Vinyl siding became popular for good reasons. It is attractive, has moderate cost, lasts many years and is relatively easy to maintain.

Vinyl siding does need periodic cleaning to keep it looking good. The frequency of cleaning depends on local conditions; some homes can go for many years between cleanings, others might need cleaning every year or two.

Siding will sometimes get dirty only in spots where it is not washed by rain, such as under eaves, bay windows and porch roofs. The siding can also pick up a variety of stains, including mildew.

Before using any cleaner on vinyl siding, test it in an inconspicuous place to make sure it doesn't do any damage. I've found that the siding is highly resistant to damage by most cleaners, but it pays to check.

When using any soap-type cleaner on a wall, start cleaning and rinsing at the bottom and work up. If you start at the top, dirty water and soap suds will run through the dirt at the bottom, causing streaks that can be very difficult to remove.

Vinyl siding that is only moderately dirty can often be cleaned by spraying with a forceful stream of water from a hose or by using a soft-bristled car-washing brash attached to a hose. A long-handled brush makes it easier to reach high places.

If more vigorous cleaning is needed, the following solution is recommended by Owens Corning, a leading siding manufacturer:

Mix 1/3-cup powdered laundry detergent and 2/3-cup powdered household cleaner in one gallon of water. If there is mildew on the siding, substitute one quart of chlorine bleach for a quart of the water. (Note: Never mix chlorine bleach with ammonia-based cleaners; it can produce a dangerous gas.)

Apply the cleaning solution with the car-washing brush and rinse with a hose.

If mildew is the chief problem, here is another formula that can eliminate it: Mix 1/3-cup non-ammoniated household detergent, 2/3-cup trisodium phosphate and one quart of chlorine bleach in one gallon of water. Apply with a brush and rinse with clear water.

Special vinyl-siding cleaners are also available at some home centers and hardware stores.

Pressure washing is a fast and effective way to clean large areas of siding, but improper use of a pressure washer can cause lasting damage to a wall. The stream of water should never be squirted upward, or it can get behind the siding and damage sheathing, insulation and structural timbers. Always direct the stream of water downward or directly at the siding. Special extensions for pressure-washer wands are available to make it easier to direct the stream of water properly.

Avoid using a pressure washer while standing on a ladder. Also use extreme care when washing near electrical wiring to avoid shocks. A high-pressure stream of water can also damage windows, especially on older houses.

Special "house wash" cleaners for pressure washers are sold at most home centers. Most of these will work on vinyl siding. Pressure washers can be rented at most tool-rental centers for $50 to $60 a day; a washer suitable for cleaning siding can be bought for $400 or less. In general, though, if siding needs pressure washing, it is best to hire a contractor with the skill and special equipment to do the job properly.

Questions and comments should be sent to Gene Austin, 1730 Blue Bell Pike, Blue Bell, Pa. 19422. Send e-mail to doit861@aol.com. Questions cannot be answered personally.