Wood shingles were the most common roof covering in Colonial America -- and several hundred years later, they are a choice material for historic restoration.
With proper care and maintenance, these roofs can be attractive and reliable protection for your historic home. Most buyers of old homes view the cedar roof as an historically correct material over their home and are eager to take the steps necessary for its preservation.
In this column I'll discuss the maintenance and repair of this traditional roofing material.
Cedar is the most commonly used wood in North American these days for roofing. Although many modern wood roofs have a rustic appearance, a smooth sawn shingle is more historically accurate.
Cedar roofing comes in two varieties -- shingles or shakes. A shingle is tapered and smooth sawn on both surfaces for a uniform appearance. A shake is split to reveal the uneven natural grain of the wood on the face and is usually much thicker than a shingle. A cedar shake roof has a much more rustic appearance, but may not be historically accurate for most homes. Early handmade shingles were hand split, but then shaved smooth and tapered with a drawknife, appearing closer to today's sawn shingles.
Installation
This wood roof installation allows plenty of ventilation.
Traditionally wood shingles and shakes were installed on spaced wood strips. This type of installation allows the wood to dry evenly after absorbing precipitation. The recent practice of installing wood roofs on solid wood sheathing or directly on roofing felt paper has significantly reduced the life expectancy of this type of roof. Cupping and curling of the shingles is now a common condition and deterioration of the wood is occurring much earlier than older roof systems with adequate ventilation.
Building codes on wood roofs vary from municipality to municipality. Some building codes require tarpaper under each individual coarse of cedar shakes. Some contractors and municipalities interpret this to include cedar shingles as well. Solid sheathing under wood roofs is often required in seismic regions. You, or your roofer, should check with the local building inspector for specific installation requirements.
Maintenance tips: Dealing with mold and mildew
Mildew can usually be treated successfully with trisodium phosphate (TSP) or household bleach mixed with water into a solution and scrubbed with a soft brush. The roof surface should then be rinsed thoroughly with fresh water.
Moss can usually be treated with a sprayed application of an herbicide that contains zinc sulfate or again a household bleach solution. After the moss dies off, it needs to be brushed or sprayed with a garden hose off the surface.
To impede the return of the moss, exposed strips of zinc can be installed just below the top course of shingles above each roof surface. Each rain picks up some zinc and perpetually treats the roof. Trimming overhanging branches can eliminate shade that is conducive to moss formation.
Chemical solutions should be used with caution. Overspray and run-off can kill desirable vegetation growing around the building and at the base of the downspouts.
Repairs
All maintenance and repairs should be left to the experienced. Walking on a cedar roof can be tricky and can also damage a roof -- even one in good condition. Contractors inexperienced with wood may damage surrounding materials. Individual damaged, loose, missing, cupped or curled shingles and shakes can be quickly replaced by an experienced roofing contractor. New materials can be blended with the old to some degree with this simple formula:
- Dissolve one pound of baking soda in a half-gallon of water. Dip, brush or spray the replacement materials and lay them in the sun. After about 4 hours, the shingles should permanently turn gray.
Local (and successful) real estate agents my be able to recommend a qualified contractor. Ask around in your neighborhood, especially if houses being worked on are of similar age and style to yours. Local historic districts may also have names of contractors who specialize in restoration and traditional materials. Finally, your home inspector may know of contractors who install quality cedar roofs.
Lifespan
Cedar roofs may require more care and maintenance than manufactured roofing products.
Premium grade cedar shakes and shingles, maintained properly and installed on spaced wood strips have been documented to have lasted for 50 to 60 years. Recently, we have been finding some cedar shingled roofs that can't "breathe," and are not maintained, requiring complete replacement at 15 years.
Be wary of any products claiming that a single application or treatment will preserve a roof or make it maintenance free.
