I am converting an old outhouse into a bedroom. This is a single room building apart from a small enclosed WC within the room. It is 13’x13’ with a solid double brick wall and slate roof. There is a door entrance, an opening window in the WC and an opening skylight in the vaulted roof. 4x2 stud walls with 50mm insulation foil tape and plasterboard. There is an automatic extractor for the WC and a switched extractor above a bath which is in the bedroom area. I have air bricks to vent the gap between the brick and stud walls. My question is, do I need ventilation into the room from outside? Thanks in advance.