Insulation Between Roof Rafters

Modern u value targets mean installing insulation between rafters only is rarely a viable option.

Insulation between roof rafters.

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. 7 staple sheets of 6 mil plastic over unfaced insulation to create a vapor barrier. For example if the space beneath the rafters is going to be used for a living area then you will need to insulate the roof rafters.

Common rafter depths range from 100mm to 200mm. Consider using high density r 30 batts which are as thick as r 25 batts but fit into 2x10 framing. Whether you need to insulate your roof rafters will depend on what you intend to do in the space directly beneath the rafters. Where the insulation does not fill the total rafter depth the low emissivity foil facings can gain additional thermal benefit from the air spaces they face.

A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel. Being lightweight they do not impose significant additional loads on existing structures. This generally would not be a sufficient thickness to achieve the u values required to meet building regulations and more insulation would need to be added. Unfaced insulation has no tabs and stays in place with friction between the fiberglass and the rafters.