Bathroom dry rot formed from moisture-fueled fungus

Correct insulation, installation is best protection from future damage

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Q: We have a bathroom on the ground floor, and we're replacing parts of the subfloor because they have dry rot. The subfloor is above concrete. Do you recommend putting insulation between the concrete and subfloor to make the floor warmer? If so, what kind? I know I don't want the kind of insulation that attracts mice. Also, the current subfloor is made of plywood. Should we replace the rotten parts with plywood or some type of water-resistant material? If so, what do you recommend? A: Although we're a little unclear about the structure of your bathroom floor, we recommend that you insulate regardless of how it's built. Use rigid foam insulation and replace the damaged wood members with pressure-treated material to minimize the possibility of future damage. From your description, we believe the plywood subfloor is fastened either to floor joists that are suspended above the concrete slab or to "sleepers" that are attached directly to the slab. In either case, a layer of insulation wi...