Cleaning moss off a listed or conservation-area roof: what's allowed

How many listed roofs are we talking about?

What the law actually says

The test comes from section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990. Consent is needed for works that would "affect its character as a building of special architectural or historic interest". As BuildingConservation.com points out, the Act makes no reference to consent for repairs, and minor like-for-like repairs using the same materials and techniques are generally unlikely to need it.

The consequences of getting it wrong are serious. Carrying out works that affect a listed building's character without consent is a criminal offence. We're roofers, not planning advisers, so where there's any doubt about a job, we'll suggest you check with the council's conservation team first.

Which kinds of work are likely to affect character

Conservation areas without listing

If your house is in a conservation area but isn't listed, cleaning the roof doesn't need permission. What can need permission is a change to the roof's materials or details, depending on any Article 4 direction that applies. Trees are a separate matter: in a conservation area, most tree work needs six weeks' notice to the council, which our guide to trees over your gutters explains.

The right way to clean an old Chilterns roof

• By hand. The Chilterns Conservation Board prefers moss brushed off by hand to power jets or chemicals.
• Never with a pressure washer. Marley warns that high-pressure water damages tiles, "particularly older or more delicate ones".
• Without walking on the tiles. Old clay cracks underfoot, so work should be done from roof ladders.
• Treatments only by agreement. Historic England's research on historic masonry found that common biocides are "proven to be harmful to the environment and wildlife" and that their longer-term effect "has been observed to be extremely limited".
• With matching materials ready. The Chilterns standard is a plain clay tile, usually 265 x 165 mm, in dark orange or red, and the Conservation Board says at least 40% of tiles from an old roof can usually be reused.

Bats and birds on old roofs

Old roofs near woodland can be home to bats. The National Federation of Roofing Contractors reminds roofers that all bats and their roosts are protected by law, even when a roost is empty, and that work should stop if bats are found. Nesting birds are protected too: the RSPCA notes that a nest can't be damaged or moved while it's being built or in use, which is one more reason to clean old roofs in winter.

Questions to ask any roofer before they touch a listed roof

• Will you clean it by hand, and will anyone use a pressure washer? The second answer should be no.
• What treatment will you use, if any, and is it approved for use in Great Britain?
• How will you get onto the roof without standing on the tiles?
• If a tile breaks, will you replace it with a matching old tile?
• Will you photograph the roof before and after, and tell me if anything needs consent?

How we work on listed and historic roofs

We clean listed and historic roofs by hand, from roof ladders, with no pressure washer and no treatment unless you've agreed to it. We photograph every slope before and after, flag anything we think might need consent before we start, and replace any broken tile like for like.

Written by Hawkes Roofing, roofers based in St Albans who clean and repair historic roofs by hand across Amersham, Beaconsfield and the Chalfonts. Last reviewed 26 October 2026.