Daylighting performances and visual comfort in Le Corbusier's architecture. The daylighting analysis of seven unrealized residential buildings

Accepted Manuscript

Daylighting performances and visual comfort in Le Corbusier’s Architecture. The daylighting analysis of seven unrealized residential buildings Matteo Iommi PII: DOI: Reference:

S0378-7788(18)33128-1 https://doi.org/10.1016/j.enbuild.2018.12.014 ENB 8943

To appear in:

Energy & Buildings

Received date: Revised date: Accepted date:

8 October 2018 4 December 2018 14 December 2018

Please cite this article as: Matteo Iommi , Daylighting performances and visual comfort in Le Corbusier’s Architecture. The daylighting analysis of seven unrealized residential buildings, Energy & Buildings (2018), doi: https://doi.org/10.1016/j.enbuild.2018.12.014

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Experimental method for the evaluation of the daylighting performances of unrealized Modern Architectures, using virtual energy model. Daylighting Factors simulations. Illumination Levels simulations. Daylight Autonomy simulations. Luminance simulations. Analysis and evaluation of the daylighting design criteria of Le Corbusier

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Daylighting performances and visual comfort in Le Corbusier’s Architecture. The daylighting analysis of seven unrealized residential buildings Author: Matteo Iommi ([email protected]) University of Camerino. School of Architecture and Design of Ascoli Piceno Abstract

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This study is focused on the detection of the expected natural lighting levels of some unrealized residential houses of Le Corbusier. The attention and the interest of Le Corbusier on the topic of residential buildings are widely recognized. Moreover, it also relates to the research of growing performances about the quality of indoor environments, where the daylighting has certainly represented an important aspect, which would need further researches. The study aims to highlight new and inedited daylighting analysis for seven unrealized projects: Maison Fuerte, Maison Cumenge, Maison Canneel, Maisons pour Ingenieurs, Maison Fueter, Maisons des Peons and Maisons Rurales, designed by Le Corbusier, confirming and discovering some design criteria of this master of Modern Architecture related to the daylighting. According to the original drawings, available from the Fondation Le Corbusier, reliable and accurate virtual reconstructions of the projects have been made with which daylighting simulations have been performed for every project and indoor spaces. The daylighting simulations are run, by using advanced solar-lighting design tools, which use international standard calculations, providing results about illumination, luminance, daylight autonomy and daylighting factor. In this study, it has been used an experimental method to discover and to evaluate the daylighting performances of the seven unrealized housing projects. The results of the simulations, processed with values, indices and graphical representations, give a quantitative description of the natural light with high reliability, and with it has been possible to highlight the sensible awareness of Le Corbusier regarding daylighting, and considering the natural light as a fundamental parameter into his design strategy.

Keywords: Le Corbusier, daylighting analysis, visual comfort, energy building design tools, residential building.

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1. Introduction

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Just over half a century has elapsed since the death of Le Corbusier, in 27th August 1965. A few years ago, many conferences and events, around the world, were been organized to celebrate and to remember the work of this artist and architect, on the 50th anniversary of his death where participants had the opportunity to share knowledge and experiences and to renew the study on this master of Modern Architecture. Into his several multidisciplinary activities, which included industrial design, urban planning, literature, building architecture etc. The light and the daylighting have always been recognized as outstanding features in many of his projects, by using daylight as a fundamental design element to provide visual comfort, best illumination performances and to enhance indoor spaces. The relationship between Le Corbusier’s architecture and the daylighting is widely recognized in many studies and researches 1 that have shown the value of his design criteria and his innovations, such as bris-soleil, but primarily showing his constant research into the improvement of performances about daylighting 2. It is possible to assume that Le Corbusier had always involved the sun and the natural light into his design strategy. By studying the buildings

orientation, the position of the sun in relation to the buildings, evaluating the use of horizontal windows “fenetre en longueur”, which provided more access of natural light than vertical windows 3, in a general approach with the aim to achieve the better daylighting conditions as part of his vision of the modern architecture. Le Corbusier and others most relevant architects of the XX° sec. have changed the quality and the significance of the indoor natural light 4. In their works, the themes of the transparency and the natural light became to be fundamental elements of building design, according to the paradigms of the International Style, as reported by the Athens Charter in which Le Corbusier proclaimed “ to bring in the sun, that is the new and most imperative duty of architect” 5. Thanks to innovations about materials and constructive systems, daylighting became an essential aspect for modern architecture, with the purpose of providing more comfortable and more efficient indoor environments. It is possible to assume that Le Corbusier transformed the relationship between architecture and light deeply. Additionally, he had the merit to reasoning and studying the influence and the exploitation of the natural light in the design of confined spaces. The integration of the light with materials, building components and the internal

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manages the most valuable and complete archive of the works of Le Corbusier 13, is possible to explore the entire collection of his projects and to show that the unrealized projects are more than the realized, and in the first ones, many of these are houses. In some cases, the projects are only conceptual sketches or very preliminary building designs, but there are also some building projects with detailed design levels. According to the archive organization of the Fondation Le Corbusier, the architecture works are classified as: realized projects and unrealized projects. In the unrealized category, there are 215 projects, and 31 of these, are residential houses. In this count, villas and large apartment buildings are excluded, considering only small houses, low cost houses, terraced houses and similar. These types of residential buildings represent an important field of study for Le Corbusier 14, in which he was able to experience and to improve solutions, which will be applied in other realized projects. At the same time, it is possible to consider that, in the unrealized projects, the spatial configurations, the dimensions of building components, the internal distributions, etc. could be considered in a more authentic way, as showing more directly and clearly the original design intents proposed by Le Corbusier, thanks to the low constraints related to the not entirely agreement about detailed construction requirements. In this sense, seven projects have been selected, corresponding to all projects equipped with an adequate detail level, able to provide complete and inclusive of accurate information, needed for virtual reconstructions and lighting simulations (Figs 1-2-3-4-5-6-7). Looking at all the documents and drawings of the unrealized residential buildings, available from the archive of the Fondation Le Corbusier, the seven selected projects are: Maison Canneel, Maison Cumenge, Maison Fuerte, Maison Fueter, Maisons pour Ingenieurs, Maisons des Peons, Maisons Rurales.

