Heating and ventilating apartments is indispensable - especially in new buildings or renovated, newly insulated houses - as an improved thermal insulation and air-tightness can easily lead to undesired humidity damage if not in proper relation to other factors. Mildew formation is the most common symptom in this context. This booklet shows how to avoid such "dwelling damage" and unnecessary conflicts between landlords and tenants on the one hand and owners and architects or craftsmen on the other hand.