Roof soft washing kills algae, moss and lichen with a cleaning solution, usually diluted sodium hypochlorite (bleach) plus a surfactant, then rinses at low pressure instead of blasting growth off. It is the standard professional method for asphalt shingles because pressure washing strips their granules. A homeowner version needs only bleach, water, a little dish soap and a bleach-rated pump sprayer. Pro crews use 12-volt pump systems that spray from the ground or the eaves.
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Quick picks for DIY soft washing
| Pick | What it does |
|---|---|
| 12-volt battery sprayer | Steady low-pressure spray with no hand pumping; get one with seals rated for bleach |
| Bleach-rated pump sprayer | The low-cost option for small roofs and spot treatment |
| Soft wash surfactant | Helps the mix cling to the slope so it works longer and runs off less |
| Wet & Forget hose end | Bleach-free, no-rinse alternative you can spray from the ground |
| Splash goggles and chemical gloves | Essential with any bleach mix |
What soft washing is
Soft washing lets chemistry do the work that pressure does in a power wash. The solution kills organic growth on contact, and a gentle rinse or the next few rains carry it away. For asphalt shingles, this matches ARMA’s guidance: a bleach-and-water spray, 15 to 20 minutes of dwell time, and a low-pressure rinse, never a pressure washer (ARMA).
| Soft washing | Pressure washing | |
|---|---|---|
| How it cleans | Cleaning solution kills growth; low-pressure rinse | Water force removes surface growth |
| Safe for asphalt shingles | Yes (ARMA method) | No: strips granules |
| Kills algae, moss and lichen | Yes | Removes visible growth only |
| Main risks | Bleach runoff harms plants and metal | Granule loss, water forced under laps and seams |
| Best for | Shingles, tile, slate, cedar, coated metal | Concrete tile at low pressure, hard surfaces |
Soft wash chemicals and what each does
- Sodium hypochlorite (bleach). The active ingredient in most soft wash mixes. It kills algae, moss, mold, mildew and lichen. Household bleach is about 5 to 8 percent; pool chlorine and pro-grade sodium hypochlorite run 10 to 12.5 percent and must be diluted further. See our bleach guide for ratios.
- Surfactant. A detergent that lowers surface tension so the mix spreads, clings to the slope and soaks into growth instead of running straight off. A small amount of dish soap works for DIY; pros use bleach-stable roof surfactants.
- Plant protectors. Products sprayed on plants before and after cleaning to reduce bleach damage. Heavy pre-watering, plastic sheeting and a thorough post-rinse do most of the same job.
- Odor maskers. Scent additives that cover the bleach smell. Optional.
- Quat-based cleaners. Bleach-free products such as Wet & Forget use alkyl dimethyl benzyl ammonium chloride and work slowly, with rain doing the rinsing.
- Sodium hydroxide (caustic). Occasionally used by professionals for specific stains. It burns skin and is not a DIY chemical.
Soft wash equipment
Sprayer or soft wash system
A basic soft wash system is a tank, a chemical-resistant pump, hose, a trigger gun and interchangeable tips. Pro rigs pump high volume at low pressure and can reach a two-story roofline from the ground. For one home, a 12-volt battery sprayer or a bleach-rated pump sprayer covers most jobs.
On asphalt shingles, don’t swap in a pressure washer for the rinse, even turned down. ARMA’s rule has no low-setting exception. Rinse shingles with a garden hose at normal pressure. Some metal roof makers allow a gentle low-pressure rinse; DECRA, for example, says to stay under 500 PSI on its stone-coated metal (DECRA).
Safety gear
- A sturdy ladder with a standoff, set on firm ground; see how to place a ladder on a sloped roof and how to stabilize a roof ladder
- A roof safety harness, roof anchor and lifeline if you step onto the roof
- Splash goggles, chemical-resistant gloves and long sleeves you don’t mind bleaching
- Rubber-soled shoes with a soft, grippy tread
- A helmet for anyone on the roof or working below it
How to soft wash a roof, step by step
- Clear loose debris. Blow leaves and twigs off the roof and out of the gutters with a leaf blower. Leave attached moss for the chemical to kill rather than scraping it.
