Is that cold patch damp, a draught or a thermal bridge?

Start with a pattern, not a diagnosis

A cold patch on an internal wall can be associated with a thermal bridge, missing insulation, moving air or moisture. Furniture against the wall can also change the surface temperature. The camera cannot identify water directly: it detects infrared radiation and estimates the temperature of the visible surface.

Treat the image as a map of places to investigate. A sharp linear pattern may follow a structural element; a patch near a window junction may suggest a different question. Neither shape is sufficient to establish the cause.

Check the room and the conditions

Record whether the heating has been running steadily, whether sunlight has recently reached the wall and whether the surface is painted, tiled or reflective. Photograph the same area in visible light. A shiny fitting or glass surface may be showing a reflection rather than its own temperature.

Look at the building construction and repeat the observation under comparable conditions. One image taken after opening a window tells a different story from an evening survey after stable heating.

• Note indoor and outdoor temperature, heating history and the observation time.
• Record recent rain, wind and sunshine rather than guessing from the image.
• Check for furniture, curtains, vents and surface finishes around the patch.

Use another measurement to test the explanation

If moisture is suspected, an appropriate moisture investigation is needed alongside the thermal image. Moisture-meter readings also require interpretation for the material and instrument involved; one reading does not identify the source of damp.

A draught observation, a construction detail or a professional inspection can help distinguish competing explanations. The RICS, Historic England and PCA joint statement on traditional buildings stresses understanding the uses and limitations of several instruments, not just a thermal camera. Persistent or unexplained damp deserves a surveyor who can assess the building and ventilation together.

Keep a useful before-and-after record

If a repair follows, keep the visible photograph, original thermal file, weather notes and explanation together. Repeat the image with similar heating and weather conditions. Different automatic colour scales can make two rooms look dramatically different without proving a meaningful change.

Earth Notes is a useful example of why a second look matters: a professional review identified issues missed during an initial DIY survey. It is a record of one home, not a diagnostic rule for every UK property.