b'Technologypiping, flashing, slow or im-mediate release of harvested water over an extended pe-riod of time.3.Structural Requirements: Capacityofthedeck,roof assembly dead load, capacity ofroofdrainage/retention panelandstormwaterstor-age, resistance of the water-proofing membrane, insula-tion and other components.What Are the Control Parameters for NBSCR Design?1.Drain Specifications:i.Number of Roof Drains(N RD ):Whenusingcon-trolled-flowroofdrains, there must be at least one Figure 2: Hydrographs for a stormwater detention assessment. drainforupto10,000 squarefeet(900m 2 )of roof area, and at least two What Are the Risksweightofdetainedstorm- 3.Material Integrity: FailureWhat Are the Overalldrains on roofs larger than Associated with the NBS water and snow, should beto ensure the integrity of theDesign Requirements for10,000 square feet.CR? assessed in the early stages ofroof before and during theNBSCR? ii. Release Rate per Drain the design process. installation of the VRA and(Q i ): Q iis the release rate Ensuring optimal performance2.DrainageandDrainSys- SDA may lead to leaks alongThree factors need to be closelyfromtherooftopdeten-ofNBSCRtechnologiesre- tem: A common concern inseamsbetweenroofingconsidered and determined for a suc- tion (Q ROOF ; ft 3 /s) divided quirescarefulconsiderationofcold climates is ice build-upsheets. Leaks are common atcessfuldesignandfunctionofthebythenumberofdrains thefollowing: and melting snow that thenand around penetrations inNBSCR: (N RD )inft 3 /s(Eq.1): 1.Structural Loading: Struc- refreezes. This may result inthe roofing membrane, e.g.,1.ClimaticLoadDetermi-turaloverloadingfromtheice dams that could preventdrains or fastening brackets.nation:Geographicalloca- Eq.1:Q i =Q ROOF/N RDweight of NBSCR tech- meltedwaterfromflow- Thus,thewater-tightnesstion and roof orientation are nologiesisthequalityrisk,ingtothedrainsandlargetest is recommended for theimportant parts of designingiii. Depth of Flow at Drains especiallyforretrofitsce- poolsofsnowandwaterNBSCR climatic load de- (D R ):D R isdetermined narios. Adding extra mass tothatmayleadtostructuralroof membrane assembly totermination. Future stormbased on the relationship the roof presents the risk offailure.Topreventlossofensuretheintegrityoftheeventsintensity,dura- betweenthereleaserate structural deflection and de- function, regular inspectionroofing before it is covered.tion and frequency shouldand the ponding depth, as formation,drainagefailureand maintenance of drains isTheroofdesignshouldbeestablished. specified by the roof drain and, in extreme cases, struc- necessary, and the roof mustpreventmoisturedamage2.DrainageRequirements:manufacturer.Thisflow tural collapse. Thus, the ex- be designed and built to ac- from running water passingIncludingthecontrolleddepthmustbelessthan pected loads from VRA andcommodate regular access byaroundandovertheroof- flowdrainswithhydraulicor equal to the maximum SDAroofs,includingthemaintenance personnel. ingassemblies. pressurecalculationsforponding depth (D max ) (Eq.87 Bakersfield St., Toronto, Ontario, M3J 1Z4 Tel: 416-787-0649Fax: 416-787-0640 Email: service@crawfordroofing.ca www.crawfordroofing.caIndustrial Commercial Institutional Roofing Solutions - PMI Programs- Modified Bitumen- Built Up Systems - Metal Roof Systems- Waterproofing- Restoration- Emergency Services- Roof Anchors- Single Ply - Roof Top Decks- Sheet Metal- Inverted Committed to Safety, Quality & Service for 40 years Services Fully Bonded & Insured 10ONTARIO ROOFING NEWSISSUE 4 2022/23 THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ORN'