Insulation Between Roof 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 into.

Insulation between roof rafters. If your attic is going to be converted into livable space then you will need to insulate the roof rafters. Insulation can be installed between the rafters using a ventilated roof construction or an un ventilated roof construction. Unfaced insulation has no tabs and stays in place with friction between the fiberglass and the rafters. For rolled insulation place it between roof rafters.

Make sure it is flush against the wood as even a 1 inch gap can cause a 20 percent heating loss. Common rafter depths range from 100mm to 200mm. 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. We would always recommend having a breathable membrane in place between the tiles and the rafters too to allow the roof to breathe.

7 staple sheets of 6 mil plastic over unfaced insulation to create a vapor barrier. The decision on which method to use is usually dependent on the sarking or underlay. 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. This roof type will require a breathable membrane like kingspan nilvent to be.

Install ventilation baffles into the space between the rafters before you install the insulation usually by stapling into place. Being lightweight they do not impose significant additional loads on existing structures. This limits the maximum thickness of the insulation between the rafters to between 50mm and 175mm. Modern u value targets mean installing insulation between rafters only is rarely a viable option.

Then feed the rolled insulation under wires and pipe if either is present. 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.