b'Drainage Roof Drainage Design Pitfalls to avoid and retrofit options By Allen Lyte, B.Tech., C.E.T., RRO and Barb Kemp, B.Tech., C.E.T., RRO Thefollowingarticleoriginallyscenario, leaks could be catastrophicTable 2.4.10.11. (Courtesy of the National Plumbing Code) appeared in the December 2023 issueby allowing large amounts of waterMaximum Permitted Hydraulic Load Drained to a Leader of Construction Canada magazine.toenterthebuildingbysurpass- Forming Part of Article 2.4.10.11.A ppropriatedrainageismembranefromtheincreasedhy- Circular Leader Non-Circular LeaderIt is reprinted here with permission. ing roof curbs or breaking the roof criticaltoensuredurabledrostaticload.performanceofanyroof,Heavy Waterbut this is especially so forJust one litre of water is equal toNominal Pipe SizeMaximum HydraulicArea of Leader,Maximum Hydraulic largeindustrialandcommercialone kilogram (2.2 pounds). Whereof Leader, NPS Load, L cm 2 Load, Lroofs.Duringaroofrepairorthere is standing water, there is an replacement project, it is importantincreaseinload.If1mmofwater2 1,700 20.3 1,520to consider having options to removedoes not drain from the roof surface, waterfromyourroofassemblytoan extra kilogram per square metre2 3,070 31.6 2,770ensure that the structural roof slopeis added to the load. An overloaded and drain locations achieve positiveroofdeckcancausedeflectionor drainage.Thisarticlewilldiscusseven collapse, most often at the mid- 3 5,000 45.6 4,500pitfalls to avoid during roof designdle section of the roof area.and retrofit options that are availableSlippery When Wet 4 10,800 81.1 9,700to improve the roofs drainage afterIn cold climates, standing water the roof has been installed. can freeze and cause hazardous sur- 5 19,500 126.6 17,600Why Standing Water onfaceswhenaccessingtherooffor maintenance and repairs to rooftop6 31,800 182.4 28,700a Roof Can Cause Bigequipment. Thick layers of ice can Headaches cause disconcerting ice quakes to the Numerous complications can oc- tenants below. 8 68,300 324.3 61,500cur if water is able to stand or pondAngry Birdson the roofs surface.Standingwatercanalsoattract Beginning of the End birds,andwheretherearebirds,Table 2.4.10.10. (Courtesy of the National Plumbing Code) If the roof assembly has startedtherearefecesanddebris,whichMaximum Permitted Hydraulic Load Drained to a Roof Gutter to deteriorate, standing water couldcan result in blocked drains leadingForming Part of Article 2.4.10.10.enter the assembly, risking leakage.to additional water build-up. While Thisleakagecancauseconcealedcreating a good environment for theMaximum Hydraulic Load, Lmoisturedamagethatcangoun- birds, this will create an angry opera- Nominal noticed for years. In the worst-casetions manager. Pipe Size ofArea of2 SlopeGutter, NPS Gutter, cm1 in 200 1 in 100 1 in 50 1 in 253 22.8 406 559 812 1,1404 40.5 838 1,190 1,700 2,4105 63.3 1,470 2,080 2,950 4,1706 91.2 2,260 3,200 4,520 6,5307 124.1 3,250 4,600 6,500 9,1908 162.1 4,700 6,600 9,400 13,20010 253.4 8,480 12,000 17,000 23,60010ONTARIO ROOFING NEWSISSUE 4 2023/24 THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ORN'