The short answer
A typical house roof takes around a day to clean on site, with smaller roofs sometimes finished sooner and large or awkward ones taking longer. The time depends on roof size, how much moss has to be lifted by hand, the covering and the access. The treatment then continues to work, so the roof looks its best several weeks after the visit, not the same afternoon.
A realistic length for a house roof
For a typical semi-detached or terraced house, a roof clean is a one-visit job, and a single day on site is a reasonable expectation. A small outbuilding or garage may take a couple of hours. A large detached house, a long terrace or a roof with several slopes and a number of chimneys will take longer, and it can run to more than one day.
These are typical figures, not a promise. The honest answer depends on the roof in front of us. We give you a time once the survey has shown the size, covering and condition, so that you know what the day will involve before it is booked.
Think of it as two timescales. The work on site is measured in hours. The effect on the roof is measured in weeks, and a second look a couple of months later is the fair way to judge whether the clean has done what it should.
Weather plays a part. Cleaning is done from the outside and at height, so strong wind or heavy rain can move the visit by a day or two. Treatment also needs a dry spell afterwards to settle. We would rather rearrange a visit than apply a treatment that will be washed straight off.
What stretches or shortens the visit
Roof size is the obvious factor, but it is not the only one. Heavy moss takes time, because it is lifted off by hand in clumps before any treatment is applied, and a thick growth can be more work than the treatment that follows. A light film of streaks on a clean slope goes much faster. Our page on the risks of DIY moss removal shows why that hand work is not as simple as it looks.
The covering changes the pace. Natural slate and old stone tiles are brittle and need careful footwork, so the work is slower than on a sturdy modern tile. Steep pitches and complicated shapes, with dormers, valleys and abutments to work around, add time. A flat roof is usually quicker to treat, though standing water and the edge details need attention.
Chimney stacks and roof lights each add a little, because the surfaces around them need hand work and the flashings, the strips of metal sealing the joins, must be treated with care rather than scrubbed. A roof with solar panels needs a plan for the area beneath them, which can be awkward to reach.
Debris is another variable. A roof with a lot of moss and leaf litter produces a good deal of waste, and the gutters will need clearing. When we finish, we clear the site and remove the waste.
Access: the setup before the cleaning starts
Part of the day is the setup, not the scrubbing. Getting people safely onto the roof, and keeping everything below protected, takes time at the start and the end of a visit. A house with easy ground access and a ladder-friendly frontage is simple. A house hemmed in by neighbours, a long garden or a roof reachable only over an extension takes more planning. We explain the options in whether scaffolding is needed to clean a roof.
If a tower or full scaffold is required, it is usually put up before the clean and taken down afterwards, which adds time to the whole job even if the cleaning itself is quick. That is one reason we prefer to see the roof before giving a time.
Why the result keeps improving after we leave
The surprising part for many customers is that the roof does not look finished on the day. Cleaning has two parts: removing the moss by hand, and applying a biocide that kills the growth beneath it. The biocide does its work slowly. Over the following weeks the dead growth loosens and is washed away by rain, and the surface lightens gradually.
That is why you may see a patchy roof straight after a visit, and a clean one a month or two later. This is the treatment doing its job, and it does not mean something went wrong. A roof that is blasted clean in an afternoon looks better at once but has often lost more of its surface, and the growth has little to stop it returning. For the kind of change you can expect, see what black streaks are and how they go.
Planning the day around the work
For a standard clean, you do not need to be at home all day, though it helps to have someone available at the start to agree access and at the end to look over the finished roof. We ask that cars are moved away from the front of the house and that windows are shut. Pets are best kept indoors while the work is going on.
If the survey finds something the clean cannot cure, such as slipped tiles, split lead or a failing covering, we tell you directly and price the repair separately. In some cases it makes better sense to repair or recover than to keep cleaning, and our page on cleaning roof tiles explains how we decide.
Our roof cleaning service begins with a free look at your roof, and the quote that follows is fixed. If you have a date that matters, such as a sale or a family event, mention it early so the clean can be fitted around the forecast. Ring 01225 285181 to book a time.
