how to assess the sustainability of building construction …

How to assess the sustainability of Fifth Urban Research Symposium 2009 building construction processes

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HOW TO ASSESS THE SUSTAINABILITY OF BUILDING

CONSTRUCTION PROCESSES

Luc Floissac & al1 Ecological buildings researcher

LRA/GRECAU Toulouse school of architecture

[email protected]

Summary: We propose a way to assess the sustainability of a building construction process. Building materials, energy and material consumption, waste and nuisance generation, materials end-of-life, building construction organisation social impacts are used to evaluate it. We propose indicators that can reach the above challenges and describe the results of their application. Our case study concerns the construction of three private houses in a developed country (France). These houses have the same architecture but each one uses a different building process: local materials or standard industrial productions or “fashionable” industrial materials. This paper shows that our indicators can help to facilitate the choice of construction materials in respect with sustainability.

Key Words: Embodied energy, sustainable buildings, ecological building, social impacts

HOW TO ASSESS THE SUSTAINABILITY OF

BUILDING CONSTRUCTION PROCESSES

I. INTRODUCTION Since the beginning of the industrial era, human species has developed tools and knowledge that have gradually amplified their capacity to multiply. Due to its population and individual power of predation of each of its members, the impact of the human species on the Earth has considerably grown. Therefore the remaining quantities of fossil energy resources (coal, gas, oil, uranium) will be completely depleted before the end of this century. Renewable resources, already partially tapped, will only replace a portion of these fossil resources. This substitution will be even more difficult to accomplish since the level of predation of human beings on the planet is causing serious malfunctioning of the biosphere.

1 Alain Marcoma, Luc Floissacb, Anne-Sophie Colasc, Quoc-Bao Buic, Jean-Claude Moreld ∗ a Réseau Ecobâtir, RAH Inventerre SCOP, Francarville, France. b Réseau Ecobâtir, LRA-GRECAU – Ecole Nationale Supérieure d’Architecture de Toulouse, France. c ENTPE (Ecole Nationale des Travaux Publics de l'Etat – Vaulx en Velin, France). d Réseau Ecobâtir, ENTPE (Ecole Nationale des Travaux Publics de l'Etat – Vaulx en Velin, France).


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The idea that the earth is a finite planet in the mathematical sense is commonly accepted today. In 1972, both the Club of Rome, in its report, (Meadows et al, 1972), and the first Earth Summit in Stockholm expressed this idea. The building sector does not escape from today's spotlight on the environmental impacts of human activities. In "developed" countries, the problem is defined as follows: buildings are major energy and resources consumers during both construction and usage, and also generate large quantity of waste. The building sector's industrialized organization destroys local cultures and know-how. It disqualifies workers, increases social inequalities among them by separating "knowledge-holders" from manual workers, It separates owners from tenants and standardizes landscapes. Subjected to the strong constraints of real estate speculation, buildings can only exist under the absolute rule of short-term economic profitability; it means that environmental quality (pollution, GHG emissions), health (asbestos, VOCs) and social questions (massive sub-contracting, jobs with no security, sub-qualification) are considered as simple adjustment variables. This situation contributes to reinforce tensions between human beings. Having been promoted as a model throughout recent decades, the standard industrial construction mode naturally imposes itself on new economic groups in the emerging countries. This contributes to create a worldwide "shear effect" between growing demand and supply limitation. Soon we will have to be forced by the law or by reality to adopt more environmentally-friendly practices. For building project owners, whether professional or private, the choices are therefore very complex, since sales arguments, social and environmental requirements differ widely. The goal of this paper is to help decision-makers. It proposes solid indicators for the building sector that reflects environmental and social quality of products, practices and operations.

II. BUILDING CONSTRUCTION, USAGE AND DESTRUCTION IMPACTS The indicators that we propose are focused on construction itself. Nevertheless it’s always important to take into account all building's phases: construction, usage and end-of-life.

Construction phase

Waste and nuisances Production Each year, 50 million m² (except agricultural storage) are built in France (SITADEL). It represents a large consumption of raw materials and energy (roughly 2.9 GJ/m2) and generates a large quantity of waste (ADEME). Waste processing remains a nebulous subject, in respect to the lack of interest of civil society for it. Environmental and health declaration forms published by material providers, often lack precision and transparency even if they comply with standards. Based on self-declaration, these documents should be used with caution because they are very complicated to understand for many professionals and the measurements performed are very different from one country to the other (Morel et al 2001). It is highly probable that waste and nuisance generation during construction is more alarming than the figures tend to show.

