We just purchased a summer house, but will be insulating, and heating to make 365 day use. Will use single room MVHR or dMEV.   Floor insulation will be circa 150mm PIR with floating wooden floor.    Roof will be warm roof, EPDM, OSB, PIR, breathable membrane(?), Tongue and groove 18mm timber. Does this sound about right?   Walls, are 70mm solid wood, wanting to add 50mm of insulation to inside and plasterboard.  Can I just add this inside the timber walls, or do I