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distributions is a fundamental aspect in his building design process 6-7, where the perfect integration of light, colors and materials ensures the desired spatial impression and better functions. The spatial and luminous theories were also expressed in the famous Five Points with which Le Corbusier proposed a new architecture made of air, light and color, to support its architectural vision. With the plan libre and the fenetre en longuer, he reaffirms the value of a more luminous architecture, with thanks to natural light 8, bearer of benefits and advantages about form and function. The use of shading devices, top-lighting solutions, double side-lighting solutions and selected dimensions of transparent surfaces, either full height or very small, represent some of the daylighting design elements provided by Le Corbusier, with which distribute, calibrate and increase light into its projects 9. Without discussing the extraordinary ability of Le Corbusier regarding the use natural light to emphasize his architecture and to arouse emotions, the purpose of this study is to discover and highlight daylighting performances in relation to the residential architecture of Le Corbusier, in particular for some unrealized projects. The daylighting of Le Corbusier’s architecture could be further explored, studying the projects designed for some unrealized residential buildings with which is possible to confirm some daylighting solutions and criteria and to highlight detailed and validated performances, providing in general a further contribution on the study of this master of Modern Architecture with new information and new considerations.

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1.2 The residential architecture Corbusier: the unrealized projects

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A large part of Le Corbusier’s work focuses on residential building, which represents a significant contribution to his cultural heritage. The attention and the interest of Le Corbusier to the residential theme is widely recognized, and the value of his work is also related to the research of growing performances about the indoor environmental comfort 10-11. The work of Le Corbusier has produced radical changes in the building architecture, about the design approaches of internal distribution, to the building functions, to the privacy aspects and to the relationship between indoor and outdoor 12, where the natural light always played a fundamental role. In his career, Le Corbusier, designed about sixty residential buildings, but only some of them have been realized. Thanks to Fondation Le Corbusier, which

Fig.1. Original drawing board of Maison Fuerte (1925). © FLC-ADAGP

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Fig. 2. Original drawing board of Maison Cumenge (1926). © FLC-ADAGP

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Fig. 3. Original drawing board of Maison Canneel (1929). © FLC-ADAGP

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Fig. 6. Original drawing board of Maisons des Peons (1952). © FLC-ADAGP

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Fig. 4. Original drawing board of Maison pour Ingenieurs (1940). © FLC-ADAGP

Fig. 5. Original drawing board of Maison Fueter (1950) © FLC-ADAGP

Fig. 7. Original drawing board of Maisons Rurales (1956) © FLC-ADAGP

1.3 Opportunities to study the architectural heritage by using energy simulation tools This study follows a research topic, with a focus on the evaluation of historic buildings and architectural heritage, by using recent and innovative analysis techniques 15, to discover new building performances and improve the knowledge on the design strategies related with these building types. In particular, this study is focused on the detection of the expected natural lighting levels of some unrealized residential houses of Le Corbusier. The possibility to study unrealized buildings is based on the capability which the virtual simulation tools can provide. In

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The possibility to conduct daylighting analysis on the unrealized housing projects of Le Corbusier is based on the analysis of the original documents, such as the project boards published by Fondation Le Corbusier. The daylighting analysis, performed by using virtual energy models, requires adequate information about the following: site and coordinates, orientation and architectural drawings with dimensions, to allow to make lighting simulations with 3D models. In this sense a preliminary and preparatory activity has been the evaluation of the original documentation of the entire collection of the unrealized projects, where only the seven selected projects were equipped with all the required information, with an adequate detail level able to perform reliable simulations. The starting activity has been the virtual reproduction of the original drawings in 2D CAD drawings with which have been generated as 3D CAD models. The 2D CAD drawings are used as import data for Ecotect Analysis, while the 3D models have been used as import data for Velux Daylight Visualizer. All the CAD models have been modeled with specifications and techniques useful to permit the better management into the energy simulation tools. Another starting activity has been the production of weather files, which correspond to the climate data of the locations where the unrealized houses are sited. The weather files have been performed with Meteonorm 6.1 24 or obtained from the Energy Plus weather library. The next activity has been the production of the virtual energy models of each building, according to the specific requirements of the two simulation tools to allow to run correct lighting simulations. Starting with the energy models, daylighting simulations have been performed about Daylighting Factor, Illumination Levels and Luminance Levels. The Results from simulations have been extracted and processed with numerical data and graphical representations. In the end, analysis and comparisons on the provided results have been made to evaluate the quality of daylighting and to highlight and to discover intended relationships between daylighting performances and architectural solutions.

