Roof Insulation Board Between Rafters

The usual way to do this is by inserting rigid insulation boards between the rafters.

Roof insulation board between rafters.

In this blog post we will be looking at insulating pitched roofs and why putting insulation just between the rafters isn t a viable solution. As this requires fitting insulation above the rafters the roof covering will have to be removed in order to fit the insulation. Rafter boards are fastened to the ridge board at the peak and the top plate where they join the wall. 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.

Once up at roof level the between rafter boards can be cut accurately to fit the rafter spacings. To get the required 270mm thickness of insulation you may have to insulate over the rafters as well using insulated plasterboard. Check out our how to video at the link below. 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.

Being lightweight they do not impose significant additional loads on existing structures. We would always recommend having a breathable membrane in place between the tiles and the rafters too to allow the roof to breathe. The boards creating the slope of the roof are wider than lumber used to build trusses 2x8s 2x10s and 2x12s are most common in rafters vs. Fit the cut quinn therm qr insulation boards tightly between the rafters with the quinn therm branded side facing into the building.

This roof type will require a breathable membrane like kingspan nilvent to be. The general advice we give is that you should always insulate between and above the rafters or between and under the rafters on our u value calculator we don t give an option for putting insulation between 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. Modern u value targets mean installing insulation between rafters only is rarely a viable option.

In finished space insulation is placed between the rafter boards and drywall or other material is fastened to the face. Measure the space between the rafters where the insulation will be placed and cut the insulation boards marginally wider than the space to ensure a friction fit upon installation. They should be cut to exactly the right size so they fit snugly and don t allow any draughts through.