Why Slates Slip — and Why It's Often Fixable

A slipped slate is one of the most common problems on a period roof, and it usually looks worse than it is. Slate itself is remarkably durable — a good Welsh or Westmorland slate can last well over a century. What fails first is the fixing. Traditionally, slates were hung on timber battens and held with two nails, and those nails were often mild steel. After 60 to 100 years of wet-and-dry cycles, the nails corrode, lose their grip, and the next strong gust lifts a slate out of position.

That's good news for you. If the slate is still intact, and the batten behind it is sound, it can often be rehung the same day. The trick is knowing which of those conditions applies before you commit to a repair — or to a full re-roof you may not actually need.

Safety and Consent Before You Start

Roofing is one of the most dangerous trades in the UK, and the Working at Height Regulations apply to homeowners and contractors alike. Be honest about your limits:

• Only consider working at gutter level on a single-storey extension or garage, from a properly footed ladder with a stand-off bracket.
• For anything higher, use a scaffold tower or a roof ladder with crawl boards — never rely on a ladder simply leaned against the eaves.
• Never walk directly on slates. They are brittle, they crack, and they give way without warning.
• Avoid wet, frosty or windy days entirely. Slate is slick when damp.

If your home is listed or sits in a conservation area, check with your local authority before changing materials or methods. Like-for-like repairs are usually fine; swapping materials is not.

Refixing a Slipped Slate, Step by Step

Assuming the slate has slipped rather than shattered, you've got two realistic options.

If the nail holes are sound: gently lift the slate above, slide the slipped slate back into its course, and re-nail through the existing holes into the batten. Use copper or stainless steel nails — they will outlast the building. Make sure the slate sits level with its neighbours and that the headlap, the overlap with the course below, is restored.

If the nail holes are broken or the slate is cracked: a period roofer will use a slate hook, or a tingle — a strip of copper or lead dressed over the slate and fixed to the batten above. The hook holds the slate without needing a nail hole. This is the traditional repair and, done properly, it lasts decades.

To fit one:

• Slide the hook up behind the slate and hook it over the batten.
• Dress the tail flat across the face of the slate.
• Check the slate sits flush with the courses either side.
• Reclaimed slate of a matching size and colour is preferable to a modern import on an older roof.

Check the Battens and Underlay While You're There

Once a slate is off, you have a rare view behind the roof covering — use it. Run a hand along the batten. It should feel dry and firm; if it crumbles, or a nail pulls out with no resistance, the batten has rotted and replacing one slate will not solve the problem.

Look at what sits below the battens too. On older roofs that's often roofing felt or bituminous felt, and on many Scottish properties, sarking boards. Tattered felt means water will reach the battens and the rafters. Also check flashings around chimneys, valleys and abutments while access is easy — lead that has cracked or lifted is a common source of damp, and it is far cheaper to sort now.

When a Single-Slate Repair Isn't Enough

Individual refixes make sense for one or two slates. Beyond that, think harder about the roof as a whole. The signs it is time for a proper survey:

• Slates slipping across the entire roof rather than in a localised patch — that points to widespread nail fatigue.
• Crumbling battens found in more than one spot.
• A sagging or wavy roof line, which suggests trouble with the rafters or battens.
• Damp patches on ceilings or in the loft after driving rain.
• A roof that has been patched repeatedly with mortar and mastic.

In these cases, re-slating in sections — sometimes just one elevation — is often the sensible middle path. The slates themselves may be perfectly reusable; you are replacing the battens, underlay and fixings underneath them.

Keeping On Top of a Period Roof

Old roofs reward a little attention. Twice a year, ideally in spring and autumn, check from ground level with binoculars: look for slipped or missing slates, moss build-up, blocked gutters, and anything loose at the ridge. Clear the gutters before winter arrives. Keep a written note of repairs and dates, and photograph anything that worries you. A roof that is inspected and maintained will often outlast its owner — and if you do need to call someone in, an accurate description of what has happened will get you a quicker, cheaper answer.