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this sense, it is possible to assume that the only way to provide very reliable evaluations and assessments with novel representations, for buildings that either no longer exist or were never realized can be possible thanks to the current energy building design tools 16-17. There is obviously the opportunity to make surveys, diagnostics or audits with the related equipments, for existing buildings. However, for the unrealized ones, the most effective opportunity to study them is through energy simulation tools which can manage detailed parameters, like visible transmittance coefficients of windows or different sky conditions, etc. providing more reliable results with different data representations, than other possible simulation techniques like 3D printings or mockups. In recent years, in particular, the capabilities of the energy simulation tools are ever more efficient and have made it possible to obtain analysis on buildings that no longer exist or were never realized. Thanks to these design tools, which can produce virtual models, and to simulate many physical and energy aspects with high reliability, it is now possible to investigate and to obtain information, which would have been very difficult to calculate until a few years ago. The most recent energy building design tools allow to run detailed and validated simulations and to produce analysis of several physical and energy aspects, because of the advanced calculation techniques in which it is possible to obtain results, as data and representations about building performances 18-19. About daylighting analysis and about natural and artificial lights, in general, there are many advanced tools, very efficient and powerful, which can simulate light dynamics and to give back reliable results, in few time and without much effort, allowing to obtain simulations and result quickly 20-21. These tools use virtual models, can be very complex, to run calculations, reproducing the interactions between light conditions, building geometries and the visual proprieties of the model surfaces, starting from a relatively small amount of input and required data. For the daylighting analysis of the selected unrealized projects of Le Corbusier, the simulations are made with the following: Ecotect Analysis 22, and Velux Daylight Visualizer 23. The two tools are able to provide reliable lighting simulations and they can also provide very effective representations as output results. At the same time, these tools do not have limitations on the complexity of geometries that may be simulated and the calculation methods are

2.1 The virtual reconstruction of the original unrealized houses

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skylights never provided direct light but only reflected sunlight. The second selected project is Maison Cumenge, designed in 1926 and sited in Bordeaux (France). The original drawings provide all plans with dimensions, fronts with orientations, one section and an axonometric representation (Fig. 9). The Maison Cumenge is a single family house with a rectangular form and dimensions 8,2m x 10,7m. The building has three levels and it is characterized by a large portico at the ground floor and the roof terrace with a pergola at the third level. The south facade is the only facade without openings. The windows provide daylight in every indoor space, also in the little toilet room at the second floor thanks to a skylight. The number and dimensions of the windows increase from the ground floor to the top floor. One staircase, sited in the middle of the building, provides the vertical distribution. The next selected project is Maison Canneel, designed in 1929, sited in Woluwe Saint Pierre (Bruxelles), and specifically in rue J. G. Eggericx, providing the exact orientation of the building.

Fig. 8. 3D virtual representation of Maison Fuerte

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Studying the documents of Fondation Le Corbusier, seven unrealized housing projects have been selected. The detail level of these projects, with plans, sections, dimensions, orientation and site location, allow to reproduce, with reliable input data, virtual models and to run lighting simulations. For each project, a complete digital reconstruction is provided with plans, fronts, sections and 3D models. In particular, the 3D CAD models of the seven unrealized houses represent a first and partial result because they can be considered a new contribution, providing reliable and novel images and whole representations of these projects. Thanks to the high resolution copies of the original drawings, the 3D models are modeled with the highest possible accuracy, in compliance with the dimensions, the geometries and the building elements designed by Le Corbusier, and only in some cases it has been necessary to deduce the most probable solutions. The first selected project is Maison Fuerte, designed in 1925 and sited in Paris (France), in the Auteuil district. The original drawings provide plans for all the levels, three sections and one front with complete and detailed dimensions. Only the orientation of the building is not assured with the south established in front of the only exposed façade (Fig. 8). This single family house is a multilevel building with a form similar to a square with dimensions 8,1m x 7,9m, having two underground levels and four levels. The building is characterized by the only one exposed facade, while the other facades don’t have any openings, probably flanked by other buildings. The only exposed facade is mainly characterized by two very large windows, the first one at the ground floor with dimensions 5m x 3m and the second one from the first floor to the second floor with dimensions 5m x 4,1m, which have a little balcony. The vertical distribution is provided by two staircases. The first staircase starts from the second underground level to the first level, while at first level which is a double height living room the second circular staircase, sited in the middle of the building, starts until the roof terrace. Another external staircase provides an independent access to the first underground level. The roof terrace also provides with three skylights the natural light into some interior spaces at the second floor, like toilet room, bathroom and one bedroom. The skylights proposed by Le Corbusier, represent a top lighting solution. He designed horizontal voids with vertical openings, always sited in the roof terrace, which capture sunlight, allowing daylight to penetrate into the rooms below. This type of

Fig. 9. 3D virtual representation of Maison Cumenge

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sketches. Thanks to the original drawings with floor area indices and metric scales, it has been possible to determine accurate dimensions, (Fig. 11). It is a modular building system in which Le Corbusier implemented the previous studies for Loucheur House, giving the opportunity to make multiple combinations. The building system is characterized by structural parallel walls and prefabricated façades with glass or timber panels. The indoor spaces are designed to provide a specific distribution of functions, dividing private residential activities and work areas. At the top floors, there are two semi-open terraces, south oriented. In particular, the south and north facades of the building are characterized by the alternation of transparent and opaque modular panels 25. Another selected project is Maison Fueter, designed in 1950 and sited in Altnau (Switzerland). For this project, Le Corbusier designed a first solution in 1949 and a second solution in 1950.

