Roofing Materials, Systems, and Installation Practices
Roofing Materials, Systems, and Installation Practices
This domain tests whether you can choose the right assembly and install it so it passes inspection, satisfies the manufacturer's warranty, and sheds water at every penetration.
- Slope drives the system. Asphalt shingles are limited to 2:12 and steeper; from 2:12 up to 4:12 the code requires double underlayment. Below 2:12, use a low-slope membrane such as modified bitumen or single-ply.
- Decking: sound, code-compliant sheathing fastened to the framing. Replace rot, re-secure loose panels, and correct dips before underlayment; shingle fasteners must penetrate the deck as the code and manufacturer require.
- Underlayment: full deck coverage, lapped per manufacturer (commonly 2 inches on side laps, 4 inches on end laps), with eave protection where the adopted code requires it.
- Flashing sequence: water flows over, so upper layers lap over lower. Drip edge at eaves goes under the underlayment; at rakes it goes over. Step flashing at sidewalls is woven with each shingle course; headwalls get a counterflashed apron. Valleys are open metal or closed-cut, never a caulk joint.
- Fastening: nails driven straight, flush with the shingle surface, placed in the manufacturer's nailing line. In Mississippi's design wind zones, most manufacturers and the code call for six nails per shingle. High nails and overdriven nails are the leading cause of blow-offs.
- Ventilation: soffit intake balanced with ridge exhaust, sized to attic volume, never blocked by insulation.
Worked example. A 6:12 gable roof over 1/2-inch OSB, architectural shingles in a 130-mph wind zone. The crew uses four nails per shingle and sets them high. Inspection fails and the manufacturer declines the wind warranty: the design pressure requires the six-nail pattern placed in the nailing line, not above it.
Traps. Reusing old flashing; adding a third shingle layer; shingles on a 1:12 porch; caulk instead of step flashing; nailing through the exposure; and blocking soffit vents with insulation.