In short
No. Jet washing can crack tiles, strip their protective surface and force water up under the tiles into the loft. The National Federation of Roofing Contractors says power-washing may cause damage to the roof. If moss needs to come off, it should be scraped off by hand.
This is a job for our Moss Removal & Roof Cleaning service.
What jet washing does to a roof
The NFRC, the roofing trade body, describes power-washing as a "violent" way to clean a roof that may cause damage, and points out that the extra foot traffic involved can crack or break tiles too. We see the results. We have been called to roofs left with broken tiles after a jet wash, and replaced them.
There are three ways it goes wrong:
- Cracked tiles from the pressure and from people walking on the roof to do it.
- Stripped surfaces. A jet washer can take the top coat off a tile, leaving it rougher and more open to water and frost.
- Water in the loft. Spraying a roof forces water up under the laps, where rain would never normally reach.
Does the moss even need to come off?
Often not. The NFRC says "moss on roof tiles is rarely a problem", and that removal is only needed when it blocks gutters or drainage points. A light covering is mostly cosmetic. Thick moss is a different matter: it holds water on the tiles and, when it slides off, fills the gutters, and an overflowing gutter can soak a wall.
Painting and coating
Some firms offer to coat or paint a roof after cleaning. The NFRC says claims about better thermal efficiency and longer tile life should be treated with caution unless the product has credible, UK-based, third-party accreditation. Ask for that before you agree to it.
How we clean a roof
- We look first and tell you honestly whether the moss is a problem.
- The moss is hand-scraped and wire-brushed off, working down the roof.
- It is bagged and taken away, not left in your gutters.
- Gutters and downpipes are cleared.
- We check the tiles while we are up there and photograph anything cracked or slipped.
- A preventative treatment can go on afterwards to slow the moss coming back.
The NFRC also suggests getting more than one quote for roof work and using a reputable roofing contractor. That is good advice for a roof clean as much as a re-roof, because the person cleaning your roof should know how to look after it.