Fig. 11. 3D virtual representation of Maisons pour Ingenieurs

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Thanks to the drawings of the fronts with dimensions has been possible establish matching dimensions of the plans of all levels (Fig. 10). The Maison Canneel is probably one of the most known unrealized buildings of Le Corbusier. It is mainly characterized by its shape, as a narrow building with dimensions 6,3m x 15,5m, and the sloping ground floor, having one underground level and four level. The building is also characterized by a detached volume, corresponding to the swimming pool and the garage above. The main facades are the short ones which are almost completely glazed, while the south facade is without openings and the north facade show some narrow windows and a balcony. Part of the third level is a double height space. The building has a roof terrace at the fourth level in which a skylight is designed to daylight a little office room above. Thanks to the several and large windows, the daylight is available from different exposures in many indoor spaces. This residential house is also characterized by the central staircase, designed as a double vertical distribution system. The wavy and complex shape of the stair is a topic in the architectural research activity of Le Corbusier with structural, functional and aesthetic functions. The next selected project is Maisons pour Ingenieurs, designed in 1940 and sited in Lannemezan (France). For this project, it has been selected the second solution, designed in May, because it is equipped with more accomplished information.

Fig.12. 3D virtual reconstruction of Maison Fueter Fig. 10. 3D virtual representation of Maison Canneel

The original drawings provide three fronts with orientation, all plans, one section and some

The second solution has been used for the virtual reconstruction, equipped with a general plan, plans, fronts, one section and with a detailed design of a section and of the south façade (Fig. 12). This building is a little one story house, except

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walls and furniture are designed with prefabricated solutions. The structural system is a steel frame and the windows have different dimensions and forms.

Fig. 13. 3D virtual representation of Maisons des Peons

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for the underground cellar room above the garage. It is designed by Le Corbusier for the mathematician professor Fueter. The house has a gross floor area of 98m2 and it is characterized by the wavy shape of the roof which is designed as a green roof. The wavy roof is visible both in the indoor spaces and in the facades which have very common windows, equipped with external roller blinds. The bigger windows are on the south facade, corresponding to the living room. In this project Le Corbusier applied his Modulor “It was a most modest programme. Such problems constitute a veritable algebra, a game of chess. Here the architectural solution had such clarity that the humble house in which the old savant had hoped to spend his old age, became dignified. The harmony of mathematics was brought to it by the Modulor” 26. The next selected project is Maisons des Peons, designed with several configurations and solutions from 1950 to 1965. The project is sited in Chandigarh (India) as part of the new urbanization program of the city. The original drawings are dated between 1950 and 1952 with urban plans, building plans with orientation and dimensions, sections and fronts (Fig. 13). Le Corbusier designed a system of residential buildings for laborers to provide large residential districts. The concept of these modular houses is based on the climatic grid with the aim to provide a building solution according to the environmental and climatic conditions of Chandigarh in India. Each residential module has dimensions 22,6m x 4,87m with surrounded walls and it is composed by a garden in front of the public street, a veranda, the house and another back garden with a toilet. The building solution is characterized by several passive energy devices like a bris-soleil, perforated walls, partial interior walls and the jutting curved roof which is equipped with a sunshade. The last selected project is Maisons Rurales, designed in 1956 and sited in Lagny (France). The available original drawings provide an urban plan, building plans with dimensions and orientation, fronts and some sketches. The original drawing boards show some differences between the first project of February and the latest solution of November, which has been chosen to solve some discrepancies (Fig. 14). The Maisons rurales represent a building design study proposed by Le Corbusier to provide prefabricated houses. The single modular system is composed by two coupled houses, separated by a wall. Each house has dimensions 7,32m x 7,95 with a portico and a garage at the ground floor and the residential activities at the first floor. The facades, interior

Fig. 14. 3D virtual representation of Maisons Rurales

3. Modeling and lighting simulations Starting from the 2D and 3D CAD reproductions, specific energy models have been modeled, which requested a supplementary modeling activity. To perform the planned simulations, it has been necessary to model 14 different 3D energy models, two for each projects: seven for Ecotect Analysis and seven imported into Velux Daylight Visualizer. Ecotect is a whole energy building tool, which couples 3D modelling interface with extensive solar, thermal, lighting, acoustic and cost analysis functions. It is one of the few tools in which simulations and analysis are simple, accurate and visually responsive. Velux Daylight Visualizer is another professional simulation tool for the analysis of daylight conditions in buildings. Velux is a validated simulation tool based on state of art rendering technology, dedicated to give daylight indices in building interiors. These tools are selected against other lighting simulation tools because they are

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light, the visible transmittance value is set at 0.80, representing an average value for the most probable single glazed glass. The daylighting simulations are run for all the indoor spaces of all the seven projects. The simulations provide indices and results for different analysis techniques: DF (daylighting factors), ADF (average daylighting factors), Daylighting Levels in lux and DA (daylight autonomy) 31-32-33. The simulations related to DF, ADF and DA have been made with Ecotect Analysis, which use a split flux method, giving numerical and graphical outputs (Figs. 15-16-1718-19-20-21-22-23-24-25-26). All the simulations are performed at 1 m. above the floors. This reference has been established against the current conventional height for light measurements which is set around 0,8m above the floors, because in some of the selected projects, Le Corbusier designed furniture like desks and shelves with greater height.

