Thermal imaging has become a common part of roof surveys. The pictures look convincing, with bright and dark patches across a roof or ceiling. But a thermal image is easy to misread. It shows differences in surface temperature, and there are many reasons a surface can be warmer or cooler than the area around it.
This guide explains what a thermal camera can show on a roof, why conditions matter so much and how findings are checked.
What a thermal camera measures
A thermal camera picks up infrared energy given off by surfaces and turns it into an image. Warmer areas look different from cooler ones. It doesn’t see through a roof, and it doesn’t see water. It shows patterns in surface temperature.
Those patterns can point to things like:
- trapped moisture in a flat roof build-up
- missing, slipped or damp insulation
- heat escaping through gaps in the roof or loft
- wet areas on ceilings from a leak above.
Why conditions matter
Wet insulation holds heat longer than dry insulation. That difference is what makes trapped moisture show up on a flat roof. Fluke’s guide to infrared roof inspection explains how this works (Fluke on infrared roof inspection). Thermal imaging on roofs works best:
- after a sunny day, when the roof has had a chance to warm up
- when the roof surface is dry
- when there’s little wind.
Rain, standing water, wind and cloud can all hide or distort the patterns. Some roofs and finishes are also harder to read than others. The weather on the day decides how much the images can show, and the report says so.
Sometimes the honest answer is that conditions on the day weren’t right for useful thermal images. When that happens, the report should say so plainly rather than read too much into unclear pictures.
Want a roof surveyed? We cover London and the South East, with written reports and photos from £150 including VAT. Book a survey or call 07833 053749.
What it can’t do
A thermal image on its own isn’t proof of a leak. Things that can look like a problem include reflections from shiny surfaces, shadows from nearby buildings, changes in materials, extra layers of felt from old repairs, and pipes or services under the roof. Pitched roofs with slates or tiles are especially hard to read from outside, because the air gap under the coverings evens out temperatures. From inside, a thermal camera can still help show damp patches on ceilings and gaps in loft insulation.
Checking findings with moisture readings
Because a thermal camera shows temperature, not water, findings need checking. Moisture readings taken at the suspect areas, and at dry areas for comparison, help confirm whether a pattern is damp or something else. A careful report says which areas were confirmed, which are only suspected and what would be needed to be sure, such as opening up a small area.
When thermal imaging is worth it
It’s most useful when:
- a flat roof leaks but there’s no obvious hole
- you want to know how much of a flat roof has wet insulation before deciding on repair or replacement
- ceilings show damp but the source isn’t clear
- you suspect gaps in loft insulation.
Our thermal roof survey starts from £400, including VAT, and thermal imaging is included in our Premium Survey. For active leaks, see our roof leak investigation.
Quick answers
Can a thermal camera see a leak through the roof?
No. It shows surface temperature differences. Those can point to a leak or trapped moisture, but they need checking with moisture readings.
Does it work in the rain?
Not well. Rain and standing water hide the patterns. A dry roof surface and little wind give the best results.
Is thermal imaging better than a visual survey?
It adds to a visual survey; it doesn’t replace it. Most defects are still found by looking carefully at the roof and roof space.
Related services
More advice
- How Electronic Leak Detection Works
- Why Roof Leaks Are So Hard to Find
- Flat Roof Problems: Ponding, Blisters and Splits
- Condensation or a Roof Leak? How to Tell
- All advice
This guide is general information about roofs and roof surveys. It isn’t legal, insurance or structural engineering advice; for those, speak to a suitably qualified professional.