Soft washing is a low-pressure exterior cleaning method that uses a chemical solution (sodium hypochlorite, water, and a surfactant) to kill algae, mold, mildew, and lichen on roofs, siding, and similar surfaces. The chemistry does the cleaning. Water rinses the dead organic matter off. Most pros apply the mix at 60–150 PSI. A standard pressure washer runs at 3,000–4,400 PSI.
Pressure washing blasts a surface clean with force. Soft washing sanitizes it at the root using bleach chemistry. That's why a properly soft-washed roof can stay clean for years while a pressure-washed roof streaks again within months.
We manufacture the proportioners and pumps that pros run, so most of this guide comes from what we see in the field every week: what works, what fails, and where the wrong tool gets used on the wrong surface.
What Soft Washing Actually Is
Soft washing is the low-pressure application of a diluted bleach-and-soap solution to exterior surfaces. The goal is to kill biological growth (algae, mold, lichen, moss), not strip it off with water force. The solution sits on the surface for 10 to 20 minutes, kills the organisms at a cellular level, and a low-pressure rinse carries the dead material away.
A few markers separate soft washing from any other exterior service:
- Pressure stays low. Usually under 150 PSI at the nozzle. Often a lot less.
- The active ingredient is sodium hypochlorite (SH), the same chemical family as pool chlorine and household bleach.
- A surfactant gets added so the mix clings to vertical or sloped surfaces long enough to work.
- The operator either batch-mixes the solution upfront or runs a proportioner to dial in ratios on the fly.
The term itself came from AC Lockyer of SoftWash Systems, who built one of the first formal training programs around chemical-first exterior cleaning in the U.S. The technique is older than the name. The structured methodology goes back roughly two decades.
Soft Washing vs. Pressure Washing
The usual misconception: "Soft washing is just pressure washing with less pressure." Not quite. The two methods do different work on different surfaces.
| Soft Washing | Pressure Washing | |
|---|---|---|
| Nozzle pressure | 60–150 PSI | 1,500–4,400 PSI |
| Cleaning mechanism | Bleach kills organisms at the root | Water force shears dirt off the surface |
| Best for | Roofs, siding, stucco, screens, wood | Concrete, brick, driveways, sidewalks |
| Result longevity | 2–5 years (organisms killed) | 6–12 months (regrowth common) |
| Equipment | 12V or gas diaphragm pump + proportioner | Piston pump, high-PSI rated hose and gun |
Pressure washing uses water force. Soft washing uses chemistry. On asphalt shingles, vinyl siding, stucco, and cedar, that difference is the gap between a roof that lasts a full warranty cycle and one that fails years early. A deeper breakdown lives in our pressure washing vs. soft washing guide.
What's in a Soft Wash Solution
Three ingredients. Each does a job. Skipping one weakens the result.
Sodium hypochlorite (SH). The active ingredient. Same chemical family as pool chlorine and household bleach, just at a different starting strength. Pros buy SH at 10% or 12.5% concentration and dilute it for the job. Our SH 101 guide covers the chemistry in depth. Short version: SH oxidizes the cell walls of algae, mold, and bacteria and breaks them down at the cellular level instead of just rinsing them off the wall.
Surfactant. Soap that lowers water's surface tension so the mix clings to vertical or sloped surfaces instead of running off. Without one, the mix sheets off before it can do its job. Most pro surfactants come scented to mask the bleach smell. More on this in our surfactant guide.
Water. Dilutes the SH down to a safe applied concentration. This is where applied concentration math matters, and where most consumer articles get it wrong.
Applied Concentration by Surface
What matters is the strength of the bleach at the wall, not the strength of the jug in the truck. Working ranges:
-
Asphalt shingle roofs. Target ~3–4% applied SH. ARMA's well-known "50/50 mix" assumes laundry-strength bleach (~6%); if you're using 12.5% commercial SH, a straight 50/50 is roughly double the needed strength, so cut it to about 1:3 (bleach:water) to land in range.
- Stucco, brick, and EIFS. 2–4% applied SH.
- Vinyl and aluminum siding. 1–2% applied SH.
