Drone roof survey in Topsham

Topsham's historic core is one of the more complicated stretches of roof in East Devon. The merchant houses along the Strand and Fore Street were built on Dutch trade money and they show it: curved and stepped gable ends, tall narrow frontages, and roof planes that meet at angles a modern builder would refuse to draw.

Behind the frontages, the roofs run back in a jumble of catslides, dormers, lean-tos and later additions, with valleys and secret gutters where one century's building meets another's. Slate is the dominant covering, with clay pantile in places and a lot of lead: valleys, soakers, flashings, and box gutters hidden behind parapets.

A high proportion of these buildings are listed. That changes what can be done about a problem, and it makes finding the problem early far more valuable than it is on a modern house, because the repair itself will need planning and patience.

Topsham sits on the water on three sides, and the air is damp and salt-laden all year rather than just during storms. That works on the metalwork first. Nails, clips, brackets and the fixings holding a lead flashing in place corrode faster here than a couple of miles inland, and a slate that has been sound for a hundred years slips because the nail behind it has finally gone.

The second effect is the wind. There is a clear run up the estuary from the south, so the seaward facing slopes take driving rain at an angle that finds the head lap of every slate. On the older buildings, where the slate is laid to a traditional lap and the underlay is either ancient or absent, that is exactly how water gets in without anything visibly being wrong.

Organic growth is the third. Damp air and shade mean moss establishes in valleys and along the bottom courses quickly, and moss in a lead valley is what turns a functioning gutter into a dam.

Much of the old town is unsuitable for a scaffold lorry. The Strand and the lanes off Fore Street are narrow, parking is contested, and several stretches have restricted vehicle access altogether. A scaffold that would be routine in a modern cul-de-sac becomes a logistics exercise with a permit attached.

This is where a flown survey earns its money in Topsham. The aircraft launches from wherever is lawful and reaches the ridge, the gable and the back slope without a single pole going up. For a listed building it also means nothing is tied to, drilled into or leaned against historic fabric.

The imagery matters for the next step too. A conservation officer looking at a proposal for repair work is easier to satisfy with photographs of the actual defect than with a description of it.