To clean a metal roof, rinse it with plain water, then use a soft brush and a mild soap on whatever is left, and skip the harsh chemicals. Most of what lands on a metal roof is pollen, dust and leaves, and a garden hose handles a lot of it. The roof’s finish is what you are protecting.
The short version
- Start with plain water and a soft brush. Reach for soap only if water leaves stains behind.
- Skip solvents, abrasive pads and harsh chemicals. They can dull or strip the paint.
- Keep leaves and debris off, because wet debris sitting on metal causes trouble over time.
- Stay off a steep, wet or slick roof. Clean from a ladder or the ground, or hire it out.
- Read the roof maker’s care sheet first, since the paint warranty may have rules.
How often does a metal roof need cleaning?
Not often. This Old House says occasional washing can help (opens in a new tab) a metal roof keep its appearance and performance, and that homes near trees or with a lot of pollen may need it more often. A roof under open sky may go years before it looks dull enough to bother.
Cleaning is a looks job most of the time. A roof with a film of yellow pollen is still keeping water out. What matters more than a washing schedule is a yearly look at the roof itself, which we get to below.
What do you use to clean a metal roof?
Use plain water first, and nothing stronger than a mild soap after that. The Insurance Institute for Business and Home Safety says that in many cases washing with plain water from a hose or pressure spray is adequate (opens in a new tab) on a metal panel roof.
For stubborn spots, a soft-bristled brush on a long pole does the job. This Old House suggests a soft-bristled brush or a pressure washer on a low setting (opens in a new tab) for dirt, debris and algae. A hose and a brush are the safer pair. A pressure washer in the wrong hands can force water under panel edges, and it is easy to hold too close.
A little mild soap in a bucket of water is the usual choice. Whatever you use, rinse it all off, so no film is left behind to catch more dust.
What should you never put on a metal roof?
Keep solvents, abrasive cleaners and harsh chemicals off it. The IBHS guide says solvent and abrasive type cleaners should be avoided (opens in a new tab), and warns that abrasive or chemical cleaners can damage painted finishes. This Old House gives the same advice: avoid harsh chemicals that could damage the finish (opens in a new tab).
That includes a few things people reach for out of habit:
- Wire brushes, steel wool and scouring pads, which scratch the paint and can start rust.
- Paint thinners and similar solvents.
- Strong cleaners from the garage that were never made for painted metal.
One more point trips people up. The Asphalt Roofing Manufacturers Association does give a 50:50 bleach and water mix (opens in a new tab), but that page is about asphalt shingles. It is not a recipe for a painted metal roof, and the metal sources above say to avoid harsh chemicals. Do not carry advice from one roof type to another.
Can you pressure wash a metal roof?
You can on some roofs, with care, but a hose and brush cover most jobs. This Old House allows a pressure washer on a low setting, and the IBHS guide lists pressure spray as fine for rinsing a metal panel roof. The risk is in the details. Spray aimed upward can push water under laps and around fasteners, and a strong jet held close can damage the finish.
If you do use one, keep the nozzle wide, stay back from the panel, and spray down the slope, never up under the edges. Check the maker’s care sheet first, since it may say what the finish can take.
Is it safe to walk on a metal roof to clean it?
For most homeowners it is not. A wet metal panel with a film of soap on it is slick, and the fall is the danger that matters. OSHA says falls are the leading cause of work-related deaths among residential construction workers (opens in a new tab), which tells you how often even trained people get this wrong.
If someone does go up, the IBHS guide says to never step on the major rib of a panel and to walk within the flat part (opens in a new tab). It also says never to walk, stand or sit on an unsecured panel. On a steep roof, a two-story house or any roof that is wet, stay on the ground and wash from there, or hire someone with the right gear.
Roof washing is not one of the services we offer. Cleaning your gutters is, and we cover how often in how often gutters should be cleaned.
Why does debris matter on a metal roof?
Wet debris left on metal causes corrosion over time. The Pacific Northwest National Laboratory says corrosion can be caused by ponding water and debris accumulation (opens in a new tab). Leaves banked against a seam, packed into a valley or piled against a wall act like a sponge that never dries out.
That is the problem we see most on Ellicott City lots with a lot of trees: branch overhang, leaf pile-ups in valleys and clogged gutters that back water up. On a metal roof, clear leaves with a soft broom or a leaf blower, and keep metal rakes and shovels off the panels. The IBHS guide also says keep the roof free of debris (opens in a new tab) as part of routine care.
What should you look for while you clean?
Use the wash as a yearly check. This Old House recommends inspecting a metal roof at least once a year (opens in a new tab) for damage and loose fasteners, and touching up scratches in the finish to prevent rust.
Look for these:
| What you see | What it can mean |
|---|---|
| Orange or brown spots | Rust starting where the paint is scratched or worn |
| Screw heads sitting high or tilted | A screw backing out, or a washer that has failed |
| Gaps or lifted edges along a seam | Movement or wind damage |
| Pooled water or damp debris | A blocked valley or gutter |
| Chalky, faded paint | The finish wearing out |
Loose screws are a common cause of leaks on screw-down roofs, and we explain why in why metal roof screws leak. If cleaning shows a faded finish, our guide to painting a metal roof covers what that takes.
Common questions
Does cleaning a metal roof void the warranty?
It can if you use the wrong product. IBHS says routine maintenance should follow the manufacturer’s recommendations (opens in a new tab). Read the care sheet that came with the panels, or call the maker, before you use anything beyond water and mild soap.
Do metal roofs grow algae and moss?
Yes, mostly on shaded roofs under trees. This Old House lists algae among the things a soft brush or low-pressure wash removes. Shade, damp leaves and debris are what give it a place to start.
Is it okay to leave a dirty metal roof alone?
Usually, yes, for looks alone. Dust and pollen do not hurt the metal. Leaves and standing water do, so keep those clear and look the roof over once a year.
What to do next
If your roof is streaked, rusting or leaking, have it looked at before you scrub. Our free roof inspection includes a walk on the roof and a written report with photos, and there is no obligation to book work. If the roof is near the end of its life, see our page on metal roofing installation for what a new one involves, or book a free roof inspection first.