- Wood decks and cedar shake. 0.5–1% SH, or sodium percarbonate (oxygen bleach) as a safer alternative.
The classic DIY mistake: someone reads "3% mix" online and pours in 3% of a gallon of bleach without checking whether his bleach is 6% household strength or 12.5% pool strength. Those two bottles produce very different applied concentrations on the wall. The forum thread that gave him the number didn't mention which one.
Which Surfaces Need Soft Washing
Soft washing is the right call for any exterior surface that's either too delicate for high pressure or carrying biological growth that won't come back unless you kill it at the root.
- Asphalt shingle roofs. Those dark vertical streaks aren't dirt. They're colonies of Gloeocapsa magma, a cyanobacterium covered in the next section. The Asphalt Roofing Manufacturers Association recommends low-pressure chemical cleaning over pressure washing for shingled roofs. Pressure washing voids most major shingle warranties (GAF, Owens Corning).
- Vinyl and aluminum siding. High pressure forces water behind panels, which is how hidden mold problems start. Soft washing rinses the surface from outside without driving water into the wall assembly.
- Stucco and EIFS (synthetic stucco). Stucco is brittle. A pressure washer wand within a foot of the wall can chip the finish coat.
- Wood decks, cedar shake, and fences. High pressure raises wood fibers and ruins the finish. A diluted soft wash, often using sodium percarbonate instead of SH on raw wood, cleans without gouging.
- Pool decks, screen enclosures, painted surfaces. Anything where the surface itself is softer than the contaminant on it.
One thing soft washing won't fix: chalky oxidation on old vinyl or aluminum siding. That's a degraded coating, not biological growth, and it needs a metasilicate or oxidation-specific cleaner instead of bleach. Spot-testing the surface before any job is a habit we drill into every operator. Our guide on spot-testing before soft washing covers what to look for.
Why Black Roof Streaks Matter
The dark streaks on the north and west faces of suburban roofs aren't cosmetic. They're colonies of Gloeocapsa magma, a photosynthetic cyanobacterium that feeds on the calcium carbonate (limestone) filler in modern asphalt shingles.
The organism is eating the roof. As it consumes the filler, granule adhesion weakens, granules shed faster than the shingle's rated wear cycle, and the ceramic layer thins. Once granule loss accelerates, two things follow. The shingle loses UV protection and ages faster. The darker stained roof absorbs more solar heat, which raises attic temperatures and pushes the A/C harder all summer.
A soft wash on a streaked roof interrupts that decay. Without it, the shingles keep losing material. ARMA's guidance and GAF's Technical Bulletin TAB-R-102 both lay out approved bleach-based cleaning methods for exactly this reason.
Landscape and Pet Protection During a Soft Wash
This is the section that should be in every soft washing article and usually isn't. SH is plant-toxic at the concentrations used for roof cleaning. A careless soft wash will scorch landscaping. We've seen it happen. Our withered roses cautionary story walks through a specific case.
The framework experienced operators run is sometimes called the "4 D's":
- Divert. Tarps, sandbags, and downspout extensions redirect runoff away from garden beds.
- Dilute. Plants and soil get saturated with clean water before, during, and after the wash. A wet plant can't take up much chemical-laden runoff. A dry plant pulls it in fast.
- Decontaminate. A neutralizer (typically sodium thiosulfate) goes on plants and beds after the rinse to break down any residual SH. Our bleach neutralizer guide walks through the chemistry.
- Detect. Walk the property afterward looking for stress signs: drooping leaves, yellowing, visible soil shifts in the beds.
Pets stay indoors during the service and until treated surfaces are completely dry. Usually one to two hours. Dried residue at applied concentrations isn't generally hazardous, but pets shouldn't be on wet treated surfaces.
DIY vs. Pro Soft Washing
A common assumption on homeowner forums: any pressure washer with a chemical injector can soft wash a house. Mechanically, that's not quite true. This is the point where we push back on the broader narrative that frames soft washing as just "lower pressure cleaning."
