Roof insulation at rafter level

Roof insulation at rafter level

The insulation of a pitched roof at rafter level (as opposed to joist level) enables maximum utilisation of roof space in both new and refurbished residential and non-residential buildings.

Even if that space is not immediately intended for use, the requirement for greater energy efficiency in all types of building demands the installation of efficient insulation.

While the precise configuration of a rafter level insulation system will depend on the particular requirements of the buildings, the basic principle involves the installation of glass wool between the rafters, following the pitch of the roof. As well as maximising thermal efficiency, this will also improve the acoustic performance of the roof.

If the depth of the rafters enables the installation of sufficient insulation to meet the required thermal performance, this ‘between rafter’ insulation is the simplest solution and offers the addition benefits of eliminating the need for special fixings and allowing easy installation from inside the roof space.

However, when ‘between rafter’ insulation is not enough, insulation boards can be installed either above or below the rafters.

Boards installed above the rafters keep the rafters within the insulated building envelope, eliminating the possibility of condensation forming on them. This method is usually used when low U-values are required but the use of internal lining would impact on headroom. Insulation boards installed below the rafters enable low U-values to be achieved even with shallow rafters.

Benefits of Mineral Wool

  • Value for money - more cost effective than any other material available
  • Thermal performance - compression fit minimizes gaps at joints
  • Environmental - uses recycled material, zero ODP & GWP, BRE Green Guide A+ to B
  • Fire properties - non-combustible and A1/A2 Euroclass fire rated
  • Easy-to-fit - simple installation process, covers large areas quickly
  • Versatility of form - roll, batt, mattress or blown, a form to suit any project