking to reduce the energy “embodied” in buildings. In the developed countries there is a growing demand for an environmental impact assessment of all building projects which will include considerations of embodied energy [1]. After Habitat II, Agenda for sustainable communities and adequate shelter for all, the issue of environmental impact assessment has become critical for cities in developed and developing countries alike. Building projects o?er large potential for the reduction of energy consumption. Besides the challenges of building for environmental sustainability, cities in developing countries face the more urgent problem of meeting the demand for adequate shelter for citizens. Various reports [2] have detailed the inE-mail address: [email protected] (P. Tiwari).

adequacy of the living standards experienced by many millions in such countries. The scarcity and cost of durable building materials is regularly identiBed as one of the obstacles to better housing standards. As populations grow and become more urbanized the soil and vegetable materials on which the traditional rural building methods have depended are no longer cheaply or freely available, and they are being replaced by processed or factory-made materials. Many of the well-established technologies for small-scale processing are highly energy intensive and have been inherited from a time when energy, in the form of biomass, was more abundant than it is today or will be in future. As a result the materials that they produce are too expensive for the poor. Likewise the large-scale processing technologies imported from the industrialized countries are energy-intensive and tend to rely on high-grade energy imports. Now that energy conservation has become an important issue in building design, it is logical to apply the same principle to the energy costing of a building project, and to look for ways to minimize the total energy consumed during their lifetime comes from the annual energy

c 2001 Elsevier Science Ltd. All rights reserved. 0360-1323/01/$ - see front matter
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consumption, most attention understandably tends to give to ways of reducing this component of the total energy, and it is easy to ignore the other components. Yet, even though the total quantity of energy consumed in a building during its lifetime may be many times that consumed in its construction, there are number of reasons why the energy use in the construction process, and in particular in the building materials used, should be treated as a matter of importance in looking for ways to minimize the energy use in the built environment as a whole. Although smaller than the households energy use, energy consumed in building-materials production is by no means insigniBcant in national and global energy budgets: the materials industries, and have been shown to account for over 20% of world-fuel consumption [3]. Energy is consumed in housing construction mainly in three ways: • in the procurement, manufacture, processing and recycling of building materials, • in transporting building materials to the building site, and • in on-site construction activities. The Brst two ways may be called indirect while the third is called direct energy consumption. For any building project, the relative amount of energy used in each of these three areas will vary; it is, thus, not possible to conclude in which area the greatest savings in energy can be made. In most developing countries, labor costs, particularly of unskilled labor, are relatively low compared to the cost of the materials, equipment and transport. There is some evidence [4 – 6] that building materials often constitute approximately 70% of actual construction costs in developing countries. It is clear that the availability of low-cost materials is important, if the need for housing is to be met, and, with increasing energy costs, low-cost building materials are synonymous with materials that consume little energy in their manufacture. In both large and small developed countries, such as the USA and the New Zealand, the energy consumed in the production of materials amount to 70% of total construction energy, the remaining 30% being primarily consumed by on-site construction-related activities [7]. In developing countries this proportion ranges between 90 and 100%, as the on-site energy consumption in construction of housing is low due to rare use of machinery. A systematic method for assessing and comparing the energy costs of alternative construction materials (and methods) is the reference materials system (RMS) [8]. This system traces materials from their basic resources to end-use, and the energy costs incurred at each stage and in each process can be identiBed and assessed. Fig. 1 illustrates the process of energy analysis, and shows that four levels of energy use can be distinguished. The Brst is the energy used in the production of the materials used in the process itself. The second is the energy used in the

Fig. 1. Materials and energy Kows in building production.

production of the materials used in the process. The third combines the energy used in the equipment and the other inputs to the production process. The fourth includes the machinery needed to make machines and material inputs. It has been found that the levels 3 and 4 are unlikely to contribute more than 10% at most to gross energy requirement, so they can be generally ignored [7]. Fig. 2 illustrates the range of inputs, which may need to be considered in estimating the gross energy requirement of a fairly simple building, the embodied energy. The range of building materials used is very wide, and the source of each material, which is usually not known at the time of specifying the building, can have signiBcant inKuence on the total embodied energy. Lack of reliable and comprehensive statistical data of energy consumption of overall construction process restricts the use of RMS for developing countries. The present paper is a step in the direction of assessing and comparing the energy costs of alternative construction techniques. An optimization model called ENEHOPE (energy e!cient housing options evaluation) has been developed and used. The question that we are trying to address is: Is there any (ENE) hope (HOPE) for energy e!cient buildings? Rest of the paper is structured as follows. Section 2 brieKy discusses the importance of energy in building material production. Section 3 describes the ENEHOPE model. Section 4 analyzes and discusses results and Section 5 presents the magnitude of energy savings that can be achieved at the national level. Section 6 concludes.

