In Europe 10-15 % of the human population is sensitized to allergens of house dust mites (Pyroglyphidae). Population development of house dust mites is primarily influenced by water activity (aw) of the mite habitat. The availability of H20 (water-activity and relative humidity) in the niches of mites may correlate with the absolute humidity of the room air. Absolute humidity also plays a role in technical indoor climate classifications of Dutch and Belgian buildings. To investigate the effects of dry and humid room conditions on mite abundance, dust samples were taken in 14 living-rooms and bedrooms in the Netherlands. Mite numbers in floor and furniture dust from dry rooms (class II) did not exceed allergologically relevant no-sensitization thresholds of 10 mites/g of floor dust and 100 mites/g of dust from furniture. Climate classes might be different in the various spaces of a dwelling. Assessment of the indoor climate class should be done in the bedrooms as well as in the living-rooms. Results suggest that the technical classification of indoor climate is useful for future building design or when managing home sanitation.