Roofing, Insulation, and Weatherproofing
What this domain tests
This domain covers the building envelope: roof slope and underlayment, flashing, attic ventilation, air sealing, vapor retarders, and Michigan energy-code insulation levels. The recurring theme is that water and heat move in predictable paths, and the code details exist to control them.
Core rules
- Roof slope: asphalt shingles require a minimum 2:12 slope; between 2:12 and 4:12, doubled underlayment is required. Below 2:12, use a roof system rated for low slope.
- Ice barrier: self-adhering membrane at the eaves, extending at least 24 in. inside the exterior wall line - mandatory in Michigan's climate.
- Flashing: step flashing at sidewalls, counterflashing above it, pan flashing at valleys and penetrations, drip edge at rakes and eaves, all lapped shingle-fashion so water runs over, never behind.
- Ventilation: about 1/150 of the vented ceiling area in net free area, relaxed to 1/300 where a vapor retarder is installed and intake and exhaust are balanced; roughly half low, half high.
- Air sealing and vapor: seal bypasses before adding insulation, and keep a single vapor retarder on the warm side. Two retarders trap moisture between them.
- Energy code: the Michigan Uniform Energy Code drives ceiling and wall R-values; blown attic insulation must not block soffit vents - use baffles.
Worked example
An attic floor of 1,500 sq ft: 1,500 ÷ 150 = 10 sq ft of net free vent area, split 5 sq ft intake and 5 sq ft exhaust. If each soffit vent provides 0.5 sq ft of net free area, that is 10 soffit vents plus matching ridge or roof exhaust. Using the 1/300 relaxation without a documented vapor retarder understates required venting by half.
Traps that cost marks
Single underlayment at 3:12; treating ice dams as a roofing defect when the cause is attic heat loss; stuffing insulation against the roof deck without baffles; omitting wall flashing because the siding "covers it."