Prevention of moisture damage by ventilation of the foundation.

Rising moisture from the ground has caused quite a lot of damage on foundations of Swedish buildings, in particular for the type concrete slab on the ground. Some of these constructions may be repaired by mechanical ventilation, for example below the floor or below the concrete slab , if there is an air-permeable layer below the slab. Summarized results from a few field studies and tests, which have been going on for a period of 2-3 years, are reported. Different methods with mechanical ventilation systems have been found to work quite well so far, i.e. under two and a half years of experience, provided that the air flow is well distributed over the whole area exposed to the ground. The temperatures immediatly below the slab is an important factor for the condensation. The time-dependent, two-dimensional thermal process in the ground, coupled to the convective heat transfer in the air-permeable layer, is simulated by a computer model. Preliminary results from the field measurements showed that it was necessary to take into account the heat of evaporation in order to get better agreement between calculations and field measurements. A few results from parameter studies are reported. The influence of air flow intensity, inlet air temperature, climate, thermal insulation thickness, thermal properties of the ground and moisture supply to the inside air and from the ground is discussed.