Towards a circular economy in the construction sector?

With an annu­al turnover of around €300bn¹, the con­struc­tion and pub­lic works sec­tor accounts for 40% of annu­al waste pro­duc­tion in France². These wasted mater­i­als can still often be tech­nic­ally used but they can be costly to dis­pose of, have some­times gone “out of fash­ion” or no longer com­ply with mod­ern con­struc­tion stand­ards. This same sec­tor also accounts for approx­im­ately 30% of green­house gas emis­sions³, mainly from two sources: the energy con­sumed for com­fort of use (heat­ing, air con­di­tion­ing, arti­fi­cial light­ing, mech­an­ic­al vent­il­a­tion and hot water) and the energy required for extract­ing the con­struc­tion mater­i­als, trans­form­ing them into products, trans­port­ing them and finally treat­ing them at the end of their use­ful life.

The first life cycle ana­lyses car­ried out by con­struc­tion pro­fes­sion­als have shown that the car­bon impact of mater­i­als over an entire life cycle is 50% for a new build­ing and 30% for a refur­bished one⁴. Roughly speak­ing, half of the car­bon impact of a build­ing is paid for monthly by its energy bill, and the oth­er half (“invis­ible” to the inhab­it­ant), lies in the products and mater­i­als used to con­struct the building.

Solu­tions for lim­it­ing the car­bon impact of energy con­sump­tion are now well known and are gradu­ally being put in place. They include: lim­it­ing energy needs through biocli­mat­ic archi­tec­ture and a thermally effi­cient con­struc­tion; good product con­sump­tion man­age­ment; and using low-car­bon energy pro­duc­tion (heat pumps, wood-fired boil­ers, thermal and photo­vol­ta­ic sol­ar pan­els and low-car­bon urb­an heat­ing networks).

Such decar­bon­isa­tion solu­tions are less com­mon when it comes to mater­i­als, but if we take a closer look, they already exis­ted in the past: bio-sourced mater­i­als (struc­tures made of wood or insu­la­tion made of veget­able or anim­al wool) and recycled or reused mater­i­als (that do not require an unreas­on­able amount of energy to recycle).

Mobi­us strives to devel­op re-employ­ment (a door becomes a door again), reuse (a door becomes a table⁵) and recyc­ling (a door is shred­ded and then used as chip­board or burnt for energy).

Our approach first involves dia­gnos­ing build­ings to define the quant­ity, qual­ity, ease of remov­al and car­bon impact of each of the products and mater­i­als used in their con­struc­tion. This step is fol­lowed by the devel­op­ment of a “mas­ter plan”, which involves either mater­i­al con­ser­va­tion, dona­tion or sale. If the mater­i­als can­not be kept, because, for example, they are deemed too old, they can be donated to asso­ci­ations or build­ing com­pan­ies, for example, who could then trans­fer the mater­i­als to a build­ing site and/or reuse them for their own needs, so dis­pens­ing with the need to pur­chase new mater­i­als and avoid­ing the asso­ci­ated car­bon emis­sions. The waste there­fore becomes a valu­able com­mod­ity because it is no longer con­sidered as waste but as a resource.

These mater­i­als can also be recovered by a con­ven­tion­al waste-treat­ment or demoli­tion com­pany, but using pro­cesses that allow them to be reused, pack­aged and trans­por­ted. This implies cre­at­ing and man­aging stor­age on site, which is often lim­ited in terms of the space avail­able, so that these ele­ments can be dir­ectly recu­per­ated or sold. The per­cent­age of sales is cur­rently rel­at­ively low, how­ever, and the main mar­kets are gen­er­at­ors, wooden frames and radiators.

In con­trast, we pro­pose integ­rat­ing mater­i­als ori­gin­at­ing from reuse into new or rehab­il­it­ated build­ings. This approach involves car­ry­ing out an archi­tec­tur­al and tech­nic­al feas­ib­il­ity study, from the design phase onwards, to eval­u­ate wheth­er these mater­i­als are bet­ter in terms of envir­on­ment­al impact than com­pletely new materials.

It is then a mat­ter of look­ing for future demoli­tion sites from which to recov­er poten­tial mater­i­als for reuse and then recon­di­tion them before send­ing them to a new site. This approach has been developed, for example, in the ZAC Saint-Vin­cent-de-Paul in the 14^th arron­disse­ment of Par­is, where more than 60 000 m²⁶ of build­ings have recently been demolished.

The main prob­lem with integ­rat­ing mater­i­als com­ing from reuse is the lack of treat­ment chan­nels: if you want to install 1,000 recon­di­tioned radi­at­ors in one oper­a­tion in 12 months, for example, it is not easy to find a com­pany big enough to do this. Indeed, reuse is a new domain and requires a cer­tain amount of expert­ise – for example: identi­fy­ing demoli­tion sites; recov­er­ing the mater­i­als; trans­port­ing them from a recov­ery site to a recon­di­tion­ing site; and then recon­di­tion­ing these ele­ments and send­ing them to a new, install­a­tion, site.

This is the chal­lenge we have taken on by devel­op­ing reused sub­floor­ing, which comes from demoli­tion sites through­out France and which is then sent to our Rosny-sous-Bois fact­ory, where, after being brushed, sanded and re-graded, will be reused in office build­ings, mainly in the Par­is region. The res­ult is a 75% car­bon sav­ing com­pared to using a new product, and more than 2 400 tonnes of waste avoided. The return is low, how­ever, because a product made by trans­form­ing or assem­bling exist­ing mater­i­als is still cheap­er. Reuse is the oppos­ite: you have to pay people to recov­er, treat, trans­port and repack­age the waste.

The reuse of con­struc­tion mater­i­als is good for the envir­on­ment, but, at present, it remains more expens­ive than using new mater­i­als. It is there­fore dif­fi­cult to imple­ment without a par­tic­u­lar will­ing­ness on the part of con­struc­tion companies/builders. That said, from next year the con­struc­tion sec­tor will be sub­ject to reg­u­la­tions requir­ing the lim­it­a­tion of car­bon emis­sions⁷. The ques­tion will then be: is it bet­ter to build with wood, stone, recycled or reused materials? 

Finally, as we have seen in recent months, the prices of raw mater­i­als can fluc­tu­ate sharply and deliv­ery times can become longer. For example, the price of wood and met­al has been par­tic­u­larly affected, lead­ing to both addi­tion­al costs and a slow-down in con­struc­tion or even fact­ory clos­ures. The advant­age of reuse is that it does not depend on these mar­kets and prices can there­fore remain stable over time.