Building Dampness Calculator


Select the w-Value
Absorption of liquid
water per m2 per day*
49 g/m²d
Select the Sd-Value
Release of watervapour
per m2 per day* (V-value)
At 23oC - normal climate
2100 g/m²d
At 3oC - autumn winter
525 g/m²d

Next to service life protecting buildings from dampness is one of the most important criteria in the selection of masonry coatings. This factor should always be considered when specifying paint.

Building dampness is the ratio between water penetrating through a coating (Water absorption) and the quantity that can be given off (water release)

Rule of thumb: the water release (through water vapour diffusion) must be larger than the water absorption (through rain, fog or condensation), otherwise substrate damage can occur.

The relevant data for accessing façade paints are the so-called w-value (water absorption) and the Sd -Value (water release). The water reception is measured on sample bodies with plaster and paint coats, the water duty, over water diffusion, is measured on paint coated ideally permeable glass chips. Both figures are calculated in accordance with international standards.

This calculator provides a simple comparator of these technical measures. The result shows the quantity of water per m2 area that can penetrate in a day or as the case may be in form of water vapour, which can be released.

IMPORTANT: the water absorption is basically independent of the temperature. The water release in the drying phase on the other hand is dependent on the ambient temperature. In a temperature decline of 10 the water release reduces by approximately half and in a decline of around 20 to a quarter.

Water absorption and water release (drying) through vapour diffusion on façades are complicated physical processes. The calculator gives a simplified interpretation of these complicated effects while also providing important indications for assessing façade paints.