b'tem reaches the critical threshold of 85 per cent of its initial weight (W ),whicheverhappensfirst. VSThe threshold for weight loss is based on a consensus-based crite-rion to prevent excessive growing medialossand/orsystemover-Windturning. The VRA weight moni-toring is carried out via integrat-ing load cells as part of the testing rig. The procedure stipulates that the wind speed at which the mea- Figure 4: Landing web page of Wind-RCI.sured weight reaches 85 per cent of the Wis defined as the re-VScordedspeedandthepreviousFor BVRA, the as-built test- Code Compliance ProcessFigure 2: Typical VRA setup for wind flow evaluation as per CSA 123.24-21. incrementalwindspeedlevelasing permits to evaluate the system the sustained speedsee Figurewithoutthenecessityofwait- Theprocesstoverifycode 3. The sustained speed is usedcompliancecanbesummarized W VSto calculate the wind resistance. ingforvegetationgrowth.Thein three steps:VRA wind resistance is basedexpectedenhancementdueto1.Establishthedesignvalues85% of W VSon the evaluation of three iden- vegetationgrowthistakenintoof wind uplift (P D ) and wind ticalas-built(VRAconditionaccountbyaso-calledGrowthspeed(V )accordingto Wind speed, km/hMeasured weight (kg) immediatelyafterconstruction)ModifierFactor(GMF).Under- DNBCC 2020.systems. The three repetitions arestandingthatdensityisakey2. Determine the resistance val-requestedtoverifythevariabil- parameter for vegetation growth,uesofwinduplift(P )and ity of resultswhich should beRthe GMF (GMF = min [(1.6-( xwind speed (V ) according to less than 15 per cent. This is alsoR0.5))]) is a function of the vegetat- CSA 123.24-21.recorded speed km/hneeded to calculate the resistanceed system density (gr/cm3 ). VRA3.Compare resistance (P Rand factor()toapplyaLoadandwind resistance (V R ) is calculatedV R ) with the design values (P Dsustained speed km/hResistance Factor Design (LRFD) as follows: V R= Vxx GMF,andV D ).Forcodecompli-approach of NBCC 2020.is anavwhereV istheaverageoftheance,bothresistancesmust engineeringmethodtoaccountav for the variability associated withsustained speed of three as-builtbesimultaneouslyhigher Figure 3: Schema of flow test protocol and instantaneous VRA response materials, installation and others.systems evaluated.than the design values.(according to CSA 123.24-21).+Build SolutionsTotal Design F architek.com | 1 888 317 9226or Your Green Roof Projects.ORN THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ONTARIO ROOFING NEWSISSUE 4 2021/2213'