2. Energy intensity in building materials production The relevance of energy consumption in building construction can be illustrated in a much better way by analyzing the energy consumption of various building materials. There are numerous studies estimating the energy costs in the manufacture of various materials [3,9],

P. Tiwari / Building and Environment 36 (2001) 1127–1135

1129

Fig. 2. (a) Direct and indirect material inputs (HOPE Model); (b) Direct and indirect inputs (COHOPE).

although many of them derive from the 1970s when work on energy conservation began to be taken seriously. Since in most cases there are a mixture of electrical and thermal costs, the most suitable basis of comparison is in terms of primary energy, which includes energy used in the energy conversion and supply system. On the basis of energy intensity, (the gross energy requirement to manufacture unit weight), building materials

have been classiBed [9] into three categories: high, medium and low energy intensive. 2.1. High-energy materials The high-energy materials are those with energy intensities greater than about 5 GJ=ton of the manufactured material and include aluminum, steel, plastics, glass and

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Table 1 Comparative energy requirements of building materials Material

Primary energy requirement (GJ=ton)

High energy Steel Lead, Zinc Glass Cement Plasterboard

30 – 60 25+ 12–25 5 –8 8–10

Medium energy Lime Clay bricks and tiles Gypsum plaster

3–5 2–7 1– 4

Concrete In situ Blocks Precast Sand-lime bricks

0.8–1.5 0.8–3.5 1.5 –8 0.8–1.2

Low energy Sand, aggregate

¡ 0:5

cement. Processes characterized by large-scale operations, and incorporating high-temperature operations manufacture all these materials. 2.2. Medium-energy materials The medium-energy group of materials comprises those requiring energy inputs between about 0.5 and 5 GJ=ton of the manufactured material. The group includes concrete, lime, plaster and most types of building blocks based on cement or lime, and Bred-clay bricks and tiles. Scales of production tend to be smaller than the previous group, and they often use traditional technologies, some of which are of poor e!ciency. 2.3. Low-energy materials The low-energy group of materials comprises those requiring energy inputs less than about 0.5 GJ=ton. The group includes aggregates for concrete and mortars, natural and artiBcial pozzolanas, soil and stabilized soil. The high-energy materials commonly depend on highgrade fuels such as electricity, oil and pulverized coal in their manufactured processes. By contrast, the mediumenergy materials, particularly bricks, lime and tiles, can often use low-grade fuels such as Brewood, low-grade coal or oil, sawdust and crop-waste, which may be available more. Most of the low-energy materials use little purchased energy, though they may use signiBcant amounts of human and animal energy. Table 1, to some extent indicates that there are possibilities of reducing energy consumption in building construction, as many of these materials are substitutes for one another.

Fig. 3. Room considered for analysis.

3. Energy ecient housing options evaluation model (ENEHOPE) The building, considered for analysis, is deBned as multiples of a room of hypothetical size (3:5 × 3:5 × 3:14 m3 ); as shown in Fig. 3. These rooms can exist anywhere in the building up to three Koors. Up to three Koors, the minimum wall thickness is one brick and beyond this, the minimum wall thickness increases [10]. However, in normal construction practices, the walls beyond the third Koor are rarely load bearing. Generally, a framework of columns and beams is constructed which is load bearing and the space in between is Blled with non-load-bearing brick walls. The energy estimates for buildings above three Koors will be a slight underestimation since emissions due to columns are not accounted for. ENEHOPE identiBes a combination of methods at different stages of construction (viz., foundation, wall, etc., as deBned below) to meet optimal levels for various activities required at each stage of construction of the structure, subjected to speciBed objectives and engineering and economic constraints. The model has three types of activities: activities related to primary resources required to produce the intermediate and Bnal inputs to be used for construction of the structure and activities related to various technological alternatives of construction of each stage of the building. Primary resources include fuel (electricity, coal), limestone, gypsum, etc. which are required in the production of cement, bricks, lime, steel, etc. which can be either directly used in construction (Bnal inputs) or can be used in manufacture of Bnal inputs such as concrete blocks, which are Bnally used in construction. In the later case they are called intermediate inputs. In this model, di?erent technical speciBcations that provide the same outputs (room) are considered. The levels of resources and production activities are determined so that the overall cost of construction of the speciBed room is a minimum. The notations for di?erent sets appearing in

