Fixing and buying guide

What this product is and who needs it

The underfelt collar is a flashing component that sits beneath the rooflight frame on flat roof installations. It provides critical weather protection by creating a seal that directs water away from the rooflight opening and prevents wind-driven rain from entering the building. This product is essential for any VELUX rooflight installation on a flat roof and is used by roofers, builders, and serious DIY installers working on new builds or retrofit projects.

Checking compatibility and sizing

Before ordering, confirm that this collar is specified for your VELUX rooflight model and that the 55cm x 118cm dimensions match your project requirements. The BFX CK06 1000 is designed for flat roof applications only. Check your rooflight specification sheet or consult the VELUX documentation to verify that this underfelt collar is the correct component for your installation. Measure your rooflight opening to ensure the collar dimensions will provide adequate coverage and overlap for a proper weather seal.

• Confirm VELUX rooflight model compatibility before purchase
• Verify flat roof application suitability
• Check that 55cm x 118cm dimensions suit your rooflight opening
• Review manufacturer guidance for overlap and positioning requirements

Material and durability

This collar is manufactured from durable polypropylene with a weather-resistant coating to withstand exposure to rain, wind, UV light, and temperature changes. The material is designed to remain flexible and maintain its seal integrity over time, even in harsh weather conditions typical of UK roofing environments. The weather-resistant finish helps prevent degradation and extends the service life of the flashing component.

Installation and fixing

Install the underfelt collar in line with current best practice and VELUX manufacturer guidance. The collar should be positioned beneath the rooflight frame to create a weather-tight seal, with adequate overlap to direct water away from the opening. Use suitable fixings appropriate to your roof construction and follow the detailed installation instructions provided with the rooflight kit. Ensure the collar is properly secured and sealed to maintain weather protection throughout the life of the installation.

• Follow VELUX manufacturer installation guidance
• Position collar beneath rooflight frame for weather-tight seal
• Use fixings suitable for your roof construction type
• Ensure adequate overlap and proper sealing around the opening