How and where to use guide
VELUX Underfelt Collar 94x140cm BFX PK08 1000
Suitable applications and installation location
This underfelt collar is designed exclusively for use with compatible VELUX roof window and Sun Tunnel systems in the PK08 size range. It is installed at the roof penetration point, sitting between the roof structure and the window or tunnel frame to create a weather-tight seal. The collar is suitable for pitched roofs in both new build construction and refurbishment work, where it forms part of the complete flashing and sealing system. Always verify compatibility with your specific VELUX product before ordering, as the PK08 designation indicates a particular window size and fixing specification.
- Install only with compatible VELUX roof windows and Sun Tunnels (PK08 range)
- Position at the roof penetration, between roof deck and window frame
- Suitable for pitched roof applications in new build and refurbishment
- Forms part of a complete VELUX daylight and ventilation system
- Not suitable for use with non-VELUX products or alternative window systems
Installation and positioning
The collar must be positioned correctly to function effectively. The transverse drainage gutter is engineered to direct water run-off away from the roof penetration, so orientation is critical. The underfelt layer sits against the roof structure and should be integrated with the roof's existing underfelt or breather membrane to maintain continuity of the weather barrier. Ensure the collar is fully seated and secured according to VELUX installation instructions, and that all edges are properly sealed to prevent water ingress. The 940x1400mm dimensions are fixed, so the roof opening must be prepared to match these specifications.
- Position the transverse drainage gutter to direct water away from the penetration
- Integrate the underfelt layer with existing roof membrane or breather layer
- Ensure full contact between collar and roof structure
- Secure and seal all edges according to VELUX guidance
- Verify roof opening dimensions match the 940x1400mm collar size
Weather performance and maintenance
This collar is engineered specifically for UK roof conditions and provides reliable weather protection when installed correctly as part of a complete VELUX system. The integrated transverse drainage gutter is the key feature that prevents water pooling and directs moisture away from the roof penetration. After installation, inspect the collar periodically to ensure the drainage gutter remains clear of debris, leaves, or moss, particularly after autumn and winter weather. Check that all seals remain intact and that no gaps have developed around the edges. Regular maintenance of the gutter will preserve the weather-tight performance of the installation.
- Inspect the transverse drainage gutter regularly for blockages or debris
- Clear leaves and moss from the gutter, especially after autumn and winter
- Check seals and edges annually for signs of deterioration or gaps
- Do not apply additional sealants that may obstruct the drainage gutter
- Replace the collar if damage to the underfelt or gutter is discovered
Limitations and important notes
This collar is designed for use only with compatible VELUX roof window and Sun Tunnel systems and cannot be used as a standalone flashing product or with alternative manufacturers' products. The fixed dimensions of 940x1400mm mean the roof opening must be precisely prepared to these measurements. The collar does not include the window frame, glazing unit, or installation hardware; these must be sourced separately as part of a complete VELUX system. Installation should be carried out by experienced builders or roofers familiar with VELUX products and UK roof construction standards. Improper installation or use with incompatible products will compromise weather performance and may void warranties.
- Compatible only with VELUX PK08 roof windows and Sun Tunnels
- Fixed dimensions require precise roof opening preparation
- Does not include window frame, glazing, or hardware
- Installation by experienced builders or roofers recommended
- Incompatible use or poor installation will compromise weather protection