Insulation Between Roof Rafters

Whether you need to insulate your roof rafters will depend on what you intend to do in the space directly beneath the rafters.

Insulation between roof rafters.

Unfaced insulation has no tabs and stays in place with friction between the fiberglass and the rafters. A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel. You can also add rigid foam insulation under the rafters which adds r value and eliminates thermal bridging through wood rafters. Once up at roof level the between rafter boards can be cut accurately to fit the rafter spacings.

7 staple sheets of 6 mil plastic over unfaced insulation to create a vapor barrier. Modern u value targets mean installing insulation between rafters only is rarely a viable option. Although there are many different. It allows insulation to be installed in a watertight roof either after the roof covering has been fixed on a new build or without disturbing an otherwise sound existing roof covering as part of a renovation.

Consider using high density r 30 batts which are as thick as r 25 batts but fit into 2x10 framing. Common rafter depths range from 100mm to 200mm. This limits the maximum thickness of the insulation between the rafters to between 50mm and 175mm. Being lightweight they do not impose significant additional loads on existing structures.