How long does a roof clean take?

No one figure fits every roof, so be cautious of a time given over the phone before anybody has looked at the house. Five things do most of the work in setting the length of the job.

• Size. A small semi has less surface than a detached house with two wings, and a long terrace run takes longer than a single bay.
• Pitch. Steep slopes slow the work because the roofer moves more carefully and needs safer positions.
• Access. Where a ladder reaches, setup is quick. Where a tower or scaffold is needed, the frame goes up first, and that adds time at both ends.
• How thick the moss is. A thin green film clears fast. Deep, old cushions wedged into the laps take more passes, and the roofer slows down to avoid lifting the tiles.
• The covering. Slate and old clay tiles are handled gently and slowly. Concrete tiles are more forgiving.

For a normal house, the cleaning itself is usually a single visit. A large or awkward roof can run longer or be split across two days. The survey fixes the plan, and the written quote reflects it.

Set-up comes first. Plants, cars and garden furniture are moved or covered, access is put in place and the roof is looked over before anything is applied. Gutters and downpipes are protected or cleared, depending on the plan.

Then the treatment. Loose moss is brushed or lifted away by hand where that is safe, and a low-pressure biocide wash is applied across each slope, working from the ridge down so that run-off does not stain clean areas. The biocide is left to work. We cover why we avoid high-pressure jets on our black streaks on a roof page, where the same principle applies.

Then there is a pause that homeowners sometimes miss. The biocide needs time on the surface before anything is rinsed or brushed, and a roofer will often work on another slope while one soaks. That waiting is built into the day and is not a sign of delay.

Last comes the clear-up. Debris is bagged and taken away, gutters are cleared where included, and the ground is left tidy. If the survey spotted slipped tiles or cracked pointing, we explain what we found and quote for that work. Most of the visit is access, application and clearing; the actual treatment is the shortest part.

A biocide kills moss, algae and lichen but does not remove the dead growth instantly. It stays on the surface, changes colour, and breaks down over the following weeks as rain, wind and frost loosen it. A roof can look patchy for a while before it settles to an even finish.

That is why a clean roof on the day of the visit is not the final look, and why a quick judgement after a fortnight can mislead. Weather also plays a part: a dry spell slows the rinse, and a wet one speeds it. Slopes in shade take longer to clear than those in the sun.

Lichen is slower still. It grips the surface more firmly than moss, and thick patches can take a long time to fade. Our guide to lichen on roofs explains why it behaves differently. If you are planning to sell or photograph the house, allow time for the treatment to finish before you start.

Smaller roofs are quicker, but not always by as much as you might expect. A conservatory roof is low and often easy to reach, yet the glazing bars, seals and polycarbonate or glass panels need careful hands, and cleaning the inside face of a panel can mean a second access point. Our page on conservatory roof cleaning covers what is involved.

Garages and outbuildings are similar. A garage with a pitched concrete tile roof is a short job once the ladder is up. A flat roof with felt needs a gentler method and a closer check of the covering. Setting up and clearing away still take time, however small the roof.

Concrete tiles are covered on our page about cleaning concrete tiles. They are often the most forgiving covering, which helps the time. Slate and aged clay take longer because they are handled with more care. Combining jobs saves repeat visits, so ask for the main roof and the outbuildings to be quoted together.

We confirm the plan before the day. The survey photographs your roof, notes the access and the amount of growth, and the written quote follows with the work described. If the weather turns on the day, we move the visit rather than work in conditions that make the roof unsafe or the treatment ineffective.

Wind, heavy rain and frost all affect a clean, and we do not promise a specific date or hour over the phone. What we can say is that we will keep you informed, and that if something unexpected turns up once the moss is gone, we show you a photograph and explain the options.

Ring 01793 626096, or send the address and a picture of the roof by WhatsApp or the contact form. Our written 10-year workmanship guarantee applies to the work we carry out, and the site is left clear when we go. For the wider picture, see our roof cleaning and moss removal page.