P. Tiwari / Building and Environment 36 (2001) 1127–1135

this model are: p is the set of primary inputs (p = 1 − P); i is the set of intermediate inputs (i = 1 − I ); j is the set of production-activity levels (j = 1 − J ); q is the set of di?erent wage classes (q = 1 − Q); and g is a set of di?erent stages in construction (g = 1 − G). The notations in this section may be considered entirely independent of notations used in earlier section. The stages of construction considered are: stage 1 — foundation bed under load bearing wall; stage 2 — foundation bed under partition wall; stage 3 — foundation for load bearing wall; stage 4 — foundation for partition wall; stage 5 — wall construction; stage 6 — partition wall construction; stage 7 — roof construction; stage 8 — Kooring; stage 9 — external plastering; stage 10 — internal plastering. We classify construction techniques into three groups: Commonly used techniques — these are brick, stone and cement-based technologies like concrete blocks, stone or brick masonry in cement-based mortar, etc.; Pucca construction — this grouping is more or less similar to earlier except that besides other materials mentioned above lime-based techniques are also evaluated; Low-cost techniques — This group includes di?erent forms of mud blocks, mangalore tiles etc. For a listing of technology refer Tiwari et al. [11]. Our common techniques are akin to CP of Tiwari, pucca techniques are similar to HOPE and low-cost techniques are same as COHOPE. Model equations are given below

i

j

+



q




Final inputs aij xj 6 ri ;

j

requirements

6

availability:

The element ri is the total amount of the ith Bnal input required to run the production activity at a level X . The element bpi gives the requirement of the pth primary input to produce unit output of the ith Bnal input, i.e.


b  ri

Primary inputs 6 tp ;

i

requirements

6

availability;

where tp (p = 1; P) is the total amount of the pth primary inputs required to produce the intermediate inputs ri . Combining Eqs. (11) and (12) yields Primary inputs

tp ¿ b aij xj ; i

availability ¿

j

requirement:

3.3. Direct, indirect and total employment

wq dqj xj ;




j

Intermediate inputs +Direct labor where ci is the cost coe!cient for the ith intermediate input corresponding to the ith activity and wq is the wage rate for the qth class of labor. The requirement for the ith intermediate input to produce unit output of the jth activity is given by element aij . xj is the level of the production techniques. dqj is the qth type of labor employed directly for unit production level of activity j. The matrices aij ; dqj and input prices have been compiled from Tiwari et al. [11]. 3.2. Resource constraint If Ng is the number of alternative techniques available at stage g; the total number of techniques available is
Ng : N= g

All levels of activities from G stages taken together are represented as (x1 ; x2 ; : : : ; xj ; : : : ; x n ) = X
:

For detailed list of xj refer to Tiwari [11]. aij is the requirement of Bnal inputs to produce unit output of the jth activity, i.e.

dqj is the qth type of direct labor required for the jth activity, sqi are the indirect labor requirements of the qth earning class to produce the ith intermediate input. The indirect labor requirement for each wage class is

3.1. Objective function We minimize

cost = ci aij xj

1131

i

sqi aij

requirement

Indirect labor; 6 lqi ; 6

availability;

where lqi is the qth type of labor required to produce the ith intermediate input. The total aggregate employment (not by labor class) is

(lqj + dqj )xj : q

j

3.4. Output constraint The task level for every stage of building a room varies with the choice of the technique of construction. For example, to support the same load, the thickness of a stone wall should be more than that of a brick wall. The type and quantity of materials required change according to the principles of structural engineering. The material requirement at every stage is a polynomial function of the area and height of the building [11]. The output constraint is
zjg xj 6 yg ; j

Output 6 Task level:

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The element zjg represents the output coe!cient of the jth activity at stage g, yg is the task level for each stage. 3.5. Engineering constraints In building construction, the choice of techniques for one stage is not entirely independent of the choice of techniques for other stages. These interdependencies and internal balances in production have to be taken care of. These engineering constraints are written as uij xij ¿ 0: To understand this constraint, it is necessary to explain how the uij ’s are derived. Consider two activities x1 and x2 corresponding to stages 1 and 2, respectively. Let 1 correspond to the foundation and 2 to the superstructure wall. Now, if the wall is constructed by using technique x2j ; it is required that the foundation is to be built only by using x1j . This constraint is introduced as follows. Let x2 = superstructure wall work in m3 built by using technique x2j ; and x1 = foundation work in m3 built by using technique x1j . As the dimensional details of both wall and foundation are known from engineering calculations, the lengths for which x1 and x2 are built are calculated by multiplying their levels by proper constants. If k1 x1 is the length for which the foundation is built by using x1j and k2 x2 the length for which the wall is built by technique x2j ; then x2 depends only on x1 ; so that k1 x1 should be at least equal to k2 x2 ; i.e. k1 x1 − k2 x2 ¿ 0 ∨ x1 − (k2 =k1 )x2 ¿ 0: The coe!cients of xi and xj become the uij . 3.6. Non-negativity constraint To restrict the choice variables to positive values, the following constraints are applied tp ¿ 0 ∧ xj ¿ 0: 4. Results The results of the model are very interesting. Under each grouping of technology three scenarios are presented. First is base; when the objective is to minimize the cost of construction. Second is coal; in this case we introduce a constraint on coal use. The numbers along with coal scenario indicate the percentage by which coal consumption is reduced compared to the base case. For example coal-10% indicates that compared to the base the coal consumption is less by 10%. Third is elect; in this case we introduce constraint on electricity use. The number along with the elect scenario has the same meaning as for coal scenario. To simplify the results are presented only for the maximum possible reduction case. Beyond this no further reduction in energy consumption is possible.

The results are discussed under following headings: • • • • •

Cost Final inputs Intermediate inputs Primary inputs Employment

4.1. Cost It is quite evident from Table 2 that if we reduce energy use, the cost of construction rises within the same group of technologies. For example a 10% reduction in coal consumption in building construction by common practices technique increases the cost by around Rs. 2675 per room. Similarly, a 44% reduction in electricity increases the cost by Rs. 1462. There are corresponding changes in intermediate input consumption and wages. With coal reduction as objective, wages go up in all three groups because brick-based technologies are replaced by stone-based technologies for foundation and walls. With coal reduction, additional advantage in terms of carbon dioxide reduction is also associated. From Table 2 it is clear that even within the same group of technologies it is possible to reduce cost. However, there is not much advantage in terms of savings in energy use. If we use low-cost techniques there are distinct advantages in terms of cost as well as energy use. Even in base case of low-cost techniques, the coal consumption is one-third of the common practices. The electricity consumption is also less by 2.5 times than the base case of common practices. Table 2 is self-illustrative and explains various costs and energy requirement for different group of technologies and objectives. 4.2. Final inputs Table 3 presents the level of Bnal input requirements corresponding to various scenarios. As is obvious from the table under coal constraint, the consumption of surkhi and bricks reduce. Stone in construction replaces brick. The use of surkhi also reduces and more and more cement is used in construction. However, with electricity as constraint the use of cement reduces because the manufacture of cement consumes electricity and the lime and surkhi are used as cementing material. Corresponding technologies are chosen for construction. 4.3. Intermediate inputs Intermediate inputs are required only in case of low-cost technologies. The requirements of intermediate inputs are shown in Table 4. 4.4. Primary inputs As mentioned earlier, primary inputs are one linkage behind the Bnal inputs, which are used directly in con-

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Table 2 Cost of various inputs Common practices Cost (Rs) Input cost (Rs) Wage (Rs) Coal (ton) Elect (kWh) CO2 (ton)