Social impacts From another standpoint, a considerable nuisance is linked to the almost inhuman working conditions in France today. In his recent book entitled "Worksite prohibited to the public", (Jounin, 2008) describes in a simple, precise way the very difficult, insecure construction working sites conditions (intense productivity, social standards disrespect…). We do not propose any directly relevant indicator for this problem, but it is possible to put forward the argument that the most deteriorated social and human conditions can be found on the worksites where the highest level of productivity is required. There is a


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strong convergence, due to the economic context, between the choice of highly mechanized techniques that destroy jobs yet generate just as much waste, and the lack of respect for the people working with these techniques. There is therefore a link between the embodied energy quantity and the respect for the workers. It is also highly likely that the self-esteem that allows individuals to resist high pressure is correlated to their use of recognized know-how. Techniques that use materials with a low degree of transformation harness workers' know-how much more than techniques using highly transformed materials. Thus there is a strong link between the increase in standard techniques used for economic reasons and the decrease in self-esteem. We propose indicators that highlight the extent of material transformation and show the social impact of construction.

Resources consumption

Energy consumption According to the Carbon Balance tool (ADEME), 2.9 GJ are currently required in France (slightly more than 1 barrel of oil) to build one square meter of a house space. Likewise, 3.7 GJ/m2 are required to build one office space square meter. In a very rough approximation, a square meter of artificial space are requires 2.4 GJ/m2 to be built. According to the (IFEN), the artificial space of French land represents 8.3% of its metropolitan area. This increases 50 000 km2 each decade. Thus in 2004, each French inhabitant "owned" 760 m2 of artificial space (including housing, activities and networks). This means that France artificial space immobilizes an energy capital of 1820 GJ per citizen. In respect to this information, the current worldwide annual oil production, i.e. 6.5 billion tons should be necessary at today's energy cost to rebuild the French building stock or to build the entire world new constructions. This shows that it is not possible to continue this way, from the point of view of energy consumption, climatic impact and equality between the planet's inhabitants.

Raw material consumption The building sector uses 2/3 of the 23 Mt of cement used annually in France, 1/3 is used for infrastructure construction, (SFIC 2007). To make construction practices more legible and their changes more measurable, reliable indicators are required to evaluate resource consumption, waste and nuisance generation, and social quality of a building construction.

Usage

Energy consumption The current heating and air conditioning consumption in France is roughly 0.4 GJ/m2 per year (Duffaure-Gallais 2007). Within seven years, this usage will consume as much energy as the building's construction. Because of their low thermal quality, the buildings heating and air conditioning needs are currently very high. This will radically change when the impact of usage will be divided by five or ten, as legislators intend and as solidarity invites us to do. In this case the energy consumption during construction will be equivalent to fifty to seventy years of usage energy consumption. Like building usage, building construction must also aim to consume less energy resources.

Thermal control The energy impact during usage is fairly well known today. Thermal consumption objectives for buildings are controlled by widely disseminated regulations and labels. The role of water in porous


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materials is neither well understood nor taken into account, although the contribution of thermal exchanges through water vapor transfer is significant, (Hall 2008). However, in response to the fairly wide gap observed between real and calculated thermal performances, this characteristic is beginning to be more widely examined. Including a permeance indicator in the building design phase would bring this calculation closer to reality (Collet et al, 2008).

Health impacts The materials composing impacts on human health requires information from the manufacturers. Trade secrets are often used as an excuse to justify the lack of this information. The REACH regulations should improve this situation in the next 15 years, if they are accompanied by a serious monitoring of health impacts.

GHG emissions reductions In addition, given the environmental urgency, GHG emissions must be reduced as rapidly as possible. Finally, it would be logical that if we divide usage consumption by five or ten in the next decade. However, in today's technical, economic and cultural context, it is much easier to make a building energy-efficient than to build ecologically, as we will see further on.

Buildings end of life Deconstruction and destruction are also partially covered by the scope of our indicators. Definitions:

- Deconstruction, consisting in dismantling a building and its materials in order to extract and separate its components and then sort them for re-use, recycling or waste disposal. - Demolition, involving their simple destruction, which makes subsequent waste sorting extremely difficult. In practice, mainly metals can be easily extracted and recycled, and the rest is disposed of as waste.

