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Simplified and reproducible building Life Cycle Assessment:

Validation tests on a case study compared to a detailed LCA with

different user’s profiles

Authors: Bonnet, Romain1; Hallouin, Thibault1; Lasvaux, Sébastien2; Sibiude Galdric2

1 Bouygues Construction, Guyancourt, France 2 University Paris-Est, Scientific and Technical Centre for Buildings (CSTB), Saint Martin d’Hères, France

Abstract: The Life Cycle Assessment (LCA) is a methodology to evaluate the building

environmental impacts for the production, use and end-of-life phases. Two main barriers still

limit the LCA to be largely used in the construction sector: time-consuming approach and non

reproducible results between practitioners. In this study, we present a combined approach to

conduct reproducible and simplified building LCAs. The simplified methods were defined

based on the target group needs (e.g. construction companies). Each approach decreases the

degree of freedom for the users while focusing on the main impact sources. Results show a

deviation of results no more than 20% between the complete and simplified LCA methods. A

better reproducibility between users is found for the simplified methods due to the predefined

parameters (in opposite to the complete LCA). In addition, considerable time saving was

reported. Our proposal should now be applied to a bigger sample of professionals of the

construction sector to collect more feedbacks.

Keywords: LCA, embodied impacts, buildings, simplification, reproducibility

1. Introduction

The Life Cycle Assessment (LCA) is more and more recognized as a relevant methodology to

evaluate the building environmental impacts for the production, use and end-of-life phases. It

has been applied in the construction sector for many years and led to the development of

several LCA softwares in Europe [1] [2]. Two main barriers still limit the LCA to be largely

used with confidence in the construction sector. First, it is due to the time-consuming of a

complete LCA study, especially for the assessment of the embodied impacts related to

construction products integrated in a building. Unlike simple manufactured products, a

building can be breakdown in dozens or hundreds of elements. Secondly, without detailed

rules, we can still find very different results between two users on the same LCA tool

depending on the chosen system boundaries, the quality of the bill of quantities, the user

profiles and experiences. Previous studies already showed that the LCA embodied impacts for

buildings can diverge due to the different scope of the modelling e.g., different boundaries,

different LCA data, different representativeness of the studies [3]. A first requirement to

harmonize LCA practice in the building sector is to rely on the same scope. In Europe, a first

contribution was provided by the CEN TC 350 committee, which released two standards on

products and buildings LCA [4]. In addition, a recent operational guidance InfoHub for

building LCA (derived from the EeBGuide project) recommends using the EN 15804 and EN

15978 standards in the LCA practice [5]. The EeBGuide outcomes also proposed to go further

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by developing different study types (screening, simplified and complete LCA) in a building

LCA tool according to the stakeholders’ needs [6].

In this paper, we are interested in deepening the EeBGuide proposal for simplified LCA of a

building. The interests of a simplified LCA method are mainly the reduction of the modelling

time and the improvement of reproducibility between different users of the tool, due to the

definition of harmonized parameters e.g., for LCA data or system boundaries. The simplified

solutions have to be adapted to the user profiles and should be provided with guidance to be

used in decision making. Moreover, the simplification should not decrease the accuracy of the

global LCA results by keeping the sensitivity of results to major design parameters. Indeed,

the simplification rules should be focused on the LCA tool interface by provided the limited

number of parameters, based on empirical knowledge (e.g., previous LCA results of buildings

can lead to the identification of the main impact sources and the simplified LCA method can

benefit from them). In this study, we present a collaborative work with a LCA tool developer

and a construction company conducted in the framework of a national research project [7]. A

combined approach is proposed for reproducible and simplified building LCAs.

2. Scope of the study

The simplified LCA methods are only developed and applied on new multi-residential

buildings. This building type, in Europe and in France, mainly represents low energy

buildings e.g. consuming less than 50 kWh/m²/year for the regulatory uses of the thermal

regulation (heating, cooling, domestic hot water, lighting, auxiliaries).

