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Soft washing is the industry-standard method for cleaning roofs — and for good reason. High-pressure washing blasts shingles, voids warranties, and sends contractors sliding down wet pitches. Soft washing uses a low-pressure chemical solution to kill algae, mold, lichen, and the bacteria that cause black staining (Gloeocapsa magma) at the source, not just at the surface.

What Is Soft Washing?

Soft washing uses a diluted sodium hypochlorite (SH) solution — typically at 3–6% concentration on roofs — applied at low pressure (under 100 PSI) to dwell on organic growth and dissolve it chemically. You rinse, not scrub. The surface stays intact. The biology dies. Pressure washing a roof damages asphalt shingles by stripping the granule coating and does nothing to address root systems of moss or lichen. Most shingle manufacturers explicitly state that high-pressure cleaning voids the warranty.

Chemicals: What You Need and Why

Sodium Hypochlorite (SH)

Pool-grade SH is the active ingredient, concentrated at 10–12.5% from chemical suppliers. Dilute to a working concentration of 3–6% depending on severity:

• Light algae or maintenance clean: 3% working solution
• Moderate staining or moss: 4–5% working solution
• Heavy lichen or long-neglected roofs: 5–6% working solution

Dilution math (to hit 5% from 10% SH): Mix 1 part SH concentrate with 1 part water. Do not use bleach from a hardware store — it is only 3–6% SH and often contains thickeners that cause runoff issues.

Surfactant

Surfactant lowers surface tension so the mix clings to sloped surfaces instead of sheeting off. Common options: Elemonator (citrus-based, strong cling) or EBC (concentrated, handles multiple organic sources). Typical ratio: 2–4 oz per gallon of mixed solution.

Neutralizer and Plant Protection

Use a sodium thiosulfate neutralizer solution (1–2 oz per gallon in water) as a pre- and post-rinse on all plant material in the fallout zone. Pre-wet all plants before application. This is non-negotiable — dead landscaping is the fastest way to get a bad review.

Equipment

For small residential roofs (under 2,500 sq ft): 12V soft wash pump (5.5 GPM) with 50-gallon poly tank, 200–300 ft of 1/2-inch chemical-rated hose on a reel, soft wash gun with variable tips, chemical-resistant gloves (nitrile or neoprene, wrist-length minimum), chemical splash goggles (not safety glasses), Tyvek suit or old clothes.

For commercial work: Gas-powered soft wash skid (8–12 GPM, 200–500 gallon tank) with dedicated proportioner.

Safety equipment: ANSI-rated fall protection harness, roof anchor or ridge hook, rubber-soled non-slip boots. Wet-weather policy: do not work on roofs during or immediately after rain.

Step-by-Step: How to Soft Wash a Roof

Step 1: Inspect from the Ground

Walk the perimeter. Identify roof pitch, substrate type (asphalt shingle, tile, metal), growth type, gutter condition, and any surfaces to mask or pre-wet. Do not quote off satellite imagery alone.

Step 2: Clear Gutters and Protect Plants

Clean gutters before you start — chemical-laden water in a clogged gutter overflows onto landscaping. Pre-wet all shrubs and grass within the runoff zone.

Step 3: Wet Surrounding Vegetation

Before applying SH, soak all plants around the structure. Saturated plants are more resistant to dilute SH in runoff.

Step 4: Mix Your Solution

Confirm SH concentration from your supplier (10% or 12.5%). Calculate dilution to hit your target concentration. Add surfactant last. Agitate gently — do not shake.

Step 5: Apply Bottom to Top

Apply starting at the lower edge and working toward the ridge. Keep pressure under 100 PSI. You are wetting, not blasting. Overlap passes by 6–8 inches.

Step 6: Allow Dwell Time

10–15 minutes for most residential roofs. Heavy lichen may require a second application or extended dwell up to 20 minutes. Do not let the solution dry on the surface.

Step 7: Rinse Top to Bottom

Rinse starting at the ridge and working down using low pressure (garden-hose flow is sufficient). Simultaneously rinse all plant material with neutralizer solution.

Step 8: Post-Job Inspection

From the ground, check for even rinsing, gutter condition, and plant health. Document with photos before you leave. Most organic growth lightens within 24–72 hours as residual SH continues to work — set client expectations accordingly.

