thermal imbalance

102D: mould, underfloor heating, door curtain, unducted vent into loft

This is a recently refurbished modern end-of-terrace bungalow with solid floor. Changes include double glazing with no trickle vents and underfloor heating.

Surveyor Tips:

  • Be careful with underfloor heating, it is prone to cold spots, which can result in high humidity.
  • Ensure loft insulation is evenly distributed.
  • Curtains trap humid air.
  • Make sure you check that bathroom fans are being vented out.
  • Kitchen extractor fans should be vented out.
  • Look to neighbours properties for things that work, or don’t work.
  • Bungalows are at greater risk of mould and condensation as the surface area exposed to cold air and ground is relatively high, similar to detached (semi-detached) property, extensions etc.

Survey follow-up question:


mould on ceiling above curtain
The primary concern is mould, such as here above the front door.

Mould grows where relative humidity exceeds 85%RH for 6+ hours. Excessive humidity results from insufficient ventilation, poor air circulation and a cold surface. See

I used a Protimeter damp meter in radio frequency mode to test for dampness above the doorway.

Radio frequency meters can’t differentiate moisture from other dense matter such as metal and concrete. They help trace damp in a normal, homogeneous wall. Readings below 300 REL indicate that a wall is dry below the surface. The meter reading was 177REL, I therefore conclude that the wall is dry.

We can exclude penetrating damp, e.g. from a defective gutter as the root cause of the mould.

Looking through a thermal imaging camera where blue is about 5 ̊C colder than yellow.

We can see distinctive heat loss above the curtain rail.

lack of heat
Looking at the floor through the thermal imaging camera.
Laser thermometer
The temperature of the wall surrounding the door opening was 12.7°C.

There are three components to the low temperature around this door opening:

1) inevitable heat loss around the opening of the door window,
2) less heat since the underfloor heating does not extend to the door, and
3) the curtain is stopping warm air from circulating around the door.

insulation imbalance
The loft insolation had been moved away from the eaves, presumably when electrical wiring was recently laid.

I moved to the installation back in under the eaves, to insulate the loft above the front door.

bathroom insulation
There is a similar story in the bathroom.

Mould is growing across the bathroom but especially in the cold corner of the ceiling.

thermal image showing loss of heat into the corner

Leave a Comment

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.