Insulation Between Roof Rafters

To create a warm pitched roof insulation such as kingspan kooltherm k7 pitched roof board should be fitted between and over the rafters.

Insulation between roof rafters.

This limits the maximum thickness of the insulation between the rafters to between 50mm and 175mm. Then feed the rolled insulation under wires and pipe if either is present. Common rafter depths range from 100mm to 200mm. 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 into.

7 staple sheets of 6 mil plastic over unfaced insulation to create a vapor barrier. Being lightweight they do not impose significant additional loads on existing structures. This roof type will require a breathable membrane like kingspan nilvent to be. When you use solid insulation board to create a warm loft the key thing to remember is ventilation you must keep a 50mm gap between the roof and the rigid insulation board.

As this requires fitting insulation above the rafters the roof covering will have to be removed in order to fit the insulation. Install ventilation baffles into the space between the rafters before you install the insulation usually by stapling into place. Place the plastic sheeting on top of the rolled insulation. Modern u value targets mean installing insulation between rafters only is rarely a viable option.

The decision on which method to use is usually dependent on the sarking or underlay. Make sure it is flush against the wood as even a 1 inch gap can cause a 20 percent heating loss. 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. We would always recommend having a breathable membrane in place between the tiles and the rafters too to allow the roof to breathe.

For rolled insulation place it between 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. If your attic is going to be converted into livable space then you will need to insulate the roof rafters.