What happens during a house wash, roof cleaning or deck cleaning, and how long it takes

Updated November 10, 2026 · KeystoneProGuide editorial team

What happens when a pressure washing company comes?

A careful job follows the same order whatever the surface: protect what is not being cleaned, test on a small hidden area, apply the cleaner or the water at the gentlest level that works, rinse, and check the result. What changes from one surface to the next is the pressure and the chemistry, and for both the guidance below comes from the bodies that speak for each material.

Before the work starts

Plants, stone and neighbors' property. The shingle makers' trade association, ARMA, says a roof cleaning solution should be applied carefully to avoid damage to other parts of the building and the surrounding landscape. The vinyl siding industry's association, PEPA, says to cover brick or stone accents so runoff from siding does not reach them.

Water and power. Ask whether the crew will use your outdoor tap. Fixr's cost survey says you may pay about $2 an hour for the water used, which arrives on your own bill.

Where the engine sits. If the machine has a gasoline engine, the Centers for Disease Control and Prevention (CDC) says it should never run less than 20 feet from any window, door or vent. The Consumer Product Safety Commission says engines produce carbon monoxide and that enclosed spaces can trap it even with doors and windows open. It is fair to ask the crew to park the engine well away from the house and to close windows near the work.

Children and pets. The CDC says to keep children at a safe distance while a pressure washer is in use, because the spray can throw objects that strike people nearby.

What is different on a house built before 1978?

If painted surfaces will be washed, a lead-safe certified firm has to contain the work first. The U.S. Environmental Protection Agency's (EPA) archived answer says the firm must isolate the work area so that no dust or debris, including in the waste water, leaves it. It must keep its plastic or other sheeting from tearing or shifting, and must set up the containment so that it does not block anyone's way out in an emergency. Expect to see sheeting on the ground and a plan for the water before any spraying.

Will they test first?

They should. The National Park Service says to test any cleaning method in a small, inconspicuous area before full-scale work, and suggests test patches of six inches by six inches or less. For pressure washing historic masonry, another Park Service article suggests a larger patch, 36 by 36 inches, before large-scale cleaning. PEPA likewise says to test any cleaner on a hidden spot of siding first.

How is each surface cleaned?

• Asphalt shingles. ARMA describes a solution of household bleach and water, dispersed gently, left on for at least 15 minutes but no more than 20, then rinsed by gently spraying with water. It says not to scrub, which may loosen granules, and to work from a ladder or walkboards where possible rather than standing on the roof.
• Vinyl siding. PEPA says to work from the bottom of the house up to prevent streaking, to rinse a cleaning solution off before it dries, and, if a power washer is used, to hold it straight at eye level so water is not forced behind the panels.
• Wood decks. A Forest Products Laboratory chemist described spreading a cleaner with a broom or sponge mop, leaving it about 15 minutes while keeping the deck wet, treating no more than 200 square feet at a time, and rinsing with plenty of water from a garden hose for at least 10 minutes.
• Old brick and stone. The Park Service recommends a low-pressure spray of 100-400 psi, with the wand at least 12 inches from the surface. It lists pressure, volume, temperature, nozzle pattern, angle, water quality, operator skill and chemical additives as the variables that decide the outcome.

How long does it take?

No authority source read for this guide gives a typical length for a house wash. The figures that do exist are for steps within the job: ARMA's 15 to 20 minutes for its roof solution, and the Forest Products Laboratory chemist's 15 minutes of dwell time and 10 minutes of rinsing for each patch of deck. The size of the house and the number of surfaces decide the rest, so ask the company for its own estimate of the time on site.

What should you check afterward?

• The deck. The Forest Products Laboratory chemist said to let a cleaned deck dry for at least a day in the sun, that two or three are probably better, and that you can wait two to three weeks before finishing. Loose fibers coming away during the rinse were his sign that the wood had been over-cleaned.
• The siding. Look inside for any water that got behind the panels.
• The brick. Look for etched or scarred faces; the Park Service says excessive pressure can remove surface material.
• The ground. The Park Service says cleaning waste should be collected on drop cloths so the ground or water is not re-contaminated.
• Mold stains. The EPA says mold may leave staining that cannot be fully removed, so it is worth agreeing before the job what result to expect.

Questions to ask before you hire turns these points into a checklist, and how often to wash covers timing. Companies offering the service are on the pressure washing directory page.

Sources

1. Algae Discoloration of Roofs, Asphalt Roofing Manufacturers Association (ARMA)
2. How to Clean Vinyl Siding, Polymeric Exterior Products Association (PEPA)
3. Springtime Means Deck Maintenance for Many Homeowners, USDA Forest Service, Forest Products Laboratory (news release via Newswise)
4. Preservation Matters: Maintenance - Graffiti Removal from Historic Features, National Park Service
5. Protecting Historic Structures from Oil Contamination, National Park Service
6. How do RRP requirements apply to pressure washing? What containment and other preparation are required?, U.S. Environmental Protection Agency (January 2025 archived copy)
7. Pressure Washer Safety, Centers for Disease Control and Prevention
8. Carbon Monoxide Fact Sheet, U.S. Consumer Product Safety Commission
9. How much does it cost to pressure wash the exterior of a house?, Fixr
10. Mold Cleanup in Your Home, U.S. Environmental Protection Agency