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Under One Roof

Canadian Roofing Reference Manual

10.7 Underlayments

Underlayment is required under most metal roofing. This should consist of at least one layer of #30 asphalt-saturated (non-perforated) felt applied horizontally. All felt sheets should have a minimum head lap of 100 mm (4 in) over the preceding felt, and side laps should be a minimum of 150 mm (6 in). The felts should be nailed as necessary to hold the felts in place until the metal roofing panels are applied. Regardless of the type of underlayment required, the installation of eave protection membrane is required as with other types of steep roofing when the building is heated.