Circular Economy Strategies in Densification and Refurbishment of Residential Buildings – State of Application and Future Directions

de Souza Rocha, Fernanda Andreia; Reitberger, Roland; Staudt, Johannes; Lang, Werner Article — Published Version Circular Economy Strategies in Densification and Refurbishment of Residential Buildings – State of Application and Future Directions Circular Economy and Sustainability Provided in Cooperation with: Springer Nature Suggested Citation: de Souza Rocha, Fernanda Andreia; Reitberger, Roland; Staudt, Johannes; Lang, Werner (2024) : Circular Economy Strategies in Densification and Refurbishment of Residential Buildings – State of Application and Future Directions, Circular Economy and Sustainability, ISSN 2730-5988, Springer International Publishing, Cham, Vol. 4, Iss. 3, pp. 1899-1912, https://doi.org/10.1007/s43615-024-00365-7 This Version is available at: https://hdl.handle.net/10419/316980 Standard-Nutzungsbedingungen: Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden. 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If the documents have been made available under an Open Content Licence (especially Creative Commons Licences), you may exercise further usage rights as specified in the indicated licence. http://creativecommons.org/licenses/by/4.0/ ORIGINAL PAPER Received: 12 April 2023 / Accepted: 21 March 2024 / Published online: 3 April 2024 © The Author(s) 2024 Roland Reitberger [email protected] 1 ChairofEnergyEfficientandSustainableDesignandBuilding,TechnicalUniversityof Munich(TUM),Arcisstraße21,80333Munich,Germany Circular Economy Strategies in Densification and Refurbishment of Residential Buildings – State of Application and Future Directions Fernanda Andreiade Souza Rocha1· RolandReitberger1· JohannesStaudt1· WernerLang1 Circular Economy and Sustainability (2024) 4:1899–1912 https://doi.org/10.1007/s43615-024-00365-7 Abstract Thefastpopulationandeconomicgrowthputtremendouspressureontheplanet’sresources.Inthiscontext,thebuildingsectorisrecognizedasoneofthemostsignificantcontributorstogreenhousegasemissionsandtheuseofrawmaterials.TheCircularEconomy (CE)isexpectedtocontributetoareductionofwastelandfills,extractionofrawmaterials, andgreenhousegasemissions.ThisstudyaimstounderstandtowhatdegreeandhowCE strategiescan be appliedto the refurbishmentand densification ofresidential buildings. Usingaqualitativeapproach,thisstudyexaminestheapplicationofCEstrategiesinthe building sector through five semi-structured expert interviews. The literature identifies five CE principles for buildings: building in layers, designing-out waste, designing for adaptabilityandflexibility,designingfordisassembly,andselectingmaterials.From the interviews, designing-out waste was the most common approach for refurbishment and densification of residential buildings. Nevertheless, the implementation of CE strategies withinthebuildingsectorisstilllimitedandchallengingduetovariousbarriersandlittle encouragement. More stimuli from governments through regulations and guidelines, increasedcollaborationbetweenstakeholders,andtechnologicaladvancementsareexpected toreducetheobstaclestoimplementingCEstrategiesinrefurbishmentanddensification. Keywords Circularity·UrbanDensification·Refurbishment·ExpertInterviews· CircularEconomy 1 3 Circular Economy and Sustainability (2024) 4:1899–1912 Introduction Exponentialeconomicgrowthcannotproceedperpetuallyinafiniteworld[1],necessitatingachangeinthecurrenteconomicandenvironmentalrelationship.Projectionsindicatea 130%increaseincumulativeglobalgrossdomesticproductfrom2016to2050[2],withthe