Drone survey in Tavistock

Steep sites and tall stone chimneys are the defining feature of Tavistock's roofscape, and chimney stacks are the part of a building that takes the most wind loading and gets inspected the least. A stack that has lost its pointing or developed a crack in the haunching is a real risk as well as a leak path.

Photographing a stack properly means getting level with it, which is precisely what nobody can do from the ground. That single capability accounts for a large share of the work in towns like this one.

The Victorian planned centre in green Hurdwick stone is remarkable and it was built on mining money, with Georgian survivals among it and terraced miners' cottages in the surrounding villages. Delabole and natural slate dominate the roofs, with stone-bedded ridges.

That is durable construction, and the failures when they come are at the details rather than in the fields: bedding at ridges, flashing at abutments, and the interface between stone and slate where the two move differently.

Dartmoor is to the east and the prevailing south-westerly brings rain up the Tamar valley from the west, so the town is wet from both sides. Prolonged wetting is the main agent of decay and it favours organic growth on any shaded slope.

The World Heritage mining landscape around the town brings its own building stock: engine houses, historic industrial structures and converted mine buildings, all with roofs that are difficult to reach and often historically significant.

In the town the streets are tight and the ground is steep, so a take off position often has to be found rather than assumed. Outside it there is open country in every direction and no shortage of space.

Weather is the practical limit, as it is at Okehampton. A settled day here produces very good photographs because the flat light off the moor suits roof detail.

Around the pannier market and the abbey remains the buildings are old, close together and significant, and the roofs behind those frontages are frequently more complicated than the street elevation suggests. Later additions at the rear are common and they are where the awkward junctions live.

A PL19 town centre survey usually spends more time on the back of the building than the front for that reason. The front is maintained because everybody sees it, and the rear is where a lean-to meets a parapet meets a valley that was formed by hand a very long time ago.

The Tavy and the surrounding countryside give plenty of open ground just outside the centre, so approaches are straightforward once the take off position is settled.