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

Honiton is about thirty five minutes from Exeter on the A30. Its long high street was rebuilt after eighteenth century fires and is famously uniform as a result, with Victorian additions behind and post-war and modern estates to the north and west.

A street rebuilt in one campaign is a gift to a surveyor. The buildings share a construction date, a roof pitch, a covering and a drainage arrangement, so a defect found on one is worth checking for along the row, and a comparison between neighbours is a fair comparison rather than an apples and pears exercise.

The characteristic problem on a continuous terraced frontage is what happens at the back and in between. Rear slopes drop into shared yards, valleys run between properties in different ownership, and rainwater from one roof passes across or beside another before it reaches a drain.

None of that is visible from the high street, and much of it is not visible from any single owner's property. A flight covering a run of buildings shows the whole system at once, which is what somebody dealing with a persistent damp problem in a party wall actually needs.

Coverings are natural slate and clay plain tile in the town, thatch on outlying cottages, and concrete tile on the modern estates. Plain tile is worth a note: it is a small unit with a double lap, it relies on the nibs and the battens, and when a batten softens the tiles slip in ones and twos over years rather than all at once.

The town is sheltered from the sea but exposed to weather coming over the Blackdowns, and the valley is prone to sitting fog that keeps roofs damp through the winter months. Sitting fog is an underrated agent of decay. It does not run off, it does not dry quickly, and it keeps a surface at a moisture level where organic growth thrives and mortar stays saturated.

The practical consequence for a survey is that a Honiton roof can look far worse in February than the same roof looks in July, and neither view is wrong. If a decision about money is going to be made from the report, the end of winter is when the evidence is most useful.

For a flight, sitting fog is simply a reason to reschedule. Visual line of sight is not negotiable and the imagery from a foggy morning is worthless anyway.

Dumpdon Hill and the Blackdown Hills rise steeply to the north and east, and the outlying properties up towards them are a different survey from the ones on the high street: detached, exposed, often thatched, and standing in wind that the town itself never feels.

Where a job is out of the town and up on the hills, the wind check matters and the local forecast is the one to trust. Where it is on the high street, the constraint is people and parked cars rather than weather.