I am building an insulated outbuilding of about 20 square meters, where half will be a storage space for outdoor furniture, garden tools, etc., and the other half will be a workshop. It will be heated to around 16 degrees.
The outer roof consists of tongue and groove boards, felt, battens, and sheet metal. The inner ceiling will be plywood, with 20 cm of insulation on top of that, leaving about a decimeter of air space between the insulation and the outer roof.
There is no ridge ventilation, but it is open at the eaves on both sides.
I was thinking of creating an air gap against the outer roof with oil-hardened hardboard, but should I lay it from eave to eave, which means there will be no ventilation of the space between the hardboard and the insulation, or should I not extend the hardboard all the way up and leave an opening at the ridge?
If you leave an opening, will the air movement make the insulation less effective?
