How often should you pressure wash your house, deck or roof, and when?
Updated · KeystoneProGuide editorial team
How often should a house be pressure washed?
No government body or trade association read for this guide sets a fixed schedule for washing a house. What they do give is the thing that decides the interval for each surface: how fast growth returns on a roof, how long a finish lasts on a deck, and whether the moisture that feeds mold has been dealt with. None of them gives a yearly rule.
That makes the useful question "what is this surface telling me", which the warning signs guide covers, rather than "has it been a year".
How often does a deck need cleaning?
As often as it needs refinishing, because cleaning is the step before a new finish. A chemist at the U.S. Forest Service's Forest Products Laboratory said a deck must be cleaned before it is refinished, and the laboratory's release gave a service life for each kind of finish.
| Finish | Typical life, per the Forest Products Laboratory release |
|---|---|
| Clear water repellent or water-repellent preservative | about one year |
| Tinted water-repellent preservative | about two years longer than clear |
| Semitransparent stain | about four to six years |
The chemist said that in general the more pigment a finish has, the longer it lasts and the harder it is to refinish. Clear finishes are the easiest to reapply. He described his own routine as cleaning and refinishing his deck every year or two with a clear water-repellent preservative, while noting that some people prefer a stain they can leave for a few years. Water-repellent preservatives contain a mildewcide or preservative to help control mold, mildew and algae, so the finish itself helps hold back regrowth.
When in the year should a deck be cleaned?
The same release gave specific timing. The chemist said mid to late March is the best time to clean a deck before refinishing, that a cool, cloudy day is ideal because it keeps the deck wet while the cleaner works, and that warmer weather helps penetrating finishes work better. He liked to wait until April to apply the finish.
Two cautions go with that. He works at the laboratory in Madison, Wisconsin, so his calendar was written for that climate, not for Pennsylvania. And he said to let a cleaned deck dry at least a day in the sun, that two or three days are probably better, and that you can wait two to three weeks before finishing.
How often does a roof need cleaning?
ARMA sets no interval, and it warns that a cleaning does not last. The shingle makers' trade association, ARMA, says a bleach solution may lighten algae streaks but that the effect is only temporary and the discoloration may recur. It says algae grow to some degree everywhere, especially in warm, humid conditions, and are most widespread in the Gulf States and along the Northwest and Eastern Seaboards.
If the streaks keep returning, ARMA points to the longer answer: when the roof is replaced, algae-resistant shingles are available, designed to inhibit algae growth for extended periods.
How often does siding need washing?
The vinyl siding industry's association, PEPA, describes vinyl as needing only periodic cleaning, often no more than a rinse with a garden hose. It sets no interval.
For mildew, the interval depends on moisture. The U.S. Environmental Protection Agency (EPA) says none of them will grow without water or moisture, and lists cleaning and repairing gutters regularly among ways to prevent moisture problems. If one wall goes green every spring, the gutter or the shade above it is setting the schedule, and fixing that may lengthen the gap between washes more than any cleaner will.
Should you wash before painting?
Yes, if there is mold. The EPA says to clean moldy surfaces and dry them before painting, because paint applied over mold is likely to peel. On a house built before 1978, plan the wash with the paint job, since the EPA's lead-safe rules apply to paid work that disturbs painted surfaces.
What about cleaning up after a storm or flood?
That is the one occasion when the official guidance expects more washing, and more injuries. The Centers for Disease Control and Prevention (CDC) says pressure washers may be used more often during disaster clean-up, when the risk of injury may be higher. If you are cleaning up after a storm yourself, its rules apply with extra force: check the ground fault protection first, keep cords and connections out of standing water, and keep a gas engine outdoors and at least 20 feet from any window, door or vent. Mold that follows water damage is a separate job, and the EPA says the moisture has to be fixed before the cleanup can be considered finished.
Does weather matter on the day?
For a deck, a cool and cloudy day helps, according to the Forest Products Laboratory chemist. For old masonry, the National Park Service treats water temperature, along with pressure and nozzle, as one of the variables that change the result. For safety, the Centers for Disease Control and Prevention says to keep extension cord connections out of standing water and away from runoff.
What happens on the day describes a visit from start to finish. Companies offering the service are listed on the pressure washing directory page.
Sources
- Springtime Means Deck Maintenance for Many Homeowners, USDA Forest Service, Forest Products Laboratory (news release via Newswise)
- Algae Discoloration of Roofs, Asphalt Roofing Manufacturers Association (ARMA)
- How to Clean Vinyl Siding, Polymeric Exterior Products Association (PEPA)
- A Brief Guide to Mold, Moisture and Your Home, U.S. Environmental Protection Agency
- Mold Cleanup in Your Home, U.S. Environmental Protection Agency
- Lead Renovation, Repair and Painting Program, U.S. Environmental Protection Agency
- Protecting Historic Structures from Oil Contamination, National Park Service
- Pressure Washer Safety, Centers for Disease Control and Prevention