world’spopulationexpectedtosoarfrom7.8billionin2020to9.9billionin2050,ariseof over25%[3].Additionally,almost70%oftheworld’spopulationisprojectedtoresidein urbanizedareasby2050,exertingimmensepressureonnaturalresources[4].Consequently, alleconomicsectorsarestrivingtodecoupleeconomicprogressfromitsenvironmental impact[5],withtheEuropeanUnionleadingeffortsbypromotingpoliciessuchasreuse andrecyclingsince2014.ThesepoliciesaimfortransitiontoaCircularEconomy(CE), reducingrawmaterialextractionandwastegeneration[6,7].Duetoitssubstantialenvironmentalfootprint,theconstructionindustrystandsoutasaprioritysectorfortransitioning fromalineartoaCE.Buildingsaccountfor38%ofgreenhousegasemissions,40%of rawmaterialsconsumption,and40%ofwastegenerationglobally[8,9].Specifically,they consume1.6billiontonsofmaterialsannually,resultinginaCO2 footprint of250milliontons[10].Moreover,theEuropeanUnionacknowledgestheimperativeofrenovating existingbuildingstoachievethegoalofanet-zeroeconomyby2050,whichmeansanearcompletedecarbonizationofthebuildingsector[11].With76%oftheEuropeanbuilding stockpredatingenergyefficiencyregulationsandover85%ofbuildingsexpectedtoremain inuseby2050alreadyconstructed[12–14],refurbishmentanddensificationofresidential areasbecomeparamount.Furtherlegislation,suchastheEU’sfocusonlandusestrategies thataimtopreventurbansprawlandsoildegradationbyreducingbuildingongreen-field areas,evenmoreemphasizesthenecessityforrefurbishmentanddensificationofexisting residentialareas[6,15]. Inthiscontext,theCEconceptcanbeintroducedasanapproachtoreducewastelandfills,extractionofrawmaterials[16],andassociatedgreenhousegasemissions.Byusing CEstrategiesduringtherefurbishmentanddensificationprocess,materialscangainadded valueafterthebuilding’sendoflifebybeingreused,repaired,refurbished,recycled,and recovered.Additionally,theusabilityofthebuildingitselfcanbeextended[17].Studies conductedbyLeeetal.andAljaberetal.identifiedthecurrentsituationofCEstrategiesin theconstructionindustryandthefeasibilityofCEadoptioninthebuildingsector[18,19]. Thesepapersshedlightonconstructioncompanies’attitudestowardstheimportanceofCE strategiesandhighlightedthebarriersandenablerstotheadoptionoftheCEconceptinthe buildingsector.Theirfindingsprovidevaluableinsightsthatinformourunderstandingof thelandscapeandchallengesassociatedwithimplementingCEprinciplesinconstruction practices. Buildingontheseinsights,thisstudyaimstodeeplyunderstandtowhatdegreeandhow existingCEstrategiescouldbeappliedtotherefurbishmentanddensificationofresidential buildings.Theinvestigationseekstobridgethegapbetweentheoreticalunderstandingand practicalimplementationofCEprincipleswithinthebuildingsector,particularlyfocusing onthechallengesassociatedwithrefurbishmentanddensificationprojects.Ultimately,the studysuggestsfutureresearchdirectionsfortheadvancementofCEinitiativesandtherealizationofenvironmentallyresponsiblebuildingpractices. 1 3 1900 Circular Economy and Sustainability (2024) 4:1899–1912 State of the Art Inthecontextofcircularstrategiesforthebuildingsector,itisessentialtounderstandthe CEconcept.ThisstudyconsiderstheCEasdefinedbytheEllenMacArthurFoundation: “TheCircularEconomyis asystemwherematerialsneverbecomewaste,andnatureis regenerated.Inacirculareconomy,productsandmaterialsarekeptincirculationthrough processeslikemaintenance,reuse,refurbishment,remanufacture,recycling,andcomposting.Thecirculareconomytacklesclimatechangeandotherglobalchallenges,likebiodiversityloss,waste,andpollution,bydecouplingeconomicactivityfromtheconsumption offiniteresources.”