The Best Roof Cleaner and Moss Killer for Asphalt Shingles
Six products, ordered by how little they ask you to do on the roof. That sounds like a convenience test and it is not: the manufacturers' own instructions rule out pressure and discourage scrubbing, so the products needing neither are the ones least likely to cost you granules.
The short version
What to buy, and the one rule underneath it
Everything on this page follows from a single line in ARMA's guidance, which is the trade body for the companies that make your shingles.
Their wording: do not use a power washer or any type of brush or broom to clean algae from the roof surface. The reason is granules. They are the layer protecting the asphalt from sun, they are glued on, and pressure takes them off. A roof that has been power washed looks clean and has had years removed from it.
No power washer, ever
Pressure takes off the granules that protect the asphalt underneath. The roof looks clean and has had years removed from it.
No brush and no broom
ARMA names both. The friction loosens granules the same way pressure does, just more slowly.
Let the chemistry work
You spray, you wait, and then you either rinse gently or leave it to the weather. That is the whole method.
So the ranking below is not a taste test. Products needing no rinse and no agitation come first, because those are the ones where a homeowner cannot accidentally break the rule. Within that it is cheapest first. The order is worked out in code from the price and the rinse requirement, not arranged by hand, and we clean roofs for a living, so read the recommendations knowing that.
The table
Six products, and what each one asks of you
Price is for the concentrate or the ready-to-use bottle as sold. The last column is the one that matters.
Product
Active ingredient
Price
After spraying
Spray & Forget
Quaternary ammonium concentrate
$29 to $32
Nothing
Wet & Forget Outdoor
Quaternary ammonium (ADBAC), about 9.9% in concentrate
The streaking most Triangle roofs have is algae. Moss is a different organism, it grows in different places, and it needs different chemistry. Buying for the wrong one is the usual mistake.
1. Spray & Forget, the cheapest of the two no-rinse sprays
$29 to $32 No rinse needed, so nothing to do after spraying.
Same chemistry and the same no-rinse routine as Wet & Forget, and it ranks above it here on price alone. The gallon of concentrate makes up to ten gallons of solution, so across a whole roof it works out cheaper per square foot than ready-to-use bottles.
The catch. You are mixing it yourself, so the dilution is on you. The quart hose-end bottle costs more per treatment but takes the guesswork out.
2. Wet & Forget Outdoor, the easiest to buy and the one most reviewers pick
$25 to $40 No rinse needed, so nothing to do after spraying.
Spray it and walk away. No rinse, no scrubbing, no ladder work beyond getting the spray up there, which is the whole point: every step ARMA warns you about is a step this product does not ask for. It works gradually, over days and weeks, as weather carries the dead growth off.
The catch. Gradual means gradual. If you want the roof to look different by the weekend this is the wrong product, and people who expect that end up on the roof with a brush, which is exactly what you were avoiding.
3. DIY bleach soft wash, cheapest, and the method the manufacturers actually publish
$5 to $12 Needs a low-pressure rinse afterwards.
This is not an off-brand shortcut. It is what ARMA and GAF both describe. GAF's bulletin gives the mix as four gallons of water, one gallon of bleach and a cup of TSP, applied with a garden sprayer. ARMA says leave it at least fifteen minutes and no more than twenty, then rinse gently.
The catch. A wet bleached roof is slippery, which is why ARMA tells you to hire someone. The runoff kills plants under the eaves, and overshooting the twenty minutes is its own problem. Cheap on materials, not cheap on risk.
The one product here where the stain fades while you are still standing there, rather than over the following month. If you are cleaning a roof before listing a house and the photographer is booked, this is the reason to pick it.
The catch. It may want a light rinse or a second pass, so you are back to handling water on a roof. Speed costs you the walk-away part.
5. Simple Green Oxy Solve House & Siding, best where bleach runoff is the problem
about $24 Needs a low-pressure rinse afterwards.
Oxygen chemistry rather than chlorine, so it is the option to reach for when the beds under the eaves matter to someone or there is a pond below the downspout. It needs a low-pressure rinse afterwards.
