How Long Does Roof Cleaning Take?

The stages of a roof clean

Removing the heavy growth. Thick moss is scraped off by hand first. This is the slowest part on a badly affected roof, because every row of tiles and every ridge and valley needs attention.

Cleaning the surface. Depending on the tile and its condition, the roof is then soft washed, low pressure washed or cleaned with hot steam. Delicate or older tiles get the gentlest method, which is not always the fastest one.

Clearing the gutters. Moss that comes off the roof ends up in the gutters, so they are cleared at the end. Skipping this would leave you with blocked gutters within weeks.

Treatment. A biocide treatment goes on last to kill the spores left behind, and is intended to prevent the moss returning for up to three years. It is sprayed on and left to work, so it does not add much time on the day.

What makes one roof slower than another

Size and pitch are the obvious ones, but the shape of the roof matters just as much. Dormers, valleys, chimneys, hips and extensions all break the roof into smaller areas that each need working round.

The depth of moss is the other big factor. A roof that was treated a few years ago might only need a light clean. One left for a decade can have moss so thick it lifts the edges of the tiles, and removing it carefully takes time.

Tile type also plays a part. Concrete tiles tolerate more than old clay or slate, so the method chosen, and the pace of the job, follows what the roof can safely take.

Weather and timing

Roofs are best cleaned in dry spells. Heavy rain makes the surface slippery, washes away cleaning products before they work and can stop a treatment from bonding. Strong wind is another reason to wait. A good roof cleaner will move a date rather than work in the wrong conditions, which sometimes means a job booked for one day is spread across two.

Autumn and early winter are popular, because clearing moss before the worst weather keeps gutters flowing, but a roof can be cleaned at any time of year when conditions allow.

What you will notice on the day

Expect some noise from scraping and equipment, and some debris falling that is cleared away afterwards. It is worth moving cars away from the house and keeping pets indoors while the work is under way. The treatment keeps working after the visit, so the roof often looks a shade brighter a few weeks later than it did when the team left.