How to Properly Maintain a Wood Roof
Though most wood shakes and shingles have been replaced by those with an asphalt base, many homes today still have wood roofs. Some homeowners prefer a wood roof. In order for wood shakes and shingles to remain serviceable for a number of years, they must be properly maintained to prevent decay and moss and mildew growth.
What are Shakes?
Shakes are split from blocks of wood. They are not as uniform in thickness as shingles. They have little or no taper and are sometimes grooved. They can be sawn after being split to provide some taper and a flat side, which is installed next to the existing roof. Shakes are often used on log houses or summer cottages to provide a rustic look. What are Shingles?
Wood shingles are more uniform than shakes. They are sawn from blocks of wood and tapered. They have a fairly smooth surface.
Shakes and shingles can be used on sidewalls and roofs. This article will focus on roofs. However most of the information also pertains to sidewalls.
Selecting Shakes and Shingles
When selecting shakes and shingles, you need to choose those that are made of quality wood. This makes them more durable and not prone to decay. One of the best types of wood for shakes and shingles is western red cedar because it is naturally durable. The wood from the heart of old-growth western red cedar has extractives that give it an extremely high durability. Keep in mind that the durability of all wood decreases over time, as inclement weather leaches the extractives from the wood. Because of this, today’s market for wood shakes and shingles demand that they are treated for increased durability.
The second most popular wood for shakes and shingles is southern yellow pine. Other species of wood can be used if properly treated. When wood shakes and shingles are properly treated and maintained, a roof will last between 25 and 30 years without signs of decay.
Wood is subject to weathering by debris, erosion, precipitation, sun and wind. Weathering doesn’t necessarily mean decay. Weathering removes unprotected soft wood at a rate of ¼ inch per century on a vertical exposure, but much faster when the wood is used on a roof. If shakes or shingles are left to weather naturally, they will turn brown, gray or silver. If you wish your wood roof to weather at a slower rate, it should be treated with a finish that has a pigment.
There are types of treatments that can retard both weathering and decay. If you choose top quality materials for your wood roof, it will be both durable and serviceable. Lower grades of wood shakes or shingles shouldn’t be used because they will begin to deteriorate quickly.
There are a wide variety of finishes available to treat wood roofs. These are used to reduce decay and weathering or to give shakes and shingles color. It is easy to finish a wood roof, but be sure to select one that is not highly flammable.
The most effective finish for a wood roof is a semi-transparent oil-based stain that penetrates. These stains can be colored, yet they allow the grain and texture of the wood to be seen. They last longer on roughly finished wood. Stain should contain a wood preservative as well as a water repellent. Check your local home improvement store for semi-transparent oil based stain that is formulated especially for wood shakes and shingles. Stains that contain a high concentration of pigment are long lasting and they help to decrease decay and erosion of wood roofs.
Paint, solid color stains, shellac and varnish should not be used on wood roofs. These types of finishes are unable to tolerate the swell and shrinkage caused by weather and will crack. This allows water to enter and become trapped, which causes wood to deteriorate.
Varnish will only last a few months if applied to a wood roof. Paint will last a few years, but will require constant maintenance. When these finishes crack and water causes deterioration, the wood roof will be very difficult to refinish and the wood will begin to rot.
Water repellent preservatives can be used on wood roofs but their life expectancy is short. This type of finish contains a water repellent such as wax, preservatives and solvent. It is not the best choice of finish for wood roofs.
The First Finish Coat
When applying a finish to a wood roof, the first coat is best applied before the shakes or shingles are installed. This allows the butt-end, back and face of the wood to be thoroughly sealed. The first coat can be applied with a paintbrush or by dipping or with a paint roller or sprayer. The best application is dipping. The second best is using a paintbrush.
Proper installation of wood shakes and shingles is imperative because it influences moisture conditions. Be sure to install asphalted felt as a barrier over sheathing. Provide airspace between the asphalted felt and the shingles. Both of these steps help wood to dry quickly.
To create airspace, attach furring strips to the asphalt felted roof deck. These should be installed parallel to the trusses, which are also known as rafters. When this is done, attack nailers that are widely spaced to the furring strips. This allows any moisture or water that gets under the shingles to drain and dry in a minimum amount of time.
If you would prefer not to use the above method, there is an alternative on today’s market. Cedar Breather is a commercial plastic mesh that can be installed over the asphalted felt. It is thick enough to create airspace between the felt covered sheathing and the shingles.
In order to prevent the growth of moss and mildew on a wood roof, you will need to install copper flashings. The best type are the ones that turn slightly green as they age because normal corrosion from the metal controls moss and mildew growth. Use the copper flashing under the top course with a minimum of one-inch exposed, or use the flashing to cap the ridge. You may also wish to install additional strips further down the roof. Each flashing protects approximately 15 feet.
Always keep gutters and valleys clear of debris and leaves. These should be cleaned on a regular basis to prevent moisture from being trapped in or under the shakes or shingles. Keep tree branches and vines that hang over the roof trimmed. If a wood roof is kept constantly shaded, shakes and shingles will remain wet for longer periods of time, which will promote moss and mildew growth as well as decay.
Check your roof several times a year. If you find lichen or moss growth apply a solution of three quarts of warm water, one ounce of detergent and one quart of chlorine bleach.
Commercial treatments can be purchased from home improvement stores. No matter what type of treatment you choose, apply it with a brush or by dipping for optimum protection.
Whether or not the wood roof has been surface treated, it’s best to treat it with a solution that will protect exposed areas. The better a wood roof is protected, the longer it will last. Without protection a wood roof will begin to decay within ten years. With protection it can last as long as thirty years.
If you choose to use any type of commercial protection on your wood roof, be sure to read the manufacturer’s directions and follow them explicitly. This will ensure that your wood roof lasts many years and will also prevent toxins from reaching humans, pets and plants.