Fixing and buying guide
VELUX Underfelt Collar 94x140cm BFX PK08 1000
What this product is and who needs it
This underfelt collar is a flashing component that sits between your VELUX roof window or Sun Tunnel and the roof structure. It creates a weather-tight seal at the point where the window frame penetrates the roof, and its transverse drainage gutter directs water safely away from the installation. You need this collar if you are installing a compatible VELUX roof window or Sun Tunnel system in either a new build property or during a refurbishment project. It is a critical part of the weatherproofing system and must be used with the correct VELUX window or tunnel model to ensure proper performance.
Compatibility and sizing
This collar is specifically designed for VELUX PK08 compatible roof windows and Sun Tunnels. The 940 x 1400mm dimensions are fixed and match the standard opening size for PK08 products. Before ordering, confirm that your VELUX window or Sun Tunnel is a PK08 model; using this collar with an incompatible product will compromise the weather-tight seal and void performance guarantees. Check your VELUX product documentation or the model number on your window frame to verify compatibility.
What is included and pre-installation checks
You receive one underfelt collar with integrated transverse drainage gutter ready for installation. Before fitting, inspect the collar for any damage in transit and ensure the roof opening dimensions match the 940 x 1400mm specification. Check that the roof structure is sound, level, and ready to receive the collar, and that your VELUX window or Sun Tunnel frame is to hand and matches the PK08 specification. Ensure you have appropriate flashing materials, sealants, and fixings as specified in your VELUX installation instructions; this collar works as part of a complete system and must be installed according to the manufacturer's guidance.
Installation and professional finish
The collar must be installed by a competent person following VELUX's detailed installation instructions. Correct positioning and sealing are essential to achieve the weather-tight performance this product is engineered to deliver. The integrated transverse drainage gutter must be positioned to direct water away from the window frame and towards the roof surface. Once installed correctly, the collar provides a visually consistent, professional roof finish suitable for both new build and refurbishment work. Poor installation or use with incompatible products will result in water ingress and potential structural damage.