Maintaining A Cedar Shake Roof

HOME CLINIC: My house has a 14-year-old cedar shake roof. It doesn't leak, but I've been advised to have it pressure cleaned periodically and to have a preservative applied. A roofer I talked to said no, that cedar has to breathe. A second roofer recommended an oil application. Folklore says if it ain't broke, don't fix it, but preventive maintenance is often a good idea. I don't want to be conned or do something that damages the roof. G.R., Vashon Island

DEAR G.R.: It certainly makes sense to have your shake roof cleaned periodically. The issue of chemical treatments, however, is not as clear cut.

Let's deal with cleaning first. Experts at the Cedar Shake and Shingle Bureau say that good housekeeping is basic to maintaining the longevity of the roof. Try to keep leaf or needle debris off the roof. They tend to trap moisture resulting in moss or fungal growth. Clean your roof at least once a year using a stiff broom or a pressure jet of water. Be careful not to damage the shakes and pay special attention to cleaning the spaces - called keyways - between them. If you have nearby trees with overhanging limbs, you can consider trimming branches to minimize the build up of debris.

This simple housekeeping step will probably have the greatest effect on how long your roof lasts. However, some homeowners choose to periodically treat their cedar roofs with a preservative. Every three to five years is typical. The preservative retards the growth of mold, moss and fungi. While these preservatives certainly extend the life of roofing materials, they are less effective on a roof that has aged for many years, simply because exposure has started the process of deterioration. So the older the roof (30 years is a typical lifetime), the less you can expect from a preservative.

You will need to weigh the benefits of the preservative with the fact that the chemicals are toxic and do eventually end up in our environment. If you decide to go with a preservative make sure it is applied to the butt of the shake - the exposed end - as well as the face of the shake. A number of firms in the area provide both cleaning and preservative service. You can now buy new cedar shakes which have been pretreated in a preservative.

Oil treatments are of more questionable value, particularly if they have no preservatives in them. Petroleum-based products break down quickly in sunlight and would have at best a short-term effect.

In closing, we want to salute the closing observation of your letter. A healthy dose of common sense mixed with the desire to do the right thing only needs a bit of practical information to produce good decisions. We hope we've helped.

DEAR READERS: Like California, we sit on the ring of fire. When a major earthquake hits, you need to protect your family and your home by knowing how to turn off your electricity, gas and water.

For a free publication on "Earthquake Energy Tips," call our Energy Hotline at 1-800-962-9731. Or, in Seattle, call 296-5640. The publication addresses the effect an earthquake - and its aftershocks - can have on your home utilities and heating system. You will learn how to be better prepared in such an emergency.

Home Clinic answers questions about home maintenance, repair and energy conservation. It is prepared by the Energy Extension Service, a division of the Washington State Energy Office. It appears Sundays in the Home/Real Estate section of The Times.