Want to know what a proper roof cleaning actually covers? See what’s included, step by step.
Every roof material responds differently to cleaning. The method that’s safe for one type can void the warranty or cause permanent damage on another. Before anyone touches your roof, the first question should be what it’s made of — because that determines everything that follows.
Why Roof Type Dictates the Cleaning Method
Asphalt shingles, metal panels, concrete tile, cedar shake, and flat membrane roofs all have different tolerances for pressure, heat, chemicals, and agitation. A method that’s fine for standing-seam metal would destroy a composition shingle roof in minutes. A chemical that cleans concrete tile safely could corrode copper flashing on a metal roof.
The short version: there is no single “roof cleaning method.” There’s only the right method for your specific roof material, applied by someone who knows the difference.
Composition Shingle Roofs (Asphalt)
Composition shingles are the most common roofing material in the Pacific Northwest and across the country. They’re also the most vulnerable to cleaning damage when the wrong method is used.
What works: Soft wash — a low-pressure application of a cleaning solution that kills moss and algae without mechanical force. The solution does the work, not the water pressure. After treatment, dead moss sheds naturally over the following weeks as rain and wind carry it away.
What causes damage:
- Pressure washing strips the protective granule layer off shingles. Those granules are the UV and weather barrier — once they’re gone, shingle life drops dramatically. Most manufacturer warranties explicitly exclude pressure washing damage.
- Bleach-based solutions dry out the asphalt binders that hold shingles together. One application won’t destroy a roof, but repeated bleach treatments accelerate aging in a way that’s invisible until it’s too late.
Our approach: We use RoofRX™ MossBlock — a plant-derived, biodegradable soap applied as a visible foam. No bleach, no high pressure. You can see exactly where the roof has been treated, and the shingles keep their granules and binders intact.
Wondering what a bleach-free roof cleaning actually costs? See our full cost breakdown.
Metal Roofs (Standing Seam, Corrugated, Stone-Coated)
Metal roofs are durable and long-lasting, but they’re not maintenance-free. Moss, algae, and debris still accumulate — especially in shaded areas and at panel seams. The cleaning approach depends on the finish.
What works: Low-pressure rinse combined with a pH-neutral or mildly alkaline cleaning solution. Metal panels can handle slightly more pressure than asphalt shingles, but the goal is still chemical cleaning, not mechanical blasting.
What causes damage:
- Aggressive pressure washing can dent thin-gauge panels, damage seam caps, and strip protective coatings
- Acidic cleaners corrode the finish on painted or coated metal panels
- Bleach or chlorine solutions can cause oxidation and discoloration, especially on galvanized or Galvalume surfaces
- Abrasive scrubbing scratches the factory finish, exposing bare metal to rust
💡 Key consideration: Stone-coated steel (like Decra or Gerard) has a granule surface similar to asphalt shingles — it needs the same gentle approach as composition shingles, not the standard metal roof treatment.
Concrete and Clay Tile Roofs
Tile roofs are built to last 50+ years, but moss and algae growth can work into the porous surface of concrete tiles and under the overlap of clay tiles. Cleaning needs to be thorough without cracking or displacing tiles.
What works: Low-pressure soft wash with a solution formulated for masonry surfaces. The cleaning agent penetrates the porous tile surface to kill growth at the root. Some heavily colonized tile roofs benefit from a two-stage treatment — an initial application followed by a second pass after the first round has loosened established growth.
What causes damage:
- High-pressure washing cracks tiles, breaks edges, and can dislodge individual tiles from their mounting. A single cracked tile may not leak immediately, but it creates an entry point for water damage over time.
- Walking carelessly on tile during cleaning causes as much damage as the wrong cleaning method. Tiles are strong under compression but brittle under point loads — stepping in the wrong spot snaps them.
💡 Key consideration: Concrete tiles absorb water; clay tiles don’t. This affects drying time and how cleaning solutions interact with the surface. Your cleaner should know which type you have before they start.
Cedar Shake and Wood Shingle Roofs
Wood roofs require the most careful approach of any roofing material. Cedar shake is naturally rot-resistant, but it’s also organic — aggressive chemicals or excessive water exposure can accelerate the very decay the roof was designed to resist.
