Installs exterior finishes (roofing, siding, trim, windows and doors)
Exterior finish questions test the water-shedding sequence: layers are arranged so water runs down and out, and each material is installed in the order that keeps the layer below it protected.
Roofs
The roof is built as a system: eave protection (an ice-and-water membrane in cold climates) at eaves and in valleys, underlayment lapped shingle-style, drip edge at rake and eave, and flashing in valleys and at wall intersections. Asphalt shingles are nailed above the exposure line with the number of fasteners the wind zone requires - four is common, six where uplift is a concern - and courses are offset so joints do not line up. Exposure is set by the manufacturer; adding to it to save material is a common failure.
Walls and openings
The weather-resistive barrier goes over the sheathing, lapped shingle-style from the bottom up, seams taped. Siding clears the ground by about 200 mm (8 in) and clears roof surfaces, and is nailed to allow movement. Windows are flashed in the order that puts the barrier over the flange at the sides and under it at the head: sill pan, window, head flashing, barrier, then trim and siding. Sealant supplements flashing; it never replaces it. Windows are set level, plumb and square, shimmed at sill and hinges, checked for reveal and operation, then insulated at the gap with low-expansion foam.
Worked example
Shingles for a roof 12 m × 9 m at a 6:12 slope. Plan area = 108 m². The slope factor for 6:12 is 1.118, so true area = 108 × 1.118 = 121 m². A square covers 9.29 m², so 121 ÷ 9.29 = 13 squares; at three bundles per square that is 39 bundles, and 10 % waste brings it to 43. Waste grows with hips, valleys and dormers.
Traps
Caulking a joint instead of flashing it; running the weather barrier the wrong way so laps catch water; driving siding tight to grade; and high-nailing shingles above the exposure line where the next course will not cover the heads.