Insulation Between Roof Rafters

Common rafter depths range from 100mm to 200mm.

Insulation between roof rafters.

Being lightweight they do not impose significant additional loads on existing structures. 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. 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. 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. This limits the maximum thickness of the insulation between the rafters to between 50mm and 175mm. 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. Modern u value targets mean installing insulation between rafters only is rarely a viable option.

Although there are many different. Unfaced insulation has no tabs and stays in place with friction between the fiberglass and the rafters. 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.