Design strategies for integration of green roofs in sustainable housing

56 The Li ing Roo - Academy o Sciences by Daniel Rami ez, 03/03/2010, used unde CC BY 2.0, modi ica ion: cu , sou ce: h ps://www. lick .com/pho os/dan ama ch/4439864056/in/album-72157623562136212/ Vi u io In e na ional jou nal o A chi ec u e Technology and Sus ainabili y Volume 0 57 ABSTRACT Design s a egies o In eg a ion o G een Roo s in Sus ainable Housing A i F iedman1 1 School o A chi ec u e, McGill Uni e si y G een oo s a e he in eg a ion o plan ma e ial and i s suppo ing s uc u es in buildings. Such an app oach p o ides a habi a o local lo a and auna, helps manage s o m wa e , educes hea demand in win e and he cooling load in he summe , enhances he aes he ic alues o dwellings, p o ides he occupan s wi h com o and ameni ies and s eng hens en i onmen al esponsibili y. Because oo s ep esen app oxima ely 40 pe cen o 50 pe cen o he su aces in u ban a eas, g een oo s ha e an impo an ole in d ainage and as a esul wa e managemen as well. In ac , when a g een oo is ins alled on 50 pe cen o mo e o he oo ’s su ace, i gua an ees 2 poin s and can con ibu e 7 addi ional poin s owa d LEED ce i ica ion - almos 20 pe cen o he equi ed a ing. This pape classi ies g een oo s and o e s s a egies o hei in eg a ion in esiden ial buildings and examines hei bene i s, cons uc ion p inciples and applica ions. KEYWORDS G een Roo , classi ica ion, main enance, ege a ion, cons uc ion h p://dx.doi.o g/10.4995/ i u io-ija s.2015.4475 58 1. CLASSIFICATION OF GREEN ROOFS A G een Roo o Eco-Roo is an ex ension o wha is adi ionally called a ‘ oo - op ga den’, whe e g owing is done in plan e s. A B own Roo is also included in his classi ica ion, o dis inguish oo s ha a e no in en ionally plan ed, bu a e illed wi h laye s o a ious ma e ials ha would ha e o he wise been was ed in land ill such as g a el, b ick ubble, c ushed conc e e and subsoils. This acciden al p ocess can c ea e aluable ecosys ems o plan s and insec s h ough sel - coloniza ion, simila o b own ield condi ions (Mau i ius EcoBuilding, 2008). Pi ched G een Roo is ano he ype, which o igina ed in Iceland whe e sod oo s and walls ha e been in use o he mal easons o cen u ies and sp ead h oughou he Scandina ian coun ies (G eenRoo s, 2010). Pi ched oo s a e ypically simple o design han la ones. The slope allows ain all and excess wa e o d ain mo e easily, educing he isk o leakage. Sloped g een oo s, he e o e, need less wa e p oo ing and d ainage me hods han la ones, he eby sa ing ma e ials and labou cos s (Mau i ius EcoBuilding 2008). The design o he pi ch is also simpli ied since i is ha de o access and use pi ched g een oo s o di e se ac i i ies and plan ing. Slopes o up o a maximum o 35 deg ees a e possible, hough some sys ems manda e no mo e han 20 deg ees o p e en soil slippage and slump, as will be discussed below (Kwok and G ondzik, 2007). Ano he classi ica ion o g een oo s is acco ding o hei main enance le el and upkeep. The e a e h ee common ca ego ies: in ensi e, semi- in ensi e and ex ensi e (Fig. 1.1). These sys ems also a y in cos , dep h o soil and ype o plan s hey can suppo (Lawlo e al., 2006).  %84%.3)6% 3%-)).4%.3)6% Ø.$ INTENSIVE ROOFS VARY DEPENDING ON THE DEPTH OF PLANTING MEDIUM AND THE AMOUNT OF MAINTENANCE REQUIRED. Ex ensi e G een Roo s ypically equi e minimal main enance, a e ligh weigh , inexpensi e and ha e li le plan di e si y. The plan s a e g own in a mix u e o sand, g a el, c ushed b ick, leca, pe li e, pea , o ganic ma e and some soil (Peck and Kuhn, 2008). This mix u e is usually be ween 2 in. o 6 in. (5 cm o 15 cm) in dep h, and ull Figu e 1.1 Ex ensi e, semi-in ensi e and in ensi e oo s a y depending on he dep h o plan ing medium and he amoun o main enance equi ed. Vi u io In e na ional jou nal o A chi ec u e Technology and Sus ainabili y Volume 0 59 sa u a ion will cause a inc ease in weigh be ween 16 lb./sq. . o 35 lb./sq. . (78.1 kg/m2 o 169.4 kg/m2) (Peck and Kuhn, 2008; Lawlo e al., 2006). Once