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able to perform reliable simulations and very effective output results without limitations of the geometries of the models, with import-export data facilities and because they use calculations, corresponding to the international standard methods. The compliance of simulations with standard calculation methods is fundamental to achieve assessable results. The calculation formulas used by these simulation tools are according to the International Commssion of Illuminance (ISO/CIE: CIE 171:2006), which ensure reliable reproduction of natural light performances 27. The sky model, used for all the daylighting calculations, is CIE Overcast Sky method (ISO 15469:2004 E/CIE S 011/E:2003) with outdoor illumination values related to the project sites 28. About the refractive and reflectance indices of opaque materials, a regulatory compliance mode has been applied, according to CIBSE lighting references 29, using the BRE split flux method 30. About transparent surfaces, which are fundamental in order to determine the amount of indoor natural

Fig. 15. Daylighting simulations of Maisons des Peons. Daylight Autonomy at 500 lux (%), Illumination levels (lux) and Daylighting Factors (%). Representations of false coloured maps overlaid on 2D CAD drawings. Ecotect Analysis

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Fig. 16. Daylighting simulations of Maison Fuerte. Daylight Autonomy at 500 lux (%). Representations of false coloured maps overlaid on 2D CAD drawings. Ecotect Analysis

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Fig. 17. Daylighting simulations of Maison Fuerte. Illumination level (lux). Representations of false coloured maps overlaid on 2D CAD drawings. Ecotect Analysis

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Fig. 18. Daylighting simulations of Maison Fuerte. Daylighting Factors (%). Representations of false coloured maps overlaid on 2D CAD drawings. Ecotect Analysis

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Fig. 19. Daylighting simulations of Maison Cumenge. Daylight Autonomy at 500 lux (%), Illumination levels (lux) and Daylighting Factors (%). Representations of false coloured maps overlaid on 2D CAD drawings. Ecotect Analysis

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Fig. 20. Daylighting simulations of Maisons pour Ingenieurs. Daylight Autonomy at 500 lux (%). Representations of false coloured maps overlaid on 2D CAD drawings. Ecotect Analysis

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Fig. 21. Daylighting simulations of Maisons pour Ingenieurs. Illumination levels (lux). Representations of false coloured maps overlaid on 2D CAD drawings. Ecotect Analysis

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Fig. 22. Daylighting simulations of Maisons pour Ingenieurs. Daylighting Factors (%). Representations of false coloured maps overlaid on 2D CAD drawings. Ecotect Analysis

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Fig. 23. Daylighting simulations of Maison Canneel. Daylight Autonomy at 500 lux (%) and Illumination levels (lux). Representations of false coloured maps overlaid on 2D CAD drawings. Ecotect Analysis

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Fig. 24. Daylighting simulations of Maison Canneel. Daylighting Factors (%). Representations of false coloured maps overlaid on 2D CAD drawings. Ecotect Analysis

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Fig. 25. Daylighting simulations of Maison Fueter. Daylight Autonomy at 500 lux (%), Illumination levels (lux) and Daylighting Factors (%). Representations of false coloured maps overlaid on 2D CAD drawings. Ecotect Analysis

Other simulations are made with the aim to know and to show illumination performances in lux, with isolux representations and visual comfort performances with luminance simulations in cd/m2 with false colour representations (Figs. 27-28-2930-31-32-33). These simulations are made with Velux Daylight Visualizer, only in the most relevant indoor spaces. Considering the modeling process, the calculation methods and the reliability of the original building projects reconstruction, it is possible to assume that the expected results of simulations could be proper and represent the most

Fig. 26. Daylighting simulations of Maisons Rurales. Daylight Autonomy at 500 lux (%), Illumination levels (lux) and Daylighting Factors (%). Representations of false coloured maps overlaid on 2D CAD drawings. Ecotect Analysis

probable estimations of the natural light conditions for these projects. 4. Results The performed simulations provide quantitative data about daylighting levels for all the projects, giving information for every indoor space with indices and values about illumination, luminance, daylight factor and daylight autonomy. It is possible to describe how and how much is the expected natural light into these projects, studying the results of the simulations.

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Fig. 29. Visual comfort analysis of Maisons Cumenge. View of the atelier room at the second floor. Illumination levels (lux) with isolux and Lumiance level (cd/m2) with false colours. Velux Daylight Visualizer

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Fig. 27. Visual comfort analysis of Maisons des Peons. View of the veranda. Illumination levels (lux) with isolux and Lumiance level (cd/m2) with false colours. Velux Daylight Visualizer

Fig. 28. Visual comfort analysis of Maisons Fuerte. View of the living room at the first floor. Illumination levels (lux) with isolux and Lumiance level (cd/m2) with false colours. Velux Daylight Visualizer

Fig. 30. Visual comfort analysis of Maisons Ingenieurs. View of the library room at the fourth level Illumination levels (lux) with isolux and Lumiance level (cd/m2) with false colours. Velux Daylight Visualizer

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Fig. 31. Visual comfort analysis of Maisons Canneel. View of the lunchroom at the second floor. Illumination levels (lux) with isolux and Lumiance level (cd/m2) with false colours. Velux Daylight Visualizer

Fig. 32. Visual comfort analysis of Maisons Fueter. View of the living room. Illumination levels (lux) with isolux and Lumiance level (cd/m2) with false colours. Velux Daylight Visualizer

Fig. 33. Visual comfort analysis of Maisons Rurales. View of the living room at the first floor. Illumination levels (lux) with isolux and Lumiance level (cd/m2) with false colours. Velux Daylight Visualizer

