b'Technical Article roofing system in the Silver category. TheSIGDERScommitteeintends Table 2: Wind load determination for Toronto (City Hall), Ontario. toreviewthisCSAA123.26 5 re-quirementgiventheimpracticality Location-specific wind loads per Wind-RCI 7and Climate- of such an installation, questionable Location-specific wind loads per Wind-RCI 7 RCI 13with increase of 30 per cent for Silver and 50 perperformanceintermsofthermal cent for Gold bridgingandchallengesrelatedto the continuity of air barrier and wa-terproofing. Also, this drainage sys-Roof Performance Levels Field wind load,Edge wind load,Corner wind load,Field wind load,Edge Wind load,Corner wind load,tem requirement conflicts with the kPa kPa kPa kPa kPa kPa intent of the building code to reduce overstress on the drainage system.Bronze -1.0 -1.3 -2.6 -1.0 -1.3 -2.6Rainwater Runoff Silver -1.1 -1.4 -2.7 -1.43 -1.82 -3.51 Management on Roof Gold -1.1 -1.4 -2.7 -1.65 -2.1 -4.05 SurfacesCurrentindustrypracticein Note: NBCC = National Building Code of Canada. 1 m = 3.3 ft.; 1 kPa = 20.9 lb/ft 2 . roofdrainagedesignistoachieve Wind loads for Bronze categories are compliant with current NBCC requirements; wind loads for Silver and Gold categories are increased 30 per cent and 50atwo-per-centminimumpositive per cent, respectively, from the NBCC code requirements. slope towards roof drains; typically, theroofingsystemwillhavetwo-directional drainage achieved using Table 3: Rain load determination for Toronto, Ontario. AffairsandHousingsSupplemen- 152 mm (6 in.) with a drain slopea sloped structure towards a central taryStandardSB-1,Climateandof two per cent under the roof andvalleywithcricketsbuiltusingta-Seismic Data. 16The hydraulic loada roof area of 9,290 m 2(100,000 ft 2 ),peredinsulationatthecentrethat Rain Load Calculation in litres from a roof is equal to thea total of 14 drains is required. Re- lead runoff water to drains. This in-maximum 15-minute rainfall inten- fer to Table 4, showing comparativedustry practice is further reinforced Roof area 9,290 m 2 sity multiplied by the sum of area ofcalculations for a 4 drain and forinCSAA123.26, 5 whichrequires the horizontal surface and one-halfsevere and extreme conditions. that roofing assemblies in the Silver theareaoftheadjoiningverticaland Gold categories achieve the min-15-minute rain intensity per NBCC 2 25 mm surface (with the areas measured inRoof Drainage Systemimumtwo-per-centpositiveslope square metres). For instance, basedDesign for the main roof surface, which also 2 on the NBCC 2Table C-2, the maxi- The intent of the building codeincludes a back slope at the crickets One-day rainfall per NBCC 97 mm mum15-minuterainfallintensityis to discharge rainwater off the roofthat is double the slope of the main (one-in-10-year return) for Torontoattheearliestpossibletime,butroof.TheGoldrequirementpre-15-minute rain intensity for severe condition per(City Hall) is 25 mm. NBCC 2Tablescribes the entire roof structure to Climate-RCI 13 Unavailable C-2alsoprovidesinformationonwithout adding stress to the drain- haveaminimumoftwo-per-cent one-day rainfall that has one chanceage system during rapid accelerationpositive slope.One-day rainfall for severe condition per Climate-RCI 13 116.69 mm in 50 of being exceeded in any singleofrainfallintensity;thispurposeCurrentindustrypracticealso year. The one-in-50-year return val- isachievedbyallowingacertainlimits the interference to free drain-ue one-day rainfall is used mainly toamount of time for the rainwater toage on the roof surface by suitably Extrapolated 15-minute rain intensity = (25 mm *30 mm determine the additional (structural)flow across and down the roof be- positioningrooftopunits,rooftop 116.69 mm) / 97 mm dead load due to ineffective drains. fore