Why are Cotswold stone slates hung on oak pegs?

Turn a stone slate over and the principle is simple. A hole is drilled close to the head of the slate. A wooden peg goes in, wide enough at one end that it cannot slip through, and the peg rests across a timber batten, the horizontal strip fixed over the rafters. The slate dangles from it. Cotswold District Council's 2000 technical guidance says the peg was usually cleft oak, and that a slate might hang from one peg or occasionally two.

Nothing is clamped. The slate sits on the course beneath it, is overlapped by the course above, and the peg only stops it from sliding down. That suits a stone that is both heavy and irregular. The council's note gives the roof's weight as about 1,000 kg for every 10 m², and no two slates are exactly the same thickness. A rigid fixing would load a hand-split edge until it cracked. A hanging fixing allows each piece to bed down on its neighbours.

Oak was the sensible choice for makers using what grew nearby. It is dense, it stands up to rot better than most native timbers while it stays dry, and a peg cut from it is hard enough to carry a wet slate. Cleft means the timber is split along the grain instead of sawn across it. A split peg follows the natural lines of the wood, so its fibres run the full length and it keeps its strength.

The same logic explains how a pegged roof ages. Pegs seldom fail in the open, since they live in the dry space under the stone. They give out where water has been seeping in for a long time, or where a slate has slipped and left the batten bare. On a survey the pegs rank among the earliest items on our checklist, from the slope and from the loft, because a tired peg is the early sign of a slipped course. Our answer on how long a stone roof lasts sets that against the roof's whole life.

The batten is the peg's partner. Each course hangs from its own batten, and the gap between battens follows the length of the slates in that course. Because the stone is sorted into diminishing sizes, with the longest at the eaves and the shortest towards the ridge, the batten spacing narrows up the slope too. That arrangement is laid out in our guide to diminishing courses.

Hanging from battens, rather than lying on a continuous board, lets air move beneath the stone. A pegged roof is a drained and ventilated build, and a leak at a single slate tends to show as a drip rather than soaking into a deck. The cost is that the pegs and battens are the working parts. When they go, the stone above is still sound but has nothing to hold it.

What re-laying does about it

When a slope is stripped, the stone is sorted by size and quality, the old battens are judged, and fresh pegs are cut for the holes that are still sound. The process is covered in the relaying guide.

You will sometimes hear that metal fixings can replace oak. They can, and some repairs have used them. A roofer who proposes one should explain why, which metal, how it grips the slate and whether it suits the building. Stone is brittle, and a fixing driven in tight, or one that corrodes and swells, can split a slate that has survived centuries. The whole point of an oak peg is its gentleness.

Where the house is listed, or stands inside a conservation area, the choice of fixing can interest the planning officer as much as the choice of stone, since it touches the historic fabric and decides how the roof can be mended later. We would ask Stroud District Council's planning team before swapping traditional pegs for anything else on a protected building. On an ordinary home the same like-for-like thinking holds: if the roof hung on oak, we price the repair on oak first, and any alternative is a decision for you to take once you have heard the trade-offs.

From the ground, watch for slates that have sagged a few centimetres below their neighbours, gaps in a course, or a lumpy tail line where a row used to run level. In the loft, watch for chinks of daylight between slates, loose pegs lying on the insulation or boards, and battens that are dark, soft or crumbling. Any of these says the fixings are giving up somewhere, even when the stone looks perfect.

We photograph what we find, then send a written quote covering stripping, pegs, battens, stone and scaffold. After any repair we leave you a ten-year written guarantee on our own workmanship. Pitch is part of why a pegged roof holds together, and why stone roofs are so steep follows on from this. The old names for the slates are on the slate names page, and the full service is on our Cotswold stone roofing hub.