403A Roofing Systems 2 — Questions and Answers
Question 1: What causes ice dams on Canadian roofs and what is the primary prevention method?
- High winds cause snow to melt; installing wind barriers prevents them
- Heat escaping through the roof melts snow, which refreezes at the eaves; adequate insulation and ventilation prevent them (Correct answer)
- Rain freezing on cold shingles; heated gutters prevent them
- Condensation from bathroom fans; proper duct routing prevents them
Correct answer: Heat escaping through the roof melts snow, which refreezes at the eaves; adequate insulation and ventilation prevent them
Ice dams form when heat escaping from the living space warms the roof deck, melting snow that runs down and refreezes at the cold eaves overhang. The primary prevention is maintaining consistent roof deck temperature through adequate insulation and continuous attic ventilation.
Question 2: What is roof sheathing and what material is most commonly used in Canadian residential construction?
- Plywood or OSB panels nailed to the rafters or trusses to create the roof deck (Correct answer)
- Metal sheets fastened directly to the trusses
- Concrete tiles set over purlins
- Rigid foam insulation boards with integral nailing surfaces
Correct answer: Plywood or OSB panels nailed to the rafters or trusses to create the roof deck
Roof sheathing consists of plywood or OSB (oriented strand board) panels fastened to the rafters or trusses to create a solid roof deck. In Canada, 12.5 mm (1/2 inch) or 15.5 mm (5/8 inch) panels are most common, providing the nailing base for roofing materials.
Question 3: What is the purpose of step flashing where a roof meets a vertical wall?
- To add structural support at the junction
- To prevent water from penetrating the joint by directing it over each shingle course (Correct answer)
- To provide a decorative trim at the transition
- To secure the wall sheathing to the roof framing
Correct answer: To prevent water from penetrating the joint by directing it over each shingle course
Step flashing consists of individual L-shaped metal pieces woven into each course of shingles where the roof meets a vertical wall. Each piece laps over the one below, creating a shingled waterproof barrier at the joint.
Question 4: What is the function of a drip edge on a roof?
- To add weight to the roof edge for wind resistance
- To direct water away from the fascia and into the gutter (Correct answer)
- To support the first course of shingles
- To provide ventilation at the eave
Correct answer: To direct water away from the fascia and into the gutter
A drip edge is a metal flashing installed at the eaves and rakes of a roof. It directs water runoff away from the fascia board and into the gutter, preventing water from wicking back under the shingles or rotting the fascia and soffit.
Question 5: What is a valley in roofing and what are the two main methods of finishing it?
- A valley is the peak of a hip roof; finished with cap shingles or metal ridge
- A valley is where two roof slopes meet forming a V-channel; finished with open metal valley or closed-cut (woven) shingles (Correct answer)
- A valley is a low area in flat roofing; finished with extra membrane layers
- A valley is the space between dormers; finished with siding or stucco
Correct answer: A valley is where two roof slopes meet forming a V-channel; finished with open metal valley or closed-cut (woven) shingles
A roof valley is the internal angle formed where two sloping roof sections meet. The two main finishing methods are open valleys (lined with metal flashing left exposed) and closed-cut or woven valleys (where shingles from both sides are interlaced across the valley line).
Question 6: When installing asphalt shingles, what is the recommended nail placement?
- At the top edge of the shingle
- In the nailing strip (tar line) just above the cutout slots (Correct answer)
- At the exposed portion of the shingle
- Through both the shingle and the metal drip edge
Correct answer: In the nailing strip (tar line) just above the cutout slots
Asphalt shingles should be nailed in the manufacturer-specified nailing strip, typically located just above the cutout slots or the self-seal adhesive strip. This placement ensures the nails penetrate through two layers of shingles while being covered by the course above.
403A Roofing Systems 2
What causes ice dams on Canadian roofs and what is the primary prevention method?