Required Eave Protection
(1) Except as provided in Sentence (2), eave protection shall be provided on shingle, shake or tile roofs, extending from the edge of the roof a minimum of 900 mm up the roof slope to a line not less than 300 mm inside the inner face of the exterior wall.
(2) Eave protection is not required,
(a) over unheated garages, carports and porches,
(b) where the roof overhang exceeds 900 mm measured along the roof slope from the edge of the roof to the inner face of the exterior wall,
(c) on roofs of asphalt shingles installed in accordance with Subsection 9.26.8.,
(d) on roofs with slopes of 1 in 1.5 or greater, or
(e) in regions with 3 500 or fewer degree-days.
Article 126.96.36.199. Ontario Regulation 332/12 Building Code, Information published by oncodes.ca for educational purposes only.
Eave protection is achieved by installing a membrane along the edge of the roof to prevent water from entering the roof. It is not required over unheated garages and porches, on roofs with a slope of 1:1.5 or greater or in regions with 3,500 or fewer heating degree-days. Eave protection should extend at least 900 mm (36 in.) up the roof to a point at least 300 mm (12 in.) inside the inner face of the exterior wall. Eave protection is installed under the shingle starter course and is most often a self-adhering bituminous or roll roofing membrane.
During cold weather, heat loss through the ceiling insulation combined with sun exposure may provide enough heat to melt the snow on a roof but not on the projecting eaves. Water from the melting snow can freeze and form ice dams at the eavestrough and roof overhang. As temperatures fluctuate, the melted snow freezes, causing the ice dam to progressively grow larger (Figure 100).
When a thaw occurs, this ridge of ice causes a dam that prevents melt water from escaping down the roof. The trapped water backs up under shingles and could leak into the attic, ceiling and wall. To prevent ice damming from occurring, do pay attention to air-sealing at the ceiling, the ceiling/wall junction and at all penetrations through the ceiling air barrier during construction. Provide sufficient ceiling insulation to comply with building code requirements for your location, and ensure that the attic space is vented to the exterior at the eaves.
Source : Canada Mortgage and Housing Corporation (CMHC)
Note : Ice dams cause damage to your roof’s shingles, keeping water trapped behind the ice dams. Eave protection acts like a gutter for water trapped by ice dams, routing it to your main gutter instead of continuing downward and infiltrating into the roof.