Every year France building demolition produces 31.2 Mt of waste, i.e. 20% more than household waste. Deconstruction, still embryonic in France, requires deep modification of habits concerning the design, manufacturing and installation of construction materials and buildings. In recent years the automotive sector has made efforts in this direction, while the construction sector is lagging behind. The building sector should do the same.

Deconstruction and destruction building materials as resources for re-using, recycling or energy generation Today according to the (IFEN, 2007): 2/3 of the 340 Mtons of construction waste (demolition 31.2 Mt, rehabilitation 13.5 Mt, new construction 3.2 Mt, and public works 295 Mt) are re-used as fill or as road sub-layers. Therefore 100 Mtons of remaining waste are not re-used, and we have no indication of the type of materials involved or their potential for re-use. We can imagine that a "building demolition" sector could be added to the waste treatment circuit to make it possible to reuse dismantled materials (structural timber, roof tiles, electrical or sanitary fittings, earth, stones, etc.). In a second step dedicated designed materials should be recycled with minimal environmental impact. This does not require large quantities of energy nor produces large quantities of waste, and creates new jobs (Thomark, 2002). This means that materials would have to be designed in order to separate their components with respect of health and environmental requirements conditions. Finally, as a last resort, their recovery for energy generation or possibly as aggregates could be envisaged provided that health and environmental safety are guaranteed.


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The existence of a network of building & public works material reclamation centers could already reduce the depletion of resources and the production of waste today, while guaranteeing the economic viability of numerous jobs, many of which would be accessible to the "employment-challenged". Furthermore, if an approach that clearly encouraged re-use was applied as early as the design phase and continued during the manufacturing and use of the materials, then other materials (earth, stones, insulation, floor coverings, partitions, joinery, masonry units) could also enter the re-use circuit.

III. CONSTRUCTION SUSTAINABLE DEVELOPMENT INDICATORS PROPOSAL The existing indicators can be classified in 2 categories: physical and social. Physical indicators such as thermal conductivity, permeance, specific heat, effusivity and emissivity are relevant for buildings' energy efficiency and usage comfort. It is essential to take them into account at the design phase. However, one drawback is that they only offer possibilities in the restrictive industrial framework of the products and processes recognized today by existing legislation. These indicators have not yet been sufficiently extended to non-standard materials. The data bases in design or energy performance diagnosis software applications, blind to the parameters of these materials, do not encourage their integration in the discussions during the preliminary phase. We can only hope that this will rapidly change. Since they are purely physical, these indicators cannot shed light on the social and cultural aspects of a building. As for social indicators, the most well-known one is the (Human Development Index). It is very useful but far removed from the specific features of building sector. The "ecological footprint", (Rees and Wackernagel 1996), is evocative and counts the planets surface part required to absorb a person's lifestyle. Here again, the fact that these indicators cannot be applied to several scales of territory or activity limit their usefulness in a strategy requiring overall harmonization of actions. We are faced with a problem whose solution includes both technical and cultural aspects. It is no longer simply a question of very short-term efficiency in a limited context (excluding the social environment for example); for technical efficiency to become operational, it must acquire social effectiveness. In the threefold framework of sustainable development (environmental, social, economic), we propose that the Wemb (embodied energy in GJ), MTCO2Eq (GHG emission in equivalent metric tons of carbon dioxide) and L.I. (labor intensity in hour of work per unit of embodied energy) indicators should be accepted as the first building blocks in an international effort to standardize construction activity.

Environmental impact: Wemb The embodied energy is the amount of physical work required to transform a raw material into building element. In the building sector it is measured in unit of work (GJ) per volume (m3), per weight (ton) or element (Harris 1999, Morel et al 2001). The embodied energy (Wemb) throughout the life cycle of a dwelling or commercial building provides information about its resources consumption. The scarcity or the abundance of the used raw materials is not taken into account. The embodied energy indicator allows to compare the amount of work definitively immobilized in the building according to territories, operations or techniques. This informs the energy resources allocation. It is also a good representation of global consumption, since it reveals these disparities. In the example illustrating our paper, we chose the GJ/ton unit because it allows us to link the work immobilized in the life cycle analysis with the work consumed by usage.


