Moss and algae on a roof aren't just ugly -- they're slowly destroying the shingles underneath. Moss holds moisture against the surface and lifts granules over time. Left untreated, it shortens roof life by years. The good news: removing moss and algae is a high-demand service with strong margins, and the technique is straightforward if you know what you're doing. Here's exactly how to clean a roof safely and what to charge for the job.

The Quick Answer

Soft washing is the only safe method for most residential roofs. Here's what you need to know up front:

Method: Soft wash only -- low-pressure chemical application, not high-pressure blasting
Solution: 50:50 sodium hypochlorite (bleach) and water, plus a few drops of dish soap
Dwell time: 20-30 minutes for algae, 45-60 minutes for moss
Pricing: $0.30-$0.80 per sq ft -- average $600-$1,200 for a 2,000 sq ft roof
Results last: 2-4 years vs 6-12 months with pressure-only methods

Never use a high-pressure washer directly on asphalt shingles. It strips the protective granules and voids most manufacturer warranties. Soft wash keeps you out of trouble and produces better results.

Pressure Washing vs Soft Washing a Roof

Here's the thing most homeowners get wrong: "pressure washing the roof" usually means soft washing when done correctly. The difference matters.

High-pressure washing (1,500+ PSI): Physically blasts debris off. Strips granules from shingles, can crack tiles, forces water under overlaps. Voids most roofing warranties. Don't do this.
Soft washing (50-150 PSI or pump sprayer): Applies a chemical solution at low pressure. The chemistry does the work -- kills algae and moss at the root rather than just blowing off visible growth. Results last 2-4 years.

The Asphalt Roofing Manufacturers Association (ARMA) explicitly recommends the soft wash method for all asphalt shingle roofs. That's the industry standard, and it's what you should be offering customers.

The Correct Chemical Solution

ARMA's official recommendation is simple:

50% household bleach (sodium hypochlorite)
50% water
A few drops of liquid dish soap to help the solution cling to the surface

For lighter algae staining, you can go 3:1 water-to-bleach -- but for heavy moss growth, the 50:50 ratio is more effective. The dish soap acts as a surfactant, slowing runoff and keeping the solution on the surface longer.

Apply with a 12-volt pump sprayer or a soft wash system (a dedicated low-pressure pump with chemical lines). Garden-style pump sprayers work for smaller roofs but get tiring on anything over 1,500 sq ft. A dedicated soft wash unit saves labor time and delivers a more consistent application.

Step-by-Step Roof Cleaning Process

Here's the full process for a residential asphalt shingle roof:

Walk the roof first (or use binoculars from the ground). Check for missing or cracked shingles, exposed flashing, or areas where water could pool. Document any pre-existing damage before you start.
Pre-wet landscaping below. Bleach runoff will kill grass and plants. Pre-wet shrubs, mulch, and lawn around the house with plain water before applying the solution. Rinse again after the job.
Apply the solution from the ridge down. Start at the peak and work your way down. This prevents you from walking on a slick, wet surface and lets gravity help distribute the solution evenly.
Let it dwell. Algae: 20-30 minutes. Moss: 45-60 minutes. Don't rush this step -- the chemistry needs time to kill the organisms at the root. Visible algae will start to fade during dwell time.
Rinse with low pressure. Use a garden hose or a soft wash wand at under 150 PSI. Rinse from ridge to eave, thoroughly. Avoid standing water under overlaps.
Do a second pass if needed. Heavy moss growth sometimes needs two applications. Apply again, let dwell 30 minutes, and rinse. Dead moss can be gently brushed off after rinsing -- never while it's wet.

Pricing Your Roof Cleaning Jobs

Roof cleaning is priced by square footage, with variations by roofing material and pitch:

Asphalt shingles: $0.30-$0.50 per sq ft
Metal roofs: $0.25-$0.60 per sq ft
Tile roofs: $0.50-$1.00 per sq ft (more delicate, slower process)
Wood shakes: $0.75-$1.50 per sq ft

For a typical 2,000 sq ft ranch home with asphalt shingles, you're quoting $600-$1,000. A 3,000 sq ft two-story runs $900-$1,500. Always set a minimum of $350-$400 -- the setup time and chemical cost make anything less not worth the drive.

Steep pitches (8/12 and above) add 25-50% to the price. Extra chemical passes for severe moss add another 15-20%. Be upfront about these variables when quoting -- customers appreciate knowing what changes the price.

Safety on the Roof

Falls are the number one injury risk in roofing work. If you're getting on the roof, use proper safety equipment:

Non-slip footwear (rubber sole, no worn treads)
Safety harness anchored to a ridge anchor rated for fall arrest
Chemical-resistant gloves and eye protection when mixing and applying bleach solutions

For most soft wash jobs, you don't need to get on the roof at all. A long-reach soft wash wand from a ladder lets you apply solution and rinse from the gutterline. This is the safer approach and speeds up the job significantly.

Preventing Moss From Coming Back

Here's a good upsell to mention after every roof cleaning: zinc or copper strips installed near the ridge line. When it rains, trace amounts of zinc leach down the roof and prevent moss and algae from re-establishing. Zinc strips run $30-$60 for a 50-foot roll and take about 30 minutes to install. Charge $75-$150 for the labor and materials. It's a small ticket but keeps your customer's roof clean longer -- which they'll appreciate when they remember where to call next time.

Roof Cleaning vs DIY

Homeowners can technically do this themselves, but most won't. Getting on a slick roof with a bleach sprayer is dangerous, and mistakes damage shingles or kill landscaping. Professionals charging $600-$1,000 for a 3-4 hour job with proper equipment and insurance are an easy sell against the DIY risk. Position it that way when customers push back on price.

Bottom Line

Soft washing roofs is a high-margin service with real demand -- especially in humid climates where moss and algae grow fast. A 2,000 sq ft roof job earns $600-$1,000 in 3-4 hours, the chemistry does most of the work, and results last 2-4 years. Add roof cleaning to your service menu and you'll book jobs from homeowners who are already paying you to clean other surfaces.

If you want customers to be able to get an instant quote for roof cleaning right on your website, try QuoteSnap for free. Set your per-square-foot rate, add your roof cleaning service, and let customers price themselves before they call you.

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