Loft Conversions Insulation – Sitework

Loft conversions insulation


  1. Attach timber battens to the sides of the rafters to maintain the 50mm cavity below the underlay.
  2. Cut Ballytherm Insulation boards sized to fit between rafters.
  3. Attach the second layer of Ballytherm boards across the underside of the rafters and secure with battens.
  4. Tape joints between boards using Ballytherm metalised tape.
  5. Fit the internal finish to the batten.


  • The cavity beneath the underlay must stay clear and vented.
  • Ballytherm boards should be cut and fitted neatly around penetrations, then sealed with expanding foam.

Further Advice

For advice on putting in a thermal insulator in your loft conversion, speak to an insulation expert at Ballytherm.  Phone us at 0800 644 6900, email us at or use our contact form.

Roof Insulation


Design Guidance