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Full services directory How it worksFor prosAbout Get matched Call (866) 582-8523A metal panel does not lose granules and does not crack underfoot. What it can lose is its factory coating, and that coating is what carries the warranty and keeps the steel underneath from rusting. That single fact reorganises the whole job.
On a metal roof the thing you are protecting is the factory-applied finish, not a granule layer. Coating manufacturers publish their own cleaning guidance and it generally amounts to the mildest thing that works: plain water first, then a mild detergent, then a specific cleaner only if needed. The complication is that the chlorine-based solution used as a default across roof washing is not automatically appropriate on every metal roof, particularly bare or unpainted panels. Match the method to the panel, not to the crew's usual mix.
Establish what the panel and the coating actually are
Painted steel, bare galvanised, Galvalume, aluminium, copper and zinc all behave differently. So do the coating systems — a premium architectural finish, a builder-grade paint and an uncoated panel have different tolerances and different published care instructions.
Watch for: A quote that treats "metal roof" as one thing. It is the category with the widest spread of correct answers, and there is no universal solution.
Check the manufacturer's cleaning guidance before choosing a product
Coating manufacturers publish cleaning instructions, and those instructions are also the terms under which the finish warranty stands. This is the one roof type where the paperwork genuinely governs the method.
Watch for: An operator who has never read a coating care sheet. Damaging a finish warranty to remove a streak is a bad trade and an avoidable one.
Test in an inconspicuous area first
Any cleaner goes on a small hidden section — a rear slope, a section behind a chimney — and is checked before it goes on the whole roof. Coatings vary batch to batch and age differently on different exposures.
Watch for: Straight to full application. On a coated roof this is the step that separates a professional from someone who cleans driveways.
Working with the panels, not across them
Rinsing is done down the slope, following the run of the panel, so nothing is driven up under the laps or into the seams. On standing seam, weight goes near the seams and near the supports rather than in the middle of an unsupported pan.
Watch for: Footprints denting the flat of the panels. Oil-canning and dents are cosmetic but permanent, and they are the most common visible damage after a metal roof clean.
Rinse thoroughly, and mean it
Residue left on a metal finish is not neutral — it keeps working. Every published care instruction ends with a full clean-water rinse, and on metal that step matters more than it does anywhere else on a roof.
Watch for: A crew that packs up while the roof is still coated in solution. On asphalt that is sloppy. On metal it can mark the finish.
Dealing with rust bleed separately
Streaks from a corroding fastener or a raw cut edge are not biological and will not wash off. They need the source addressed — usually a fastener or flashing repair — which is a roofing job, not a cleaning one.
Metal roof cleaning is generally quoted per square foot or as a job price. Expect it to sit near or slightly above asphalt work: the wash itself can be quicker, but testing, careful access and thorough rinsing add time. Steep standing-seam roofs cost more. The Cost Guide carries current ranges.
See the full metal roof cleaning cost guide — by material, size and region →
Everyone else ranking for this is paid when you say yes. Here's when you shouldn't.
Wet painted metal at pitch is among the most slippery surfaces on any house, and a metal roof gives no grip and no warning. Add the fact that stepping in the wrong place dents panels permanently and this is a roof type where the DIY line sits unusually low. If it needs more than a hose from a ladder, it needs someone with fall protection.
What panel and coating do I have, and how does that change your method?
If the answer is the same regardless of the panel, the method is not being matched to your roof.
Have you checked the coating manufacturer's cleaning guidance?
On metal the published care instructions are also the finish warranty terms. This is the one roof type where the paperwork sets the method.
Will you test on a hidden area before doing the whole roof?
Coatings age unevenly. A test patch costs ten minutes and is the only way to find out something has gone wrong while it is still small.
Where will your crew put their weight on the panels?
Near seams and over supports, not mid-pan. Dents are permanent, visible from the street and not covered by anything.
How will you avoid driving water up under the seams and laps?
Rinsing across or up the slope on a metal roof pushes water where it is not designed to go.
What is your plan for rinsing off residue?
Residue keeps reacting with the finish after the crew leaves. A thorough clean-water rinse is the last step in every manufacturer's instruction, and the easiest one to skip.
Are any of the stains rust rather than growth, and what do you do about those?
The honest answer is "that is a roofing repair, not something I can wash off". An operator who claims otherwise is guessing or selling.
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