Changes

==Resources to review==

==Resources to review==

Examples of roof failures due to water ponding have led to formal declarations being required from building designers as part of permit applications across Canada, confirming whether roof control drains are proposed and that appropriate measures (including structural capacity, number of drains, and overflows) have been taken (EABO, 2016). Because all roofs in Canada must be designed to support peak snow loads, this provides capacity for supporting an equivalent weight of ponded water. Building codes permit designers to assume that snow and water loads are not cumulative, up to a maximum depth of 150mm of water, if precautions are taken to prevent flooding by providing a sufficient number of roof drains with overflows. It is therefore uncommon for roof water detention systems to be designed to permit more than 150mm of water to accumulate. This also means that these systems can be incorporated into existing roof structures that have been designed to support conventional snow loads.<ref>Richard Hammond (2017). Evaluating Green and Blue Roof Opportunities in Canadian Cities. UWSpace. http://hdl.handle.net/10012/11463</ref>

Because all roofs in Canada must be designed to support peak snow loads, this provides capacity for supporting an equivalent weight of ponded water. The Ontario building code permits designers to assume that snow and water loads are not cumulative, up to a maximum depth of 150 mm (water equivalent), if precautions are taken to prevent flooding by providing a sufficient number of roof drains with overflows. It is therefore uncommon for roof water detention systems to be designed to permit more than 150 mm of water to accumulate. This also means that these systems can be retrofitted onto existing roof structures that have been designed to support conventional snow loads.<ref>Richard Hammond (2017). Evaluating Green and Blue Roof Opportunities in Canadian Cities. UWSpace. http://hdl.handle.net/10012/11463</ref>