How and where to use guide
VELUX Underfelt Collar 55x78cm BFX CK02 1000
Typical applications and compatibility
This underfelt collar is engineered specifically for compatible VELUX roof window and Sun Tunnel systems. It is suitable for pitched roof installations in residential properties where daylight and ventilation solutions are required. The collar works as part of a complete VELUX system, so verify compatibility with your specific window or tunnel model before ordering. It performs reliably in typical UK weather conditions including exposure to rain, wind, and temperature variation.
- Use only with compatible VELUX roof windows and Sun Tunnel products
- Suitable for pitched roofs in new build and refurbishment projects
- Designed for residential applications requiring weather-tight installation
- Check product compatibility documentation before installation
Installation and positioning
The collar must be positioned between the roof underfelt and the roof covering material. It sits directly beneath the underfelt layer, with the transverse drainage gutter facing downslope to direct water away from the window frame. Proper positioning is critical to the collar's water management function. The 550 x 780mm dimensions are fixed, so ensure your roof opening matches the specified size. Installation should follow VELUX guidance to maintain the weather-tight seal and visual consistency of the roof finish.
- Position collar beneath roof underfelt, above the window frame
- Align transverse drainage gutter to face downslope
- Ensure roof opening dimensions match 550 x 780mm collar size
- Follow VELUX installation instructions for weather-tight sealing
- Secure collar firmly to prevent movement during roof covering installation
Water management and maintenance
The integrated transverse drainage gutter is the collar's primary defence against water ingress. This gutter channels rainwater away from the window frame and prevents pooling around the installation. After installation, inspect the gutter periodically to ensure it remains clear of debris, moss, or leaves that could obstruct water flow. In refurbishment projects, check that the collar sits flush with existing roof structure to avoid creating dips or high spots that could trap water.
- Inspect drainage gutter regularly for blockages or debris
- Clear moss and leaves to maintain water flow effectiveness
- Ensure collar sits flush with surrounding roof structure
- Check seals annually in refurbishment installations
- Do not allow water to pool around the collar perimeter
On-site handling and limitations
The collar comprises aluminium and synthetic components designed for outdoor roof exposure. Handle carefully to avoid denting or damaging the aluminium frame, which could compromise the weather seal. Do not attempt to modify or cut the collar to fit non-standard openings. The collar is not suitable for flat roofs or roof pitches outside the design specification. Store on-site in dry conditions before installation to prevent corrosion or contamination of sealing surfaces.
- Handle carefully to avoid denting aluminium components
- Do not modify or cut the collar to fit non-standard openings
- Not suitable for flat roofs or non-standard roof pitches
- Store in dry conditions before installation
- Ensure sealing surfaces remain clean and free from dust or debris