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The Planning, Installation and Maintenance of Green Roofs

BERND W. KRUPKALandcape architect and urban plannerBad Pyrmont (Germany)hHp:l lwww.gruendachexperte -krupka.de l

Planning Criteria for Vegetation Techn iques to be usedin Extensive and Intensive Green Roofs

1 I Planning Procedure and its ContentsIn order to establish a foundation for the planning ofthe vegetation techniques, the strud ura l and technicalchorccteristics o f the con structions and roof surfacesin questi on mu st be ascertained and evaluated . Theearlier 1he planning of the green roof con be incorporated into 1he planning of the bu ild ing as a whole, thegreater influence the green roof will have on proceedings . If the type o f green roof to be built hos o lreodybeen determined, the existing building situation conresult in lirnitotion s be ing ploced on the quoliiy of 1hegreen roof. In certoin cases it is recommended that arisk analysis be performed, particularly where specialconstruction meth ods are required .In each case it is necessary to formulate and co- ordi nate objectives for the green roofs. These objectiveswill then be modified ba sed on the analysis of the local conditions during the preliminary de sign stage. Theprel iminary design is then turned into a detailed implementation plan that con be achie ved.

Objectives con include : Aestheti c qualities Requiremen1s for the use of the green roof

(quality of free space) Rainwater management Ecologicol qualities The fulfilment of fund ing guidelinesIt must be ascertained whi ch essen1iallocat ion Ioctorsba sed on the buildings connot be influenced or canno longer be influenced ond what consequences thi swill have regarding the green roof. The late r use of theroo f space is the decisi ve foetor in the planning stage sregarding the conception o f pa ved areos or resilientlawns.During the planning of the gr een roof. the client mustbe g iven on explanation which recogni ses all the potential risks. The follow-up costs concerning ma intenance and upkeep must al so be incorporated into theplanni ng from the outset and must be clearly repo rtedto the client . The development of the plans , includingall of the individual deci sion s made, mu st be recordedin a document rhat is comprehensible . Thi s al so appliesto the statements made by the specialist engineers of


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ihe associated trades (structures, utilities management).In the case of roofs in light structures, steep roofs orstructures covered with soil, For example undergroundgarages, there are both particular water-proofing andvegeiation conditions which must be carefully applied .The adherence to and the interpretotion of the "recognised state of affairs" and "store of the al i technology"form the prerequisites for high quality green roofs. Indifficult cases, new findings fram the world of scienceand technology may need 10 be incorporated , forexample through the use of special advice .Rules and standards like norms, directives and qualityassessments , from both the building and landscapingsectors, must be adhered 10 and correctly interpretedto ihe object in question and applied as port of theplanning crilerio . The "Guildeline for the Planning,Execution and Upkeep of Green-Roof Sites" [ll are ofkey signi ficance here. In certain cases there are severalgood reasons 10 deviate from respedive requirementsof a rule or standards . These must be conclusively justi fied in writing .

21 Structura l Requiremen tsRoof gradient , roo f dra inage, irrigat ionThe design of the roof pitch or the roof gradient formsa decisive planning criterion, because it is the basis onwhich the necessity and dimensions of drainage layers ,drainage facil ities and ir rigation , as well as shearingprotection and any special anti-erosion measures, arecalculated. The current "recogn ised stote of af fairs " stipulates planning for a roof pitch of at least 2 %. Cre ating a pitch on flat roofs generally accommodates thevegetative requirements for extensive green roofs . Intensive green roofs can also be realised on roofs witha pitch of up fa 4 %, with low averfalls where necessary. Additional irrigation must be designed so thai aslittle excess water runs of f as possible. A non-pitchedroof is odvaniageous fo r the accumulation of water; itis permissible as a special form of construction in therules and standards. In these coses it should be ascertained whether a classification of roof waterprooFingin accordance with DIN 18531 , or in accordance withDIN 18195 , port 5 or port 6, "construction waterproofing" is necessary.The steeper the roof pitch the worse the ab sorption andretention capabilities are for rainwater in the build-upof layers . Extreme location characteristics must formthe basis of the vegetation [4J. Xerathermic plant locations arise in connection with the maximum angle