[17]. InlinewiththeprinciplesoftheCE,buildings’lifecyclecanbeextendedbydesigningthemtobemoreadaptableandbyguaranteeingthatmaterialsandcomponentscanbe recoveredandreusedattheirendoflife.Understandingthedifferenttypesofmaterialsand componentsofabuildingensuresthatbiologicalmaterialscanreturntothebiosphereand technicalmaterialscanberecoveredandreused[20].Figure1illustratesthefiveprinciples ofCEwhenappliedtobuildings.Thenestedcirclesdemonstratethehierarchicalstructure, withthefirstthreeinternalcirclesbeingthemostpreferable.Themostresource-efficient strategyistoretainthealreadyexistingbuildingstockandrefitandrefurbishexistingbuildings.Fortheotherthreecircles,themostimportantstrategiesarereclaimingorremanufacturingmaterialsandcomponents,withthelastoptionbeingtorecycle[20].Thefivesections superimposedonthecirclesarethedesignprinciplesappliedtobuildingstoreducewaste andextendtheirlifecycle.Fromtheliteraturereview,itbecomesclearthattheconceptof circularityinthebuildingsectorisstilldiffusesinceCEstrategieswereappliedinvarious waysduringbuildingdesignandconstruction.Eberhardtetal.identified16differentCE strategydefinitionsintheliterature[21].Nevertheless,theauthorsalsonameddesignfor disassembly,materialselection,anddesignforadaptability&flexibilityasthemostapplied CEstrategies. Fig. 1 Circulareconomyprinciplesappliedtothebuildingsectoradaptedfrom[20] 1 3 1901 Circular Economy and Sustainability (2024) 4:1899–1912 Building in layers (shearing layers model) Thebuilding-in-layersconceptdefinesseverallayersinabuilding,eachwithadifferentlife cycleduration.Theshearinglayersmodelincludessite,structure,skin,services,spaceplan, andstuff[22].Thefirstlayeristhesite,thegeographicallocationofthebuilding.Thesite doesnothaveadeterminedlifespansinceitisˈeternalˈ.Thesecondlayeristhestructureof abuilding,whichincludesthefoundationandtheload-bearingelements.Itslifespanranges from30to200years.Thethirdlayeristheskinofabuilding,whichcontainsthefaçadeand roofandlastsaround50years.Thefourthlayerconsistsoftheservicesofabuilding,such aspipes,wires,energy,andheatingsystems.Thelifespanofsuchsystemsvariesbetween7 and25years.Thefifthlayerconsistsofthespaceplan,whichrepresentstheinternallayout, includingwallsandfloorsandtheaveragelifespanis15years.Finally,thesixthlayerconsistsofthestuff,includingfurniture,pictures,lighting,etc.Thelifecycleofthislastlayer rangesfrom1dayto7years.Thesetimespansareestimatesandfurtherresearchisrequired tobetterunderstandthisconceptinpractice[22]. Designing-out Waste (DoW) Designing-outwastemeansmakingefficientuseofresourcesduringthedesignphaseofthe constructionproject.Themainconceptistoimplementavailablematerialsasefficientlyas possibletodecreasethedemandforresourcesusedintheconstructionsector[23].Forexistingbuildings,DoWdemandstorefitandrefurbishexistingbuildingsinsteadofdemolishing andbuildingnewones.Refittingandrefurbishingexistingbuildingsmeansusingasmuch oftheoriginalbuildingaspossibletodecreasetheneedforvirginmaterialsandsavetime onsite. Design for Adaptability & Flexibility Designingforadaptabilityisacrucialstrategyfordevelopingsustainablebuildingssince itdecreasesthelikelihoodofthebuildingbecomingobsolete[24].Bydesigningforadaptability,buildingscanbeeasilymodifiedtoaccommodatetheneedsofnewusersaswell astointegratenewtechnologies[20].Thereisadifferencebetweenflexibleandadaptable buildingdesigns[13].Flexiblebuildingdesignsenableaneasyreorganizationofthebuilding’sinternalfit-outtomatchthechangingrequirementsofoccupants.Incontrast,adaptable buildingdesignsrefertobuildingsthatcanbeeasilymodifiedtotheextentoftheirlifeand suitnewuses.Nevertheless,theseterminologiesareoccasionallyneglectedorinterchanged intheliterature[25]. Design for Disassembly Beingabletoassembleanddisassemblebuildingmaterialstoenableaneconomicrecovery ofstructuralcomponentsandtheirassociatedvalueisanimportantpartofimplementingthe CE[26].Planningfordeconstructioninvolvesthedevelopmentofadetaileddeconstruction plan,whichshouldincludeinstructionsonhowtodisassembleelementsandacomplete inventoryofthebuildingcomponentsandmaterialsandhowtheycanbereused,recycled, orreclaimed[27]. 