403A Roofing Systems — Questions and Answers
Question 1: What is the minimum roof slope generally recommended for asphalt shingle installation in Canada?
- 1:12
- 2:12
- 4:12 (Correct answer)
- 6:12
Correct answer: 4:12
Most asphalt shingle manufacturers recommend a minimum slope of 4:12 for standard installation. Slopes between 2:12 and 4:12 require special low-slope application techniques including full ice and water shield underlayment.
Question 2: What is ice and water shield membrane and where is it required in Canadian roofing?
- A type of flashing for chimneys only
- A self-adhering waterproof membrane applied at vulnerable areas like eaves and valleys (Correct answer)
- An insulation product installed over roof sheathing
- A vapour barrier placed under the roof deck
Correct answer: A self-adhering waterproof membrane applied at vulnerable areas like eaves and valleys
Ice and water shield is a self-adhering rubberized asphalt membrane applied to the roof deck at areas vulnerable to ice damming and water infiltration. The NBC requires it at eaves (extending at least 900 mm past the interior wall line), valleys, and around penetrations.
Question 3: What is the standard exposure (amount of shingle visible) for a typical three-tab asphalt shingle?
- 100 mm (4 in.)
- 127 mm (5 in.) (Correct answer)
- 152 mm (6 in.)
- 178 mm (7 in.)
Correct answer: 127 mm (5 in.)
Standard three-tab asphalt shingles have a typical exposure of 127 mm (5 inches), meaning each course overlaps the one below by approximately two-thirds of the shingle height, providing triple coverage.
Question 4: What is the purpose of a ridge vent on a sloped roof?
- To prevent wind uplift on the ridge cap
- To allow warm, moist air to exhaust from the attic at the highest point (Correct answer)
- To strengthen the ridge beam
- To direct rainwater away from the ridge
Correct answer: To allow warm, moist air to exhaust from the attic at the highest point
A ridge vent runs along the peak of the roof and allows warm, moist air to naturally exhaust from the attic. Combined with soffit vents providing intake air, it creates continuous ventilation that prevents moisture buildup and ice damming.
Question 5: What is a roof truss and how does it differ from conventional rafter framing?
- A truss is a curved structural member used in arched roofs
- A truss is a prefabricated triangulated framework that spans the full building width without interior bearing walls (Correct answer)
- A truss is a type of heavy timber beam used in post-and-beam construction
- A truss is a metal connector used to join rafters at the ridge
Correct answer: A truss is a prefabricated triangulated framework that spans the full building width without interior bearing walls
A roof truss is a pre-engineered, prefabricated triangulated framework typically made from 2×4 or 2×6 lumber connected with metal connector plates. Unlike conventional rafters that may require interior bearing walls, trusses span the full width of the building.
Question 6: According to the NBC, what is the minimum attic ventilation ratio for a residential roof in Canada?
- 1:150 of the insulated ceiling area
- 1:300 of the insulated ceiling area (Correct answer)
- 1:500 of the insulated ceiling area
- 1:1000 of the insulated ceiling area
Correct answer: 1:300 of the insulated ceiling area
The NBC requires a minimum ventilation ratio of 1:300 of the insulated ceiling area when ventilation is provided at both the soffit and ridge/upper area. If ventilation is only at one level, the ratio increases to 1:150.
403A Roofing Systems
What is the minimum roof slope generally recommended for asphalt shingle installation in Canada?