of solar irradiation. If fhe solar irradiation meets therooftop surface at on angle of 90 throughout the day,fhen the result is extreme conditions.The hydraulic conditions on rooftops with a geometryunsuited to drainage must be inve stigated with regardsthe additional drainage required. In the case of roofswithout any gradient, drainage will only have on extremely limited affect again st the waterlogging of thinlayer build-ups . Drainage is also necessary in caseswhere large amounts of front wall water is directedover the rooftop surfaces or where there is not a sufficient gutterol gradient. The following basic rule applies : excess rainwater must be discharged from boththe layer of waterproofing and from the surface of thegreen roof vegetation . Generally, the effeds of waterlogging [6) on extensive landscaping can prove to bea serious problem .Assumed LoadsAll materials used in the drainage and plant layers areto be calculated in their saturated (with water) condition.The build-up of water through standing water must beoscerloined. The weight of the landscaping itself mustnot be forgotten . In the case of solitary trees, the windload should be token into account.

31Vegetative Planning Criteriafo r Green RoofsThe amount of careful preliminary planning work involved in testing the qualit y of the locat ion for vegetationis often underestimated. It does not so much dependon the size of the area as on the strudure and locationof the construction. A step-by-step procedure has beenproven to be successful. A general location and riskassessment is followed by small-scale analyses.Location Assessments as Planning CriteriaThe classification of lhe quality of the location [2] insurface-related differentiation is the ba sis for the vegetative work on the one hand and the basis fo r theselection of planls on the other. A standard quality oflocation is also found on rooftops with constant geometry ina layer in the rarest cases.During the planning stages , it has proven advantageous to clas sify the rooftop surfaces as planting locations in the following way, taking into account the


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The Planning, I stallatio and Maintenance of Green Roofs

greenery planted in the subzones and stating the chorocterislic key fa ctor s of location quality: not loaded (ideal locat ion) slightly loaded medium loaded high ly loaded very highly loaded [extreme lccotion]The chall enge is not just 10 recognise the problematicqualities of the localian, but ra ther 10 ide ntify theireffects on the plants and the development of the vegetation in the evaluation. This can, however, only beachieved wi th a pr ecise knowledge oi the ecologicalrequirements of different types of plants and their loadlimits, as well as Iheir sociolisolion.The clas sifica tion of the locotion qualily is always closelyconnected with the car rying capacity of the veg etationand p lant selecti on [1 ,3 J. A marginal location o f in1ensive green roofs w ith trees can be a "nor mal location"fo r extensive gree n rools . Therefo re such statementsa re only rele vant when considered in connection withthe type o f landscaping for the extensive green roofand the simple intensive and inten sive gr een roof .The following can generally be applied as attributesfo r marginal locations: lull solar irratia tio n, in particular on sloping surfaces

(steep roo fs) constant exposure to strong w inds heat re tention an d/o r reflecti on , In particular on

small ar eas Or courtyards exposure to coldness from below danger of expo sure to co ld air (cold ai r pockets,

early and la te fro sts) rain shadows w ith wind load and /o r direct solar

irradiation all full y exposed sorfoces by the coa st or at o n ele

vation equivalent to a low mountain rang e all full y expo sed surfcces on higher floo r level s, onor near high-rise building s and in city centres.

The addit ion of all individual factors has a negative eF-feet wh ich is more pr on ounced the narrower the depthof the layers are - especially in the ca se of intensivegreen roofs. The location assessme nt must also includethe mi croclimatic optimal zon es; the se a re espec iallysignificant in the case of intensive green roofs . Theyare generally availab le on all areas which ha ve beensufficiently screened by the structure and other construction s. Aport from the gen eral city climatic the rmalload, more o ptimal ar eas for intensive green roofs

can be found in conc entrated urban areas than in lesscrowded surroundings.Ascerta in in g he Roinw otal an dWater Run -e Rotio sWh ile exposed areas that do not have an y neighbou ring toll buildings receive an equal di stribution ofra infall , bui ldings with variations in height feature rainshadow zone s and zones with increased proportionsof rainwater du e to turbulence or facade run-off. Plan ning tasks: Calculating the regional average a nnual rai nFa ll

with a city premium of 10 to 20 percent [inforrnotionfrom the meteorological service)