1 3 1902 Circular Economy and Sustainability (2024) 4:1899–1912 Selecting Materials Materialsplayavitalroleincircularbuildingdesign.Hence,therightchoiceofmaterials fromaCEperspectiveduringthedesigningprocesssignificantlyreducestheenvironmental impactsofbuildings[10].ToachieveaCE,materialsandcomponentsofabuildingneed tobedeclaredanddefinedinaninventory.Materialsshouldbeselectedaccordingtotheir lifespanandmaterialtype(biologicalortechnical).Additionally,materialsshouldretain theirpuritybypreventingthemixtureofbiologicalandtechnicalsubstancessothatbiologicalmaterialscanreturntothebiosphereandthetechnicalonescanbekeptinaclosedloop. Methodology ThisstudyadoptsaqualitativeapproachtoexploretheimplementationofCEstrategies inrefurbishmentanddensificationprojectsinthebuildingsector.Themethodologycomprisessemi-structuredinterviewswithexperts.Thequestionnairewascomposedofopen questions.Additional questions were asked to achieve a deeper insight into the respondents’knowledgeregardingtheapplicationofCEintherefurbishmentanddensification ofresidentialbuildings.Concerningthesampleselection,fivearchitecturecompanieswere chosen.Table1showsallparticipatingcompaniesandtheirrespectivelocations.Thefirst selectioncriterionwastoelectarchitecturecompanieswithexperienceinapplyingcircular strategiesinprojectdevelopment.Hence,duringthesearch,thecompanies’websitesand projectpublicationswerecarefullyexaminedtoensurethatthecompanyhadknowledge aboutatleastoneCEstrategy.Thisstepguaranteedthattheycouldprovidesufficientdata. Regardingthefiveinterviewees’roles,fourarearchitectsresponsibleforprojectdesignand development,andoneistheheadofengineeringresponsibleforproductdevelopment.The secondselectioncriterionwastochoosecompanieslocatedinEurope.Thisisrelatedtothe factthatmanyEuropeancountrieshaveasimilarclimateand,therefore,similarbuilding featuresandrequirements[28],aswellassimilarCE-relatedregulationsandincentives. ThecollectedinformationwasabouttheusageofCEstrategiesduringprojectdesignof buildingsandthemainchallengesandbarriers.Furthermore,datawasgatheredaboutthe differenceinimplementingCEstrategiesbetweennewandexistingbuildings.Additionally, perspectivesfromtherespondentsregardingtheeffectivenessandhoweasyitistoimplementeachCEstrategywereobtained. Participatingcompanies Locations TheNewMakers Netherlands FRANTZENetal.architects Netherlands ArchitektenCie Netherlands 3XN/GXN Copenhagen, Stockholm, NewYork, andSydney Zirkular Switzerland Table 1 Interviewedcompanies andlocations 1 3 1903 Circular Economy and Sustainability (2024) 4:1899–1912 Results CE Strategies for Buildings TheinterviewsshowthatallfivecitedCEprinciplescanbeappliedduringprojectdesign. Moreover,itisevidentthattherespondentshavedifferentmethodsofapplyingCEstrategiesintheirprojects,i.e.,eachintervieweehastheirpreferredCEstrategies.Inthisregard, therespondentfromFRANTZENetal.architectssaid:‘Firstly,wetrytodesignbuildings thatcanbereusedasawholeoverandoveragain.Secondly,ifthefirstapproachisnotpossible,wemakesurethatbuildingscanbedisassembledandreusedelsewhere.Thirdly,we