Protecting a wooden roof against decay and pests; furnace economy

Q Do you know of any way that cedar roof shakes can be treated so that moss will not grow? Judi Light Penley Kingsport, Tenn.

Cedar roofing can be pressure-treated or immersed in wood preservative before delivery to the job. Surface retreatment at future intervals would be needed, of course. Wood shingles treated with a preservative or fire retardant can cost more than twice the price of ordinary wood shingles.

Fungicidal chemicals will inhibit moss, fungus, and mildew, and thus contribute to the life of the roof. Penta chlorophenol (penta) is a good protection against decay and termites. It is toxic to plants and people, so it requires care in handling.

Fungicides are contained in products sold under the general category of clear wood preservatives, many of which also include a water repellent, such as Woodguard, Woodlife, Cuprinol, CWF, and Pentaseal.

In areas of low humidity, where moss, fungus, and mildew are not a potential problem, approved commercial shingle stain or linseed oil will prevent excessive dryness and therefore prolong the natural resilience of cedar. Light pigmented stains can be used, but they need refinishing every 12 to 18 months. Since most stains contain only a mild mildewcide, they do little to extend the service life of wood.

Attic ventilation is important to the longevity of wood shakes and shingles, as is good housekeeping on the roof itself. Accumulation of debris on the roof surface may foster moisture, which, in turn, nurtures moss and fungus.

Commercial firms specializing in roof cleaning and treatment are active in some areas. The firms tackle composition, asbestos, slate, and metal, as well as wood shake and shingle roofs.The treatment consists of controlled water pressure followed by a chemical deterrent. The chemical used is designed to eliminate regrowth of moss or fungus for several years, with retreatment recommended every three years.

For more information, write Texas Forest Products Laboratories, PO Box 310, Lufkin, Texas 75901; (409) 632-6666.

Q Many items have been developed or improved over the past few years to save energy, such as solar water heaters, more efficient automobiles, air conditioners with improved evaporator coils, precoolers, and so on. Have furnaces been developed which have improved heat exchangers? I'm asking for information on ways by which the cubic-foot cost of a furnace has been or could be improved. Lloyd E. Brunn Phoenix, Ariz. This column is too small a forum to discuss so great a question, but we can recommend three booklets or sources for such data:

* Gas Appliance Manufacturers Association, PO Box 9245, Arlington, Va. 22209; (703) 525-9565. See its Directory of Certified Furnace and Boiler Efficiency Ratings, April-October 1983.

* Lundberg Letter, Volume IX, No. 47, Sept. 24, 1982, entitled ''Home Heating Heats Up,'' which we obtained from the National Oil Jobbers Council, 1707 H Street, NW, Washington, D.C. 20006; (202) 331-1198.

* Consumer Energy Council of America, 2000 L Street, NW, Suite 320, Washington, D.C. 20036; (202) 659-0404.