Steep-Slope and Low-Slope Roofs
It is a known fact that all metal roofs can be installed on steep-slope roofs. The metal roofing industry defines steep-slope as a roof with a pitch of 3:12 or greater. Some products can be installed on roofs with a slope as low as 2:12. Slope limitations vary by manufacturer. Confirmation of compliance with manufacturers’ specifications lies well beyond the scope of an inspection.
If you suspect that a roof does not comply with the manufacturer’s installation requirements, recommend further evaluation by a qualified engineer or a roofing consultant.
Metal roofing shall not be installed at a slope lower than the minimum recommended by the manufacturer. Occasionally, someone will attempt to get away with installation on a slope lower than that recommended by installing waterproof underlayment. This is insufficient and such an installation is defective.
Solid sheathing is typical for a roof deck for metal roofing, although it can be installed over closely spaced boards. Some types can be installed over battens, which are sometimes called strapping.
Architectural metal roofing is designed to be installed over underlayment. This is especially crucial when metal roof is installed over an existing roof-covering material.
Because structural panels have no deck on which to install underlayment, they may develop problems if they’re installed on homes which generate significant amounts of moisture or which have poorly ventilated attics that produce condensation.
You probably won’t be able to confirm the presence of underlayment on homes with metal roofs, and structural panels are rare in residential construction.
Metal Roofing Panels
Metal panels roofs are commonly used as residential roofing come in a variety of profiles. In high-quality roofing, panels are continuous from ridge to eave, and vary in width. You may also see some panels that overlap, and some with seams that butt or interlock.
Panels sometimes have ribs formed into the field for added strength and wind resistance. The side edges are formed to interlock, creating vertical seams in the finished roof.