"Understanding Your Home" by Building Inspector Mark Visser
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Wood shingles: Uniform thickness

Wood Shingles and Shakes
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Wood shingles. Cedar shakes. Controlling moss growth on wood shingles.

Shakes are typically made from cedar. The main differentiating feature between shakes and other types of shingles is that shakes are split while most shingles are sawn on all sides. Wood shingles are usually sawn to a uniform thickness. Shakes are thicker than shingles and have a course, uneven texture.
Wood shingles installed over spaced boards usually last longer (30-35 years) than those nailed over plywood (20-25 years). Plywood provides less or no ventilation which can lead to moisture, drying problems and rot.
Shingle joints should be spaced to allow for expansion when wet. Joints should stagger per course and should not be in line with joints in the two previous courses.
. Nail heads should not be driven in all the way to the shingle surface. Some space should be provided for expansion and to prevent premature splitting.
Slipping or missing shingles may expose joints and nails. they should be repaired or replaced to prevent leaks.
Moss and fungus control. Wood roofs, poor ventilation and lack of sunshine mixed in any combination, invite wood rot and failure.

Cedar shakes: Uneven thickness
Moss keeps the shingles damp and should be removed. Applying a clear wood preserver will preserve them and discourage further growth of moss.
Another method of keeping your roof free of moss is to install a copper ridge and, depending on the roof size, slipping a 2 or 3 inch copper strip under every 10th course. The copper, when exposed to air and water, will oxidize, creating Copper Sulphate which runs down the length of your roof in the rain water. This is deadly to moss spores and will therefore keep your roof free from moss.

Never use old wood shingles for firewood. They are saturated with chemicals and pose a real health hazard.

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