HOW OFTEN SHOULD YOU PRESSURE WASH YOUR HOME?

Once a year for most Bay Area homes. Homes in the fog belt or near the coast need it about twice a year, and sunny, dry inland properties with little tree cover can stretch to every 18–24 months. Below is what actually drives that schedule — and honest answers to the questions homeowners ask us most.

Is an annual wash really necessary, or is that just what washing companies say?

Fair question. Most professional and consumer guides — Five Star Painting, Window Genie, Angi — land on once a year. A minority of DIY voices say vinyl siding only needs cleaning every 2–3 years, and that position is defensible for dry, sunny, low-debris exposures. The reason annual is the better default: algae and mildew damage is progressive and invisible early. Growth traps moisture against the siding, which rots wood trim and soffits and makes paint and coatings fail years ahead of schedule. The math settles the argument — an average professional house wash runs about $311 nationally (Angi/HomeAdvisor), while wood siding repair averages $1,688, extensive wood rot runs $2,500 and up, and an exterior repaint on a 2,000 sq ft home is roughly $5,000. Washing is maintenance, not cosmetics.

What actually sets your schedule

A single number misses the point. Four factors move a home between every-six-months and every-two-years:

• Shade and tree cover. Algae needs moisture, and shaded, north-facing, tree-adjacent walls hold it longest. Oak and redwood debris feeds growth. Wet, humid or heavily treed properties trend toward every 6–8 months.
• The marine layer. Fog-belt neighborhoods — San Francisco's Richmond and Sunset districts, coastal Daly City, Pacifica — stay chronically damp all summer even without rain. These homes sit in the twice-a-year category, as do coastal homes dealing with salt air.
• Road exposure. Homes on busy roads or in dense urban pockets collect exhaust film and grime fast — about twice a year.
• Sun and inland heat. Sunny East Bay and South Bay exposures with little shade can hold at annual, sometimes every 18–24 months.

Frequency by siding type

• Vinyl, metal, fiber cement and composite: once a year.
• Wood siding: only when dirt or mildew visibly builds up — and gently, at low pressure. Wood does not want a schedule; it wants restraint.
• Stucco: never direct high pressure. Stucco is porous and gouges easily. It gets soft washed or it gets damaged.

What is the green stuff on my siding?

Green, black or brown streaks are almost always algae. Dark patches in damp, shaded corners with a slimy texture or musty smell are mold. The field rule: algae needs sunlight, mold grows in dark, damp spots. Both show up worst on shaded, north-facing and tree-adjacent walls, and both trap moisture against the surface — which is what turns a cosmetic problem into rotted trim and failed paint. Black "tiger stripes" running down gutter faces are the same biology plus oxidized asphalt runoff.

Can pressure washing damage siding or stucco?

Yes — when it is done wrong. Safe working pressure for vinyl siding is 1,300–1,600 PSI; stucco tops out around 1,200–1,500 PSI, and many pros — us included — will not put direct pressure on stucco at all. The bigger risk on vinyl is not raw PSI but spray angle: shooting upward drives water behind the panels, where it breeds hidden mold you will not see until it is expensive. This is exactly why the industry has shifted away from blasting houses.

Soft washing vs pressure washing — and why the green comes back

Modern professional consensus is that house siding gets soft washed: low pressure plus a cleaning solution — typically sodium hypochlorite diluted to about 0.5–1.5% at the surface with a surfactant, roughly a 1:9 mix from 12.5% stock. The chemistry does the work, not the pressure. Concrete driveways and walkways still get true pressure washing; houses do not.

The difference shows up two months later. A pressure-only blast removes the visible algae layer but leaves embedded spores, and visible regrowth returns within 6–8 weeks. A chemical soft wash kills the spores and holds clean for a year or more on siding and roughly 2–4 years on roofs. If your house turned green again a couple of months after a cheap wash, this is why — it was a false economy, not bad luck.

The best time of year to wash a house in the Bay Area

National guides split between spring-after-pollen and fall, with ideal working temperatures of 40–75°F — below 40°F risks freezing, above 75°F in direct sun risks streaks and spotting. The freeze constraint is irrelevant here. In the Bay Area the calendar is driven by the October–April rain season instead: wash in late spring after the rains and pollen settle if you want the house looking right for summer, or early fall before the rains to strip the grime that feeds winter algae. Either way, book during a dry spell so the cleaning solutions can dwell and work evenly.

Washing before exterior painting

If you are painting, washing is not optional. Paint cannot bond to chalk, mildew or algae — proper wash prep is the difference between a paint job that lasts 10 years and one that fails in 3–5. After washing, wait 24–48 hours of dry weather before painting, and 72 hours for porous wood or stucco.

Cleaning wildfire smoke and ash off your house

Ash is a different job, and California public health guidance (CDPH, LA County) is specific: use mild soap and water with a low-pressure rinse. Do not use harsh chemicals or vinegar — they react with alkaline ash. Do not use a leaf blower, which re-aerosolizes toxic ash. Wear an N95, gloves and goggles, and photograph the soot on your siding for insurance before you clean anything.

What a professional house wash costs

National benchmarks from Angi and HomeAdvisor: the average whole-house wash is about $311, with a typical range of $100–$710, or $0.10–$0.50 per square foot. One-story homes run $150–$750, two-story $400–$1,400, three-story $700–$1,800. Driveways add $100–$500, roof washing runs $0.50–$1.00 per square foot, and gutter exteriors $0.50–$1.50 per linear foot. Set that against the cost of skipping it — $1,688 average siding repair, $2,500+ wood rot, $5,565–$17,647 for full siding replacement — and an annual wash is the cheapest line item on the house.

FAQ: quick answers

Is washing the house every year really necessary, or is that an upsell? For shaded, coastal, fog-belt or tree-heavy Bay Area homes, annual washing is well supported — algae and mildew trap moisture that rots trim and fails paint early. Sunny, dry inland homes with little tree cover can often stretch to every 18–24 months. At roughly $311 for an average professional wash versus $1,688 for average wood siding repair, the annual default is cheap insurance.

Can I just use bleach and a garden hose myself? For small, ground-level areas, yes. Professionals use sodium hypochlorite diluted to about 0.5–1.5% at the surface with a surfactant — roughly a 1:9 bleach-to-water mix from 12.5% stock. Apply, let it dwell about 10 minutes, and rinse with low pressure. Pre-wet plants and rinse them after. For a full two-story house, ladders plus bleach is where DIY stops making sense.

Why did the green streaks come back two months after my last wash? The house was blasted with pressure only. That removes the visible algae layer but leaves embedded spores, and visible regrowth typically returns within 6–8 weeks. A chemical soft wash kills the spores and holds clean for a year or more on siding and roughly 2–4 years on roofs.

Can you pressure wash a house in winter in the Bay Area? Yes. The national below-40°F freeze constraint is irrelevant here. The only winter consideration is the October–April rain season — book during a dry spell so cleaning solutions can dwell and work evenly.

What PSI is safe for vinyl siding? 1,300–1,600 PSI, but spray angle matters more than raw pressure — spraying upward forces water behind panels where hidden mold grows. Stucco should not take direct high pressure at all. Most professionals now soft wash house siding instead.

Related services

• House washing in San Jose — soft washing for stucco, wood and fiber cement siding.
• Pressure washing in San Jose — driveways, walkways, patios and full exteriors.
• Bull Run wash membership — keep the schedule on autopilot instead of remembering it.