Roofing Systems Flashcards

What causes ice dams on Canadian roofs and what is the primary prevention method?

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.

What is roof sheathing and what material is most commonly used in Canadian residential construction?

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.

What is the purpose of step flashing where a roof meets a vertical wall?

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.

What is the function of a drip edge on a roof?

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.

What is a valley in roofing and what are the two main methods of finishing it?

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).

When installing asphalt shingles, what is the recommended nail placement?

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.