How to decarbonise the construction sector, without shifting the problem

When it comes to the envir­on­ment, the cure can some­times prove worse than the dis­ease. One of the best-known examples is dies­el. Since it emits few­er green­house gases (GHGs), it was long con­sidered a bet­ter altern­at­ive to pet­rol – until we became aware of the health and envir­on­ment­al effects of the oth­er gases and particles emit­ted in large quantities.

The con­struc­tion sec­tor is not immune to these false solu­tions, as Valérie Desauzi­ers illus­trates: “When ana­lys­ing the indoor air qual­ity in fit­ness centres¹, we real­ised that cer­tain recycled rub­ber mats emit sub­stances that are harm­ful to health. The ini­ti­at­ive is com­mend­able from an envir­on­ment­al per­spect­ive, but it must not come at the expense of human health.”

So, how can we ensure we do not replace one prob­lem – GHG emis­sions – with anoth­er? Or shift it geo­graph­ic­ally or over time?  “Life cycle assess­ment (LCA) is the only meth­od for eval­u­at­ing the vari­ous envir­on­ment­al impacts,” replies Adélaïde Feraille. LCA is a stand­ard­ised assess­ment meth­od that takes into account the impacts of a product’s entire life cycle – from man­u­fac­ture and trans­port through to use and end-of-life. The impacts con­sidered include not only GHG emis­sions but also numer­ous oth­er envir­on­ment­al impacts: water qual­ity, air qual­ity, soil pol­lu­tion, etc. Since the 1990s, LCA has been used in the con­struc­tion of new build­ings. It has since been exten­ded to neigh­bour­hood-scale pro­jects and renov­a­tion schemes².

“There is no mir­acle solu­tion that is com­pletely neut­ral for the envir­on­ment or health,” points out Adélaïde Feraille. “LCA should be seen as a decision-mak­ing tool: it was designed to com­pare altern­at­ive solu­tions, tak­ing into account all impacts.

Since 2022, the latest envir­on­ment­al reg­u­la­tions to come into force – RE2020 – have, for the first time, incor­por­ated the envir­on­ment­al per­form­ance of build­ings, based on life cycle ana­lys­is. The con­struc­tion of a new build­ing must there­fore meet tar­gets for energy effi­ciency, reduced car­bon foot­print and com­fort in the event of extreme heat³.

LCA proves par­tic­u­larly use­ful, for example, when choos­ing a building’s thermal insu­la­tion. Indeed, the thick­er the insu­la­tion, the great­er the insu­la­tion per­form­ance and the great­er the energy sav­ings. How­ever, the man­u­fac­ture of the insu­la­tion itself requires energy: bey­ond a cer­tain threshold, the thermal bene­fits no longer off­set the energy con­sumed in pro­du­cing the insu­la­tion. LCA enables this lim­it to be determ­ined to ensure that the choice of insu­la­tion is bene­fi­cial from a cli­mate perspective.

Nev­er­the­less, in prac­tice, it is very dif­fi­cult to incor­por­ate all the impacts of a solu­tion into a life cycle assess­ment. “Many meth­od­o­lo­gic­al issues are still under dis­cus­sion,” points out Adélaïde Feraille. “LCA is a tool developed for the pro­duc­tion of goods; adapt­a­tions are needed to apply it to the build­ing sec­tor. Assess­ments face numer­ous lim­it­a­tions: incom­plete data­bases, dif­fi­culties in defin­ing the bound­ar­ies of the sys­tem being assessed, and so on.”

One of the short­com­ings of LCA con­cerns the health impact of decar­bon­isa­tion solu­tions in the build­ing sec­tor. “Emer­ging mater­i­als, developed through an eco-design approach, may emit tox­ic sub­stances for which we lack data,” explains Valérie Desauzi­ers. These mater­i­als, used in our homes or pub­lic build­ings, can thus pol­lute indoor air or food matrices. “These may be addit­ives, but also sub­stances not inten­tion­ally added that form through chem­ic­al reac­tions dur­ing the man­u­fac­ture or degrad­a­tion of the eco-designed mater­i­al,” explains Valérie Desauziers.

A well-man­aged renov­a­tion or con­struc­tion pro­ject can mul­tiply the bene­fits for the cli­mate, biod­iversity and health

Anoth­er example: the cir­cu­lar eco­nomy. “Since the Anti-Waste and Cir­cu­lar Eco­nomy Act (AGEC), it has been man­dat­ory to carry out an assess­ment and recov­er mater­i­als dur­ing demoli­tion work or major renov­a­tion pro­jects,” adds Valérie Desauzi­ers. How­ever, whilst this approach is bene­fi­cial for the cli­mate, it can have harm­ful con­sequences for health. Cer­tain struc­tur­al ele­ments reused in fur­niture, for example, may—if they have been treated with insect­icides now banned—pose a health risk to residents.”

Con­versely, a well-man­aged renov­a­tion or con­struc­tion pro­ject can mul­tiply the bene­fits for the cli­mate, biod­iversity and health. In cer­tain con­texts, rammed earth stands out as a very inter­est­ing build­ing sys­tem: “It is a bio-based mater­i­al that does not require sig­ni­fic­ant energy expendit­ure to pro­cess or trans­port when the source is loc­ated near the con­struc­tion site,” explains Valérie Desauzi­ers. “Our ongo­ing research – not yet pub­lished – shows that, thanks to its absorp­tion prop­er­ties, this mater­i­al also helps to reg­u­late cer­tain indoor air pollutants.”

The IPCC’s Sixth Assess­ment Report⁴ high­lights the poten­tial co-bene­fits for the envir­on­ment: reduced acid­i­fic­a­tion and eutroph­ic­a­tion near con­struc­tion sites, improved biod­iversity thanks to green roofs and walls, and reduced pol­lu­tion through reduced cor­ro­sion of build­ing mater­i­als. A 2020 study⁵ cited by the IPCC assesses the poten­tial sav­ings in nat­ur­al resources – fossil fuels, met­al ores, metals – under an energy effi­ciency scen­ario for European build­ings. The res­ult is that for every mega­watt-hour (MWh, the unit of energy) of final energy demand saved in the res­id­en­tial sec­tor, 406 kg of nat­ur­al resources are saved. For non-res­id­en­tial build­ings, the fig­ure rises to 706 kg per MWh of reduced energy demand.

Adélaïde Feraille con­cludes: “There is no sil­ver bul­let, and it is neces­sary to con­sider the con­text to make the best choice. How­ever, resource effi­ciency and optim­isa­tion are con­cepts that apply to all pro­jects, and LCA helps us to imple­ment them.”

Anaïs Marechal