- Protect the area. Soak plants and lawn below the eaves, cover delicate beds with plastic sheeting, and close windows. Many pros tie bags over downspout outlets to collect runoff.
- Mix the solution. For a DIY job on asphalt shingles, use ARMA’s 1:1 mix of household bleach and cold water with a squirt of dish soap. For commercial products, follow the label.
- Apply evenly. Spray the roof until the growth is wet without flooding it into the gutters. Work from the eaves on a ladder, or from the ground with a system that has the reach.
- Let it dwell. For bleach mixes, 15 to 20 minutes, per ARMA. Don’t let it dry; mist it again if needed. Algae lightens and moss turns yellow or brown as it dies.
- Rinse at low pressure. Rinse bleach mixes with a garden hose at normal pressure. Spray-and-leave quat cleaners need no rinse.
- Flush plants, gutters and metal. Run fresh water over plants, gutters, downspouts and painted trim to dilute any residue.
- Wait for the weather. The roof often looks only partly clean on day one. Dead growth keeps fading and washing away with the next several rains. Heavy moss or lichen may need a second treatment weeks later.
What soft washing costs
Professional roof soft washing averages around $460 nationally, with two-story, steep and tile roofs costing more. Our roof cleaning cost guide breaks prices down by roof size and state. A DIY bleach job costs under $50 in supplies if you already own a ladder, and a 12-volt sprayer adds roughly the cost of a basic pressure washer. Professional soft wash rigs cost far more than one cleaning, so for a single home, hiring a crew every few years usually makes more sense than buying one.
Rather have a pro handle it?
Roof cleaning means working at height with chemicals on a slippery surface. See what professional roof cleaning costs in your area before you buy the gear. Free, no sign-up.
See local roof cleaning prices →The video below shows a low-cost DIY soft wash using bleach, water, dish soap and a sprayer.
Pros and cons of soft washing
| Pros | Cons |
|---|---|
| Safe for asphalt shingles when done the ARMA way | Bleach runoff damages plants, lawns and unrinsed metal |
| Kills growth instead of just removing it | The roof does not look fully clean until after several rains |
| Can be done from a ladder or the ground with the right sprayer | Wet bleach makes roofs slippery |
| Uses less water than pressure washing | Embedded stains such as rust or tar may need other treatments |
| Low DIY cost | Mixing too strong or leaving it too long can discolor some roofing |
Soft washing FAQs
What PSI is used for roof soft washing?
Soft wash systems spray at low pressure, typically well under 100 PSI at the pump. On asphalt shingles, rinse with a garden hose and never a pressure washer, per ARMA. For other materials, follow the roofing manufacturer’s limit.
Can I soft wash with a pressure washer?
Some pros apply soft wash mixes through a pressure washer fitted with a downstream injector and a low-pressure soap tip. For shingles, a pump sprayer and garden hose are the safer DIY setup, because it is easy to switch to a high-pressure tip by mistake.
Is soft washing safe for plants?
Not on its own. Bleach mixes harm plants and lawns, so soak and cover plants before you start and flush them with water afterward. Bleach-free quat cleaners are gentler but still need pre-watering, per their labels.
How long does a soft wash last?
It depends on shade, moisture and climate. Damp, shaded roofs can show new growth within a few years. Trimming trees, keeping gutters clear and treating early stretch the time between cleanings.
Soft wash vs pressure wash: which is better for a roof?
Soft washing, for nearly every residential roof. Pressure washing is acceptable only for some materials at low pressure, such as concrete tile up to the manufacturer’s limit. Our roof pressure washing guide lists the limits by roof type.
Soft wash system demo:
Related guides
- How to clean roof shingles with bleach
- Best sprayers and applicators for roof cleaning
- Best roof cleaning solutions
- Removing roof algae
- Roof moss removal
- Roof lichen removal
Updated November 2026. Sources: ARMA, Algae & Moss Prevention and Cleaning for Asphalt Roofing Systems; DECRA metal roof cleaning tips.
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