Safety: The Non-Negotiables

Fall protection is not optional. OSHA requires it for roof work at or above 6 feet. Do not walk a wet roof. Period. Pitches above 6:12 require anchor points and rope systems or aerial equipment. Never reach past your balance point.

Chemical safety: SH at 10–12.5% causes skin burns and serious eye damage on contact. Wear splash goggles, not safety glasses. Store SH away from acids and ammonia. Have a water source available at all times for emergency eye flush.

Pricing

Job TypePrice RangeResidential roof (1,500–2,000 sq ft)$300–$600Large residential or low-slope commercial$600–$1,200Commercial flat roof or large warehouse$1,500–$5,000+

At $0.30–$0.50 per square foot, an experienced crew completes a residential soft wash in 2–3 hours. Upsell opportunities: moss pre-treatment, annual maintenance contracts, gutter cleaning bundled with the visit.

Drone Soft Washing: The Emerging Option for Steep and High Roofs

A growing number of commercial cleaning contractors are adding drone application for jobs where putting workers on the roof is genuinely dangerous — high-pitch roofs above 8:12, multi-story commercial buildings, steep metal roofs, and industrial structures with complex OSHA access requirements.

The Lucid Bots Sherpa drone carries and sprays soft wash solutions aerially with consistent coverage, without a worker on the surface. Available at $75,000 or through the Lucid Refresh program at $2,950/month. If you’re bidding commercial roofs where fall protection logistics are eating your margin, it’s worth a look.

Frequently Asked Questions

What is the difference between soft washing and pressure washing a roof?

Pressure washing physically removes surface contamination but strips shingle granules and leaves biological root systems intact — meaning regrowth within months. Soft washing kills organic growth at the source with low-pressure chemistry. Results last 2–5 years vs. 3–6 months for pressure-washed roofs.

What chemicals are used in soft washing a roof?

Sodium hypochlorite (pool-grade SH) diluted to 3–6% working concentration, plus a surfactant (Elemonator or EBC at 2–4 oz/gallon). Sodium thiosulfate neutralizer on surrounding plant material before and after.

How often should a roof be soft washed?

Every 2–4 years for most residential roofs. Humid climates with significant tree coverage see faster recolonization. Annual maintenance treatments can extend the interval.

Can a homeowner DIY soft wash a roof?

Technically yes, but the risk is not the chemistry — it’s the roof. A wet sloped surface is where most homeowner injuries in exterior cleaning happen. Professional service ($300–$600 for most residential jobs) is a straightforward value exchange relative to the fall risk.

How much does professional soft wash roof cleaning cost?

$0.30–$0.50 per square foot of roof surface. An average 2,000-square-foot house has roughly 2,400–2,800 square feet of roof surface. Expect $300–$600 for residential, $1,500–$5,000 for commercial.

Ready to Add Aerial Capability?

If you’re bidding commercial roof cleaning jobs where worker access is the limiting factor, get a demo to see what the Sherpa Drone can do.

Is the Lucid Bots cleaning drone easy to fly? The short answer is yes! 

In fact, no prior drone experience is needed. Many of our customers had no prior drone flying experience and they are now flying successfully to complete larger jobs!

If you know how to use a video game controller, then you should be able to fly a Lucid Bots Cleaning Drone successfully. The RC controller has knobs that control flight directions such as forward and backward motion, side to side motion (left or right), height (up or down), rotation (to make the drone turn a different direction), and throttle (speed).

The drone is also equipped with avoid distance quick-select switch, which allows you to choose between multiple distance options while keeping the drone a safe distance from the building, and urban flight capabilities, which allow you to fly safely in urban environments. The drone also has a forward facing radar which can detect objects in front of it and reduce the risk of crashing, as well as fail-safe battery systems. If your battery dies mid-flight, it will automatically land in a safe location!

Sounds easy enough, right? With proper training, you should be able to fly a drone in no time. Lucid Bots partnered with DroneU to provide an easy-to-use, ongoing training through an online training portal. This online training educates you on how to operate the soft washing drone and window washing drone competently and confidently, such as:

• Battery charging
• Flight skills
• Transportation guidelines
• Safety protocols
• And more

Additionally, the ability to receive your Part 107 License is included in our training!

We also offer in-person flight demos at our Charlotte, NC facility where you can see first hand just how easy it can be. Contact us today to schedule yours!