I am planning to build a garden room/man-cave 3x7 meters. The constructions will be timberframe fully insulated so it can be used in the winter time as well. To build the base I will dig 10 concrete posts with a 4x4 treated graded beam across them. On that I will lay 4x2 timber frame with 18 mm plywoood covering the top and 10cm celotex and vapour barrier underneath it. My question is how to protect the celotex floor insulation from critters (mouse, rats etc.)
I haven't any protection to the underside of the PIR in my man cave floor, didn't even think about it. It does sit a wee way above the ground however. I would say 100mm is overkill, I used 50mm which should be more than enough in both floor and roof.
Floor 50 is fine, walls, ceiling... Acceptable, but for what it's worth, I'd go at least 75mm, leaving 1"gap for a breather
Normal celotex is already protected from everything in either foil or fabric like coat. The only real worry- UV from direct light. Creatures etc... All the gaps filled up with foam- great insulation not just for the temperature, also sound, vibrations etc