Krypgrund

A foundation with air under the floor, sensitive to moisture

A krypgrund (crawl space foundation) is a foundation where there is an air space between the ground and the house floor, rather than a slab cast straight onto the ground. That makes it easy to get into and inspect, but it also leaves it more exposed to moisture. The most common type, a krypgrund ventilated with outdoor air, is especially moisture-sensitive.

Things get sensitive at around 75 percent relative humidity

Moisture can come from the ground, from surface water, from ground moisture and from the outdoor air itself. In summer, warm outdoor air flows into the cooler foundation and cools down, and the relative humidity rises. Once it climbs above roughly 75 percent, the conditions are right for mould and rot fungi to start growing. That is why a krypgrund that smells stuffy or feels damp is worth taking seriously.

Ask for a look in the foundation before you bid

Moisture and microbial growth in the crawl space can travel on into the indoor air through joists and walls, so this is not only a problem under the floor. None of this means a krypgrund is a bad thing, plenty of houses with one are in good shape. But let a besiktningsman (home inspector) check the foundation for moisture and mould before you go further, so you know what you are buying.