Ascertaining locot ion-specific summer d ry spells Ascertaining rain shadows cau sed by rising o r

neighbour ing bu ilding s under the assumption of awindward d rift o f approximately 20 to 30 fro m theinclineCalculating the amounts of water that w ill run o ffthe Iront wal l

Calculating the special areas with rainwater tur bul ence and transportation, fo r instance by thech imney effect (waterlogg ing )

Outlining areas on steep roofs which w ill d ry outfo ster

Colculc in g h Ltg t C limateThe expo sure to sunlight of g reen roofs mu st be calculated when ascertaining the light climate. The extremel y varied an d changi ng areas of light and shadeon roofto p surfoces with strongly structured con struction s are enough to creole diffe ring locolion condi t ions. Furthe rmore, it ca n result in different loads beingcaused by ai r flows . The quality of shade can , for exampl e, be classified

into full shade, portial shade, moving shade andlight areas that are out side of direct sunlight (e. g .inclined north-facing roofs).

Temp orary pa rtial shade cau sed by bu ilding s result sin a problematic t ran sitional light which is oftencombined with refle ctions.

Furth ermore, il is po ssibl e to d ifferenti ate between dryand wet shadows, in view of th eir natural water supplyby rainfall .

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lnve st iqotinq th e Win d loo ds Calculating the area -specific air flows (direction ,speed, diversion, windward and leeward) Calculating level-specific variances Pull on roof corners and edges;

dynamic pressure on front walls Formation of wind eddies and wind bolls le t effects on the corners of buildings in

con sequence of ports of the structure beingsubject to under-currents or narrow-lying tollbuildings

In the case of difficult calculations, it is recommendedthat a computer be used for modelling purposes.Special Factors to be Aware of : Reflection of radiation and light by front walls Heat storage through certain bu ild ing materials Heat accumulation due to a lock of oil' circulation The direction and strength of outg oing air emi ssions,

particularly warm and cold ai r Risks by exposure 10 the cold for areas with oil' un

der-currents that are not thermally insulated (onlysignificant in the ca se of inten sive green roofs)

Relief-caused build up of cold oi l' Periods of heal and black frost typ ical to the areaHab itat De SIgnIn terms of the design of the habitat for the vegetation,it must be in vestigated whether the limit ing featuresspecific to the object in question can be influenced byplanning.The microclimotic condit ions can only be improved ina sustainable manner when the thermol and air circulation functions in no rraw areas. This means that thewater supply and the moislen ing of air by evaporationpla ya key role in the case of intensive green roofs. Theeffects of unnaturally hard light and shadow borderscan be mode considerably milder in the case of intensive green roofs through the use of toller trees andshrubs. The zones with half-shadow and sconered lightcan provide a natural light clirnote suitable for treesand species of shrubs. In the case of rooftops featuringintensive landscaping , on increase in the he ight of thero of lead s to 0 reduction in the quality of the microclima te due to the con stant wind load or air flo ws causedby buildings (e. g . up winds). The staggered plan tingof leaf or needle-bearing trees and shrubs can, depending on the depth of space, offer a certain amount ofprotection from the wind . Addit ional windbreaks that

ore permeable to the wind - generally wooden lotticeconstructions - are , however, often more effective.The qual ity of the location can be significantly im proved in pla ces through the implemenlation of certainmeasures, for example the thickness of the build-up oflayers and their water capacity. Alongside the ociuolquality of the substrate, the depth is the essential foetorto consider when selecting the range of plants .Moulding the soil relief is on e possibility of creatingareas of varying location quality, in as far as the loadreserves allow it. A range of layer depths can producedifferent plant habitats, particularly in the case of extensi ve green roofs, and can thus increase the biod iversity. Raising small areas of land fo r the plant ing oftrees in intensive green roofs does not, however, offerlong-term improvements to the location. The thickne ssof the build-up fo r different types of land scaping anddifferent species of vegetation as described in the FlLgreen roof directive is to be understood as a generalguideline . They must be modified accord ing fa thespecific item in que stion.

xte nsive l .ondscopinq fo r Flot Roofs - Spe cific TipsIn the case of extensive green roofs, if is rare that onl yone type of landscaping de velops on a roof-top space.In accordance with the small- scale mo saic of locat ioncondition s (layer depth, water balance, local climateand microclimate), there are often several differenttypes of vegetation that flow into one another.If the local conditions change regularly fro m one extreme to the other, for example from very dry to verymoist, a so- call ed "transition vegetation" (Wech selvegetalion) is formed .Thi s is particularly common in the following situations: Extensive O-degree roofs with waterlogged areas

