Problem: Curled asphalt shingles.
Cause: Water vapor penetration.
When water migrates to the underside of asphalt shingles, the shingles can curl, cup or shrink as shown in Figures 2a and 2b.
Figure 2a - Curled Asphalt Shingles
Figure 2b - Roofing Deterioration From Moisture
Note 1: Condensation forms on framing members, sheathing and underside of roof covering.
Note 2: Roof covering absorbs moisture and deteriorates.
Note 3: Air leakage: Warm, humid indoor air leaks through holes.
Solutions: Reduce the amount of moisture accumulating on the underside of the shingles.
- The amount of water vapor that enters the attic space can be minimized by proper installation of air and vapor barriers. Minimize all paths of potential air leakage into the attic.
- Ventilation of the roof space allows moist air to exit and dry air to enter. Most North American building codes require that the unobstructed vent area be not less than 1/300 of the insulated ceiling area. For roof slopes of less than 1 in 6, the unobstructed vent area shall be not less than 1/150 of the insulated ceiling area.
- Ventilation should be uniformly distributed, with at least 25% at the top and 25% at the bottom.
- Apply roofing only on dry roof sheathing and decking.
- Ensure that soffit vents are not obstructed by insulation.
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