Pucca techniques

Low-cost techniques

Base

Coal-10%

Elect-44%

Base

Coal-29%

Elect-25%

Base

Coal-13%

Elect-47%

16606 12366 4240 1.8 254 5.6

19281 13852 5429 1.6 282 5.4

18068 14297 3771 2.3 144 5.7

16584 12356 4228 1.8 253 5.6

18796 13362 5433 1.55 287 5.38

18078 14307 3771 2.31 144 5.7

9231 7036 2195 0.60 130 2.25

9525 7135 2390 0.53 143 2.19

11345 9104 2241 1.08 69 2.67

Table 3 Final input requirements Common practices Base Cement (ton) Bricks (thou) Coarse sand (m3 ) Fine sand (m3 ) Stone aggregate (m3 ) Unslaked lime (qntl) Surkhi (m3 ) Flyash Mud blocks Manglore tiles Stone at quarry (m3 ) Through stones (nos) Steel (kg) RNIT Sand stone

Coal-10%

2.12 3.49 2.88 3.92 5.09 5.76 1.19

2.34 3.49 6.63 1.64 5.08 0.22

0.14 47.16 88.2

8.31 47.16 66.4

Pucca construction Elect-47%

Base

1.2 6.61 2.9 0.98 5.07 11.88 2.89

66.39

2.1 3.54 2.82 3.95 5.07 5.79 1.19

46.2 88.2

12.25

Low-cost techniques Bricks Coarse sand

Coal-13% 0.06 0.54

2.40 3.01 6.18 2.44 5.31 0.86

5.90 55.78 66.39 12.25

Table 4 Intermediate inputs requirements

Base 0.06 0.54

Coal-29%

Elect-42% 0.13 0.54

struction. Table 5 illustrates the levels of primary input requirements. 4.5. Employment One distinct advantage of construction is that it leads to large employment generation through its forward and backward linkages. Our results indicate that the technologies which are chosen with coal as constraint have much larger advantage in terms of employment generation within the same group of technologies as shown in Table 6. 5. Aggregate savings in energy It would be interesting to see the sum of the critical indicators like investment, wages, fuel consumption and carbon dioxide emissions if the housing shortage of around

Low-cost techniques Elect-25%

Base

Coal-13%

Elect-42%

1.20 6.62 2.91 0.98 5.06 11.89 2.89

1.08 1.07 4.08 0.29 3.23 0.22

1.19 0.53 4.66

1.07 4.89 0.06

66.39

7.30

1.07 4.89 0.06 1.47 9.58 7.30

0.58 1.07 1.61 1.19 3.23 19.25 1.74 0.09 4.89 0.05

3.49

5.71 0.07

41 million housing units has to be met. If we assume that on an average each dwelling unit constitutes of three rooms, the level of these indicators is shown in Table 7. The scenario presented below indicates that if present method of construction is continued, ceterus paribus, the requirement for energy can also pose a constraint for any short-term fulBllment of housing requirements. The coal and electricity requirements would be 221 Mt and 31.2 Gwh, respectively. The coal requirement is nearly the overall annual requirement for the country. The only possibility of energy e!ciency in house construction is by the use of low-cost techniques that have the dual advantages of being twice as economic, being a thrice more e!cient in coal use and twice as e!cient in their consumption of electricity.

6. Conclusion This paper is one of the Brst attempts to develop a comprehensive optimization model for energy accounting in house construction in India. A step-by-step illustration of changes in cost, Bnal inputs, primary inputs, labour and energy use indicates the usefulness of the model. The concern of the paper is energy consumption in building

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Table 5 Primary inputs requirements Common practices Base (m3 )

Coarse sand Fine sand (m3 ) Stone at quarry (m3 ) Sand stone Coal (ton) Electricity (kwh) Lime (ton) Gypsum (ton) Clay (ton) Iron ore (ton) Dolomite (ton) Mangnese ore (ton)

