The finish is the roof - and it is what a bad clean destroys

What is metal roof cleaning?

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.

How metal roof cleaning actually works

1. 1

   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 forA 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.

2. 2

   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 forAn 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.

3. 3

   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 forStraight to full application. On a coated roof this is the step that separates a professional from someone who cleans driveways.

4. 4

   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 forFootprints 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.

5. 5

   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 forA crew that packs up while the roof is still coated in solution. On asphalt that is sloppy. On metal it can mark the finish.

6. 6

   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.

What does metal roof cleaning cost?

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 →

If the number is the problem, here are the ways people pay for it →