Moss and algae aren't just ugly -- they're actively shortening the life of your roof and siding. Most contractors try to blast them off with high pressure, and it works for about six months. Then they're back. Soft washing kills the organisms at the root and keeps surfaces clean for 2-4 years.

The Quick Answer

Soft washing uses low pressure (500-1,200 PSI) combined with a sodium hypochlorite solution to kill moss, algae, mold, and mildew. The chemical does the work -- pressure just rinses the dead material away. Here's how the two methods compare:

Pressure washing: removes surface staining, doesn't kill the organism, regrowth in 3-6 months
Soft washing: kills the organism at the root, surfaces stay clean 2-4 years

For humid climates with heavy tree cover, expect 18-24 month cycles. In drier, sunnier regions you can stretch to 3-5 years between treatments. That longevity is what makes soft washing a recurring revenue machine.

Why Pressure Washing Moss and Algae Doesn't Work Long-Term

Moss and algae have root systems that penetrate into shingles, siding, and grout lines. Pressure washing strips the visible layer off the surface, but the root structure stays intact and regrows within months. You're treating the symptom, not the cause.

Soft washing uses sodium hypochlorite (chlorine bleach) to break down the cell walls of the organism and kill it completely. Once the root is dead, it can't regrow. A low-pressure rinse then removes the dead material without damaging the surface beneath.

This is why the Asphalt Roofing Manufacturers Association (ARMA) specifically recommends a 50/50 bleach and water solution for roof algae -- not pressure washing.

The Soft Wash Mix and Process

The Solution

A standard soft wash mix uses sodium hypochlorite (SH), water, and a surfactant. The surfactant helps the solution cling to vertical surfaces and extends dwell time so it doesn't run off before it can work. Mix ratios by surface:

Asphalt shingle roofs: 3-6% SH solution (50/50 bleach and water gets you there)
Vinyl or painted siding: 1.5-2% SH is sufficient
Wood siding or wood shake roofs: 1-1.5% SH -- go lighter to avoid bleaching

Add 2-4 oz of surfactant per 5 gallons of mix regardless of concentration. This is what makes the solution stick on sloped roofs and textured surfaces.

Dwell Time

Let the solution sit for 15-20 minutes before rinsing. You'll see the color change as the SH breaks down the organisms -- green moss turns brown, black algae streaks fade to gray. On heavily infested surfaces, a second application may be needed before the final rinse.

The Rinse

Use 500-1,200 PSI to rinse. That's low enough to avoid damaging asphalt shingles, wood siding, or stucco. A soft wash pump, an X-jet, or even a downstream injector on a standard pressure washer all work for application. You don't need specialized equipment -- just the right chemical setup and a way to control your pressure on the rinse.

Which Surfaces Need Soft Washing

Any surface with biological growth that can't handle high pressure is a soft wash job. The list is long:

Asphalt shingle roofs: High pressure blasts off granules and voids manufacturer warranties
Wood siding and wood shake: High pressure splinters wood fibers
Stucco: High pressure chips and gouges the finish
EIFS/synthetic stucco: High pressure forces water behind the cladding and causes mold inside walls
Painted surfaces: High pressure strips paint

Concrete, brick, and pavers can handle pressure washing. But if the goal is killing algae or moss in shaded or low-traffic areas, soft washing still works better -- the chemistry kills it, pressure just blasts it around.

Soft Washing Pricing in 2026

Soft washing commands a premium because of the chemical cost and the technical knowledge involved. Here's what the market supports:

Roof soft wash (asphalt shingles): $0.30-$0.80 per sq ft
Roof soft wash (tile or wood shake): $0.50-$1.00 per sq ft
House wash with soft wash method: $0.15-$0.30 per sq ft
Minimum for any roof job: $300-$400
Minimum for siding only: $200-$300

A typical single-family home with a 1,500-2,000 sq ft roof runs $450-$700. Heavy moss infestation or steep pitch can push that to $1,200. Chemical cost on a typical job is $30-$60. Labor is one to two hours. Your margin is 85%+ on a well-priced job.

Turning Soft Wash into Recurring Revenue

Here's where soft washing beats every other service for long-term income. Results last 2-4 years, which means customers come back on a predictable cycle. Build a simple maintenance follow-up system: note when each customer's roof was treated, and send a reminder when they're due for a re-treatment.

Offer a pre-booked maintenance plan at 10-15% off the normal rate. Customers get a discount, you get guaranteed future work without paying to re-acquire the customer. Combine with annual house washing and you have a recurring relationship that generates $400-$1,200 per customer every two to three years.

If you currently only offer pressure washing, adding soft wash is a natural expansion. You're already at the job site. A $60 chemical investment and an extra hour of work at $400-$700 is hard to beat.

Bottom Line

Soft washing for moss and algae removal isn't a niche service -- it's the right tool for most roof and siding cleaning work. Let the chemistry kill the organism, use low pressure to rinse, and charge a premium for results that last years instead of months. It's better for the customer and better for your margins.

If you want to present soft wash pricing to customers the moment they land on your site, try QuoteSnap for free. Customers get an instant estimate, you get the lead before they call someone else.

Soft Washing for Moss and Algae: Why Low Pressure Wins