What causes slipped roof tiles, and how should ridges be fixed?

Why do roof tiles and slates slip?

Because something holding them has given way, and on older roofs that is usually the nail. Slates and many tiles hang from nails or from nibs hooked over battens. Over decades, nails corrode and thin where they pass through the slate and batten until they snap, which roofers call nail fatigue or nail sickness. One slate slides out of line, then its neighbour, and a slope can shed several over a winter.

Other causes include battens that have rotted at the nail holes, worn nibs on old clay tiles, wind lifting tiles that were never nailed, and people walking on the roof without crawl boards. On a slate roof, one slipped slate is often the first visible sign that the nails across the whole slope are near the end of their life.

Slate is common on older houses around here. Historic England describes the mid-Victorian terraces on Dumfries Street in Luton as having a Welsh slate roof, and Central Bedfordshire Council's design guide notes clay ridge tiles on a slate roof as a common local feature.

What does BS 5534 say about fixing tiles?

That tiles and ridges must be mechanically fixed, not simply bedded or hung. BS 5534, the British Standard for slating and tiling, was revised in 2014, and the current version is BS 5534:2014+A2:2018. It covers normal re-roofing and repair work as well as new roofs.

Under the revision, every single lap tile has to be mechanically fixed, and mortar alone is no longer deemed sufficient to secure ridges, hips and verges. LABC Warranty sets it out plainly: all ridge and hip tiles must be mechanically fixed. Marley adds that perimeter tiles need double fixing and that higher assumed wind loads mean more fixings overall.

There is a caveat for old buildings. Marley notes that the standard's recommendations may not always be appropriate for old roofs, and that owners of historic buildings should consult the planning authority or a conservation body first.

What is a dry ridge system?

A set of clips, brackets and seals that holds ridge tiles in place without mortar. The 2018 amendment to BS 5534 brought in BS 8612, the standard for dry-fix ridge, hip and verge systems, and the amendment took effect on 1 July 2018 after a four-month transition.

Each ridge tile is screwed or clipped to a ridge batten or bracket, and a roll of breathable material seals the gap along the top of the slope. Nothing has to set, so the work depends less on the weather, and there is no bedding to crack and wash out later.

The trade-off is appearance. A dry ridge gives a neat, even line with visible end caps, which not every owner wants on an older house, and on a listed building or in a conservation area the traditional look may matter to the council.

Can ridges still be bedded in mortar?

Yes, as long as each ridge tile is also mechanically fixed. Bedding in mortar with a screw, clip or wire through every tile keeps the traditional look and meets the rule that mortar must not be the only thing holding it.

Cracked ridge mortar lets water in at the top of the roof and leaves ridge tiles held only by their own weight. Pointing fresh mortar over the cracks adds no fixing, so ask any roofer how the ridge will be held once the work is finished.

We explain both options on site with photographs and say which suits the roof and the street. Our roof repairs page sets out what a visit involves.

Do I need permission to refix tiles or a ridge?

Usually not. Planning Portal says repairs generally need no building control application if they affect less than 50 per cent of the roof and less than 25 per cent of the building envelope, and roof work that does not materially affect its external appearance usually needs no planning permission.

Listed buildings are the exception to watch. Central Bedfordshire Council says repairs can usually go ahead without listed building consent if they are done exactly like-for-like, so switching from a mortar ridge to a visible dry ridge system is worth checking first. Our guide to permission and regulations for a new roof covers the wider rules.

What does a fair repair cost, and how do I spot a doorstep offer?

National guides put small tile and ridge jobs in the hundreds, and a cold caller is the warning sign. Which? (22 October 2026) gives £75 to £400 to replace one to six standard tiles and £80 to £300 for a single ridge tile, excluding VAT. More figures are in our roof repair cost guide.

Central Bedfordshire Trading Standards names "repairing loose roof tiles" as a typical rogue-trader offer, and advises getting at least three written quotes and never paying the total in cash up front. Which? advises never dealing with a roofer who knocks on your door. Bromley's Trading Standards team has warned that doorstep roofers put scaffolding up at the earliest opportunity to create urgency, so be wary of anyone who says they can start today.

If you have signed at your door, the law gives you time. A contract made at home carries a 14-day cancellation period, and the trader must not start in that time unless you have made an express request on a durable medium, such as an email or letter. For a second opinion on a doorstep claim, our Luton roofing team can look at the roof and show you photographs of what is really there.

Questions people ask us

Is a dry ridge better than a mortar ridge?

Not always better, but it meets the fixing rules without relying on mortar and has no bedding to crack. A mortar ridge with every tile mechanically fixed also complies and keeps a traditional look.

Can one slipped slate wait until spring?

It is better not to leave it. The gap lets wind-driven rain reach the underlay and battens, and on an old slate roof one slipped slate can be the first sign that the nails across the slope are failing.

Someone knocked and said my tiles are loose. What should I do?

Do not agree to anything on the doorstep. Central Bedfordshire Trading Standards names loose roof tiles as a typical rogue-trader offer; get written quotes from roofers you have contacted yourself.

Do roof tiles have to be nailed now?

Single-lap tiles do. Since BS 5534:2014, every single-lap tile must be mechanically fixed, and ridges, hips and verges cannot rely on mortar alone.

Sources and further reading

• Numbers 45–55 Dumfries Street, Luton, educational images
• Design Guide SPD Chapter 5 Context and Identity, Central Bedfordshire Council, adoption date not shown
• BS 5534:2014+A2:2018 Slating and tiling for pitched roofs and vertical cladding, BSI Knowledge, pub. 28 Feb 2018
• More stringent roof fixing requirements now in force, 23 Mar 2016
• Tech update: roof tiling and underlays, the new BS 5534 standards, LABC Warranty blog
• Changes to the British Standard for Slating and Tiling BS 5534, Marley, undated
• What changes have there been to BS 5534 since the revision in 2014?, Marley, undated
• Building Regulations: Work to an existing roof, Planning Portal, undated (© 2026)
• Roof (planning permission / permitted development), Planning Portal, undated (© 2026)
• Do I need listed building consent?, Central Bedfordshire Council, undated
• How much do roof repairs cost?, Which? (N. Turner, V. Purcell), 22 Oct 2026
• Rogue traders, Central Bedfordshire Trading Standards, undated
• How to find a reputable trader, Which? (Tom Morgan), 9 Jul 2026
• Trading Standards alert: Roofing crime warning - Avoid unsolicited doorstep traders, Bromley Council, 26 Feb 2026
• Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013, Part 3 Right to cancel (revised, up to date to 9 Nov 2026)