How and where to use guide
VELUX Underfelt Collar 78x140cm BFX MK08 1000
Typical applications and compatibility
This underfelt collar is designed specifically for use with standard VELUX roof window and Sun Tunnel ranges. It is suitable for installation in both new build construction and existing roof refurbishment work. The 780 x 1400mm size accommodates the MK08 window format. Always verify compatibility with your specific VELUX product before ordering, as different window sizes require different collar dimensions.
- New build roof installations with VELUX roof windows or Sun Tunnels
- Refurbishment and retrofit projects upgrading existing roof penetrations
- Pitched roof applications in typical UK weather conditions
- Use only with compatible VELUX window and Sun Tunnel systems
Installation and positioning
The underfelt collar must be positioned at the roof penetration point before the roof covering is laid. The collar integrates with the roof structure, with the transverse drainage gutter directing water away from the window frame and down the roof slope. Correct positioning ensures the weather-tight seal functions effectively and prevents water pooling or ingress around the frame perimeter. Installation should follow VELUX guidance for your specific window model and roof covering type.
- Install the collar before laying roof tiles, slates or other covering materials
- Position the transverse drainage gutter to direct water flow down the roof slope
- Ensure the collar sits flush against the roof structure at the penetration point
- Integrate with the roof underlay and vapour control layer as specified by VELUX
Weather protection and drainage
The integrated transverse drainage gutter is a critical feature that manages water run-off at the roof penetration. This gutter directs rainwater away from the window frame and down the roof surface, preventing water from pooling or finding its way into the building structure. The weather-tight design of the collar itself provides the primary seal, whilst the gutter system offers secondary protection. Together, these features ensure reliable performance in UK roof conditions including heavy rainfall and wind-driven rain.
- The transverse drainage gutter must remain clear of debris and moss growth
- Check periodically that water flows freely down the roof slope without pooling
- The collar provides weather-tight sealing; the gutter provides additional drainage protection
- Suitable for use in typical UK climate conditions including exposure to rain and wind
Maintenance and on-site considerations
Once installed, the underfelt collar requires minimal maintenance but should be inspected periodically to ensure the drainage gutter remains clear and functional. Debris such as leaves, moss or dirt can obstruct the gutter and compromise drainage performance. Check the collar seal visually during routine roof inspections. The collar is engineered as a permanent component and does not require replacement under normal circumstances. Always follow VELUX installation instructions for your specific window model to ensure correct assembly and performance.
- Inspect the drainage gutter annually and clear any accumulated debris
- Check the collar seal visually during roof maintenance visits
- Do not attempt to modify or cut the collar; use the correct size for your window format
- Refer to VELUX installation documentation for your specific roof window or Sun Tunnel model