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

Tiverton is about half an hour from Exeter, built where the Lowman joins the Exe on steep sided ground. The town centre sits low and the residential streets climb sharply north and west, which is the single most important thing about surveying here.

The Exe valley at this point is notably wet, well above the Devon average. Combine that with the height differences across the town and you get a place where two properties in the same postcode can be having quite different experiences of the weather.

Steep sites mean many roofs sit above the general roofline of everything around them, and wind loading is worse in that position. A house halfway up a slope is sheltered by the ones below it; a house at the top is sheltering everything else and taking the load for all of them.

That shows up in a survey as ridge and verge work. Mortar bedded ridges on the high streets go before the same detail lower down, hip tiles work loose, and verge pointing cracks and then falls in sections. Where a client has properties at different heights in the town, the comparison between them is often the most useful thing the survey produces.

The stock runs from a medieval and Georgian centre through Victorian mill workers' terraces to extensive post-war estates and large modern development on the eastern edge. The mill terraces are the classic aerial survey case: long rows, shared valleys, party wall abutments, and rear slopes reachable only from someone else's garden.

Alongside the natural slate, clay plain tile and concrete tile, there is stone slate on older outlying buildings. It is heavy, it is laid in diminishing courses, and it is expensive to put right, which makes an accurate assessment of how much of it has actually failed worth having.

The difference between a roof that needs twenty units re-fixing and one that needs stripping and relaying is a large sum of money, and it is very hard to establish from the ground. At full resolution from a few metres away it is a matter of counting.

Tiverton Castle, the Grand Western Canal, Knightshayes Court and Blundell's School give a sense of the range of building here: fortified stone, canal era engineering, a substantial Victorian country house, and institutional buildings with large complex roofs.

Institutional and estate roofs are a strong case for aerial work because of their scale. A building with a hundred metres of parapet gutter and half a dozen roof planes cannot sensibly be inspected any other way without a great deal of scaffolding, and the report needs to be systematic rather than impressionistic to be worth anything.