The catch. It generally wants dwell time and some agitation to do its work, and agitation is the thing ARMA tells you not to do. Keep it off copper and zinc flashing.
6. Lilly Miller Moss Out! for Roofs, best on thick moss rather than flat algae stains
about $43 Needs a low-pressure rinse afterwards.
Different problem, different chemistry. The black streaking on most Triangle roofs is algae and the quat sprays handle it. Actual cushions of moss growing in the keyways are what zinc sulfate is for, and that is more common on the north face of a shaded roof under pines.
The catch. Most expensive on this list, and if your roof has streaks rather than tufts you are paying for a solution to a problem you do not have.
Want to know what is actually growing up there?
We will get on the roof, photograph it, and tell you whether it is algae, moss or granule loss that looks like staining. No charge and no obligation.
The method
How soft washing actually works
Soft washing is a confusing name because it sounds like a gentler kind of pressure washing. It is not. It is chemistry doing the work and water doing almost none of it.
ARMA's sequence is specific. Wet the surface, apply the solution, leave it at least fifteen minutes and no more than twenty, then rinse by gently spraying the roof. No brush, no broom.
They also note the cleaning makes a roof slippery, which is why they encourage using professionals. That is the trade body for the shingle manufacturers saying it, not a roofer looking for work.
GAF's bulletin publishes the mix: four gallons of water, one gallon of bleach and a cup of TSP, through a garden sprayer, up to twenty minutes, rinsed at low pressure. If you are doing this yourself, that is the recipe to follow, and it is worth reading your own shingle manufacturer's bulletin because ARMA notes the directions vary between them.
The part people skip is what is underneath. Growth that heavy usually means the roof stays damp, and a roof that stays damp has a shade problem, a gutter problem or a ventilation problem. Cleaning it treats the symptom. Our ventilation calculator will tell you whether the attic has the airflow it should.
Questions
Roof cleaning questions
What is the best roof cleaner?
For the black streaking on most Raleigh roofs, a no-rinse quaternary spray like Wet & Forget or Spray & Forget. They cost $25 to $40, they need no scrubbing and no rinsing, and that matters because the Asphalt Roofing Manufacturers Association tells you not to scrub a shingle and not to put a power washer anywhere near it. If you want the cheapest route and do not mind handling water on a roof, the bleach mix GAF publishes costs under $12.
What kills moss on a roof?
Zinc sulfate for thick moss, quaternary sprays or a bleach solution for flat algae streaking. They are different organisms and the products are not interchangeable. If you are looking at black vertical streaks you have algae, which is the common one here. If you are looking at green cushions sitting up in the shingle keyways, that is moss, and it is usually on a shaded north slope.
Can you pressure wash a roof?
No. ARMA's wording is blunt: do not use a power washer or any type of brush or broom to clean algae from the roof surface. Pressure strips the granules that protect the asphalt, and GAF's bulletin warns the same loss can lead to premature shingle failure. Soft washing means chemistry and a gentle rinse, not pressure.
Does cleaning a roof void the warranty?
Cleaning it the published way does not. Cleaning it with a pressure washer can, because that causes the granule loss manufacturers exclude as damage rather than defect. Follow the manufacturer's own bulletin for your shingle, or have someone soft wash it, and keep the receipt.
How much does roof cleaning cost in Raleigh?
Materials for a do-it-yourself treatment run $5 to $45 depending on which product you pick. Having it soft washed costs more than that and less than most people expect, and the figure depends on pitch, access and how much growth is up there. We will look at it and tell you, and the look costs nothing.
Will the streaks come back?
Yes, eventually, because the algae is airborne and the Triangle is humid. How fast depends on shade and which way the slope faces. Shingles sold with algae resistance hold out longer, which is a reason to specify them when the roof is eventually replaced rather than a reason to replace it now.
Keep reading
Related guides and calculators
Staining is usually a damp roof telling you something.
Seven signs, and how to tell staining from the granule loss that matters.
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