What works: A gentle, low-pressure application using a wood-safe cleaning solution. The goal is to remove moss and algae without saturating the wood or stripping its natural oils. Some cedar roofs also benefit from a post-cleaning wood preservative treatment that restores UV protection and moisture resistance.
What causes damage:
- Pressure washing splinters cedar shake, lifts shingle edges, and drives water deep into the wood structure where it promotes rot from the inside out
- Bleach and chlorine strip the natural tannins and oils that give cedar its rot resistance — essentially accelerating the aging process by years
- Zinc strips are sometimes installed as a moss deterrent, but zinc runoff can streak and stain wood surfaces over time
💡 Key consideration: A cedar roof that hasn’t been cleaned in years may look like it needs aggressive treatment. It doesn’t. Patience and the right solution matter more than force. Established moss on cedar often takes two treatment cycles to fully clear — and that’s the right way to do it.
Flat Roofs (TPO, EPDM, Modified Bitumen, Built-Up)
Flat and low-slope commercial roofs use membrane materials that are completely different from pitched residential roofing. The cleaning approach is built around protecting the membrane integrity and keeping drainage paths clear.
What works: Low-pressure wash with a cleaner compatible with the specific membrane type. TPO and PVC membranes handle most mild detergents well. EPDM (rubber) requires a cleaner that won’t degrade the rubber compound. Built-up and modified bitumen roofs need minimal agitation to avoid disturbing the gravel ballast or loosening seams.
What causes damage:
- Pressure washing can tear seams, puncture membranes, and displace gravel ballast on built-up roofs
- Petroleum-based solvents break down EPDM rubber and can dissolve the adhesive on seam tape
- Walking with hard-soled shoes or dragging equipment across membranes creates scuff marks and puncture risks
💡 Key consideration: Flat roof cleaning is as much about maintaining drainage as it is about removing growth. Ponding water — standing puddles that don’t drain within 48 hours — accelerates membrane aging faster than any biological growth. A cleaning visit should always include clearing drains, scuppers, and gutters.
How to Tell What Roof You Have
If you’re not sure what your roof is made of, here’s a quick guide:
- Composition/asphalt shingles: Flat, flexible, overlapping rectangles with a granular texture — by far the most common
- Metal: Smooth panels with raised seams (standing seam) or wavy corrugated sheets — visibly metallic or painted
- Concrete tile: Heavy, thick, interlocking pieces — often flat or with a slight S-curve profile
- Clay tile: Similar to concrete but thinner, smoother, and often barrel-shaped or with a distinct terracotta color
- Cedar shake: Rough-textured wood pieces with natural grain patterns — they weather to a silvery gray over time
- Flat membrane: Smooth, continuous surface — usually white (TPO/PVC), black (EPDM), or gravel-topped (built-up)
If you’re still not sure, that’s fine — a qualified roof cleaner will identify your material during the pre-clean assessment before any work begins.
The One Method That Works Across Every Roof Type
Every roofing material on this list shares one thing in common: soft washing is either the correct method or the safest starting point. No roof type benefits from high-pressure washing. None of them improve with bleach over time.
The differences are in the cleaning solution, the dwell time, and the post-treatment steps — not in whether to use pressure. A company that uses the same method on every roof regardless of material is cutting corners, and your roof is paying for it.
Questions to Ask Before Hiring a Roof Cleaner
- ✔️ What method do you use on my specific roof type?
- ✔️ What chemicals are in your cleaning solution?
- ✔️ Do you use pressure washing on any part of the process?
- ✔️ Have you cleaned this roof material before?
- ✔️ What’s covered if there’s damage or if growth comes back?
If the answer to “what method do you use” is the same regardless of what roof you have — keep looking.
Still weighing whether to DIY or hire a pro? Read our breakdown of whether professional roof cleaning is worth it.
Get the Right Method for Your Roof
Your roof is one of the most expensive components of your home. How it gets cleaned — and when to clean your roof — should reflect that. If you’re not sure what method your roof needs or you want a second opinion on how it’s been cleaned before, request a free roof assessment and we’ll walk you through exactly what your roof needs — and what it doesn’t.