he plan s ake oo , main enance is only needed wice annually o weeding and sa e y inspec ions. These plan s a e ypically indigenous and ha dy enough o wi hs and ex eme clima e condi ions (G eenRoo s, 2010). Semi-in ensi e oo s ha e he same low o no-inpu p ac ice as an ex ensi e one and simila ly use ligh weigh subs a es and mode n cons uc ion echnologies, bu hey ha e sligh ly deepe laye s o g owing medium o abou 4 in. o 8 in. (10 cm o 20 cm) and he e o e enable a wide and mo e di e se ange o plan s o be g own (Dunne and Kingsbu y, 2008). While semi-ex ensi e oo s a e classi ied as in e media e be ween he o he wo g een oo s me hods, i is also easible o combine ex ensi e and in ensi e echniques on accessible oo s, wi h la ge he baceous and woody plan ma e ial in s a egically placed con aine s o plan e s o c ea e sus ainable ga dens. An In ensi e G een Roo is simila o adi ional ga dens, whe e plan s a e main ained he way hey would be kep on g ound. They can suppo di e se ege a ion, a e labou -in ensi e, ha e deepe soils and hea ie weigh , cos mo e and equi e i iga ion, e ilizing and addi ional main enance. The subs a e he e is p edominan ly soil and can ange in dep h om 8 in. o 24 in. (20 cm o 60 cm), which allows o ees, sh ubs, and a mo e di e se ecosys em o g ow and can weigh o e 61 lb./sq. . (300 kg/ m2) (Peck and Kuhn, 2008; BCIT, 2009). Also, because he oo is accessible o people, i equi es addi ional ea u es such as ailings, ligh ing, access and eg ess (BCIT, 2009; Dunne and Kingsbu y, 2008). When ees a e plan ed, hey need o be p o ec ed om, and ancho ed agains , s ong winds, which a e a conce n a high ele a ions. I is impo an o no e ha d y subs a e weighs app oxima ely 60 pe cen o 70 pe cen o i s o al weigh when i s ully sa u a ed (Op ig een, n.d.). 2. ADVANTAGES OF GREEN ROOFS Mo i es o he in eg a ion o a g een oo in esiden ial design a e oo ed in social, economic, en i onmen al and cul u al aspec s, which a ec bo h a single use and he communi y a la ge and a e desc ibed below. A oo op pa ch can be used o g ow ui s, ege ables, he bs and lowe s pa icula ly in high-densi y u ban a eas o whe e con en ional ga den space may be limi ed. Many he b species pe o m bes in ee-d aining soils in sunny condi ions, which a e a ailable on oo ops. The subs a e and ege a ion also help insula e he building om ou side noise. Soil has been ound o abso b and block lowe equencies, while plan li e blocks he highe ones (Mau i ius EcoBuilding, 2008). A g een oo wi h a soil laye o up o 8 in. (20 cm) can educe noise pollu ion by up o 50 decibels (Li eRoo s, n.d.). Fu he mo e, plan ed oo s could slow down he sp ead o i e o and om he building, pa icula ly when he g owing medium is sa u a ed. On he o he hand, e y d y ege a ion on a oo can pose a i e haza d. Whe e i e is a conce n, in eg a ing o i eb eaks such as g a el o conc e e pa e s a egula in e als and using i e- e a dan plan s wi h high wa e con en , such as sedums, is ad ised (Mau i ius EcoBuilding, 2008). G een oo s o e he mal insula ion ha is supe io o con en ional in e io insula ion. A g een oo p e en s hea om escaping ou he op in cold clima es, and p e en s hea om pene a ing h ough in summe ime. The insula ion alues can be inc eased by using a 60 low densi y soil wi h a high mois u e con en and la ge, lea y plan s. An 8 in. (20 cm) subs a e wi h an addi ional 8 in. (20 cm) hick laye o g ass has an equi alen insula ion alue o 6 in. (15 cm) o mine al wool as shown in Figu e 2 (Peck and Kuhn, 2008). 