Construction methods change life span of cedar-shake roofs

Inspector's Eye

20 years is standard without air circulation

January 13, 2002|By Dean Uhler

Cedar shakes undoubtedly make one of the most appealing roof surfaces you can install. They are attractively rustic, historically accurate and reliable.

But you pay a high price for those good looks compared with even premium quality asphalt shingles, and you aren't guaranteed a longer-lasting roof. Putting a cedar-shake roof on a house is, therefore, an aesthetic choice, not an economic one. However, innovations in the manner of installation of cedar shakes may help extend the life of new shake roofs.

During several recent inspections of houses with cedar shake roofs, real estate agents have expressed surprise upon hearing me say that the life expectancy of those shake roofs was around 20 years from when they were installed. They had heard of life expectancies more like 40 years. I used to hear the 40-year prediction frequently during the 1980s and well into the '90s, often from roofers who were installing shakes. But during the 1990s, as typical shake roofs approached the 20-year mark, it became apparent that most were nearing the end of their useful lives.

The major reason that expectations were higher than reality was the manner of installation of the shakes. Traditionally, cedar-shake roofs were installed over spaced sheathing. That is, the boards that the shakes were nailed to had spaces between them, allowing air from the attic to circulate under the shakes. The circulation allowed the shakes to dry evenly, from the bottom and the top, after getting wet from precipitation.

The more recent practice of installing cedar shakes over solid, plywood sheathing prevents air circulation, curtailing life expectancy of this type of roof. Rarely have I seen a shake roof installed in the past 25 years using any other method. Shake roofs installed in this fashion can have life spans of as little as 15 years.

Infrequently, I've seen cedar shakes installed over wood furring - strips of wood applied to the plywood sheathing as spacers under the shakes. This provides some air circulation to the shakes, but is labor intensive and increases the roofer's costs.

A more cost-effective innovation that may go a long way to increase the life of new shake roofs is a "breather" layer between the shakes and the plywood sheathing, designed to allow some air circulation under the shakes. A typical breather is an inch-thick polymer mat that is nailed to the plywood sheathing after the roofing felt is applied. The shakes are nailed right through the breather.

Hopes are high that this material, now widely used in cedar shake installations, will return cedar shake life spans to something like the historical norm.

Inspector's Eye, Dean Uhler has been a home inspector for more than 12 years and is president of Baltimore-based Boswell Building Surveys Inc. Uhler is a member of the American Society of Home Inspectors (ASHI) and is the treasurer of the Greater Baltimore Chapter of ASHI.

Questions, with name, address and daytime telephone number, about homes and home inspections can be faxed to 410-783-2517, e-mailed to or mailed to Inspector's Eye, Second Floor, 501 N. Calvert St., Baltimore, Md. 21278-0001.

Baltimore Sun Articles
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.