2.1. System boundaries

According to the EN 15978 standard “Sustainability of construction works, assessment of

environmental performance of buildings, Calculation method”, module A (impacts related to

the production of a product, its transport and the loss of the product on-site), module B (the

number of replacement rates linked to the maintenance actions considered) and module C

(end-of-life) are considered for the impacts related to the building products and technical

equipment”. Figure 1 presents the system boundaries in relation to the three study types

(screening, simplified and complete LCA) and the building type. This figure is derived from

the EeBGuide InfoHub for building LCA [5]. Table 1 presents the nomenclature used to

classify the elements according to the “HQE Performance” application rules [8].

2.2. LCA data used

Generic LCA data for building products and technical equipment are used in this study. These

are based on Environmental Product Declaration (EPD) available in the national reference

database INIES [9]. EPD are sector-specific LCA data, describing the impacts of one or

several manufacturers that sold their products on a national market (e.g. the French market).

When some EPD are missing for some products or equipment, generic data from the

ecoinvent database are used. The generic LCA data based on EPD or ecoinvent are calculated

following the NF P01-010 and EN 15804 standards from cradle-to-grave (i.e. for modules A,

B and C cf. Figure 1) [4].

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Table 1: Nomenclature used to classify the elements according to the HQE Performance application rules

Classification of the building elements in 14 parts 1. External work 2. Foundations - infrastructure 3. to 7. Building products associated to the building envelope (superstructure) Structural elements Roof elements Interior walls Windows and joinery work Interior finishes 8. to 14. Technical equipment HVAC Sanitary facilities Electricity and communication network Safety equipment Lighting Lifts On-site electricity generating units (wind power, PV panels)

2.3. Environmental indicators

Seven indicators were used based on the French and European standards for LCA in the

construction sector. Table 2 presents the names, units and abbreviations of these indicators.

Table 2: List of environmental indicators considered in this study

Indicators Abbreviations Units Total primary energy PE kWh Water consumption WC l Waste production WA kg Radioactive waste production RW kg Global Warming potential GWP kg eq-CO2 Acidification potential AP kg eq-SO2 Photochemical ozone formation potential POCP kg eq-C2H4

3. Development of simplified LCA methods

Figure 1 presents the goal and scope of the simplified LCAs (cf. section 2) in relation to the

targeted users’ group (construction companies). The simplified LCA methods are developed

based on the outcomes of the EeBGuide InfoHub for building LCA. Screening and complete

LCA are also reported to be consistent with the EeBGuide LCA guidance but are not

described in this paper. The following requirements taken into account in the development of

simplified LCA methods are as follows:

• Keep a good level of accuracy for the simplified LCA compared to a detailed LCA

• Reduce LCA modelling time by focusing on the main impact sources or on default

values

• Involve third-party (e.g. a building stakeholder) to match the simplified LCA method

to the user needs

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Improve the reproducibility of LCA results by defining harmonised and predefined LCA data

or system boundaries so that different practitioners can still achieve a similar LCA result (in

opposite to complete LCA with a higher degree of freedom). With these key requirements in

mind, the next sections present two simplified LCA calculation rules for the assessment of

embodied impacts of new multi-residential buildings. They are the results of collaboration

between a LCA tool developer (CSTB) and a building stakeholder (Bouygues Construction).

Figure 1: Goal and scope for the simplified LCA methods in relation to the targeted users’ group for the

contributor “building products and technical equipment”

3.1. Pareto simplified LCA method

The simplified LCA method “Pareto” is based on the general principle stating than “80% of

the consequences are linked to 20% of the causes”. In LCA, it means, for a same building

type, that only a limited number of building elements significantly contributes to a given

environmental impact (e.g. the global warming).

The Pareto calculation rules can be breakdown in three parts:

� First, the definition of a reduced LCA using a harmonised and predefined list of

elements associated to generic LCA data.

� Second, the calculation of ratios derived from the complete and reduced LCA results

� Third, the reduced LCA results per indicator are multiplied by the statistical ratios in

order to compensate the neglected elements leading to the simplified LCA method

“Pareto”.

