Insulation Between Roof Rafters

Unfaced insulation has no tabs and stays in place with friction between the fiberglass and the rafters.

Insulation between roof rafters.

Then feed the rolled insulation under wires and pipe if either is present. This limits the maximum thickness of the insulation between the rafters to between 50mm and 175mm. 7 staple sheets of 6 mil plastic over unfaced insulation to create a vapor barrier. Place the plastic sheeting on top of the rolled insulation.

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. 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. Once up at roof level the between rafter boards can be cut accurately to fit the rafter spacings. The decision on which method to use is usually dependent on the sarking or underlay.

If your attic is going to be converted into livable space then you will need to insulate the roof rafters. Being lightweight they do not impose significant additional loads on existing structures. For rolled insulation place it between roof rafters. Install ventilation baffles into the space between the rafters before you install the insulation usually by stapling into place.

To create a warm pitched roof insulation such as kingspan kooltherm k7 pitched roof board should be fitted between and over the rafters. This roof type will require a breathable membrane like kingspan nilvent to be. We would always recommend having a breathable membrane in place between the tiles and the rafters too to allow the roof to breathe. Modern u value targets mean installing insulation between rafters only is rarely a viable option.

As this requires fitting insulation above the rafters the roof covering will have to be removed in order to fit the insulation. 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. Make sure it is flush against the wood as even a 1 inch gap can cause a 20 percent heating loss.