Pucca construction

Coal-10%

3.34 3.92 6.93

Elect-47%

Base

Coal-29%

3.80 0.98 5.56

3.28 3.95 6.74

1.80 254 4.3 0.11 20.3 0.17 0.01

7.03 1.64 15.5 13.48 1.61 281 3.59 0.12 17.59 0.13 0.01

2.31 144 4.06 0.06 39.4 0.13 0.01

0.01

0.01

0.01

Low-cost techniques Elect-25%

1.80 253 4.29 0.11 20.6 0.17 0.01

6.52 2.44 13.43 13.48 1.55 287 3.79 0.12 15.2 0.13 0.01

3.81 0.98 5.56 2.31 144 4.06 0.06 39.44 0.13 0.01

0.01

0.01

0.01

Base

Coal-13%

4.75 0.29 3.56 0.60 130 1.67 0.05 5.74 0.01 0.000 1 0.000 1

5.26 5.61 0.53 143 1.79 0.06 3.14 0.01 0.0001 0.0001

Elect-42% 2.38 1.19 3.55 1.08 69 4.46 0.03 10.02 0.01 0.000 1 0.000 1

Table 6 Employment (Rs) Common practices Direct Indirect

Pucca construction

Low-cost techniques

Base

Coal-10%

Elect-47%

Base

Coal-29%

Elect-25%

Base

Coal-13%

Elect-42%

4240 2884

5429 2503

3771 2872

4228 2870

5433 2662

3771 2874

2195 119

2390 119

2241 233

Table 7 Resource requirement to meet housing shortage Common practices Investment (Billion Rs) Wage (Billion Rs) Coal (Mt) Elect (Gwh) CO2 (Mt)

Pucca construction

Low-cost techniques

Base

Coal-10%

Elect-47%

Base

Coal-29%

Elect-25%

Base

Coal-13%

Elect-42%

2043

2372

2222

2040

2312

2224

1135

1172

1395

522

668

464

520

668

464

270

294

276

221.4 31.2 689

197 34.6 669

283 17.7 700

221 31.1 685

191 35.3 662

284 17.7 700

74 16 277

65 17.6 269

133 8.5 328

construction in India. A simple room construction using common, not Pucca or low-cost construction would require 1.8 ton of coal and 254 Kwh of electricity. Though the coal and electricity are not consumed directly during construction but are backward linkages in the construction process used in the manufacture of cement, bricks, surkhi, etc. and should thus be accounted for the construction economics. The paper further demonstrates the impacts on investment; resources and employment associated with changes in construction types and associated reductions in energy consumption. At the national level, if the present housing shortage of 41 million units are to be met, a change in perception would be required to include the energy requirements during construction as constraints if common construction techniques continue to be used. Low-cost techniques present a solution to the above problem. However, one may argue that these tech-

niques have been researched and talked about for decades but have not been adopted and we still continue to see the same cement, concrete and brick-based technologies being used. A marketing e?ort beyond simple demonstration projects is required to infuse these technologies in building construction. A change in building codes to include and encourage low-cost or alternatively low-energy technologies is required. Coupled with these e?orts a coal tax or electricity tax may be levied on materials used in construction to discourage the use of high-energy materials. Though one can argue that we should view housing as a social issue and levying any such tax would only be transferred to consumers. A counter argument can be made that since there are technologies available, which are cheap and energy-e!cient and provide same functional utility, any increase in energy cost would induce the use of these technologies. Only if we are able to promote

P. Tiwari / Building and Environment 36 (2001) 1127–1135

low-cost, low-energy techniques, is there hope of achieving the housing targets set by the Indian government. References [1] Royal Institute of British Architects. Buildings and health: the Rosehaugh guide. London, 1991. [2] UNCHS. Global Report on Human Settlements, 1986. New York: Oxford University Press, 1987. [3] Chapman PF. The energy cost of materials. Energy Policy 1974;2(2). [4] Drakakis-Smith D. Urbanisation, housing and the development process. London: Croom Helm, 1981. [5] Gohar RD. Development and use of cheap building materials in low income housing: case study — India. In: Building materials for low-income housing. London: E. and F.N. Spon, 1987.

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[6] UNIDO. Optimum scale production in developing countries: a preliminary review of prospects and potentialities in industrial sectors. Vienna, 1987. [7] UNCHS. Energy e!ciency in housing construction and domestic use in developing countries. Nairobi, Kenya, 1991. [8] Bhagat NK, Hofman KC. The reference materials system — materials policy information system. In: Compos-Copez E, editor. Renewable resources: a systematic approach. New York: Academic Press, 1980. [9] Spence RSJ, Cook DJ. Building materials in developing countries. Chichester: Wiley, 1983. [10] Khanna PN. Indian practicing civil engineers handbook, Technical Book Publishers, New Delhi, India, 1992. [11] Tiwari P, Parikh J, Sharma V. Performance evaluation of cost e?ective buildings — a cost, emissions and employment point of view. Building and Environment 1996;31(1):75–90.