The short answer
By keeping the stones and renewing whatever holds them. The wooden pegs go first, then the battens beneath, then the ridge bedding, and the stone outlasts all three. A typical repair lifts the failed area, renews what carries the stones and relays them in their original order, adding matching pieces only where some have broken. Taking off an entire slope is the final option, and the survey tells you if that point has come.
A stone roof in the Cotswolds is a heavy, slow-moving structure, and its failures are slow too. Cotswold District Council published a technical guide to these roofs in 2000. It is dated, but the way a stone roof is built has not changed, and it remains the clearest account of the traditional method.
Q1.1How was the roof built in the first place?
The stone is oolitic limestone from two sources, Forest Marble and Stonesfield Slate. The first is split by hand soon after digging; the second needs frost to split it. Since quarried stone yields small pieces in far greater number than big ones, the largest stones, called cussoms, are laid along the eaves, doubled up, with followers above them and the shortest pieces near the top. The guide also notes that locals in the southern half of the district say tile, while the north says slate, so both words describe the same roof.
Q1.2What goes wrong with it?
Pegs rot, battens soften and stones slip. At stripping, the guide says, about half the stones have commonly perished, so a slope that looks fine from the lane may still hide a good deal of tired stone. It adds that annual scraping could give a roof twice the life, which makes the case for dealing with moss early rather than late. For smaller faults our roof repairs page explains how we scope a job.
Q1.3Where do swept valleys come in?
The traditional valley is formed from specially cut stones that curve gently into the roof. Lead valleys are cheaper, but the guide advises against them on a traditional roof. Our Cotswold stone roofing page explains how we rebuild them.