trytouseasmanyrenewablematerialsaspossible.’Inaddition,therespondentsfromZirkularandfromTheNewMakersstated,respectively:‘Ourstrategyistoreusesingleelements orthebuildingitself.First,welookatwhatisthereandwhattheclientwantstodo.Then wetrytomatchboth.Thebestistokeepthesameuse.Whenthebuildingisdeconstructed, wetrytoimplementthematerialsfromthedeconstructionprocess.’and‘Ourfocusisthe flexibilityofuseandthepossibilityfordisassembly.Thedevelopmentphasecanbeflexible tomakeiteasytovariate,ithelpstochangetheusabilityofthebuildings,andattheend oflife,youcandisassemblethem.Additionally,wemakeuseofrenewable,bio-based,and recycledproducts.’Moreover,therespondentsfromArchitektenCieand3XN/GXNargued, respectively:‘OurCEstrategieslayonselectingmaterials,buildinginlayers,andusingthe Dutchchecklistcalledthe10Rs.’and‘Wemaintainastronggeometricalblueprintofour buildingpartsthroughoutourdevelopmentprocess.Thisallowsustoapplyavarietyof assembly,modular,andsustainablemethodstoeachpartandlayerofthebuildingdesign. Ourprocessisdigitallycontrolled,butphysicalmock-upsarebeingbuilttoensurethatall partsandmaterialsarecarefullyselectedandjoinedtogetherinthewayweintended.’From theinterviewsitbecameclearthatmostoftheparticipantsusemorethanoneCEstrategy. Figure2showsthefrequencythattheintervieweesmentionedthefiveCEstrategies.The mainCEstrategiescitedbytheintervieweesaredesignfordisassemblywith26%,selecting materialsanddesigning-outwaste,bothwith22%,followedbydesignforadaptability& flexibilitywith17%. Fig. 2 FrequencythattheintervieweesmentionedthefiveCEstrategies 1 3 1904 Circular Economy and Sustainability (2024) 4:1899–1912 CE Strategies Applied to Refurbishment and Densification of Residential Buildings RegardingtheapplicationofCEstrategiesinexistingbuildings,mostintervieweesimplementacommonbasicapproach:touseasmuchoftheoriginalbuildingaspossibletoavoid demolitionandsavenaturalresources.Consideringthis,thefollowingstatementscanbe highlighted: ●‘First,welookatwhatisthereandwhattheclientwantstodo.Wetrytomatchboth.’ ●‘Wetrytoreuseasmuchaspossibleoftheexistingbuildings.’ ●‘Eachprojectisdifferentandoffersnewopportunitiesandchallenges,butourmethod andprinciplesarethesame.Wethoroughlyscantheexistingbuildingsonthesiteand evaluateifthebestandmostfeasiblemethodistoreuse,recycle,orrefurb.Alotofthe oldbuildingsstillhaveastrongstructuralsystem,butthespacesandfloorheightsneed toberedesignedandreconfigured.’ ●‘Wekeepthestructuralpartofthebuildingbyanalyzingwhatcanbeused,thengofor designcriteriadependingontheproject.’ However,someintervieweesarguedthatrefurbishmentanddensificationprojectsaremore complexandcostly.Onthismatter,onerespondentstated:‘Youneverknowwhatyoufind (intheexistingbuilding),whichmakesitmoreexpensive.Itneedsmoreskilledworkersand therefore,takingitallawayandplacinganewoneiseasier’. Additionally,twooftheintervieweesfounditverydifficulttorefurbishresidentialbuildingsduetoregulationbarriersandalackofawarenessoftheclients.Oneintervieweeargued: ‘Forresidentialbuildings,inthecaseoftheNetherlands,circularityisalmostimpossible toimplementduetostandardsandregulationsforresidentialbuildings.Forinstance,fire regulation.’However,itisimportanttohighlightthatthisperceptionisdirectlyrelatedto thecompany’sresourcessuchasthenumberofemployeeswithdiversifiedknow-how.The respondentfrom3XN/GXNpresentedoneofthecompany’sdensificationprojectsasan example.Therespondentshowedthatthedesignerswereabletoreuse95%ofthestructural wallsand65%ofthecolumns,beams,andslabsofahigh-risebuilding.Asaresult,the