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Wood roofs

William Kibbel III, The Home Inspector

wood roofsWood shingles were the most common roof covering in Colonial America -- and severalhundred years later, they are a choice material for historic restoration.

With proper care and maintenance, these roofs can be attractive and reliableprotection for your historic home. Most buyers of old homes view the cedar roofas an historically correct material over their home and are eager to take thesteps necessary for its preservation.

In this column I'll discuss themaintenance and repair of this traditional roofing material.

Cedar is the most commonly used wood in North American these days forroofing. Although many modern wood roofs have a rustic appearance, a smooth sawnshingle is more historically accurate.

Cedar roofing comes in two varieties -- shingles or shakes. A shingleis tapered and smooth sawn on both surfaces for a uniform appearance. A shakeis split to reveal the uneven natural grain of the wood on the face and isusually much thicker than a shingle. A cedar shake roof has a much more rusticappearance, but may not be historically accurate for most homes. Early handmadeshingles were hand split, but then shaved smooth and tapered with a drawknife,appearing closer to today's sawn shingles.

Installation

roof
This wood roof installation allows plenty of ventilation.

Traditionally wood shingles and shakes were installed on spacedwood strips. This type of installation allows the wood to dry evenly afterabsorbing precipitation. The recent practice of installing wood roofs on solidwood sheathing or directly on roofing felt paper has significantly reduced thelife expectancy of this type of roof. Cupping and curling of the shingles is nowa common condition and deterioration of the wood is occurring much earlier thanolder roof systems with adequate ventilation.

Building codes on wood roofs vary from municipality tomunicipality. Some building codes require tarpaper under each individual coarseof cedar shakes. Some contractors and municipalities interpret this toinclude cedar shingles as well. Solid sheathing under wood roofs is oftenrequired in seismic regions. You, or your roofer, should check with the localbuilding inspector for specific installation requirements.

Maintenance tips: Dealing with mold and mildew

Mildew can usually be treated successfully with trisodium phosphate (TSP) orhousehold bleach mixed with water into a solution and scrubbed with a softbrush. The roof surface should then be rinsed thoroughly with fresh water.

Moss can usually be treated with a sprayed application of an herbicide thatcontains zinc sulfate or again a household bleach solution. After the moss diesoff, 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 installedjust below the top course of shingles above each roof surface. Each rain picksup some zinc and perpetually treats the roof. Trimming overhanging branches caneliminate shade that is conducive to moss formation.

Chemical solutions should be used with caution. Overspray and run-off cankill desirable vegetation growing around the building and at the base of thedownspouts.

Repairs

All maintenance and repairs should be left to the experienced. Walking on acedar roof can be tricky and can also damage a roof -- even one in goodcondition. Contractors inexperienced with wood may damage surrounding materials. Individual damaged, loose,missing, cupped or curled shingles and shakes can be quickly replaced by anexperienced roofing contractor. New materials can be blended with the old tosome 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 qualifiedcontractor. Ask around in your neighborhood, especially if houses being workedon are of similar age and style to yours. Local historic districts may also havenames of contractors who specialize in restoration and traditional materials.Finally, your home inspector may know of contractors who install quality cedarroofs.

Lifespan

Cedar roofs may require more care and maintenance than manufactured roofingproducts.

Premium grade cedar shakes and shingles, maintained properly and installed onspaced 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 at15 years.

Be wary of any products claiming that a single application or treatment willpreserve a roof or make it maintenance free.

About the Author
William Kibbel III is a home inspector and restoration consultant specializing in historic residential and commercial buildings. He is vice president of Tri-County Inspection Company, serving Southeastern Pennsylvania and Central New Jersey.


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