Although asphalt shingles are the most commonly used roofing material in the United States, another type of roofing material the home inspector may encounter is wood shingles or wood shakes.
Wood shingles are sawn, lie flat on one another, and are thinner and more uniform than wood shakes. Wood shakes are thicker with an uneven surface and uneven thickness. Shakes can be split on the face and have sawn backs (handsplit), split on both sides (straight-split and tapersplit), or sawn on both sides (tapersawn). Wood shakes can come in different sizes and shapes and surfaces. The most common sizes for wood shakes are 18 inches and 24 inches in length. All shakes are available in two grades (premium and No.1) and are graded to one face according to grain angle, flaws, and amount of heartwood/sapwood.
Shingles are similar in appearance to tapersawn shakes except that they are thinner. Whereas the minimum butt-end thickness for tapersawn shakes is at least 5/8 inche, shingles have a butt-end thickness of about 3/8 to ½ of an inch. Shingles and shakes are usually cedar, but can also be made from Redwood. The minimum slope for both wood shingles and shakes is 3:12 or greater. The greater the slope, the longer they will last.
Wood shingles and shakes should be installed over solid or spaced plank sheathing. Shakes are laid with a starter course under the first course of shakes at the roof’s edge with a 1 ½ inch overhang as a drip edge. An inter-layment of roofing felt is laid between each course of shakes. With shingles, the inter-layment is not used. Shingles are laid from ¼ inch to 3/8 inch apart; shakes at 3/8 inch to 5/8 inch apart. This spacing allows the shingles and shakes to expand when wet. If the proper spacing is not observed during installation, shingles and shakes can buckle, split, and cup when they expand. Gaps between shingles and shakes should be staggered from course to course. Each shingle and shake is fastened in place with 2 nails with minimum fastener penetration of ½ inch.
When inspecting the wood shingle or shake, always take the time to determine first whether or not you should walk on the roof. Shingles and shakes that are wet, covered with moss, or mildew are very slippery. Do not walk on the roof if any of those conditions exist. If the shingles or shakes are badly deteriorated, you’ll break them if you walk on the roof. Avoid getting on the roof if the condition is bad.
If you do get on the roof, try to walk across the roof, not directly up and down from the eave to ridge. Be careful, as dry wood roofs in good condition can be tricky. However, before mounting the roof, start inspecting the wood shingle or shake roof from the ground. Looking at the roof from this low vantage point can help you spot areas that are excessively buckled or deteriorated. If the weather is dry, you may notice some curling and shingles and shakes that have slightly lifted. When it rains, they swell up and lay back down.
With a wood roof, the inspection of the roof from the attic is very important. The home inspector should be sure to check the type of roof sheathing and determine if it is appropriate. Remember, wood shingles and shakes should have solid or spaced sheathing. Spaced sheathing allows the wood to dry out from both sides.
During the exterior inspection, the home inspector should inspect the condition of the wood shingle and shake roof for the following:
- Improper Installation: In dry weather, shingles should not be butted tight against each other and certainly not tight and buckled, split, and cupped. Such shingles are laid without proper spacing. Note that gaps between shingles and shakes are staggered. Check the overhang at the eaves.
- Softness and rot: When the wood roof is not allowed to dry out, shingles and shakes can deteriorate. In dry weather, you may see wood roofs that remain damp. Or you may see those where the butt ends are breaking up, splitting, and cracking. The home inspector can probe for softness and deterioration.
- Damaged and weathered: Over time, sunlight can dehydrate shingles and shakes, causing them to become brittle and split and cup. Wind-blown sand can erode the shingle and wear it down. Watch for splits that lie directly under the gap in the course above making a pathway for water to enter the roof. Watch for damage that can occur from rubbing or falling tree branches. You may also see evidence of someone else being on the roof. There may be evidence of roof or gutter cleaners that wore shoes with spikes for traction that have left distinct holes on the roof.
- Loose or missing: Look for any areas on the roof where the shingles are loose or missing. If you come across loose or missing shingles or shakes, recommend a qualified roofer repair or replace the loose or missing shingles/shakes.
- Moss and mildew: Moss present on the wood roof should be reported. The most common cause of shingle and shake deterioration is the buildup of moss. If you see moss or algae, be careful, but you can probe these areas to see if there is any wood deterioration. Also check the roof framing below mossy areas, as it can also be damaged from moss. Moss should be removed from the roof, and there are chemical treatments available to kill moss. There are also preservative treatments available that will retard the growth of moss. If shingles and shakes are very dark or black, that is a sign of mildew. Mildew can be scraped off but seldom without damaging the shingle itself. There are chemical treatments that can kill mildew. Removal and suggestions on how to remove moss and mildew is best left to a qualified roofing contractor that is familiar with wood shingles/shakes.
- Water penetration: The home inspector should inspect the wood roof carefully for water penetration. Make note of rotted areas on the exterior and be sure to inspect the roof framing from the attic for any evidence of leaking
Perhaps the most difficult part of inspecting a wood roof is determining its remaining life. A roof in good condition with a long life ahead of it and one that is in poor condition is both easy to identify. It is the in between ones that can be difficult. It is a good idea to ask the home owner if they know the age of the roof. A 10-year-old roof in bad condition has serious problems and it is aging too fast. In general when about 15-20% of the roof requires repair, you should recommend a replacement soon.
We suggest the homeowners have a sealant applied to the wood roofing-a water resistant stain that includes a mildecide and moss retarder. This will help prolong the life of the roof.
There is much to learn about wood roofs, and we suggest that you do further studying on this subject. When commenting on a wood roof, be sure that you are not making any uneducated guesses about the causes of its condition or suggesting repairs or treatments you are not sure of.