A common type of foundation for family houses in Northern countries is crawl spaces, where mould and moisture are a common problem for a large share of these. In this study, measurement in a crawl space located in a subarctic climate has been performed for over a year. Calculation and prediction of the climate inside the crawl space are performed both for the experimental case with a dehumidifier and a theoretical case without a dehumidifier. The results show that it is not necessary to measure at several points in the crawl space since the difference between the measurement points is small. The relative humidity is below the critical in the investigated crawl space during the whole year when a dehumidifier is used and therefore is no risk for mould growth. Prediction for a naturally ventilated crawl space with ACR of 1.5 shows that mould index will reach almost four and very close not to reach zero between different years, which indicates that mould index could start to increase between the years and cause problems.