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About the scarcity of resources or the status of the reserves of each raw material, this information can be provided by the abiotic resource depletion indicator contained in the Environmental and Health Declaration Forms – (NF P01-010, 2004). In a finite world with limited resources, the Wemb can also provide a good idea of the possible social consequences of the disparities in buildings energy immobilization. This indicator shows energy immobilization of a square meter of housing in India, Brazil, USA or Europe does not consume the same amount of global resources. Moreover, the surface area available per person in these countries is very different. The Wemb is a product of both factors. The global amount of resources mobilized per inhabitant for buildings will be much clearer if it is based on a common language. For example it will make the reality of housing disparities much more tangible and help combat this inequality Owners, head contractors, constructors or deconstructors as well as policymakers will find this to be a solid decision support tool. In terms of health impacts or the comfort of a dwelling, and in the absence of a more precise analysis, the products, practices or materials with a high Wemb rate will be more likely to affect the health of professionals or inhabitants than raw materials used by a culture with an architecture based on "gathering" with a low embodied energy rate, (Shukla et al, 2009). We would then see a process of cultural, technical and regulatory change. Once the Wemb indicator has become the norm, strategies based on effectiveness and simplicity will have a tool that is perfectly coherent and appropriate. Using the Wemb, one can also represent the advantage for society as a whole of using certain building techniques. By expressing the embodied energy not per ton but per square meter of wall or habitable space, it is possible to compare the energy immobilized during construction by the different techniques envisaged for a project. We thus achieve a social indicator that allows us to choose the technique producing the largest number of square meters of walls or habitable space. Indeed, in a world aiming for more simplicity, the intelligent allocation of economic or energy resources is strategic.

The climate component: MTCO2Eq The emission of greenhouse gases expressed in CO2 equivalent represents the total amount of emissions encouraging climate change during the life cycle of a material.. We have chosen to show carbon sequestration in plant materials with negative CO2eq values. Indeed, we believe that the primary factor in climate change is the release into the atmosphere of carbon that has been trapped for thousands of years in the soil. The natural cycle of carbon in the air with a constant level of stock is not a factor in climate change. We thus distinguish between fossil energy release (positive CO2eq values since the stock of carbon in circulation in the atmosphere is increased), natural plant cycle activities (with no CO2eq since they do not change the stock of carbon in circulation in the atmosphere) and uses that sequester CO2 (negative CO2eq values since they remove carbon from atmospheric circulation). Building with plant materials means "fossilized" carbon. The carbon dioxide equivalent indicator CO2eq provides a good representation of the effects on climate change. It is also a good indicator of waste and nuisance generation, without of course entirely covering the problem. Preferring the use of renewable energies and materials that have been slightly transformed and transported, choosing human labor rather than fossil resources and machines, are simple ways to reduce CO2 emissions. The use of plant construction materials is also a good way to trap carbon. For instance, a beam made of healthy, untreated wood cut from a well-managed neighboring forest is much more environmentally-friendly than a metal beam manufactured in a centralized plant far away using coal energy. The CO2eq indicator is a perfect reflection of this situation. In addition, if we take into account building usage and end-of-life, this indicator sheds light on some of the health issues. However, in Europe the best chance of solving the health questions concerning building construction or usage lies in the concrete implementation of the REACH legislation. Indeed, in the medium term REACH should make it possible to have more information concerning the synthetic molecules placed on the market and their


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effects. Yet its true impact on the building material production cycle will only be felt 15 or 20 years from now. The CO2eq is the internationally recognized indicator for the application of the Kyoto protocol. It simply needs to be applied to the scale of an operation or a company to reinforce its effectiveness. It is also the indicator used by the ADEME for its Carbon Balance. Here again, a compilation of CO2eq measurements throughout building professionals' activity together with a compilation of the data acquired during usage and end-of-life will provide a good picture of the cultural change affecting building construction and usage.