it enters the gutter or drainageaccessories and other openings or by One-day rainfall for extreme condition per Climate- Anticipated rain loads for Silver-system. To determine the drain sizeusing crickets around such interfer-RCI 13 126 mm andGold-levelroofassembliescanand number of drains for an effec- ences. For effective management of bedeterminedusingtheClimate- tiverooftopdrainagesystem,thethedrainagepath,CSAA123.26 5Extrapolated 15-minute rain intensity = (25 mm *32.5 mm RCI 13 tool.UnliketheNBCC 2 buildingcodedirectsthedesignerincludes a prescriptive requirement 116.69 mm) / 97 mm tablesusedforBronzeassemblies,tousethemaximum15-minutetopositionrooftopunits,rooftop Climate-RCI 13 onlyprovidesone- rainfallintensityandhydraulicaccessoriesandotheropeningsa day rainfall projections. In absenceloadcalculations. minimum of 1.8 m (6 ft.) away from of the maximum 15-minute rainfallInadditiontothecurrentroof drains, low points or valleys to intensity information, the extrapola- buildingcoderequirement,CSAavoid restricting the flow of water to tion of one-day rainfall data in theA123.26 5 prescribesmaximumdrains or scuppers.Climate-RCI 13 toolissuitableasrunoff for rainwater by limiting the longasthestructuralsystemswilldistance between the roof perimeterRainwater DischargeCommercial and Residential Roofing be designed to handle the weight ofanddrainsandlimitingthespac- Ensuringtheeffectivenessof Trinity Roofing Ltd. specializes in a variety of roofing applications and the projected one-day rainfall. Theing between the drains. For roofingdrains and scuppers is a critical part waterproofing for residential, commercial and institutional buildings. 15-minute rainfall intensity can besystemsintheSilvercategory,theofhandlingthedischargeofrain-calculated using the percentage dif- standard specifies that water on thewater. In addition to a prescriptive Phone: 416-630-9213URL: www.trinitycanada.comference between the one-day rainfallsurface cannot run more than 10.7requirement for the minimum drain Fax: 416-630-1722 Email: info@trinitycanada.comdata for Silver and Gold roofs fromm (35 ft.) to a drain and scupper.diameter,CSAA123.26 5 includes Climate-RCI 13and the one-day rain- In the Gold classification, the maxi- severalqualitativerequirements fall values from the 2020 edition ofmum distance to a drain or scupperfor drains, such as the requirement NBCC. 2Refer to Table 3, showingis 6.1 m (20 ft.). Analysis shows thatfor a sump at drains, specifications an example of the rain load determi- this maximum water runoff distanceregarding the size and slope of the Pioneers of Taperednationusingextrapolationforse- requirement overwrites the currentsump and installation of strains and vere and extreme conditions. code,addingasignificantnumberscreens with specific material choices Insulation Systems Table7.4.10.9oftheOntarioofdrainstotheroofandlimitingand securement. CSA A123.26 5re-Our full-service systems, designed to slope to drain, haveBuildingCodeprovidesthemaxi- the current industry practice of us- quires a minimum drain diameter of been installed on thousands ofmumpermittedhydraulicloadingtwodirectionalslopesandval- 76 mm (3 in.) for roofing assemblies successful roofs nationwide. drained to a horizontal storm drain- leys. When the limiting distance forin the Silver category and 102 mm (4 Learn more about ourage pipe at two-per-cent roof slope.maximumrunoffforrainwaterisin.) for those in the Gold category. A products and services. Based on the determined rain load,applied to a 9,290-m 2(100,000-ft. 2 )sump is required at each main drain assuming a drain and leader size ofroof, 45 roof drains are required for ameasuringminimum1.21.2m 20ONTARIO ROOFING NEWSISSUE 3 2025 THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ORN'