Insulation between rafters for roofs and lofts

The Department for Energy Security and Net Zero estimates that only 66% of lofts in UK homes have any form of insulation whatsoever. That leaves a large number of homes that are losing significant heat through the roof in the winter and letting too much heat in over the summer. Of the homes which have loft and roof insulation, the existing insulation is often not suitable.

One option for homeowners is to install insulation between the rafters. This is insulation that is placed underneath and in between the rafters, rather than installed on top of them as part of the overall roof structure.

The potential benefits of insulation between rafters include:

• Thermal efficiency – Installing insulation between rafters correctly can contribute to improved thermal insulation in your home.
• Reduced bills – The thermal efficiency gains can play a role in reducing household bills.
• Temperature regulation – Insulation between rafters can help your home retain heat in the winter and stay cooler in the summer if installed correctly.

Moisture management – Insulation between the rafters can contribute to improved moisture management in your loft space, reducing the risk of condensation, mould, mites and structural damage.

There are two main types of insulation that can be used to insulate between rafters in the roof of your home:

• Rigid board insulation – The boards are cut to size and inserted between the rafters snugly, then secured.
• Foil – An aluminium membrane that is applied to the rafters to create a temperature barrier between the loft space and the roof itself. Can be done in either a single- or multi-layer system depending on your circumstances.

Your insulation between rafters should also help the overall roof system meet the following standards at minimum:

• U-value of at least 0.35 W/m2K under Part L of the Building Regulations.
• A ventilation gap of at least 50mm between the insulation and the roof to create an air gap.