Exterior House Cleaning in Washington: A Homeowner’s Guide

Washing the outside of a house is not one job. It is a decision that starts with a question most homeowners skip: what is this wall made of, and what does the company that made it permit?

That question decides almost everything. Fiber cement, vinyl and asphalt roofing do not tolerate the same things, and their manufacturers say so in writing — including the pressures, tools and chemicals they will not accept. A method that is right for one wall can mark, drive water behind the surface of another, and in one case void the coverage on the material itself.

Four questions decide the job, in this order:

• What is the surface? Cladding, trim, soffit, window frames, roofing, masonry and decking are different materials with different tolerances.
• What does its manufacturer permit? The limits are published, they differ, and they are not advisory — one of them ties improper cleaning to a loss of warranty coverage.
• Where does the water go? Wash water leaves the wall carrying whatever was on it, and in Washington the destination is regulated.
• Who does the work? For most single-storey walls, a household job; anything needing the roof, or a surface whose maker prohibits the method, is not.

The material sets the limits

This is the part that makes a national “how to wash your house” article useless in Washington, where a single house may carry two or three different claddings.

Fiber cement. James Hardie’s published finishing guidance is unusually specific: high-pressure water blasting and sand blasting may damage the surface, and the company does not recommend them for cleaning; low-pressure water with a soft or medium non-metal bristle brush is the suitable method; acid washing can damage the surface and is not recommended. Where a pressure washer is used at all, the instruction is wide fan tips only, at pressures under 1,500 psi, with the nozzle kept at least 6 feet from the wall — and the document adds that improper use could lead to damage and, in turn, a loss of warranty coverage.

Vinyl. The Vinyl Siding Institute’s installation manual takes the gentler route: an ordinary long-handled car-washing brush with soft bristles is the recommended tool, and stiff-bristle brushes or abrasive cleaners should be avoided because they may change the gloss of the cleaned area and leave the siding looking splotchy. For mildew it adds liquid laundry bleach to the detergent solution.

Asphalt roofing. The Asphalt Roofing Manufacturers Association is categorical about the one material on the list that must never see a pressure washer: high-pressure washing systems are likely to damage asphalt roofing and should not be used to remove algae or for any other purpose. Washing a roof is a different job from washing a wall.

Anything else. If the cladding on your house is not named above, the governing document is its own manufacturer’s care instruction, not this page. This publication does not invent cleaning limits for materials whose makers publish none, and it does not generalise one maker’s figure to another’s product.

Two manufacturers, opposite sequencing

Here is a disagreement worth knowing about, because both instructions are published and they point in opposite directions.

The Vinyl Siding Institute’s manual says that when washing down the entire house you should start at the bottom and work up to the top, in order to prevent streaking. James Hardie’s guidance says to work a small section at a time, start from the top and work your way down, to prevent dripping or streaking onto the cleaned area.

Both makers are solving the same problem — cleaner running down a surface it has already cleaned — and arriving at opposite sequences, because their products, finishes and detergent behaviour differ. What this page will not do is pick a winner. If you are cleaning vinyl, follow the vinyl instruction; if you are cleaning fiber cement, follow the fiber cement instruction. Where the two materials meet on one house, clean them as two jobs rather than inventing a compromise.

Water is the part with a rule attached

Everything above is about not damaging the surface. The water itself is a separate question, and in Washington it has an answer written down.

Wash water leaves a house carrying whatever it lifted off: dirt, biological growth, soap, and on older homes the residue of whatever the surface was previously coated with. The state Department of Ecology’s pressure-washing pollution-prevention guidance, distributed through local programs, is built around three instructions:

• Capture the wash water. For ground surfaces, use equipment with a built-in reclamation system; for equipment or vehicles, line the area with a ground tarp and surround it with a temporary berm.
• Do not put it down a storm drain. The guidance is blunt about the destination — storm drains flow to the nearest creek, lake, wetland or Puget Sound — and it forbids direct or poured discharge into a storm drain, and soap or chemicals with it.
• Dispose of it properly. Filtered plain water may go to the sanitary sewer, to the ground, or to a storm drain; soapy, dirty or oily wash water must not go to a storm drain at all, and unfiltered dirty or soapy water must not go to the ground either. Where the guidance is uncertain it says to check with the local jurisdiction, because rules vary and some jurisdictions regulate pressure washing strictly.

Two practical points follow from that. Sweeping and dry-cleaning first means less material is ever suspended in water. And the disposal route is a question to settle before the work starts, not after the driveway is covered in runoff.

