Steep-Slope Roofing Systems (Asphalt Shingle, Wood Shingle/Shake, Tile, Metal)
This domain tests the steep-slope assemblies where water sheds by gravity: asphalt shingle, wood shingle and shake, tile, and metal panels, with their slope limits, underlayments, fastening and detail work.
Asphalt shingles
Underlayment goes down first, with a self-adhered eave membrane extending from the eave to at least 900 mm inside the interior face of the exterior wall where ice damming is a risk. A starter course is required at eaves and rakes. Fasteners are placed just above the exposure line and about 25 mm from the edges, four per shingle and six where high-wind detailing applies. Valleys are built open, closed or woven according to the specification, and the chosen method must be carried through consistently.
Wood, tile and metal
Wood shingles need a minimum slope around 3:12, shakes about 4:12, and shakes are installed over spaced sheathing with an interlay of felt between courses. Tile needs at least 4:12, or 3:12 with a full underlayment, and is heavy enough that structural capacity must be confirmed. Metal panels: structural standing seam can go to about 3:12, while lapped panels need steeper slopes and sealant; fasteners and clips must allow thermal movement.
Worked example
An eave has a 600 mm overhang and a wall 250 mm thick. The interior face of the wall is 600 + 250 = 850 mm from the eave edge. The eave membrane must run 900 mm past that interior face, so it needs 850 + 900 = 1750 mm from the eave edge. A 1000 mm roll requires two courses lapped 150 mm; a 900 mm membrane needs a third course. Order the membrane width that reaches 1750 mm in the fewest laps.
Traps that cost marks
High nailing, where the nail sits above the exposure line of the course above and cannot hold the shingle. Omitting the starter course. Installing shingles below the manufacturer's minimum temperature so tabs seal poorly or crack. Using too few fasteners in a high-wind zone. Fastening metal panels rigidly so thermal movement tears the seam or elongates the hole.