Insulation Between Roof Rafters

7 staple sheets of 6 mil plastic over unfaced insulation to create a vapor barrier.

Insulation between roof rafters.

This roof type will require a breathable membrane like kingspan nilvent to be. 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. 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. Make sure it is flush against the wood as even a 1 inch gap can cause a 20 percent heating loss.

For rolled insulation place it between roof rafters. We would always recommend having a breathable membrane in place between the tiles and the rafters too to allow the roof to breathe. To create a warm pitched roof insulation such as kingspan kooltherm k7 pitched roof board should be fitted between and over the rafters. If your attic is going to be converted into livable space then you will need to insulate the roof rafters.

Place the plastic sheeting on top of the rolled insulation. Then feed the rolled insulation under wires and pipe if either is present. Modern u value targets mean installing insulation between rafters only is rarely a viable option. Unfaced insulation has no tabs and stays in place with friction between the fiberglass and the rafters.

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. Common rafter depths range from 100mm to 200mm. Insulation can be installed between the rafters using a ventilated roof construction or an un ventilated roof construction.

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. Once up at roof level the between rafter boards can be cut accurately to fit the rafter spacings.