Social Component - the "LI" Labor Intensity indicator The Labor Intensity is the ratio between the duration of human labor and the embodied energy. It is measured by the number of hours per GJ of embodied energy used to produce a building material. In the many articles on the notion of sustainable development and its three circles, social criteria are rarely defined. While this situation was relatively acceptable in a first phase, due to the fact that recent social history usually preferred to quantify consumption in terms of mass and market value rather than to qualify it in terms of cultural or environmental impact, years after the (Bruntland, 1987) report and its adoption in Rio, it is urgent today to agree upon a relevant social/environmental indicator. The Labor Intensity, or L.I., indicator could be the social/environmental equivalent of the economic energy intensity indicator used in conjunction with Gross domestic product - GDP (ton of oil equivalent per unit of GDP) in the sustainable development indicator dashboard in general and especially in the building sector. From a cultural standpoint and in order to respect human society’s diversity, the social or labour intensity indicator is representative of "know-how intensity". A significant portion of individual professional identity and self-esteem lie in the recognition and usefulness of the living, active know-how possessed by human beings in every society. This is therefore an indicator whose cultural impact we cannot yet measure, but that shows great potential. We are not aware of any use of this indicator to date.

IV. PERSPECTIVES 1) Using the same indicator at different territorial scales is a real asset that can truly accelerate change. In this way the global challenges facing the planet or a country are linked to the day-to-day actions of a large number of stakeholders. These indicators can be used to analyze, forecast and monitor action. If all of the actors in a project take ownership of them in these three phases, they can be excellent tools to profoundly modify the building culture in developed countries. These indicators can also be used in many other sectors in addition to the building sector. 2) The systemic and systematic use of these 3 indicators could be useful when planning and designing buildings. Clauses linked to these indicators concerning types of material, procurement distances, or the distance covered daily by the workers could be included in calls for tender. During the building construction and usage phases, "environmental analytic accounting" could usefully complete the financial analytic accounting. 3) At the end of the fiscal year, the income statement of professionals (industrial manufacturers, distributors, designers, public or private owners, social housing owners, contractors or real estate managers…) could also display a balance sheet according to these indicators.


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4) Used together, these 3 indicators can represent an effective tool to orient the building sector towards more environmentally-friendly practices, yet still let decision-makers choose an orientation that is more intensely social, environmental, energy-oriented or economic, by weighting each of these indicators in final choices. 5) The generalization of these 3 indicators will nevertheless require a lot of work by all of the stakeholders. In this respect, the French Environmental and Health Declaration Forms, NF P01-010 (Harris, 1999), or their foreign equivalents must be much more accessible and be made mandatory when new materials arrive on the market. They should be improved by adding a "non-technical summary" of the two indicators already included, and the labor intensity indicator should be added to all communication intended for the general public. They could use the same type of color bars used for energy performance diagnoses or household appliance ratings (scale from A to G). Measurement protocols and limits must be unified and clarified to allow relevant comparisons between materials, practices or operations. It could also be envisaged to submit bids in five sub-units: fossil (GJ), renewable (GJ), Labor Intensity, CO2 equivalent, local currency unit. To do so, the information provided by suppliers upstream will be crucial at each stage in a building's life cycle. Training of professionals will have to considerably evolve to integrate this practise. However, software (COCON 2009) programs should be developed in order to be able to reduce the workload, especially if companies can fill in their data bases their own practice.


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V. CASES STUDY

Houses projects description To illustrate our arguments, the application of these 3 indicators to the different items of a construction project in 2007 is assessed. The house shown here is located on a hillside in the Ariège area (France, Europe), Carla Bayle city. Fig. 1 shows the house under construction. Roughly 2 meters of its northern portion are underground. The east, south and west walls are made of a wooden construction filled with earth and straw on a cellular concrete base. The upstairs floors are made of wood. To illustrate our arguments, the application of our 3 indicators to the different items of a construction project in 2007 is assessed. The house shown here is located on a hillside in the Ariège area (France, Europe), Carla Bayle. Fig. 1 shows the house under construction. Roughly 2 meters of its northern portion are underground. The east, south and west walls are made of a wooden construction filled with earth and straw on a cellular concrete base. The upstairs floor is made of wood.

Figure 1. Local building materials house

Northeast view: concrete blocks and cement concrete walls

Southeast view: filling the walls with earth and straw

In order to exploit the 3 indicators presented in this paper, it was necessary to consider other technical choices to determine whether these indicators can really provide support to decision-makers, researchers, contractors and designers. We have simulated the same house built in the same context, but using different solutions: standard industrial techniques and fashionable methods), since these 2 solutions are currently the only ones frequently used in Europe. The composition of each house is indicated in Table 1. For the three projects we used the same techniques for the earthworks, foundations, and retaining walls, since there were not many alternatives to support a house whose load-bearing elements were made of terra cotta or concrete.


