Fixing and buying guide

What this product is and who needs it

The insulation collar is a perimeter seal manufactured from fibre-reinforced polymer that sits between your VELUX roof window frame and the roof opening. It is designed for builders, roofers, and serious DIY installers carrying out new roof window installations or replacing existing windows. Use it whenever you need to maintain thermal performance and prevent moisture penetration around a roof window opening.

Compatibility and sizing

This collar fits roof windows with openings up to 66cm wide and 118cm long. Check your VELUX window dimensions before ordering to ensure compatibility. The collar is suitable only for timber grades F18 and above; do not use on lower grade timber as structural integrity and weather resistance cannot be guaranteed. Verify your roof timber grading with your surveyor or structural engineer if uncertain.

Pre-installation checks

Before fitting, inspect the roof opening to confirm it is square and level. Check that the surrounding timber is sound, dry, and graded F18 or above. Ensure the opening dimensions do not exceed 66cm width or 118cm length. Clear away any debris, dust, or old sealant from the opening perimeter. Have the VELUX window frame ready for installation and confirm all components are present and undamaged.

• Measure the roof opening width and length to confirm they do not exceed 66cm and 118cm respectively
• Verify timber grade is F18 or above
• Check that the opening is square and level using a spirit level
• Clean the opening perimeter thoroughly
• Inspect the fibre-reinforced polymer collar for any damage during transit

Installation and fixing

Position the insulation collar around the perimeter of the roof opening, ensuring it sits flush against the timber frame on all sides. The collar creates a seal that prevents heat loss and moisture ingress, so it must be fully seated with no gaps. Follow VELUX installation instructions for securing the collar to the roof structure and timber frame. Ensure the window frame is then installed centrally within the collar to maintain the thermal and moisture barrier.