b'appropria Iloadssuchas teive snow, w and human foot traffic ind to eva thelity of a luatefeasibi green roofdesign.TheInternational Codesprovideguidelinesfor dsproprassigningtheseloa ap iately. Preventing and Detecting Leakage The issue oflea ge involves katwo separate factors: compatibility tween be theoverlyingvegetated coverandtheunderlyingwaterility proofing materials;and the abtodetect, isolateandre ir any paproblem areas. Materia used in conjunction ls :; .l rkDepartmentEnviro menPhotograph by: Ma Farina, Chicagoofn t ~ Weight Considerationsing,andsyntheticcomponents Itdifficult to design greensuch fabrics and mem . is notbranesroof systems that have a m Theguide inesset forth in the aximumI we of less than 13 pounds perInternationalCodesrMtreatthe ight square foot (36.5 kg/m 2 ).However,weight of aroof, greenincluding all greenroofs weighing18 poundsretained moisture, as aload. dead per square(87.9 kg/m 2)or moreHow should this weight be deterare most common. Many buildingsmined in the absence of an Americonstructed prior to 1960 incorpo can standard procedure? TheFLL rated conventional roofing systemsspecifies a laboratory test to assess Photograph y: Mark Farina, Chica Departme of E ronment thatincludedlayersoffeltandthemaximumweightcontributedb gontnviasphalt topped with stone ballast.bythemedia.The testin trees, carefulconsiderationmustwitheen roofs s u be certified volvesgr ho ld Dependingonthelocality, thesecompressingthematerialin abegivento the matureweight offoruseinwaterproofing,as to roofingsystemsweigh10-15mold witha 10-poundProctorsuchplants.Du and immedi opposed topp fingw rringdam roo oratepounds per square foot (48.8-73.2hammer, immersingately following rainfall,water willproofing. Manyn o waterthe sample forco venti nal kg/m 2 ).As a,is often pos 24hoursandthendrainingitaccumulate in the drainage layersproofing materials are suitable for resu It it sibletoremoveexistingwater briefly before measuring its weigh ofgreenroofs.Thetempo ryuse inmbination with g roof t.ra co reen proofing systems and replace themDue totheconservative nature ofincr in weight might be m installation Inmostinstan , easeores.ceswith green roofs without having tothis test,I recommend usingit toappropriatelyad as a livehoweve greenf wate ing dressedr,roo rproofresort to structural reinforcement ofevaluate the structural adequacy ofload. Howev ,greendesignsystems willincorporatethicker er inroof the roof deck.roof structures.itu inclu in the c me ranes or mu iple layers, and issuallydedalcula mb ltThe weight of aroof sys Inextensivegreen roofsthetion of dead load. T s loadthelevelof quality con in the greenhi factortrol temincludes the weight of all itsweight of plant foliage, laden withmayv widely among differentinstallation andofe coarytestingth mcomponents.In order of decreas- moisture,exceeds 2green roof systems and sh ldpleted waterproofing will gen lly rarelypoundsou beera- ingcontributionto. overallload,per square foot (9.8 kg 2 ).How specifiedby the systemprovider.alsoat arvel. /m behighe le~ hey include the growing medium,ever,whendesigningintensiveThedeadloadassociatedwith ~plants, water retention, waterproof- green roofs with large sh andgreen roofsmustbeaddedto rubs Continuedpage 10 on 9'