Drone roof survey in Okehampton

Okehampton sits at the northern foot of Dartmoor with Yes Tor and High Willhays, the highest ground in southern England, immediately to the south. Atlantic air is forced up over that moor right on the town's doorstep, which is why rainfall here is in a different bracket to the rest of the county.

Roofs in Okehampton are wet more of the time than roofs almost anywhere else in Devon. That drives everything: heavier organic growth, more freeze and thaw damage to mortar, faster corrosion of fixings, and less time for a roof to dry out between one weather system and the next.

Driving rain is the other half of it. Rain arriving at an angle rather than vertically will find the head lap of a slate, get behind a flashing and push back up a shallow pitch, and Okehampton gets a great deal of it.

The building stock reflects where it is. The town centre is granite and slate, solid and heavy, with stone bedded ridges on the older buildings. Out on the moor edge, the farms and longhouses are the same materials but far more exposed, sitting alone on open ground with nothing to shelter them.

On those buildings the wind loading is severe and constant rather than occasional, and the details that matter are the ones on the windward gable: the verge, the ridge end and the first course of slate above it.

The post-war and modern estates around the town are conventional concrete tile, and they suffer the standard problem of a specification chosen for a milder site being used somewhere considerably harsher.

Booking a survey here needs more flexibility than it does in East Devon, because the number of days when the wind is low enough and the rain has stopped is smaller. That is the reality of moor edge flying and it is better said in advance than discovered on the day.

In practice it means holding a couple of possible dates and taking the one the forecast supports. Moving for weather costs nothing, and a survey flown in marginal conditions on Dartmoor's edge produces imagery that cannot carry a decision.

The upside is that when the conditions are right, one visit covers a farmhouse, its outbuildings and its barns in an hour, on a site where scaffolding across a moorland yard in winter would be a serious undertaking.

Okehampton Castle and the ruins around it sit on the edge of the same exposed ground as the moorland farms, a reminder that this stretch of Devon has always been hard on masonry as well as roofs. Out towards Meldon and the viaduct, isolated properties on the approach to the moor take the same driving rain and wind loading as the farms further out, and the same logic applies: one flight covers a house and its outbuildings without anyone parking a scaffold lorry on a single track lane.