Thermal Leak Survey, Newtown

Jo reported water getting into the property and asked us to find where it was coming from, along with a general condition assessment of the roof covering, the chimney stacks, the rear extension and the front bay window.

This was the first job we flew with a thermal sensor, and it is the job that made the case for carrying one.

A mid terrace Victorian house in Newtown, Exeter. Natural slate pitched roof, a chimney stack at each party wall, a rendered rear extension and a front bay window with a slated canopy.

Flown on a clear day with a slight wind. Two aircraft went up: one carrying the high resolution visual camera for the roof and detail work, and one carrying a radiometric thermal sensor for the leak detection.

All four elevations were inspected, with overhead passes and close telephoto imagery of every area of concern, plus a full thermal survey across the roof and the external walls.

Thermal does not see water. It sees temperature difference, and moisture held in a wall changes how that wall gives up heat. Read alongside the visual imagery, that difference is what points at a route in.

The rendered wall of the rear extension carried a crack running down from the upper section near the roofline. The thermal imagery showed a temperature anomaly in the area around that crack, consistent with moisture sitting in the wall behind it. That was assessed as the most likely source of the reported ingress, with the crack to be cut out and the area re-rendered.

The same wall showed a second problem. The render had been carried down past the damp proof course, bridging it, which lets moisture wick up the wall from below. That was reported alongside the crack as urgent.

Just as useful was what the survey ruled out. The slate covering on the main roof was in generally fair condition with no significant slipped, cracked or missing slates, and the thermal imagery across it showed an even distribution with no anomalies suggesting water was getting in through the roof surface. That took the expensive possibility off the table.

The rest went down in priority order: minor damage to a wooden window lintel and the pointing around it on the rear wall, lead flashing above the bay window that appeared to be surface mounted rather than chased into a mortar joint, weathered pointing along the main roof ridge, and minor pointing deterioration on both chimney stacks.