2.1 COMPARISON BETWEEN INTENSIVE GREEN ROOF (LEFT) AND CONVENTIONALLY CONSTRUCTED AND INSULATED FLAT ONE (RIGHT). Reduc ions o up o 90 pe cen in passi e sola gain can be achie ed when using g een oo s. Indoo empe a u es ha e been shown o be 6oF o 8oF (3oC o 4oC) lowe unde a g een oo when ou doo empe a u es a e be ween 77oF and 86oF (25oC and 30oC). An En i onmen Canada s udy shows ha a ypical one-s o ey building in To on o wi h a g ass oo and 4 in. (10 cm) o subs a e b ough abou a 25 pe cen educ ion in summe cooling needs, compa ed wi h an un ege a ed e e ence oo (Dunne and Kingsbu y, 2008). When g een oo s a e cons uc ed p ope ly such ha he likelihood o leaks and damp pene a ion o he house is minimized, hey can las longe han con en ional ones, which will esul in ob ious cos bene i s. In ac , s udies ha e shown Figu e 2.1 Compa ison be ween in ensi e g een oo (le ) and con en ionally cons uc ed and insula ed la one ( igh ). ha g een oo s may las wo o h ee imes longe han con en ional ones and will ecei e less main enance (Mau i ius EcoBuilding, 2008). Plan s can shield he oo om he elemen s, including he sun’s ul a iole (UV) adia ion ha deg ades componen s, d y winds which cause c acks, and up o 90 pe cen less con ac ion and expansion due o empe a u e luc ua ions (Li eRoo s, n.d.). Finally, g een oo s can o e a pleasan oo scape iew, elimina ing he unsigh ly expanse o da k asphal and g a el. E en whe e oo s a e inaccessible bu clea ly isible, a ac i e plan ing can be bene icial. The he apeu ic e ec s o ha ing g een plan s and na u e a ound one a e known o be conside able and include s ess educ ion, lowe ing blood p essu e, elie o muscle ension and inc ease in o e all posi i e eelings (Li eRoo , n.d.; Sassi, 2006). When he load-bea ing capaci y is su icien , g een oo s can p o ide ou doo ec ea ional a eas o se e al dwelling uni s in neighbou hoods wi h li le g ound-le el space. In an apa men block de elopmen , o ins ance, casual ac i i ies, such as clo hes d ying, ba becuing, and i ness can ake place. I has he ad an age o con olled access, he eby c ea ing a sa e place. The enhancemen o biodi e si y h ough he use o g een oo s is closely linked o he choice o Vi u io In e na ional jou nal o A chi ec u e Technology and Sus ainabili y Volume 0 61 plan species and he habi a o ege a ion ype used. Ex ensi e oo s, which a e no designed o be walked on and a e, he e o e, isola ed, and can be po en ially e y good undis u bed habi a o lo a and auna such as bu e lies, insec s and bi ds. G een oo s can also be he place on which communi y ga den o u ban ag icul u e can be loca ed. A g een oo no only a ec s he home’s indoo he mal condi ions, i also in luences he clima e o he ci y as a whole by educing he u ban hea island e ec . Hea island e ec is caused by a la ge, ha d su ace a ea ha abso bs, e lec s and e- adia es he sun’s hea . This in u n leads o ai cu en s, dus , smog, and mic o-clima e changes. G een oo s mi iga e his phenomenon by cooling, slowing down cu en s, and il e ing ou ai pollu an s and dus (Peck and Kuhn, 2008). Rain all on land co e ed wi h ege a ion is di e en han ain all on he ha d su ace o buil - up a eas. The as majo i y o p ecipi a ion on a g een oo is abso bed by plan s and h ough hem is anspi ed back o he a mosphe e. On man-made ha d su aces (e.g. asphal , conc e e, oo iles), on he o he hand, wa e canno be abso bed and uns o , h ough d ainage sys ems, in o i e s. The main aim o con en ional d ainage sys ems is o emo e a maximum amoun o wa e om an a ea as quickly as possible o p e en lash looding. As a esul , a ound 75 pe cen o ain all on u ban a eas is los as su ace uno compa ed o a ound i e pe cen o a o es ed a ea (Dunne and Kingsbu y, 2008). G een oo s can educe he amoun o wa e lea ing a si e, ei he h ough e en ion, de en ion o by cap u ing i and eusing he wa e o i iga ion o domes ic pu poses. This also educes p essu e on u ban d ainage sys ems, enabling g ound-wa e o be eplenished, p o iding a eas o habi a and ameni y we lands, educing lood isk and lowe ing in as uc u e cos . Because oo s ep esen app oxima ely 40 pe cen o 50 pe cen o he su aces in u ban a eas, g een oo s ha e an impo an ole in such d ainage (Lawlo e al., 2006). G een oo s ha e addi ional bene i s. As ai pollu ion causes espi a o y diseases and b ea hing di icul ies, plan ed oo s can il e ou ine ai bo ne pa icles as he ai passes o e he plan s, se ling on o lea and s em su aces. This ma e ial will hen be washed o in o he soil by he ain. T ees and la ge ege a ion can also abso b gaseous pollu an s in hei issues. 