The first overall evaluation is the good natural lighting level, on average, of the all projects where high daylighting levels are prevailing and there are almost never rooms or spaces without a minimum daylight. Thanks to the several simulations, run for each project and for every plans, it is possible to know specific performances and daylight conditions (Tables 1 and 2). The performed daylighting simulations for Maison Fuerte, show high performances with average daylight factors always over 2% and average illumination levels which range around 300 lux. The daylighting autonomy analysis shows a very good availability of natural light with indices over 70%. Only the underground floors and the second floor, which correspond to indoor spaces without permanence of people, do not have optimal daylighting performances. Considering the architecture of the building with only one exposed facade, it is possible to assume that the expected daylighting levels are extraordinary, thanks to the very large windows and thanks to some solutions as skylights and narrow windows, placed on the underground floor. In the Maison Canneel there is a very constant availability of natural light on every floors and on every rooms. The simulations show average

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indoor spaces, thanks to the large narrow windows,skylights and double-side-windows. The simulations results of Maison pour Ingeniuers show different performances with low and high values. On the ground floor, intended to storage service, the available natural light is very low. In different way the upper floors, used for residential activities, have good daylighting levels with average illumination values which range between 240 lux and 360 lux, high average daylighting factors and indices of daylight autonomy always over 60%. It must be considered that the original drawings of Maison pour Ingenieurs do not provided assured information about number and distribution of windows and the results represent the outcome from a feasible solution. The Maison Fueter is the project with the lower daylighting performances. The single story house with common windows do not provide sufficient illumination levels and daylight factors with an index of daylight autonomy near 30%. Thanks to some furniture, like shelves and wall wardrobes, the distribution of daylight is increased but the overall low availability of daylight makes the indoor spaces not adequate to the residential visual tasks.

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daylighting factors from 3% to 6%, average illumination levels over 300 lux, except for the ground floor, which is an entrance and distribution space, with an average value 185 lux. The indices of daylight autonomy show values around 65% for every floors. Thanks to the several and large windows, with double-side-windows system, the distribution of illumination is very homogeneous and the luminance contrasts are reduced. In particular in the bedroom at the second floor and in the lunchroom at the third floor, the narrow windows on the northern front and the large windows on the western front provide a multilateral daylight with diffuse and direct light availability. The Maison Cumenge is another project with very high daylighting performances. The optimal orientation, and the large windows coupled with small rooms provide maximum illumination levels very high. The average illumination values increase from the ground floor with 210 lux, to the first floor with 360 until the second floor with 395 lux. At the same time, daylighting factors and daylight autonomy, show high indices, in particular at the second floor, in which the daylight autonomy is near 85%. The building provides optimal daylighting performances, maintaining enough daylight during the entire year in the main

Table 1 List of the daylighting performances of the seven projects. For each project are listed values and indices of every floors

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Daylight Autonomy Av. Min Max Av. DF Min DF Max DF Av. DA 500 Maison Fuerte Level -1 120 lux 0 lux 400 lux 2,1 % 0,0 % 7,0 % 35,9 % Level 0 300 lux 10 lux 980 lux 6,6 % 0,2 % 18,6 % 74,7 % Level +1 295 lux 25 lux 1.100 lux 6,5 % 0,4 % 20,0 % 72,2 % Level +2 100 lux 10 lux 180 lux 2,7 % 0,2 % 4,0 % 42,4 % Level +3 310 lux 80 lux 600 lux 6,8 % 1,5 % 10,0 % 82,8 % Maison Cumenge Level 0 210 lux 15 lux 1000 lux 3,8 % 0,3 % 13,5 % 54,7 % Level +1 360 lux 50 lux 1.100 lux 6,5 % 0,8 % 16,5 % 77,6 % Level +2 395 lux 110 lux 1.200 lux 7,2 % 1,5 % 16,5 % 84,2 % Maison Canneel Level 0 185 lux 40 lux 540 lux 3,2 % 0,6 % 9,0 % 60,3 % Level +1 300 lux 30 lux 720 lux 5,5 % 0,4 % 20,1 % 66,7 % Level +2 360 lux 50 lux 850 lux 6,2 % 0,8 % 18,9 % 69,9 % Level +3 360 lux 40 lux 900 lux 6,1 % 0,6 % 20,2 % 68,5 % Maisons Ingenieurs Level 0 60 lux 20 lux 90 lux 1,0 % 0,2 % 1,9 % 13,7 % Level +1 240 lux 40 lux 700 lux 4,4 % 0,8 % 11,0 % 63,0 % Level +2 245 lux 70 lux 710 lux 4,5 % 0,8 % 11,7 % 63,7 % Level +3 310 lux 60 lux 720 lux 5,6 % 0,9 % 12,2 % 75,9 % Level +4 320 lux 80 lux 780 lux 6,1 % 1,2 % 14,0 % 79,5 % Maison Fueter Level 0 90 lux 0 lux 500 lux 1,8 % 0,0 % 22,0 % 29,5 % Maison des Peons Level 0 600 lux 60 lux 1.400 lux 7,2 % 0,8 % 22,0 % 67,9 % Maisons Rurales Level +1 215 lux 0 lux 1.600 lux 4,2 % 0,0 % 20,0 % 61,5 % - British Standard 8206 “if electric lighting is not normally to be used during daytime, the average daylight factor should not be less than 5%. If electric light is to be used throughout daytime, the average daylight factor should be not less than 2%.” - IESNA RP-5-99 “When a average daylight factor is 5% or greater an interior space will appear to be well lighted. When the average daylight factor is less than 2% the interior space will seem dimly lighted.” - EN12464-1 2011. Optimal average illumination level for residential tasks (E m): from 200 lux to 500 lux