companyachievedsubstantialeconomicsavingsandasignificantreductionofCO2emissions.Accordingtotherespondent,thearchitectsandinnovationteamwerethemaindrivers forthissuccess. Whenitcomestotheinterviewees’viewpointsontheapplicationoftheCEstrategies inrefurbishmentanddensificationprojects,twodifferentperspectivesarose.ThefirstperspectiveregardsthedifferenceintheapplicationofCEstrategiesbetweennewandexisting buildings,whilethesecondperspectiveconcernsthedegreeofdifficultyapplyingCEstrategiesduringprojectdesign.Regardingthefirstperspective,forsomeoftherespondents, thereisnodifferencebetweennewandrefurbishment/densificationprojects,whileforothers,thelackofflexibilityoftheexistingbuildingisachallenge.Forexample,therespondent fromArchitektenCiesaid:‘Weworkonnewandrefurbishmentprojectsinthesameway; theonlydifferenceisthatforexistingbuildings,wefirsttrytoanalyzewhatcanbeused, thenwegofordesigncriteria.’,whiletherespondentfromZirkularsaid:‘Itisbesttokeep thesameuseofthebuildings.Otherwise,theprojectbecomescomplextoapplycircularity’. 1 3 1905 Circular Economy and Sustainability (2024) 4:1899–1912 Concerningthesecondperspective,eachrespondenthasauniqueviewpointregarding thedegreeofdifficultyinapplyingCEstrategiesduringprojectdevelopment.Inthiscontext,thefollowingstatementscanbehighlighted: ●‘Designforadaptabilityisdoable,butitcostssometimes.Existingmaterialsarethe mostcomplicatedbecauseyoumustadapttowhatyoufind.’ ●‘Theeasiesttoapplyisthedesignfordisassemblybecauseyoudonotneedadifferentdesigntodoit;itisjustdetailing.Oppositely,designforadaptability,youneeda differentdesignthatisnotnormalnowadays.Designing-outwasteisthemostdifficult becausethebuildingindustryisnotyetusedtoit,anditisaperfectsituationthatdoes notexistatthemoment.’ ●‘Materialselectionistheeasiestbecauseyoumustdoitupfront.Firstmaterialsandthen design;otherwise,youraisecostandcomplexity.(Themostdifficultis)buildinginlayers(youdoit)becausesometimesitmakessensetointegrateelements.Focusonit5% duetoitscomplexity.’ Moreover,whentherespondentswereaskedtorankthefivestrategiesfromthemosteffectivetotheleasteffective,mostofthemensuredthatarankingwasnotpossible.Forinstance, respondentsArchitektenCieand3XN/GXNsaidthatallofthemareeffectiveand,therefore,itisnotpossibletorankthem.Onerespondentarguedfurther:‘Everyapproachisso differentfromprojecttoproject,andtherefore,allofthemareimportant.Additionally,I wouldaddthatbecauseeachprojectdiffersfromthenext,therankingoftheprinciplesalso changesandisre-evaluateddependingontheproject’schallenges.’Inthiscontext,even thoughsomeoftherespondentsrankedthestrategies,theyclearlystatedthatallofthemare essentialfortheapplicationofcircularityinthebuildingsector. Challenges of the CE Strategies Severalchallenges toimplementing CE strategies in new and existing building projects werenoticeablefromtheliteraturereviewandtheinterviews.Thesecanbeassociatedwith threepredominatingchallenges:economical,institutional,andsocial.Table2showsthe identifiedchallengesandtheirsub-challenges. MostrespondentsarguedaboutthedifficultyofapplyingCEstrategiesinnewandexistingbuildingprojectsduetofinancialaspects.Forinstance,oneintervieweesaid:‘Today’s investmentstrategiesarebasedonfinancialdecisionsystemsinwhichfuturevaluesare Challenges Sub-challenges Economic •Highcosts •Lackoffutureview Institutional •Lack/notclearregulationsandguidelinesto encourageCE •Regulationsthatworkasanobstacleto implementingCE •Lackofknowledgeandexperienceofstakeholders(architects,engineers,etc.) •Lackofcommunicationbetweenstakeholders Social •Lackofawareness •Lackofencouragement •LackofcommitmenttoCEimplementation Table 2 ChallengesoftheCE strategies 1 3 1906