Building and isolating materials represent a huge burden for the environment after they are used. They take a long time to decompose through the process of weathering. Weathering, however, can be accelerated by using live organisms. We have tested the decay of building and isolating materials with indoor wood-decay basidiomycetes: Serpula lacrymans and Antrodia vaillantii. We have also used three unknown fungi that had been isolated from brick. We have named them Isolated fungus 1, Isolated fungus 2 and Isolated fungus 3. In order to grow, fungi need nutrients, water for metabolism, air, a moderate temperature, and an appropriate pH value. We have tested the most commonly used building and isolating materials, i.e. wood, brick, concrete, siporex, fibreglass batt, and extruded and expanded polystyrene. We have been growing the fungi in optimum conditions, so that they could grow all over the media. The first stages of decay are exhibited by mass and strength loss. We have used these methods to test degradation. Mass loss could be measured with all materials, and strength loss only with building materials. The results clearly show fungal influence both on building materials and isolating materials.