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.