Drone surveys in Tavistock, flown by the surveyor who writes them

Tavistock is roughly an hour from Exeter, either over the moor or round it depending on the weather. It sits in the Tavy valley on the western edge of Dartmoor, with the moor rising to the east and the Tamar valley falling away west towards Cornwall.

It is one of the more distinctive towns in the coverage because of what it is built from. The Victorian planned centre is in green Hurdwick stone, built on mining wealth, and it is a coherent piece of townscape rather than an accumulation. That coherence is useful for a surveyor: buildings of one date and one material tend to reach the same problems at the same time.

Steep sites and tall stone chimneys make wind loading on stacks a live concern here rather than a theoretical one. A tall stack in a valley that funnels wind is carrying a lateral load its mortar was never asked to resist in a sheltered town, and the failure mode is not subtle when it comes.

Stacks are therefore a first order item on any survey in this town. What gets photographed is the flaunching, the state of the pointing at every course, whether the stack is plumb, the condition of the flashings and soakers where it passes through the roof, and whether anything has been added to the top of it. All of that is close to invisible from the ground and all of it is straightforward at eight metres away with a 100 megapixel camera.

Terraced miners' cottages in the surrounding villages carry the same detail at smaller scale, in rows, which again means a fault on one is worth looking for on the rest.

With Dartmoor to the east and the prevailing south westerly bringing rain up the Tamar, this is a very wet town. Natural slate and Delabole slate dominate, with stone bedded ridges and concrete tile on the later housing.

Delabole slate is worth a specific note. It is a Cornish slate with a long service life and a distinctive appearance, and it is often found on buildings where the rest of the roof has been renewed around it. Telling an original Delabole covering from a later replacement matters when advising on what to do next, and it is legible in high resolution imagery in a way it is not from the ground.

Stone bedded ridges have the same characteristic as the granite ones at Okehampton: heavy, durable, and worth close attention once the bedding starts to go.

Tavistock sits within the Cornwall and West Devon Mining World Heritage Site, and the abbey remains and the pannier market are at the centre of the town. Working around historic fabric of that significance is a matter of planning the flight so the aircraft is where it should be and the imagery covers what was asked for, without any need to be clever about it.

The practical effect on a survey is mostly about the answer rather than the flight: where a building is listed or in a sensitive setting, a report that says exactly which slates and which metres of pointing need attention is worth a great deal more than one that recommends a general overhaul.