Steep roofs Thin layers of build -up or tho se with a low water

capacityExperienced green roofers, as well as designers fromcompanies operating in the field , inform the client inwriting before commencing work that there will be cleardifferences in the formation of the vegetarian. The indication that this is the effect of location factors thatcannot be changed is dec isive here . Furthermore , theunavoidable seNlement of foreign vegetati on must beaddressed as thi s can also turn oui in very varied ways.

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Erosion protection for the surface areas of the landscaping, particularly fo r iiems planted in late autumn ,cannot be neglected . Furthermore, the areas affectedstrongly by wind (corners, edges) should be securedagainst wind suction using suitable technical means(grovel , slobs, chequer bricks) and/or biological means(mulch adhesive, vegetation maHing ).

xte nsive Lcnclscopinq o r Pitched Roof!> Specific TipsThe gradienj of the roof incline is the decisive factor.The "directive for green roofs" describes a raol gradientof 30 as the borde r fo r high-risk. Preventative risk management is generally the fir st task in planning. Extensive green roofs on pitched roofs have very extremelocalion conditions , and their development is stipulated by the degree of the g radient and the exposu re ofthe areas. South or west -facing areas, wh ich are ex.posed to sunlight and have a steep gradient are, there fore, the most extreme locations. These include thehigher-lying areas which ha ve the most serious lock ofwater, due to solar ir radiation and being dried out bythe wind. Certain areas with desert characteristics can,therefore, ar ise and even sedum will struggle to survivehere over the long-term [4]. Irrigation is the only solution 10 this problem.Shea ring Prot ectionTechnical measures for shearing protection , whichmust be coordinated with Ihe roof leng th, i. e. thesheer lengih , include var ious techn icol possibilities l ikepreventilated o r individual constructions. It should benoted that lattice systems with holes that are too smallcan result in negative "flower pot effects". Furthermore,shear barriers should not be apparent or lie exposedamongst the vegetation .Eros ion Control MeasureThe safety of the location and protection against erosionfo r a steep green roof must be supported by certainmeasures . These include: a secure, stable-structured minerol system sub strate

with coarse groin shapes the use of anti-erosion neHing for the surface of 1he

system subs1rate landscaping methods tha1 counteract surface area

eros ion (vegetation maHing) always keeping the system substrate areas moi st

whi lst landscaping the area

landscaping the areas at times of the year when thevegetation can fully establ ish itself and when the vege tation support course roots sufficiently using odd itionol irrigation on extreme areas to maintain a complete covering o f vegetation

In tens ive Green RoofsPmti culer Co ns truc t!....e ond Veg etative IP SA sufficient compre ssion strength for the thermal insulation a nd protection of the waterp roofing mu st beensured with intensive green roofs with h igh layer buildups and when using small- size compression ports (e. g.edging ). There are certain parti cularities regarding thevegetative factors: The water supply must be ensured by ha ving wate r

connection s on every floor level or port of the roof.Fresh water should be replaced or supplementedwith retained rainwate r wherever possible. It is always advantageous to store rainwater using wa terretention method s. In the case of layer build-upswith low layer depths (less than 20 em), waterlog ging problems can occur if the water retention istoo high.

Additional irrigation e. g. with a sprinkler, can be necessary even in cases whe re water retention methodsare used; for example when larger trees and shrubsdraw the water away fram weakly-rooted greenery. Winter damage is the main cou se for the fa ilure of

plants used in intensive green roofs. Winter damageis exacerbated by narrow layer depths (drainageand plant layer} in conjunction with too much nitratefert ilisation and waterlogging from water retent ion.Evergreen lrees suffer from extended periods of frostand also from dlying out . During winter, the waterretention level s must generally be reduced.

References[1) Forschungsgesellschaft LondschaftsentwicklungsLandschaftsbau e. V. FLL:Richtlinien fUr die Planung , AusfUhrung und Pflegevon Dachbegrunungen , Selbstverlag, Bonn 2008Bewertung von Dochbegrunungen FLL 1996

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