The research projects of the Österr. Holzforschungsinstitut, Vienna, from 1975 to 1979, on 662 old roof structures in eight regions of Austria with diverse climates in altitudes from 160 to 1420 m sea-level. Several buildings and roofs were 300 and more years of age; included were castles, churches, farm-houses, town-halls, etc. The damage caused by insects, mold, and rot was evaluated in relation to all topographical and historical facts available. The results showed little decay above 700 m but much below; there was evidence of increasing damage with age, regional climatic factors and lack of impregnation. Primary and secondary forms of deterioration, instructions for protective measures and impregnation are given, including appropriate measures to be taken on windows and doors.