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Table 1: Houses descriptions

Building component Local materials house Standard house Fashionable house Foundations Concrete placed against

natural ground Concrete block retaining walls

Idem Idem

Walls Cellular concrete, wood and earth and straw construction

20 cm concrete blocks and 12 cm glass wool insulation

Self insulated cooked bricks

Ground floor Compacted fill, earthen slab except for concrete over 15m²

Compacted fill, concrete slab

Compacted fill, hemp and lime slab

Upstairs floor

Wooden floor, sand insulation and wooden flooring

Concrete floor, cement mortar covering to receive carpet

Concrete floor, hemp and lime covering to receive linoleum

Roofing

Wooden roofing frame, straw insulation, wooden covering on ceiling and roof board, half-round tiles

Cement blocks construction, 20 cm glass wool insulation, gypsum plasterboard, half-round tiles

Wooden roofing frame, hemp wool, gypsum plasterboard, half-round tiles

We have examined the house made of local materials using the proposed indicators, i.e. Wemb, CO2eq, and L.I., and compared its results with the over houses results. We then drew some conclusions, one of which is that these indicators are extremely relevant. The indicator values were calculated as follows: Wemb: the materials are quantified by weight and then multiplied by the values of the embodied energies per unit of weight of the material in question contained in the data base. CO2eq: likewise, the materials are quantified by weight and then multiplied by the values of the emissions of CO2eq per unit of weight of the material in question in the data base. The data source that allowed us to set up this indicator calculation (Table 2). We must emphasize the importance of comparing the different options, which avoids the problems of indicator values in the absolute. It is preferable to compare one solution to another relatively, by taking data from the same date base.

Table 2: Wemb and CO2eq data sources

Building component

Local materials house Standard house Fashionable house

Foundations Walls

Ground floor

Upstairs floor

Roofing

Office fédéral de la construction et de l’immobilier Carbon Footprint [14] Alcorn A, INIES sheet

When the data were too distant from each other, we established an average for them all. As for any data lacking in these bases, they were calculated based on worksite measurements

using the elementary data in these bases.


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L.I. (labor intensity): the materials are quantified in linear meters, surface area or volume and then multiplied by the number of hours of labor assigned to each technique. This labor time is then reduced to the quantity of linear meters, surface area or volume of material whose embodied energy is 1 GJ for the technique in question. The labor times were taken from Batiprix database for the standard techniques, and were based on measurements carried out on the worksite by Inventerre SCOP (ecological house Builder Company) for the others.

1.1. Local materials house The calculation of the embodied energy for the local materials house (Fig. 2) shows that concrete elements (foundation and retaining walls) use the most energy (they absorb more than 1/2 of the total embodied energy (99GJ out of a total 153GJ)). We can also observe that terra cotta tiles also have high energy consumption. These two items should attract the attention of researchers, contractors, designers and especially legislators, each in their field of competence, in order to reduce environmental impacts. Concerning health aspects (Fig. 3), we can observe that the high CO2 emissions of the foundations and the roof are compensated by a high level of CO2 sequestration in the walls, floor and roofing (large amount of straw and wood). The ground floors, essentially composed of an earthen slab, emitted very low CO2 quantities. The items that consume the most energy resources are those that need the least human labor (Fig. 4), and vice versa. In a society that claims to fight unemployment and protect the environment, the most labor-intensive techniques, consume the least energy and offer the most coherent link between messages and virtuous action.

Figure 2: Houses embodied energy repartition comparison (Wem).


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Figure 3: Houses CO2 emissions / sequestration repartition comparison, (Metric Tons of CO2eq).

Figure 4 : Houses L.I Labor Intensity indicator (hours per GJ) repartition comparison


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1.2. Houses comparison We recall that the other 2 houses (standard and fashionable) are not actually built, but are among the possible choices offered to the owner. The comparison of the Wemb (Fig. 5) for the three wall techniques is clear: - Ground floors: the hemp concrete covering has a large impact on the embodied energy in comparison with a mixture of sand, gravel and earth. - The upstairs concrete floor consumes large amount of energy. - For the roofing, the regulatory half-round terracotta tiles are the main energy consumer and the second is the insulation. Likewise, the use of plant materials for the insulation or the structure (wood, straw or hemp) completely determines the CO2eq result (Fig. 5). The techniques using very little energy resources also need more labour, and therefore call upon the most know-how, allowing the best redistribution of the added value (Fig. 5). Table 3 compares the results achieved for the 3 kinds of construction. We divided the values of each indicator by the value achieved with the house made of local materials, to allow a direct comparison of the results. We thus show that the gains range from 1 to 3 for all the indicators.

