Soft washing is the only roof cleaning method recommended by the Asphalt Roofing Manufacturers Association (ARMA). The black streaks on asphalt shingle roofs are not dirt — they are Gloeocapsa magma, a living cyanobacteria that feeds on the limestone filler inside the shingles, strips away protective granules, and shortens roof life by 5 to 10 years. This guide covers the complete process for how to soft wash a roof: the equipment setup (12V soft wash pump, proportioner valve, adjustable nozzle), the sodium hypochlorite solution, the section-by-section application technique, why professionals never rinse, and real-world pricing — including an actual $850 roof job broken down start to finish.
Mike Vidan walks through a complete roof soft wash from setup to breakdown on a real customer job.
The black staining on asphalt shingle roofs is a living organism. It is called Gloeocapsa magma — a cyanobacteria (commonly called blue-green algae) that feeds on the limestone filler used inside modern asphalt shingles. According to the Asphalt Roofing Manufacturers Association, Gloeocapsa magma is the most prevalent species responsible for roof discoloration in North America.
The organism protects itself from UV rays by producing a dark pigmented sheath — that sheath is the black color you see. By the time the streaks are visible from the ground, the colony has typically been growing for months. The north-facing slopes of a roof are usually the worst because shade holds moisture longer, and moisture is what the algae needs to thrive.
Here is the part most homeowners do not understand: a gray roof covered in this algae looks black. The stains are not the color of the shingles. They are the organism. On the job featured in the video above, the roof appeared completely black from the street — and it was a gray roof underneath.
ARMA is explicit on this point: never pressure wash asphalt shingles. High pressure strips the protective granules off the shingle surface and voids most manufacturer warranties. Worse, pressure washing does not actually kill Gloeocapsa magma — it removes the visible growth but leaves the root system and spores behind. The streaks come back faster after a pressure wash because the damaged shingle surface gives the bacteria a better environment to recolonize.
Soft washing kills the organism at the cellular level using a sodium hypochlorite (SH) solution applied at low pressure. The chemical does the work — not the water pressure. For a full breakdown of SH, surfactants, and the other chemicals professionals carry, see the guide on what chemicals pressure washers use.
The roof in the video was cleaned with a battery-powered soft wash system running a 7 gallon-per-minute pump — solar-charged, mounted on the trailer. Both gas-powered and electric (12V) soft wash pumps work. The electric systems have improved dramatically: a well-built 12V setup produces very little overspray, which nearly eliminates the need for a dedicated ground person watering plants during application.
The proportioner valve. The metering system on this setup uses a three-valve proportioner: one line drops into the fresh water tank, one drops into the SH chemical tank, and the valve blends them to the target concentration. The reason for this setup is the post-job flush — when the cleaning is done, both draw tubes go into the fresh water tank and the entire system (proportioner, pump, all lines) gets flushed clean of sodium hypochlorite. SH left sitting in a pump system corrodes seals and fittings.
The nozzle. An adjustable nozzle that switches between long-range stream and fan tip without changing tips saves time on the roof. Long range reaches peaks and upper sections; the fan pattern covers flat runs evenly.
The solution strength. A heavily infested roof gets a stronger mix than a routine maintenance clean. Roof soft wash solutions typically run 3–6% SH at the surface depending on growth severity — significantly stronger than the 1–2% used for house washes. The roof in the video got an elevated concentration because the algae coverage had turned the entire surface black.
Before any chemical touches the roof, walk it. Check for pre-existing damage, soft spots, and loose shingles. Document what you find — this protects both you and the customer. On the job in the video, the walk-through confirmed no damage or soft spots before the first drop of solution was applied.
The application technique professionals use is working in coordinates: treat one small section at a time, working from the top of the slope down. The chemical runs downhill and continues cleaning as it travels, so working top-down means gravity is doing part of the job for you. Small sections also mean no missed spots — you can focus on complete coverage of one area before moving to the next.
You will see the chemical activate within seconds. The black organic staining starts breaking down and running off almost immediately. Sections that still show staining after the first pass get touched up — and the chemical keeps working after you leave the roof.
This is the part of the process that surprises homeowners the most: after the solution is applied and touch-ups are done, the job is complete. No rinse. The chemical continues to work on the surface, and the next rain performs the final rinse naturally.
Customers sometimes call concerned when they see remaining discoloration right after the crew leaves. That is why customer education before the job is critical — explain the process up front, put it on your website, and set the expectation that the roof reaches its final result after the next rain. If a spot does not clear, a professional operation returns and re-treats it. Every job should be guaranteed.
During and after a soft wash on an older roof, you may see areas of granule loss — spots where the protective mineral surface of the shingle has worn away. This is normal on aged roofs and is not caused by the soft wash. The fastest way to gauge a roof’s age before you ever get on it: look in the gutters. Heavy granule accumulation in the gutters means the roof has significant age on it. Document granule loss in your pre-job walk-through and point it out to the customer so there is no confusion about what the cleaning did and did not cause.
The roof in the video was priced at $850. Here is the thinking behind that number, because roof cleaning pricing is about more than square footage:
| Pricing Factor | This Job | How It Affects Price |
|---|---|---|
| Roof size | Not large, but multiple sides and peaks | More sections = more application time |
| Walkability | Easy to walk | Easy walk = lower price; steep pitch adds cost |
| Algae severity | Heavy — entire roof black | Heavy growth = stronger mix + more chemical |
| Chemical consumption | Above average | Chemical cost passed through in price |
| Time on site | ~1.5 hours setup to breakdown | Efficient process = strong hourly rate |
| Bundled services | House wash + concrete on same visit | Bundling raises ticket, lowers per-service cost |
At $850 for roughly 1.5 hours on site, the effective rate on this roof exceeded $500 per hour before chemical costs — and the same visit included a house wash and concrete cleaning that pushed the total ticket higher. This is why roof cleaning is one of the highest-margin services in exterior cleaning.
