Top-Rated Cleaning a Metal Roof: What Is Different from Asphalt

Most roof cleaning advice you will find is written about asphalt shingles, because that is what most houses have. Metal is common enough around here that it is worth spelling out where the two part ways.

What you are protecting is the coating. A metal roof's finish is a factory-applied coating, and that coating is doing the work of resisting corrosion and UV. Everything about how a metal roof should be cleaned follows from not damaging it. That rules out abrasive brushing and aggressive scrubbing, both of which are fine on a shingle and wrong here.

So metal gets a soft wash. Low pressure, the right cleaning solution, dwell time, and a thorough rinse. The solution does the work rather than the machine. Done properly it takes the algae streaking and moss off without touching the finish.

Why not the brush and powder method. On asphalt I use a brush and a moss-killing powder, and the powder is granular and stays on the surface to keep working. On a metal roof the panels shed water fast and the surface is smooth, so a granular product mostly ends up in the gutter. It is the right tool on the wrong surface.

The streaking is usually algae, not rust. Dark vertical streaks on metal panels are typically algae growth following the water path, and they come off. Actual rust looks different, tends to start at fasteners, cut edges, and scratches, and is a repair question rather than a cleaning one. If I find it, I will tell you rather than wash over it.

Safety changes too. Metal is slick, and it is slicker while it is being washed. A lot of metal roof work is done from ladders and edges rather than by walking the field of the roof, which affects how long the job takes and how it gets quoted.

Standing seam, corrugated, and metal shake profiles all behave a bit differently in terms of where debris collects, but the cleaning principle is the same across all of them.

Gutters are worth doing at the same time. Metal roofs shed debris efficiently, which means more of it ends up in the gutter rather than staying on the roof.

If you have a metal roof and have only been given quotes that describe shingle methods, that is worth a second look.