In step 1, the elements that are mainly impacting in multi-residential projects are identified for

instance reinforcing steel, foundation concrete and superstructure concrete. For the same

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system boundaries (see Figure 1 and Figure 2), several building LCA case studies are

conducted to derive the statistical ratio between the complete and the reduced LCAs. Ratios R

are derived using the following formula:

Then, the ratios are applied to the reduced LCA results to convert them in simplified LCA

results “Pareto”. The statistical ratios applied enable to keep the same level of completeness

compared to a complete or detailed LCA while reducing the time spent by the practitioners.

3.2. EMMA simplified LCA method

The simplified LCA method “EMMA” is based on the general principle arguing that the

quantities of elements implemented in a building are linked to global parameters defined in

early design stages e.g., net floor surface area, number of storeys, windows surface area,

number of flats in a residential buildings. We mention that such approach has been used for

many years in cost studies, by general contractors willing to reduce time spent in response to

call to tenders. Here, the same approach is transferred to the environmental accounting.

The EMMA calculation rules can be breakdown into three parts:

� First, the definition of a list of elements

� Second, the building parameters that are linked to the elements (e.g., number of

storeys etc.)

� Third, statistical ratio of quantities based on empirical knowledge within the

construction company (e.g., taken from cost studies)

These three aspects can be determined from bill of quantities, invoices, or feedbacks from

previous projects of the same building types. Yet, the overall reliability of this simplified

LCA method will rely on the sample size of previous projects, and on the sound analysis of

relationship between the building parameters and the quantities of elements. Main

relationships for multi-residential buildings (mostly built in reinforced concrete in France) can

be per linear, surface area or units of building elements. For instance, from the linear of

facades, it is possible to have a proxy of the surface area of the facades based on the heights

of each storey. Then, an automatic estimation of quantities of concrete, steel, insulation,

interior coating can be derived (valid for loadbearing concrete structure). Similarly, the

separation between wet and dry rooms in the building lead to two types of surface area also

leading to the determination of cover floors (e.g., soft cover floors for dry rooms and ceramic

tiles for wet rooms). Finally, quantities of elements can be derived from unit of equipment

e.g., for HVAC. In that case, the statistical ratio of material quantities can be adjusted to the

type of heating or ventilation system. In the end, a reduced amount of early design parameters

enable to quantify all the elements. Then, a generic LCA data is associated. Then, the

simplified LCA provides the same level of completeness as a complete LCA though with less

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effort. This method is well fited for early ecodesing approach, because it is easier to compare

different scenarios or variants.

4. Results

The two simplified methods have been implemented in the ELODIE® LCA software for

buildings [10]. The results presented in this section concerne the assessment of the embodied

impacts of a real project of two multi-residential buildings located in France (see Figure 2).

The net floor surface area is 4687 m² and each building has six levels above the ground and

one underground car park. The LCA results are expressed per m² of net floor area per year.

The baseline reference study period (RSP) is set at 50 years.

Figure 2: 3D view of the building in advanced design

4.1. Validation of the two simplified LCA with detailed LCA on the building case study

Figure 3 presents the deviations in % between the simplified methods and a complete LCA.

We notice a fairly good accuracy of the two simplified LCA methods with systematically

more than 80% of the results of the detailed LCA. The POCP and WA indicators present the

lowest level of accuracy for the Pareto method with 85% while for all the other indicators the

error margin does not exceed 10%.

Figure 3: Results’ deviations between a detailed LCA and the two simplified LCA methods

4.2. Reproducibility tests of the two simplified LCA methods with different user profiles

Results from Figure 3 show a fairly low loss of accuracy between the two simplified LCA and

the detailed LCA. Figure 4 now presents a first pilot-test conducting on a sample of different

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user profiles from a construction company. Nine different users representing different profiles

in the construction company’s stakeholders (e.g., LCA practitioner with low experience vs.

high expertise etc.) were asked to model the multi-residential building case study using these

simplified methods. They use the same building design documents (program, plan, costing).

Results of the case study showed a fairly good reproducibility when using these simplified

tools and detailed guidance. The reproductibility with EMMA and with PARETO is quite

similar.

