How to Insulate a Roof Using PIR Insulation Boards

Proper roof insulation significantly reduces heat loss through the top of your home, enhancing energy efficiency and comfort. By using PIR insulation boards or PU foam boards, you can create a warm loft suitable for storage or conversion. These materials offer excellent thermal performance and durability. Here’s a step-by-step guide on how to insulate your roof with these boards.

Step 1: Measure All Gaps

Start by accurately measuring the gaps between the roof joists. Using a tape measure, note down each dimension to ensure precise cutting of the PIR foam boards. These measurements will help you calculate the amount of insulation material needed. You can choose to insulate between the joists, over them, or both for maximum efficiency.

Step 2: Create an Air Gap

When installing insulation boards between the joists, it's essential to create a ventilation gap to allow air circulation and prevent moisture build-up. This gap should be 50mm wide. To achieve this, attach 50mm-wide timber battens to the roof joists. Use tanalised roofing battens for durability, securing them with a screwdriver or a nail gun.

Step 3: Install PIR Insulation Boards

Cut the PIR/PU board to size using a utility knife and a straightedge ruler. Mark your cutting lines with a permanent marker for accuracy, and cut on a solid surface for stability. The boards should fit snugly between the joists. If necessary, apply sealant to the back of the boards to secure them against the battens.

Both PIR foam insulation boards and PU foam boards provide excellent thermal insulation with low thermal conductivity, making them ideal choices for maintaining a consistent indoor temperature.

Step 4: Install a Vapour Control Layer

If your insulation boards don’t have a built-in vapour control layer, you’ll need to install one separately. A vapour barrier helps prevent moisture from entering the insulation. Fix the vapour barrier to the roof using a staple gun, creating folds at each joist for a secure fit. If overlapping sheets, staple them firmly to form a continuous layer.

Step 5: Add More Boards or Plasterboard

For enhanced insulation, you can add another layer of PIR thermal insulation boards over the joists. Secure them with a nail gun for a tight fit. To complete the interior finish, attach plasterboards with plasterboard screws. Alternatively, you can use insulation boards faced with plasterboard for a quicker installation process.