Fixing and buying guide

What this product is and who needs it

This underfelt collar is an essential flashing component for installing VELUX roof windows and Sun Tunnel systems. It sits between the window frame and your roof structure, providing the critical weather-tight seal that prevents water ingress. If you are installing a new VELUX roof window or Sun Tunnel, or replacing an existing one, you will need a compatible collar. It is equally suitable for new build construction and refurbishment work on pitched roofs.

Compatibility and sizing

The BFX FK06 1000 is sized at 660 x 1180mm and is compatible with the standard VELUX roof window and Sun Tunnel ranges. Before ordering, confirm that your VELUX window model is compatible with the FK06 collar size. Check your window documentation or contact VELUX technical support if you are unsure. This collar is designed for standard pitched roof installations; verify your roof pitch falls within typical specifications.

• Dimensions: 660 x 1180mm
• Material: Aluminium with integrated drainage channel
• Compatible with VELUX roof windows and Sun Tunnel systems
• Suitable for standard pitched roof applications

Pre-installation checks

Before fitting, inspect the collar for any damage to the aluminium frame or drainage gutter. Ensure your roof structure is sound and the opening is cut to the correct size for your VELUX window model. Check that the roof pitch is suitable for standard pitched roof installation. Have all other components ready, including the window frame, flashing kit, and any additional sealing materials specified in your VELUX installation instructions.

• Verify the collar matches your VELUX window model
• Inspect for damage to aluminium frame and drainage channel
• Confirm roof opening dimensions are correct
• Check roof pitch compatibility before installation

Installation and drainage

The integrated transverse drainage gutter is a key feature of this collar. During installation, ensure the gutter is positioned to direct water away from the window frame and down the roof slope. The weather-tight seal between the collar and roof structure must be maintained throughout fitting. Follow VELUX installation guidance carefully, as proper positioning of the collar is essential for long-term weather protection and to prevent water pooling or leaks into the roof void.