Thermal imaging survey in Exeter

Exeter carries an unusual spread of construction ages within a couple of miles. The Georgian streets around Southernhay and the Victorian terraces of Heavitree, St Thomas and Newtown are solid wall, brick or stone through the full thickness with no cavity at all, so a thermal camera reading a cold patch there is reading heat moving straight through the masonry, not escaping through a gap that can simply be topped up.

The post-war ring at Wonford, Whipton and Beacon Heath is a different building altogether: cavity wall as standard, built to whatever insulation expectation existed at the time, which for most of that stock means a narrow, often unfilled cavity. Push further out to the newer development towards Pinhoe and Cranbrook and the construction changes again to modern insulated cavity or timber frame, where a thermal reading is usually checking for a workmanship gap rather than an absent material.

On the solid wall stock the pattern to look for is thermal bridging at party walls, window reveals and the junction between a main roof and a rear addition, because those are the points where the wall thickness or the roof structure changes and heat finds the shortest path out. The valley air here holds damp, and rainfall above the England average means a solid wall that is also holding moisture loses heat faster than the same wall dry, which is one reason a survey timed after a spell of wet weather needs to be read carefully rather than taken at face value.

On the cavity-built ring, the more common finding is a loft that has never been topped up to current depth, or a cavity fill that has slumped and left a gap along the top of the wall under the eaves, both of which show as a clear, sharply edged warm band rather than the more diffuse bridging pattern typical of the older stock.

A dawn flight over the tight Heavitree and St Thomas terraces works well precisely because the city holds its damp valley air overnight, giving a clean temperature difference by first light. In the conservation areas around the cathedral and the Quayside it also means nothing touches a listed elevation, which matters when the wall itself is the thing being read.

Exeter Airport sits east of the city with a flight restriction zone around it, so addresses towards Clyst Honiton, Sowton and the Airport Business Park are checked properly before a date is set rather than discovered on the morning of the flight.