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Illumination Levels

Daylight Factors

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Table 2 List of visual comfort performances of the seven unrealized projects. Values with grey background correspond to the related figures 27-33 Luminance Level Room Max ÷ Min Luminance Ratio Maison Canneel First floor bedroom 340 cd/m2 ÷ 90 cd/m2 3,7 : 1 Second floor lunch-room 205 cd/m2 ÷ 35 cd/m2 5,8 : 1 Second floor living-room Fig.30 245 cd/m2 ÷ 85 cd/m2 2,8 : 1 Third floor library room 220 cd/m2 ÷ 48 cd/m2 4,5 : 1 Maison Fuerte First underground room 190 cd/m2 ÷ 20 cd/m2 9,5 :1 floor Ground-floor living-room 220 cd/m2 ÷ 50 cd/m2 4,4 : 1 First floor living-room Fig.28 190 cd/m2 ÷ 45 cd/m2 4,2 : 1 Second floor bedroom 70 cd/m2 ÷ 15 cd/m2 4,6 : 1 Maison Cumenge Ground-floor entrance hall 100 cd/m2 ÷ 10 cd/m2 10 : 1 First floor living-room 130 cd/m2 ÷ 45 cd/m2 2,8 : 1 Second floor atelier Fig.29 180 cd/m2 ÷ 40 cd/m2 4,0 : 1 Maison Fueter Ground-floor living-room Fig.32 65 cd/m2 ÷ 10 cd/m2 6,5 : 1 Ground-floor kitchen 70 cd/m2 ÷ 10 cd/m2 7,0 :1 Maisons pour Second floor children’s 100 cd/m2 ÷ 20 cd/m2 5,0 :1 Ingenieurs room Third floor living-room 135 cd/m2 ÷ 35 cd/m2 3,8 :1 Fourth floor library Fig.31 170 cd/m2 ÷ 35 cd/m2 4,8 : 1 Maisons des Peons Ground-floor veranda 165 cd/m2 ÷ 40 cd/m2 4,1 :1 Ground-floor veranda Fig.27 270 cd/m2 ÷ 15 cd/m2 18,0 : 1 Maisons Rurales First floor living-room Fig.33 500 cd/m2 ÷ 90 cd/m2 5,5 : 1 First floor bedroom 250 cd/m2 ÷ 40 cd/m2 6,2 :1

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- EN 12464-1 2011. “Luminance ratios bigger than roughly 10:1 between work surfaces and more distant extended surfaces in the field of vision should be avoided. Luminance ratios of no bigger than roughly 3:1 between work area (inner field) and surroundings.”

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In the Maison des Peons, Le Corbusier designed a solution also based on the optimization of the daylight. Considering the context, in Chandigarh, with a too high availability of natural light, one of the targets of the project was to provide indoor spaces without too much light, providing zones with good daylight and other zones with the minimum. The building solution with only two voids, partial walls and perforated walls “claustras” provides in the veranda zone a very good average illumination levels with 600 lux and a good index of daylight autonomy near 65%, while in the bedrooms daylighting levels are lower. In the end, the Maisons Rurales, which show high daylighting performances but also some critical conditions. The average illumination level of the first floor is 215 lux with an average daylighting factor 4,2%. The minimum and the maximum values also show a not uniform daylighting distribution with very different daylighting conditions. The number, the distribution and the different size of windows generate great variations of illumination, enhancing luminance contrasts, only partially reduced by some fixed furniture, as shelves placed near the windows in the living room, providing zones with high daylighting levels and rooms with low or without daylighting.

The evaluation of the above results can provide some considerations. One considerable aspect is represented by the multiple solutions, adopted by Le Corbusier to bring natural light into every rooms. He used top-lighting system, as skylight, in Maison Fuerte, in Maison Cumenge and also in Maison Canneel, to light some minor indoor spaces, like toilet rooms or similar rooms. In the buildings with two or more exposed walls, like Maison Canneel, Maison Rurales, and Maison pour Ingenieurs, Le Corbusier always used doubleside-windows system, enhancing illumination level but primarily achieving a very homogenous distribution of illumination. Another aspect are the fixed furniture which play a role in the distribution of illumination and luminance contrasts. In the projects equipped with fixed furniture, like wall wardrobes, cabinets or shelves, these elements have a relevance about the daylight distribution, enhancing the distribution and redirecting the light like light shelves. In the Maisons Rurales as well as in the Maison Canneel and Maison Fueter, some furniture are designed near the windows, providing surfaces to reflect and re-distribute light and reducing luminance contrast. Next, it is possible to detect a voluntary strategy, applied for every multilevel building, to increase

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opaque surfaces, while in the projects sited in locations with high sky illumination, as Maison des Peons, the transparent surfaces or voids are smaller (Table 3), proving a sort of conscious evaluation of the daylight requirements by Le Corbusier. He was probably not supported by scientific data or reference indices but he was aware of the expected effects. On the other side, there are some questionable issues specifically related to glare and visual discomfort which can be detected from the luminance results. The simulations of luminance distribution have been performed using an overcast sky model and the results need to be considered as the lowest luminance conditions. In particular, the luminance ratios show indices over or very near the current recommended ones and considering clear sky or clear intermediate sky conditions, the luminance contrasts will be higher. The possibility of direct or indirect glare is very high in several rooms of many projects, due to the large windows and to the depth of the rooms, designed by Le Corbusier.

