Roofing Systems and Materials
Roofing Systems and Materials tests your ability to choose and assemble steep- and low-slope roofs that shed water in Minnesota’s freeze-thaw cycles. Questions often ask what belongs under the shingles, at the eaves, and around penetrations.
Steep-slope assembly
- Asphalt shingles generally require a minimum 2:12 slope; from 2:12 up to 4:12 use double underlayment, and above 4:12 one layer, unless the manufacturer is stricter.
- Install starter strip at eaves and rake, offset courses, and follow the shingle manufacturer’s nailing pattern-usually four nails, six in high-wind areas.
- In Minnesota, ice-dam protection is required at eaves: a self-adhering membrane at least 36 inches wide, extending 24 inches inside the exterior wall line.
- Ventilate attics at 1 square foot of net free area per 150 square feet of attic floor, with balanced intake and exhaust; do not block soffit vents with insulation.
- Use step flashing and counterflashing at sidewalls, kick-out flashing where a roof meets a wall, and preformed boots at pipes.
Low-slope
Below 2:12, asphalt shingles are not allowed. Use a membrane system such as EPDM, TPO, or modified bitumen, with seams and terminations detailed for water backup.
Worked example
A 1,800-square-foot footprint has a 5:12 slope. Pitch multiplier = √(1 + (5/12)²) = 1.083. Roof area = 1,800 × 1.083 = 1,950 square feet = 19.5 squares. Add 10% waste: 21.5, so order 22 squares. Because the slope is 5:12, one underlayment layer is acceptable under shingles; ice barrier still goes at the eaves, and a kick-out is needed at the sidewall.
Traps
Skipping ice barrier on unheated porches; using shingles below 2:12; nailing above the exposure line; omitting kick-out flashing; mixing aluminum and copper where corrosion can occur; relying on caulk instead of proper flashing.