b'BUILDING CODEcustom-designed securement. However, While the Building Code permits provenbecause ANSI/SPRI WD-1 is permitted asanextrapolationmethodforeither mechanical or adhesive securement (see past performance as a second complianceNote A-5.2.2.2. (4)), using the method is arguably a valid third compliance path. pathway, the bar is very high. In manyThatsaid,Iofferafewwordsof caution. First, this work is clearly within the wheelhouse of the registered profes-instances, the designer is better off selectingsional skilled in the work of Division B, Part 4. Second, while roof assembly a tested roof assembly. testsusingCSA-A123.21demonstrate both the cohesiveness of an assembly anditsconstituentmaterials,andthe adhesive properties of materials bonded together,thosecharacteristicsarenot necessarilytransferabletoanother assembly. Adhesive and cohesive prop-ertiesarematerial-dependent;for example, changing one insulation panel brand for another may sufficiently alter the properties of the entire assembly so that it will fail to perform as expected. Even Annex F in CSA-A123.21 provides veryconservative(andnon-binding) guidanceformaterialsubstitutions, becauseofthechainofconnectivity between roof system materials.Liquid membranes, inverted roofs, and green roofsThe first principle of Code-compliant roof design, regardless of the membrane orassemblytype,istocalculatethe SWLs; every roof on a Part 3 building must be designed to resist displacement by the wind.Liquid-appliedmembranesarenot specificallyaddressedbytheBuilding Code.Mostliquid-appliedmembranes (polyurethaneandhotfluid-applied rubberizedasphalt,forexample)are usedonlyinprotectedmembrane systems, which I will address momen-tarily, but some polyurethane membrane manufacturersmaypermittheiruse inexposedinsulatedoruninsulated systems(RoofStar-acceptedpolyure-thane membranes may be used only in protectedmembranesystems).When the membrane is exposed to the wind, defertothemembranemanufacturer fortheirwindresistancedataandapplication methods.Protectedorinvertedsystemsare securedwithballast.Ordinarily,the 28lROOFINGBC l SPRING 2022'