The complete professional process from arrival to departure.
Check for damage, soft spots, loose shingles, and granule loss before applying anything. Photograph what you find. Check the gutters for granule accumulation to gauge roof age. This walk-through protects you and informs the customer.
Position the soft wash pump (12V battery or gas), run the ag hose, and connect the proportioner valve — one draw line in the fresh water tank, one in the SH tank. Verify the pump is delivering before climbing.
Routine maintenance cleans run lower SH concentrations; heavily infested roofs need a stronger mix (3–6% at the surface). The blacker the roof, the stronger the solution. Add surfactant — always on roofs — so the solution clings and dwells instead of running off.
Work in coordinates: one small section at a time, starting at the ridge and working down. The chemical runs downhill and continues cleaning below where you spray. Small sections prevent missed spots.
The solution activates within seconds — black staining visibly breaks down and runs off. After full coverage, go back over any sections still showing staining. The chemical continues working after application.
The treatment stays on the roof. The next rain performs the final rinse and reveals the finished result. Set this expectation with the customer before the job starts. Guarantee the work: if a spot does not clear, return and re-treat.
Drop both proportioner draw tubes into the fresh water tank and run the system until the proportioner, pump, and all lines are flushed clean of sodium hypochlorite. SH left in the system corrodes seals, fittings, and pump internals.
Soft washing a roof involves walking the roof first to document pre-existing conditions, setting up a low-pressure soft wash pump with a proportioner valve, mixing a sodium hypochlorite solution matched to the growth severity (3–6% for heavy algae), applying the solution in small sections from the ridge down, touching up remaining spots, and leaving the treatment on the roof without rinsing. The next rain performs the final rinse. The system is then flushed with fresh water to protect the pump and lines.
Black streaks on asphalt shingle roofs are caused by Gloeocapsa magma, a cyanobacteria that feeds on the limestone filler inside the shingles. The organism produces a dark pigmented sheath to protect itself from UV rays — that sheath is the black color. According to the Asphalt Roofing Manufacturers Association, it is the most prevalent species responsible for roof discoloration. North-facing slopes show the worst growth because shade holds moisture longer.
No. The Asphalt Roofing Manufacturers Association explicitly recommends against pressure washing asphalt shingles. High pressure strips the protective granules and voids most manufacturer warranties. Pressure washing also does not kill the algae — it removes visible growth but leaves the root system and spores, so the streaks return faster. Soft washing with a sodium hypochlorite solution is the only ARMA-recommended cleaning method.
The sodium hypochlorite solution continues killing the algae after application, and rinsing would cut that dwell time short. The next rain performs the final rinse naturally and reveals the finished result. Professional operations explain this to customers before the job and guarantee the work — if any spot does not clear after the rain, they return and re-treat it at no charge.
Professional roof soft washing typically costs $300 to $750 depending on roof size, pitch, walkability, and algae severity. Heavily infested roofs requiring stronger chemical mixes and more product cost more. The roof featured in this guide was priced at $850 — a multi-peak roof with heavy algae coverage that consumed above-average chemical. Compared to a $10,000 to $25,000 roof replacement, soft washing every 2 to 3 years is one of the most cost-effective maintenance investments a homeowner can make.
A typical residential roof soft wash takes 1 to 2 hours from setup to breakdown. The roof featured in this guide took approximately 1.5 hours including hose runs, ladder setup, application, touch-ups, and cleanup. Larger roofs, steeper pitches, and heavier growth extend the time. Pressure washing companies often bundle a roof wash with a house wash and concrete cleaning on the same visit to maximize the day’s revenue per stop.
Yes. Gloeocapsa magma feeds on the limestone filler inside asphalt shingles, which loosens the protective granules that shield the asphalt from UV radiation and rain erosion. Industry data shows untreated algae growth shortens roof life by 5 to 10 years. The dark staining also absorbs more heat, raising attic temperatures and cooling costs. Some insurance carriers now flag algae-covered roofs as neglected during inspections.
Roof cleaning price is based on roof size, pitch and walkability, number of sides and peaks, algae severity (which determines chemical consumption), and access. Many companies measure the roof from satellite imagery before quoting — tools like MapMeasure Pro inside QuoteIQ calculate square footage from aerial views so the quote is accurate before the truck ever rolls. Presenting tiered options (roof only versus roof plus house wash plus concrete) consistently increases average ticket size.
For the complete training on soft washing, chemical mixing, equipment builds, and how to wash every surface on a residential job site, check out the How To Wash course at pwcourse.com. To run the business side — quoting, scheduling, job costing, and customer communication built for exterior cleaning — start a 14-day free trial of QuoteIQ.
Pressure Washing Business Owner (25+ Years) · QuoteIQ Co-Founder · 580K+ YouTube Subscribers
Mike Vidan has operated a pressure washing and soft washing business in Savannah, Georgia since 1997, earning 500+ five-star reviews. He co-founded QuoteIQ, a CRM for home service contractors with 40,000+ daily users. His YouTube channel teaches contractors the technical and business skills to grow. Author of Pressure Washing Marketing Domination. Co-creator of the How To Wash training program.
Entrepreneur, service business operator, and Co-Founder of QuoteIQ. 25+ years building from the ground up.
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