Figure 4: Results’ deviations between the different user profiles for the two simplified LCA methods

Conducting simplified LCA also avoid spending a lot of time modelling elements per elements the building. As an illustration, Table 3 presents the average time needed for the different practitioners. Table 3: Average time spent by the different users for each type of LCA (complete, Pareto and EMMA) in the

multi-residential case study

Indicators Average time spent Complete LCA 12 hours Simplified LCA – Pareto 3 hours Simplified LCA – EMMA 8 hours

We notice that the time allocated by the construction engineers to the LCA drop from 33%

with the EMMA simplified LCA to 75% with the Pareto method. As stakeholders cannot

afford much time to conduct a LCA study especially in early design, such a compromise

between accuracy, data requirements and efforts (time and cost) is probably the best method

to invite more building stakeholders to the LCA approach.

Further works should now be conducted to propose whole simplified LCA of building taking

into account the embodied impacts but also the operational water and energy consumption.

Similarly, further simplified LCA methods should be proposed to match the needs of other

stakeholders (e.g. architects, thermal analysis design office etc.).

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Conclusions

This paper presents a contribution towards simplified LCA following the general provisions

and guidance of the EeBGuide European InfoHub on building LCA [5]. Simplified LCA is

needed in construction LCA practices as practitioners do not have a lot of time to assess the

environmental performances of their projects. This study showed the feasibility of simplified

LCAs. Considerable time saving was reported between a simplified and a detailed LCA while

keeping a fairly good accuracy. It would now be useful to validate the simplified LCA tools

with a bigger sample of professionals of the construction sector to collect more feedbacks. In

the same time, even if useful in early design or in quick LCA of new buildings, the

practitioners should remain aware that the results of the simplified LCAs present a substantial

uncertainty due to the reduced level of description of his project. However, if more time or

more information is available, the practitioner will be able to precise the modelling and thus

decrease the level of uncertainty linked to the level of description of the project.

References

[1] Lasvaux S, Gantner J, Saunders T. “Requirements for building LCA tool developers, Deliverable 4.3”. European Project EeBGuide, 2012, 46 p., available online: www.eebguide.eu/eebblog/wp-content/uploads/2012/12/D-4.3.-Requirements-for-Building-LCA-tool-designer.pdf

[2] Peuportier B, Herfray G, Malmqvist T, Zabalza I, Staller H, Tritthart W, Wetzel C, Szalay Z. “Life cycle assessment methodologies in the construction sector: the contribution of the European LORE-LCA project”. SB11 Helsinki, 10 p.

[3] Dixit M, Fernandez-Solis J, Lavy S, Culp C. Need for an embodied energy measurement protocol for buildings. Renewable and Sustainable Energy Reviews 16 (2012) 3730–3743

[4] EN 15978: Sustainability of construction works – Sustainability assessment of buildings – calculation method. CEN – European Committee for Standardization. Brussels: CEN – CENELEC 2010.

[5] EeBGuide Project “Operational Guidance for Life Cycle Assessment Studies of Energy Efficient Buildings Initiative” InfoHub available online: www.eebguide.eu, accessed 14/05/2014

[6] Lasvaux, S., Gantner, J., Schiopu, N., Nibel, S., Bazzana, M., Bosdevigie B., Sibiude, G. 2014. Towards a new generation of building LCA tools adapted to the building design process and to the user needs? Proceedings of the International Conference on Sustainable Buildings, Construction Products & Technologies, SB13 Graz, 25-28 September 2013

[7] Benefis, 2014. Accurate, simplified and reproductible Energy and Environnemental balance of buildings, building LCA research project funded by the French National Agency, www.agence-nationale-recherche.fr/en/anr-funded-project/?tx_lwmsuivibilan_pi2[CODE]=ANR-11-VILD-0001, accessed 24/04/2014

[8] ASSOCIATION HQE. “HQE Performance: Première tendance pour les bâtiments neufs / First Trends for new buildings”. Report from the HQE Performance Test 2011. Available online: www.assohqe.org/hqe/IMG/pdf/HQE_Perf_-_BD_PPP.pdf

[9] INIES, The French EPD database for building products, retrieved on 10/05/2013 from: www.inies.fr

[10] CSTB. ELODIE® LCA software for buildings, retrived on 10/05/2014 from: www.elodie-cstb.fr

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