Roof Cleaning near you

Not everything growing on a roof is equally serious, and a good roof cleaner starts by identifying what's there. What matters is how much moisture each kind of growth holds against the roof and whether it's working its way under the covering.

Soft washing applies a cleaning solution at low pressure, much like a garden sprayer, gives it time to work on moss and algae, then rinses gently or lets the weather finish the job. Thick moss is usually loosened first by hand, working down the slope with soft brushes or plastic tools so nothing is scraped or pried up. The aim is to kill growth at the root rather than blast away what's visible.

Pressure washing does the opposite. As our pressure washing page cautions, a jet on asphalt shingles strips their protective granules and can drive water up under them; it can also crack brittle shingles, gouge cedar and break slate. If a company offers to pressure wash your shingle roof, look elsewhere. Cedar, slate and metal roofs each call for methods suited to the material, so ask what the crew plans to use on yours.

Treatments strong enough to kill moss and algae can also harm lawns, shrubs and garden beds, and some can mark metal, painted trim or stone. Whatever runs off the roof goes into the gutters, onto the plants below and often toward the street. Ask the cleaner which product they use, ask to see its label, and ask how they'll control the runoff.

Runoff rules are set by municipalities. Toronto's Sewers By-law is a clear example: the City says only rain and melted snow may flow into an outdoor catch basin, that wash water must not reach one, and that even washing with water alone carries contaminants. Check your own municipality's rules before the job is booked.

Once a roof is clean, the goal is to make it a poor place for moss to return. Strips of zinc or copper, installed by a roofer along the ridge or near the top of a slope, shed a trace of metal every time it rains, and that film discourages moss and algae below. The effect is strongest just downslope of the strip and fades farther down, so long or broken-up slopes may need more than one row. Strips are prevention for a clean roof, not a way to remove thick moss. They must be fastened so no exposed nail becomes a leak, and the metal they shed ends up in the runoff, which is worth weighing near a pond or stream.

Shade and damp matter more than any product. Overhanging branches keep a roof from drying, drop leaves and needles into valleys and gutters, and scrape shingles in the wind. Cutting them back lets sun and air reach the roof. Work on trees near a house or power lines belongs to an arborist; see our tree trimming page, and ask whether a municipal permit is needed first.

Roof cleaning combines height, a wet and slippery surface, and chemicals. Ask the company how its workers are protected from falls, whether it carries liability insurance, and whether its crew is covered by your province's workplace injury insurance. A typical job runs like this:

Most cleaners work from spring to fall, when the roof is clear of snow and ice and the weather suits the product. Many labels call for dry weather after application so rain doesn't wash the solution away before it works, which makes the forecast part of the booking. Spring is a good time to deal with growth that thrived under winter snow; late fall, once the leaves are down, is the time to clear valleys and gutters before freeze-up. A frozen or snow-covered roof is too dangerous to clean.

Cleaning removes growth but can't undo the damage it has already done. If the cleaner reports any of the following, have a roofer assess the roof, and see our roof repair and roof inspection pages: