If you’ve noticed dark streaks, green patches, or fuzzy moss creeping across your roof, you’re not alone, and you’re probably wondering whether cleaning it is safe, or whether the wrong method might do more harm than good.
The short answer: the right cleaning method not only won’t void your warranty, it’s actually required by most manufacturers to keep your roof performing as intended. The wrong method, however, can absolutely void coverage and cause real damage.
Here’s what the manufacturers themselves say.
Why Your Roof Gets Dirty and Why It Matters
That dark staining you see on asphalt shingles isn’t dirt. It’s a blue-green algae called Gloeocapsa magma, and it feeds on the limestone filler in your shingles. Left unchecked, it holds moisture against the roof surface, accelerates shingle granule loss, and shortens the life of your roof significantly.
Moss and lichen do even more damage, their root-like structures physically lift shingle edges, allowing water to penetrate underneath.
The good news is that every major shingle manufacturer acknowledges this problem and has a published, approved cleaning solution.
What the Manufacturers Actually Recommend
GAF — The Industry Standard
GAF is the largest roofing manufacturer in North America, and its Technical Advisory Bulletin TAB-R-102 (updated September 2024) is the definitive manufacturer document for cleaning algae and moss from asphalt shingles. It prescribes exactly this:
“GAF recommends cleaning the roof with a special mixture. That mixture is: 4 gallons of water, 1 gallon of bleach and 1 cup of TSP… Apply this mixture with a garden sprayer, let sit for up to 20 minutes, and rinse with low-pressure water.”
They also explicitly state: “Do not power wash the shingles… it may dislodge granules, which can lead to premature shingle failure.”
Translation: Low-pressure sodium hypochlorite (bleach) is the approved method. High-pressure washing is what voids your warranty.
ARMA — The Industry Trade Body
The Asphalt Roofing Manufacturers Association (ARMA) sets the standards that all major shingle manufacturers follow. Their technical bulletin on algae discoloration (revised June 2024) states:
“Discoloration may be lightened by applying a solution of liquid household bleach (sodium hypochlorite) and water… left on the roof for at least 15 minutes but no more than 20 minutes… rinse the solution from the roof by gently spraying the surface with water. DO NOT use a power washer.”
This is the governing standard. Any contractor who pressure washes your asphalt shingle roof is working against manufacturer specifications — not with them.
Owens Corning & CertainTeed
Both Owens Corning and CertainTeed publish near-identical maintenance guidance:
“Mix a solution of 1 part chlorine bleach with 3 parts of water. Apply this solution using a low-pressure hand-held sprayer over the asphalt shingles… After 15 minutes, rinse the bleach solution from the roof.”
The message is consistent across every major manufacturer: soft-wash sodium hypochlorite, low pressure, thorough rinse.
IKO
IKO’s official guidance approves a bleach-and-water solution applied with a garden sprayer, with a dwell time of 20–45 minutes before rinsing. Again: no pressure washing.
How Servus Cleaning Meets Manufacturer Specifications
At Servus Cleaning, we use a 4% sodium hypochlorite solution applied at low or no pressure, exactly the method these manufacturers endorse.
Here’s how our method stacks up against manufacturer specs:
| Specification |
What Manufacturers Say |
Servus Cleaning Method |
| Cleaning agent |
Sodium hypochlorite (bleach) |
✅ 4% NaOCl solution |
| Application pressure |
Low pressure/garden sprayer |
✅ Low or no pressure |
| RinsingGentle |
low-pressure rinse |
✅ Thorough rinse after treatment |
| Power washing |
❌ Universally prohibited |
✅ Never used on shingles |
|
|
|
Our method is designed to keep your warranty intact, not risk it.
Which Roof Types Can Be Cleaned with Sodium Hypochlorite?
✅ Safe to Clean with SH (Bleach Solution)
Asphalt Shingles (GAF, Owens Corning, CertainTeed, IKO, Malarkey)
The gold standard use case. Every major manufacturer explicitly recommends this method. This is the most common residential roof in Canada, and the method is fully approved.
Painted / PVDF-Coated Metal Roofing
Manufacturers, including Fabral and Firestone, approve diluted sodium hypochlorite for mildew removal on painted metal panels, with the requirement to rinse thoroughly after application.
Concrete and Clay Tile
Boral’s warranty and maintenance guide approves diluted chlorine solution for moss and algae removal on tile roofs. Soft-wash is the recommended delivery method.
IB PVC Flat Roofing (standard white, non-printed)
IB Roof Systems explicitly permits diluted bleach for heavy algae on their standard white non-printed PVC membrane — one of the few flat roof products with a direct SH approval.
❌ Do NOT Use Bleach On These Roofs
Galvalume Metal Roofing
This is the most critical exception. Galvalume is an unpainted, aluminum-zinc alloy coated steel — it has a raw silver or tin-grey appearance and is extremely common on agricultural buildings, rural barns, and some residential standing-seam roofs.
Fabral’s official maintenance documentation explicitly states: “Do not use bleach on Galvalume.” The reason: Sodium hypochlorite is alkaline, and it reacts with Galvalume’s protective zinc-aluminum coating, causing permanent oxidation and surface damage that cannot be reversed. If you’re not sure whether a metal roof is Galvalume, ask for the product documentation before any treatment.
⚠️ Proceed with Caution
Stone-Coated Steel (DECRA, Gerard)
DECRA’s technical bulletin lists only specific alternative products (Wet & Forget, Wash Safe, Spray & Forget) as approved cleaners. Sodium hypochlorite is not included in their approved list. Using SH on a DECRA roof may void the manufacturer’s warranty — we recommend confirming with the manufacturer or using their specified products.
GAF EverGuard TPO / Duro-Last PVC (Flat Roofing)
These manufacturers specify mild detergent-based cleaners only. SH is not listed as approved. For commercial flat roofs, we always confirm the specific system and manufacturer requirements before proceeding.
Cedar & Wood Shake
The Cedar Shake & Shingle Bureau doesn’t directly endorse or prohibit bleach on cedar. High concentrations of sodium hypochlorite can break down lignin (the structural compound in wood), causing greying and accelerated weathering. If you have a cedar shake roof and want it cleaned, we’ll discuss appropriate methods and concentrations before starting.
The Bottom Line: Soft Wash Protects Your Roof AND Your Warranty
Here’s what years of manufacturer documentation confirms:
1. Bleach (sodium hypochlorite) is the approved active ingredient for killing algae, moss, and mildew on asphalt shingles — not an aggressive chemical choice, but the manufacturer-recommended one.
2. Low pressure is mandatory: power washing asphalt shingles violates manufacturer specifications and voids warranties universally.
3. Roof type matters: Galvalume metal, stone-coated steel (DECRA), and most commercial flat roofing systems have specific restrictions that must be respected.
4. Regular cleaning is maintenance, not damage: leaving biological growth on your roof unchecked is far more damaging to your warranty and your roof’s lifespan than a properly executed soft wash.
Manufacturer Links and References
