Hello! I'm extending the house, and I have a new joist spacing of c/c 300. Planning to lay a 14mm solid birch floor on top, which will also be in the existing house. The question is whether I need 22mm chipboard underneath or if I can reduce the thickness? The new and old floors need to be contiguous, and it would be good to keep the height down in the new build; otherwise, I'm not sure how we'll manage the level differences...