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daylighting availability in relation to the increase of the number of floors, where the highest levels have more transparent surfaces and in the lower levels the transparent surfaces are reduced little by little. In Maison Fuerte, Maison Canneel, Maison Cumenge, and in Maison pour Ingenieurs, the daylighting factors as well as the illumination values are higher at the top floors, increasing from the lower floor to the upper floor. In the end, it is possible to highlight another sensible approach of Le Corbusier to manage in the better way the indoor daylighting. The relationship between building envelope and transparent surfaces is almost always related to the sky illumination availability, except for Maison Fueter. Looking at the values of uniform sky illumination of each location, according to CIE Standard Overcascat Sky (ISO 15469:2004 E / CIE S 011/E:2003) it is possible to highlight that there is a reliable correlation. The projects sited in locations with lower sky illumination, as Maison Canneel and Maison Rurales, have a higher windows to wall ratio, corresponding to the larger transparent surfaces in relation to the vertical

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Table 3 Comparative list of the reverse relationship between sky illumination availability of the sites and window to wall ratio of each projects Uniform Sky Window to Wall Location Coordinates Illumination Ratio Maison Canneel Bruxelles (BEL) 50°50’0N / 4°25’0E 4.000 lux 21,2 % Maisons Rurales Lagny (FRA) 48°87’0N / 2°71’0E 4.500 lux 13,1 % Maison Fueter Altnau (SWZ) 47°40’0N / 9°10’0E 5.000 lux 6,9 % Maison Cumenge Bordeaux (FRA) 44°50’2N / 0°34’5E 5.500 lux 10,8 % Maisons Ingenieurs Lannemezan (FRA) 43°07’3N / 0°23’2E 6.000 lux 16,1 % Maison Fuerte Paris (FRA) 48°51’0N / 2°16’0E 6.000 lux 8,8 % Maison des Peons Chandigarh (IND) 30°44’2N / 76°46’3E 8.700 lux 8,5 % CIE Standard Overcascat Sky (ISO 15469:2004 (E)/CIE S 011/E:2003)

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5. Discussion and conclusions

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In this study, it has been used an experimental method to discover and to evaluate the daylighting performances of some unrealized housing projects, designed by Le Corbusier. The results of lighting simulations, processed with values, indices and graphical representations, give a quantitative description of the expected natural light with high reliability, with which has been possible to highlight some design criteria of Le Corbusier, related to the daylighting design. The management of the natural light is a decisive design aspect for Le Corbusier to realize his vision of modern residential buildings 34-35, by using furniture to uniform illumination and luminance distribution, using very large windows to increase daylight autonomy and luminance contrasts, increasing

number of transparent surfaces in relation to the number of floors, using different daylighting systems as top-lighting or two-side-windows to provide natural light for every rooms, sizing windows in relation to the sunlight available for the specific site. In concerns to the adopted methodology and about the sequence of performed activities needed to achieve the daylighting analysis is possible to highlight some limits and barriers. The lighting simulations for all the projects do not consider context obstructions, eventually provided by other buildings, vegetation or other, which can affect on sunlight availability. Others simulations to investigate different scenarios, such as conditions with sunny sky and direct sunlight could have been performed. In this sense, it is necessary to consider that Ecotect Analysis with which simulations of

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I would like to gratefully acknowledge the generosity of Foundation Le Corbusier, for offer me high resolution images of the all original drawings for the required projects without which the present study could not have been appropriate and accurate.

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daylight autonomy have been performed, doesn’t use climate driven sky models and very detailed calculation formulas 36 but it provides results with an acceptable margin of error 37 and new simulations with other lighting simulation tools could be useful to bring forward and to improve this research. In addiction, the reliability of simulations could also be considered affected by the visual properties of the surfaces of the energy models, which have been set with an average regulatory mode but that could have been different and more detailed if material information were available and adequate. About the reproduction of whole 3D virtual models of the projects, which represent a preliminary contribution, it must be considered that there are already other studies and works which have already provided 3D models and representations of some projects. However it is possible to assume that these models are performed with high accuracy and with the maximum regard for the original sources, with a very low level of discretion and vagueness. The results and data showed in this study are only a part of the entire amount of simulations which were performed, referred to daylighting factor analysis for single rooms and others luminance simulations views. From this study that gives a comprehensive analysis of the daylighting performances of seven unrealized housing projects, designed by Le Corbusier, others researches could start to make comparisons or to discover further aspects. In this sense, the proposed research approach, which involves the use of energy building design tools such as lighting simulations and current digital technologies, can represent an example to be extended for thermal and acoustic performances for these projects or replicated for other buildings. It is possible to discover unknown aspects or performances to add new information or to highlight some conditions, which are not readily detectable, by using these tools on architectures from the past. In the end, it is possible to assume that Le Corbusier used in his works the natural light as a fundamental parameter, as a design strategy, considering that these unrealized projects, mainly corresponding to a preliminary design stages, already provided optimal daylighting levels. The effectiveness of the integration between architecture and daylighting levels is widely recognized by the spatial distributions continuously associated with the light levels, where in some cases, like Maison Canneel and Maisson Fuerte, thanks to the largest transparent

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