If you are thinking about installing aluminum or vinyl siding on your historic house, don't do it.

It will destroy the character of the house by hiding or stripping away the original material. But, you may protest, it will protect the material underneath, conserve energy and save money.

A new publication effectively responds to all those claims. It is "Aluminum and Vinyl Sidings on Historic Buildings," from the technical preservation services division of the Heritage Conservation and Recreation Service.

Written by John Myers, an historical architect, the publication is the most recent of a series of preservation briefs for owners of historic buildings. The briefs have well-researched information on building materials, maintenance techniques and design elements.

The problems associated with vinyl or aluminum siding stem from two sources, the design and manufacture of the material and its installation. The siding is mass-produced in a limited range of colors by a limited number of manufacturers.

The manufacturers provide a warranty against production defects but they are not responsible for problems caused by bungled installation. And installation is often done by remodellers or contractors who may know how to put up the siding but know nothing about historic buildings.

These contractors also tend to go out of business fairly frequently because of the seasonal nature of their work. Finding them to collect on a warranty may not be possible.

The siding is nailed to furring strips that are themselves nailed to the old siding. The procedure opens the old wood to insect and water damage. When you then cover the old material you can also be covering over minor problems, such as peeling paint or the stains that are your clues to possible serious damage. Your ability to check the condition of your house regularly also reduced.

The most serious result is that the siding can seal in moisture -- and warm, wet wood is rot's favorite home. Most old houses were not insulated, so moisture went out through the walls. Seal those walls and the dampness has nowhere to go.

To prevent this problem, you must insulate the warm side of the wall, and put in a vapor barrier. Myers said that weep holes and vent tubes just don't do the job.

Historic buildings were built of materials that were often made by hand or represented local preferences. Mass-produced vinyl or aluminum siding, especially that with the ersatz wood patterns, cannot duplicate the texture and patina of the original.

But, it is alleged, siding will reduce maintenance costs and conserve energy. Myers maintains that both claims are false.

Most heat is lost through windows, doors and roofs, not walls. Insulating and caulking will save money. The siding is too thin to be a good insulator and too expensive to have a reasonable payback.

Siding will cost you a minimum of two to three times as much as a good paint job that lasts at least seven years. To justify that expense and to break even, the siding should not need any maintenance for at least 14 to 21 years.

But some siding will fade and look as though it needs painting in as little as seven years, especially in areas that are subject to "acid rain" from industrial pollution. Once painted, the vinyl or aluminum siding will have to be painted as often as wood.

Aluminum siding scratches and dents easily. Vinyl siding shatters in very cold weather. You may not always be able to get a replacement and if you can, you may not be able to match the weather-faded color of the existing siding.

New siding is not an answer to maintenance problems of an old house. It is an expensive investment that can change the appearance of your old house by eliminating the materials that give it character. Old buildings are more durable than you think. Proper maintenance and concern can preserve what you have.

Preservation Brief 8 on aluminum and vinyl sidings is available from the Technical Preservation Services Division, HCRS, Washington 20243.