Figure 5: Global comparison between the 3 houses according to embodied energy, human labor content and GHG.

-50,00

0,00

50,00

100,00

150,00

200,00

250,00

300,00

350,00

400,00

Local materialshouse

Standard house Fashionable house 0 €

200 €

400 €

600 €

800 €

1 000 €

1 200 €

1 400 €

1 600 €

1 800 €

2 000 €

Embodied energy

Human labor content (days)

CO2 Emissions / sequestrations

Price (€ / m²)

Table 3: Dimensionless ratio coefficients between the 3 houses Local materials house Standard house Fashionable house

Wemb 100% 160% 240%

CO2eq 100% 170% 180%

L.I (Labor intensity). 100% 30% 20%

Price 100% 87% 120%

The local materials house is use as the reference.


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In the end, it is the house built of local materials in Carla Bayle (France) depletes the least energy resources. Although it traps carbon and therefore slows down climate change, meets social criteria much better than the other 2 solutions. The standard house has a mediocre balance with respect to energy consumption, a poor CO2 balance, and tolerable labour intensity. The fashionable house has the worst energy consumption impact, a poor CO2 emission balance and a low social performance. Yet this house as built only improves the energy resource consumption results of the standard solution by 1/3. The question of the type of foundation, immobilizing half of the total energy in this solution, must be re-examined. It should be interesting to re-examine techniques using stone, by continuing public works research focused on roadwork ballast or ground support systems on top of gabion layers. Another way to explore could also be compacted or rammed earth foundations such as those found under very old rural buildings, as well as under the ancient Roman ruins of Carthage. For the roofing and insulation, solutions already exist such as wooden shingles or thatching for the roofing, and all sorts of more or less agglomerated straw for the insulation. However, for many of these existing solutions, we need regulations that are more sensitive to the advantages of eco-materials. To be more effective, the regulations should also place stronger constraints on materials and techniques that are not environmentally-friendly.

VI. CONCLUSION Historians have shown us that the use of energy combined with human intelligence has been a determining factor in the relationship between human being and his environment. Starting with fire, then horses and slaves and finally oil, nuclear and solar energy. The energy consumed by machines improves comfort, intensifies the depletion of resources, and radically increases the direct or indirect production of waste that cannot be assimilated by the biosphere. In this article we propose three simple indicators to assess the sustainability of house construction. This study shows that these indicators can help to distinguish between several choices of construction materials. The house made of local materials has a performance at least 1.6 times better than the other two. By contrast, the house made of fashionable materials has the lowest performance in terms of "sustainability" and up to 5 times lower for labour intensity. These indicators are the most relevant when used relatively, since they depend on data that can vary according to the environment and also the reliability of the sources. For a given project, these indicators also make it possible to identify the item with the strongest impact. For our study, this item was the foundations, at least twice as impacting as the rest of the carcass. Even though these indicators do not take the entire construction process into account (for example finishing and technical equipments are not considered), they can produce results that allow deliberation. The choices have to be made in a way that is comprehensible to all, and applied in the most participatory way, with widespread acceptance by the populations concerned. It is important that all of the stakeholders use the same tools. These tools must also be accessible and easy to adopt by all, and policies must be developed in consistency with the realities measured by these tools and the results of public deliberations.


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VII. BIBLIOGRAPHY Journals: Ashish Shukla G.N. Tiwari M.S. Sodha,(2009) Embodied analysis of adobe houses, Renewal Energy, 34

755-761 Collet, F; Bart M, Serres, L; Miriel, J. Porous (2008) structure and water vapour sorption of hemp-based

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Development Hall M, Allinson D. (2008) Assessing the effects of soil grading on the moisture content-dependent thermal conductivity of stabilised rammed earth materials. Applied Thermal Engineering, doi:10.1016/j.applthermaleng.2008.03.051 Hall M, Allinson D. (2008) Assessing the moisture-content-dependent parameters of stabilised earth materials using the cyclic-response admittance method. Energy and Buildings; 40(11): 2044-2051. Harris D.J. A quantitative approach to the assessment of the environmental impact of building materials.

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