3. CONSTRUCTION PRINCIPLES AND COMPONENTS Despi e i s many bene i s, he cons uc ion o g een oo s poses a challenge. Ca e ul a en ion needs o be paid o a ious ac o s ha a ec he oo ’s pe o mance, which will be ou lined below. S uc u al conside a ions o g een oo s ha e o ake in o accoun he in ensi e and he ex ensi e ypes ha we e discussed abo e, since each one has a di e en weigh . Ligh weigh ex ensi e sys ems wi h subs a e dep hs o 2 in. o 6 in. (5 cm o 15 cm), o ins ance, inc ease he load on a oo by be ween app oxima ely 14 lb./sq. . and 35 lb./sq. . (70 kg/m2 and 170 kg/m2). Each coun y o egion will also ha e i s own building s anda d o he minimum capaci y o a oo . In On a io, Canada, o example, oo s mus be designed o suppo a loading o a leas 40 lb./ sq. . (195 kg/m2) (Peck and Kuhn, 2008). This akes in o accoun a ypical win e snow loading o 22 lb./sq. . (107 kg/m2). I hen lea es 18 lb./ sq. . (88 kg/m2) spa e capaci y – enough o a simple ex ensi e sys em (Dunne and Kingsbu y, 62 i is necessa y o use special media mixes and de ices (Dunne and Kingsbu y, 2008). 3.1 GREEN ROOFS CAN BE DESIGNED WITH VARIOUS SLOPES. STEEPER SLOPES WILL BE SUBJECT TO GREATER MOISTURE STRESS AND WILL REQUIRE DIFFERENT DESIGNS. In addi ion, oo s also need o wi hs and high wind upli due o hei exposed condi ions. A s ip o g a el, s ones o pa e s a ound he oo ’s edge can p e en wind damage. Such s ips a e also o en used as ege a ion ba ie s, p e en ing damage by plan s o he edges whe e he wa e p oo ing laye ises abo e he su ace o he g owing medium. Finally, i iga ion o g een oo s should also be designed and con olled, pa o which could be p o ided by ainwa e s o age and ecycling sys ems. Fou main i iga ion me hods a e used on g een oo s: su ace sp ay wi h adi ional sp inkle s, d ip and ube, capilla y and s anding wa e sys ems. Figu e 3.2 illus a es hese me hods. In gene al, 2008). Fu he mo e, in calcula ing load, i mus be no ed ha he weigh o g een- oo ma e ials will a y g ea ly depending on how compac ed and how mois hey a e (Po land Online, 2006). Besides bea ing capaci y, ano he cons uc ion conside a ion in pi ched g een oo s is slippage. The maximum possible slope is con olled by he ic ion coe icien be ween he wo slippe ies ma e ials. Vi ually no g een oo s a oid ha ing a ab ic-memb ane o memb ane-memb ane in e ace o example, a oo ba ie s and shee d ains. These a e he planes along which slope mo emen will occu . Wi hou addi ional slope s abiliza ion measu es, i is unwise o design g een oo s o slopes s eepe han 2:12 (9.5 deg ees). Figu e 3.1 illus a es wo g een oo slope designs. Slipping and slumping can be coun e ed by he use o ho izon al s apping, la hs, ba ens o g ids. In using hese me hods, g een oo s can eadily be cons uc ed on pi ches up o 7:12 (35 deg ees) ha is he angle o epose o mos g anula ma e ials. To build on s eepe pi ches, han he ones no ed abo e, Figu e 3.1 G een oo s can be designed wi h a ious slopes. S eepe slopes will be subjec o g ea e mois u e s ess and will equi e di e en designs. Pi ched oo up o 20 deg ees Pi ched oo up o 35 deg eeswi h a slippage- p e en ing measu ep e en ing measu e Vi u io In e na ional jou nal o A chi ec u e Technology and Sus ainabili y Volume 0 63 adi ional su ace sp ay is less ecommended because i was es wa e and can cause su ace oo ing (G eenRoo s 2010). 3.2 VARIOUS IRRIGATION METHODS FOR GREEN ROOFS. G een oo s can be cons uc ed o e any ype o deck, whe he s eel, wood o conc e e, as long as he s uc u al conside a ions discussed abo e a e me . Laye ing componen s in a g een oo o esiden ial use emains consis en h oughou he di e en si ua ions. These componen s ha e o sa is y wea he -p oo ing, p o ec ing he oo su ace om oo pene a ion and damage, d ainage and he suppo and g ow h o he ege a ion laye (We hmann 2007). These componen s a e illus a ed in Figu e 3.3 and a e discussed below. 