Fixing and buying guide

What this product is and who needs it

The underfelt collar is a flashing component that sits beneath the roof covering (tiles, slates, or other materials) around a VELUX roof window or Sun Tunnel opening. It manages water drainage and creates a sealed interface between the window frame and the roof structure. You need this collar if you are installing a compatible VELUX roof window or Sun Tunnel system and want to ensure a weather-tight, professional finish that meets building standards for water management.

Compatibility and sizing

This collar is sized at 1340 x 1400mm and is designed for the UK08 VELUX roof window and Sun Tunnel range. Before ordering, confirm that your roof window or Sun Tunnel model is compatible with the BFX UK08 1000 specification. Check your window documentation or contact VELUX technical support if you are unsure. The collar dimensions must match your roof opening to ensure proper fit and water management.

• Product code: BFX UK08 1000
• Dimensions: 1340 x 1400mm
• Compatible with standard VELUX roof window and Sun Tunnel ranges
• Verify compatibility with your specific window model before purchase

Installation and pre-install checks

The underfelt collar is installed as part of the roof window flashing system, positioned beneath the roof covering to direct water away from the penetration. Before installation, ensure the roof opening is cut to the correct size and that the roof structure is sound and level. The transverse drainage gutter must be positioned to allow water to flow freely down the roof slope. Follow VELUX installation instructions carefully, as incorrect positioning will compromise weather-tightness. This product is suitable for both new build and refurbishment work.

• Install beneath roof covering (tiles, slates, etc.)
• Ensure roof opening is correctly sized and level
• Position transverse drainage gutter to direct water downslope
• Follow VELUX installation guidance for your specific window model
• Suitable for new build and refurbishment projects

Pack contents and storage

Each pack contains one underfelt collar sized 1340 x 1400mm with integrated transverse drainage gutter. Store the collar flat and dry before installation to prevent damage. Protect it from direct sunlight and weather exposure during storage on site.