Standard downstream injectors on a pressure washer dilute the chemical mix at roughly 5:1 to 10:1. Even filled with 12.5% SH, the downstream tank puts about 1.5–2% on the wall. Fine for light siding. Not enough for an asphalt shingle roof, which needs 3–4% applied to kill the algae. The injector physically can't deliver the strength the surface requires.
That's why dedicated soft wash systems exist. They pair a 12V diaphragm pump or a gas-driven pump like the Comet P40 with a soft wash proportioner: a manifold that lets you dial water, SH, and surfactant ratios independently before the mix ever reaches the pump. The output hits the wall at the exact applied strength the surface needs, and you can change the mix on the fly moving from siding to soffit to roof.
The other DIY trap is using consumer-grade pumps that weren't built for SH. We've written about why a Harbor Freight gas pump is not a soft wash pump, even when the YouTube videos make it look like a deal. SH eats cast iron. A pump corroded from the inside will fail in the middle of a job. Usually on a Saturday.
If you're learning the trade on siding and small decks, a basic 12V kit and a careful mix will handle the work. For roofs, especially multi-story or steep, you'll want a real proportioner setup and proper insurance before you take the job.
Soft Wash Pricing: What These Jobs Pay in 2026
Pricing varies regionally, but 2026 national averages for residential soft washing land in these ranges:
| Service | Typical Range | Main Cost Drivers |
|---|---|---|
| Full house wash | $250–$800 | Square footage, stories, siding material |
| Roof soft wash | $450–$1,200 | Pitch, height, moss density, landscape complexity |
| Concrete or driveway | $150–$300 | Oil staining, square footage, access |
(Source: Housecall Pro, Thumbtack, Angi, 2026 aggregated data.)
For an operator, that's the rate to price against. For a homeowner, that's the rate to expect.
The flag on cheap quotes: a roof soft wash priced under $200 usually means a downstream injector and a 1.5% mix on a roof that needs 3%. That's how you end up paying twice. Once for a service that didn't work, and again six months later when the streaks come back.
Next Steps
If algae is taking the roof apart and you're hiring this out, get quotes from contractors running proportioner-based systems. Ask the applied SH concentration they use for the surface and whether they neutralize landscaping after the rinse. Membership in Power Washers of North America or SoftWash Systems certification are useful third-party signals.
If you're building toward running this work yourself, three places to go next:
- 12V vs. gas soft wash pumps: which one fits the jobs you're chasing
- What is a soft wash proportioner: the piece that makes pro-grade mixing possible
- Essential soft washing tools: the full rig breakdown
Frequently Asked Questions
Is soft washing the same as pressure washing?
No. Pressure washing uses high-pressure water (1,500–4,400 PSI) to physically remove surface dirt. Soft washing uses low pressure (60–150 PSI) to apply a bleach-and-surfactant solution that kills algae, mold, and mildew at the cellular level. Two services. Different surfaces. Different problems.
Will soft washing damage vinyl siding?
No, when it's applied correctly. Soft washing runs well below pressures that damage vinyl, and 1–2% applied SH is safe on standard vinyl panels. It won't remove chalky oxidation, though. That's a degraded coating and needs a different chemistry, usually a metasilicate-based cleaner.
Will the bleach in a soft wash kill plants and grass?
It can if the operator skips landscape protection. Pros pre-wet landscaping, divert runoff away from beds, and apply a sodium thiosulfate neutralizer after the rinse. With those steps, plant damage is rare. Without them, sensitive plants (roses, azaleas, most flowering ornamentals) can scorch within days.
Is soft washing safe for asphalt shingle roofs?
Yes. It's the method ARMA, GAF, and most major shingle manufacturers recommend. The 50/50 bleach-and-water mix in ARMA's published guidance falls within shingle warranty parameters. High-pressure washing voids most shingle warranties because it strips the ceramic granules off the surface.
How long does a soft wash last?
A properly done soft wash lasts two to five years on a roof and one to three years on siding before you'll need re-treatment. The chemistry kills algae and mold at the root rather than just clearing surface buildup, so regrowth is much slower than after a pressure wash. Shaded north-facing surfaces re-stain fastest. Sun-exposed surfaces hold up longest.