3.3 THE VARIOUS COMPONENTS OF GREEN ROOFS. The wea he p oo memb ane consis s o he buil -up oo , single-ply and luid-applied memb anes. Buil -up oo s a e commonly encoun e ed and a e composed o con en ional bi umen/asphal oo ing el o bi uminized ab ics. These oo ing ma e ials gene ally ha e a li espan o i een o wen y yea s and a e suscep ible o deg ada ion om empe a u e ex emes and ul a iole adia ion – bo h o which cause c acking and leakage, al hough a laye o subs a e and ege a ion will educe his. Equally impo an is hei suscep ibili y o plan oo g ow h. A oo p o ec ion ba ie mus he e o e always be used wi h such memb anes. This ype o oo , howe e , is no ecommended as a base o a g een oo (Can o , 2008). The e a e o he ypes o buil -up oo ing sys ems ha a e mo e obus and en i ely di e en in ma e ial Figu e 3.2 Va ious i iga ion me hods o g een oo s. and pe o mances han con en ional asphal / el buil -up sys ems. Single-ply oo memb anes a e olled shee s o ino ganic plas ic o syn he ic ubbe ma e ial ha a e o e lapped a he join s and sealed wi h hea . They may also be a ailable as iles (i.e. some imes made o ecycled ubbe ). These memb anes can be e y e ec i e i p ope ly applied. The seams o bonds be ween he shee s and iles can, howe e , be weak poin s ha may be exploi ed by plan oo s and can cause leaks. Sealing ma e ial can be suscep ible 64 o deg ada ion om UV ays, he e o e i is essen ial ha all pa s o he line a e p o ec ed om sunligh . On he o he hand, luid-applied memb anes a e a ailable in ho o cold liquid o m ha is sp ayed o pain ed on o he su ace o he oo and o ms a comple e seal when se , elimina ing join p oblems. They a e also easie o apply o e ical o i egula ly shaped su aces (We hmann, 2007). A oo p o ec ion ba ie is ex emely impo an . I he memb ane on a oo upon which a g een oo is o be ins alled con ains bi umen, asphal , o any o he o ganic ma e ial, i is c ucial ha a con inuous sepa a ion is main ained be ween he memb ane and he plan laye because he memb ane will be suscep ible o oo pene a ion and he ac i i y o mic o-o ganisms – hese o ganic oil-based ma e ials a e no oo p oo . I he oo is no comple ely la , hen any pocke s o wa e can also o m he basis o plan g ow h on a oo – again he e mus be p o ec ion om oo damage. Plan s pa icula ly known o ha e agg essi e oo s ha can pene a e he memb anes a e bamboo, lupines and blackbe y (BCIT 2009). A d ainage laye is necessa y o p o ec he wa e p oo oo memb ane. The unc ion o he d ainage laye is o emo e excess wa e o unde low as quickly as possible o p e en sa u a ion. Wi hou “g eening”, la oo s a e 50 pe cen mo e suscep ible o damage a e i e yea s han sligh ly sloped oo s as a esul o wa e collec ing and pooling. Roo s equi e a slope o a leas wo pe cen and a d ainage laye o d ain p ope ly. I is impo an o place he d ains a he lowes poin hal way be ween s uc u al suppo s. Regula main enance is necessa y o p e en he d ains om any clogs o blockage ha migh cause wa e accumula ion (BCIT, 2009). Also, one needs o a oid using ine plan s on he edge o a g een oo because hese migh g ow in o he gu e s and block he d ainage pa h. Because g een- oo ege a ion, pa icula ly o he ex ensi e ype, is selec ed o be d ough - esis an and ole an o d y, ee-d aining soils, p olonged soil sa u a ion is likely o cause plan ailu e, o ing, sou and anae obic condi ions and may also lose i s he mal insula ing p ope ies. D ainage can be achie ed in se e al ways, especially o la oo s less han i e deg ees, which equi es mo e specialized echniques. In addi ion, combining a d ainage laye wi h a wa e -s o age laye below i no only u he educes uno compa ed o hose wi hou such a laye by 11 pe cen o 17 pe cen , bu ac s as a ese oi o plan s o d aw upon in d y wea he (Dunne and Kingsbu y, 2008). The las laye o g een oo s is he g owing medium o subs a e, which abso bs and e ains wa e while a he same ime p o ide ee- d aining p ope ies. Speci ica ions o ma e ials used in he subs a e laye should be ad ised by expe s since i is no necessa ily a conce n o he a chi ec . Figu e 3.3 The a ious componen s o g een oo s.