Insulation Between And Below The Rafters – Sitework

Insulating between and below the rafters

When working at a height ensure risk assessments have been carried out and that all necessary protective measures are in place. Do not walk on Ballytherm boards nor use them as a working platform.

Installation sequence (working from inside the roof)

  1. Fix timber battens to the sides of the 
rafters so the space below the battens matches the thickness of the Ballytherm Insulation boards.
  2. Cut Ballytherm insulation boards to fit tightly between the rafters. Starting at eaves, fit the boards between the rafters, starting at eaves and working towards the ridge. Push the boards against the battens.
  3. Set Ballytherm boards across the underside of the rafters in a continuous layer. Secure with timber battens. Tape board joints with Ballytherm metalised tape.
  4. Fix plasterboard to the battens and skim.

Points to watch

  • At verges cut and fit Ballytherm insulation between the wall and first rafter.
  • Cut boards to fit neatly around penetrations such as SVPs.
  • Seal gaps and junctions with expanding foam.

Further Advice & Information

For more information about Ballytherm products, technical advice, or guidance on the suitability of our products for your project, contact us at + 353 (0)49 95 27000,, email us at or use our contact form.

Floor Insulation


Design Guidance