Two sets of limits, one direction

Read those manufacturers’ instructions side by side and something useful falls out: they disagree about the sequence, but they agree about the direction of force. Both permit low pressure and soft tools. One allows a pressure washer only inside explicit limits — under 1,500 psi, nozzle at least 6 feet from the wall, wide fan tip only. The other does not mention a pressure washer at all in its cleaning instruction and recommends a car-washing brush instead.

The practical principle for a house exterior is therefore that pressure is the last tool you reach for and the first one that causes damage, not the default starting point. Cleaning chemistry, dwell time and a soft tool do the work; pressure is what you use when the surface and its maker both accept it, and only as far as the maker permits. Evaluating that trade-off properly — what a soft wash is, what a pressure wash is, and which surfaces suit each — is the comparison this cluster treats separately.

Sweep first, and the debris has a destination

Whatever comes off the wall has to go somewhere, and Washington closes one destination. The Department of Ecology states that dumping yard waste into state waters or storm drains is illegal, and that fines can come from the agency or from the local jurisdiction. Its alternatives are a compost bin, the curbside yard waste container from your hauler, or a yard debris drop-off site.

Which is why the dry half of the job matters. Sweeping a wall, a walkway or a deck before water touches it means the bulk of the material never becomes a slurry that has to be contained, filtered and disposed of. It also means less of it ends up suspended in the wash water that reaches the ground — the same water the guidance above tells you not to send down a drain.

Choosing the day

Two timing constraints apply here, and neither is about convenience.

On the east side of the state, the fire season sets a deadline: exterior debris work belongs before the window opens in early July, not during it. Across the whole state, a surface has to be able to dry. Washing a wall and then leaving it wet through a freeze is a way to put water where it cannot drain, which is the same problem this cluster deals with at the gutter; the publication’s position is that a cold snap is a reason to postpone exterior cleaning, not to work faster. What a frozen gutter does and does not mean is a separate subject.

What grows on a Washington exterior

The reason exteriors here need cleaning at all is the climate. WSU Extension puts Puget Sound at about 40 inches of rain a year with less than an inch in some summer months, Spokane and Pullman at about 20 inches, and the arid south-central part of the state at about 9 — a wet season long enough to keep exterior surfaces damp, followed by a dry season that bakes what is left behind.

What that growth is, and how to tell one kind from another without diagnosing it from a photograph, is treated separately in this cluster. The roof versions of the same question are an association matter with published answers, and the roof cluster covers them.

The wildfire version of exterior cleaning

In the parts of Washington exposed to wildfire, exterior cleaning has a second purpose. The Pacific Northwest wildfire retrofit guide distributed by the Washington Military Department treats wind-blown debris on and around the house as part of the ignition problem, and its checklist covers keeping the roof clean of debris, screening vents, removing branches that overhang the roof — pruning them back a minimum of 10 feet — and keeping vegetative debris clear of the deck-to-wall junctions, under decks and at the base of exterior walls.

That is not the same job as washing a wall, and it is not a substitute for it. It is the reason a spring clean of the exterior in eastern Washington has a deadline attached: the state’s wildland fire season usually begins in early July and typically culminates in early October, when regular rain returns.

Hiring it out

Some of this work — the parts at height, the parts on a surface whose maker restricts the method, the parts where the runoff has to be contained — belongs to someone with the right equipment and the right insurance.

Washington gives the homeowner a free verification tool for that decision. The Department of Labor & Industries requires contractors working on residential property to be registered, requires the registration number to appear in all advertising, and its Verify tool reports registration status, bonding, liability insurance and outstanding infractions; workers’ compensation is a separate check required where the contractor employs others. Several written bids, compared on scope rather than price alone, is the state’s own advice.

One question is worth adding to any exterior-cleaning quote, because it is the part a provider can get wrong without the homeowner noticing: how the wash water will be contained and where it will be disposed of. A provider who cannot answer that is not working to the state guidance quoted above.

What a quote should include, and how to compare quotes beyond the bottom line, are their own subjects.

The decision, by surface

Next step

Walk the outside of the house and write down what each face is actually made of — cladding, trim, soffit, and anything painted or coated. Then find the maker’s care instruction for each material, and read it before deciding on a method, a pressure setting or a chemical.

That single step separates a cleaning job that ages well from one that leaves a mark, strips a finish, or costs the coverage on the material it was meant to protect. If the answer is that the work needs the roof, or a surface whose maker prohibits the method, the next question is who does it rather than how.