Why cold walls make the room feel cold
We perceive warmth from air temperature and from the radiation of the surrounding surfaces. A cold wall draws radiant heat from the body. The room feels draughty even though no window is open. Many people then turn the thermostat up, which costs energy and does not solve the cause.
The dew point as a yardstick
At 20 °C room air and 60 % relative humidity, the dew point is around 12 °C. A wall surface just above it is still critical: by calculation, a surface at 13.0 °C has a relative humidity of about 94 %. As a rule of thumb, more than 80 % at the surface over a long period counts as a mould risk (DIN 4108-2).
What was measured
In the block of flats from 1960, the inner surface of the exterior wall rose from 13.0 to 19.7 °C after coating with 1 mm of PScoat, and the U-value fell from 2.63 to 0.096 W/(m²K). With the same room conditions (20 °C, 60 %), the calculated surface humidity falls from about 94 % to around 61 %. The example shows the order of magnitude; the address calculator works out your own building.
The right sequence
- Measure first: surface temperature of the exterior walls and corners, thermal image if available.
- Cold or damp wall? Condensation on cold surfaces is a temperature problem; moisture penetration from outside is a waterproofing problem.
- Coat on the outside where possible: the wall becomes warmer overall and remains vapour-permeable (V1). Where nothing is possible on the outside, PScoat ECI Interior takes care of the inside; for individual thermal bridges there is the thermal-bridge package (anti-mould).
- Treat thermal bridges such as reveals, corners and radiator recesses as well.
Evidence
CE marking to EN 15824 (declaration of performance PSC250T-2026-01) · TÜV NORD Verified Product, mark ID 141649 · U-value guarantee per package · Measurements · All evidence and case studies