Oak pegs
What are oak pegs on a stone roof?
The short answer
Oak pegs are small, hand-cut pins of oak that hold stone slabs on a roof. The slab has a hole near its top edge, and the peg passes through it and hooks over a timber batten, so the slab hangs from the roof instead of resting on it. Oak is used because it is hard, durable and kind to the old timbers. When pegs rot or split, slabs slip.
How an oak peg holds a slab, what it looks like when pegs fail, and why a stone roof is repaired in oak rather than steel.
How one small peg carries a heavy slab
A stone slab is far too heavy to depend on friction. Near the top edge of each slab, the mason cuts or drills a hole right through the stone. A peg is slipped into the hole, and its shoulder catches on a batten, the narrow timber lath running across the rafters. The slab then hangs from the batten, while the slab in the course above laps over it to keep rain off both the peg and the hole.
It is a plain system, and it has kept slabs on Wealden roofs for centuries. A peg is not clever, but it suits stone. It takes the load in the right direction, it can be replaced singly, and it does not corrode. Because the pegs sit out of sight under the covering, nobody gives them a thought until a slab starts to slide, at which point the whole arrangement suddenly matters a great deal.
Why oak, and how a peg is made
Oak is hard and strong, stays serviceable through repeated wetting and drying, and keeps its shape in a cold, damp loft. It also grew in the woods of the Weald, so it was to hand when these roofs were built. Pegs are normally cleft or whittled from straight-grained timber, then trimmed so the shaft fits the hole closely without being forced, because forcing a peg can split the stone around it.
When we renew pegs we cut them to suit the hole in the slab in front of us, since holes in old stone are never uniform. Fit matters more than speed here. A peg that rattles lets the slab shift and wear itself into a slot, and one that is too tight can crack the slab as the timber swells in wet weather. A neat, snug peg is one of the small details that show a stone roof has been mended by someone who knows the material.
How pegs fail
Pegs have a shorter life than the stone around them. Years of damp can soften an oak peg until it shears, and a peg that has worked loose for decades can wear its hole into an oval. A cracked slab gives the peg nothing to grip. Rot and insects favour pegs in wet corners, such as under a valley or behind a chimney stack.
From the garden, the sign is a slab that has dropped below its row, leaving a gap above it and sometimes a paler patch of stone where it used to sit. From the loft, daylight between slabs, or old pegs lying on the ceiling joists, tells the same story. Our answer on why stone slates slip goes through the other causes, including the batten behind. A peg seldom fails alone: the timber it hangs from usually shares its age and its damp, so both need checking together. Finding one rotted peg and stopping there is how a roof ends up leaking again a season later.
Why we do not swap pegs for modern fixings
A modern nail or clip can look like an upgrade, but on stone it often is not. A steel nail driven through a slab can split it, and a hole in the wrong place leaves a weak point. Nails also rust where they sit in damp timber, then let go, and a loose stone slab is a heavy thing to have falling.
On a re-lay we look at each slope and decide, yet the starting point is the original method: oak pegs, sound battens, and every slab set in its own place in the diminishing courses. If the original fixing was a nail, we keep to what suits the roof, using stainless steel where a metal fixing is called for, and the quote records it. On a listed building, changing the way slabs are held may need a conversation with the conservation officer, and our guide to like-for-like consent sets out the position.
Mending a roof where pegs have gone
If only a few pegs have failed, the job is local. We lift the slabs over the fault, test the battens for rot, fit fresh pegs and lay the stone back in its original courses. A leak that returns to the same spot usually points at something hidden, such as a soft batten, so we look for that before closing the slope up again. Old pegs lifted out are kept to one side for you to see if you want, which is a simple way to judge how far gone they were.
When pegs are giving way across a full slope, patching is the wrong answer, because the next gale finds the next weak one. A re-lay makes more sense then, and our guide to repair or re-lay on a Horsham stone roof shows how that choice is reached. The price is a single total figure, confirmed in writing after the survey. If you would like the wider background, start from the Horsham stone roofing page.
Related questions
Pegs on stone slates
How can I tell if my stone roof is pegged or nailed?
Look from the loft hatch with a torch. Wooden pegs show as pale pins hanging over the battens, while nails show as dark heads or rust streaks. If you cannot tell, we photograph the underside during the survey and note which method each slope uses.
Can one failed peg be replaced without lifting much of the roof?
Sometimes, from outside, by easing up the slabs around it. We normally check the batten at the same time, because a peg often fails for a reason, and finding that reason is the point of going up in the first place.