How and where to use guide
VELUX Underfelt Collar 134x98cm BFX UK04 1000
Typical applications and suitability
This underfelt collar is designed specifically for flat roof installations where a rooflight aperture measures 134x98cm. It is commonly used in flat roof conversions, building extensions, and new build projects. The collar sits between the rooflight frame and the roof structure, providing the critical interface that prevents water penetration. It is not suitable for pitched roof installations or apertures of different dimensions.
- Flat roof conversions and loft extensions
- New build flat roof projects
- Building extensions with flat roof sections
- Replacement of existing rooflights on flat roofs
Installation and positioning
The collar must be positioned correctly to function effectively. It sits on top of the roof structure and beneath the rooflight frame, creating the weather-tight seal that protects the junction. Before installation, ensure your rooflight aperture is accurately sized at 134x98cm and that the roof structure is level and sound. The FSC certified timber should be handled carefully on site to avoid damage or moisture absorption before fitting. Position the collar centrally over the aperture and secure it according to the rooflight manufacturer's instructions, ensuring all edges are properly sealed.
- Verify aperture dimensions match 134x98cm before ordering
- Inspect timber for damage upon delivery
- Position collar centrally over the roof aperture
- Ensure roof structure is level and structurally sound
- Follow rooflight frame manufacturer's fixing instructions
Weather-tightness and sealing
The primary function of this collar is to create a weather-tight seal. Once positioned, all gaps between the collar and the rooflight frame must be sealed using appropriate roofing sealant or flashing tape as recommended by your rooflight supplier. The timber itself provides a solid base, but the seal between components is critical. Pay particular attention to the junction where the collar meets the roof covering material, ensuring no water can penetrate at this vulnerable point.
- Seal all gaps between collar and rooflight frame
- Use compatible sealant or flashing tape specified by rooflight manufacturer
- Ensure roof covering material is properly sealed around collar edges
- Check seals during and after installation for complete coverage
Building regulations and maintenance
This collar is designed to comply with UK building regulations for rooflight installations on flat roofs. Its use as part of a complete rooflight assembly helps ensure your installation meets thermal, structural, and weather-tightness requirements. After installation, inspect the collar periodically, particularly after severe weather, to ensure seals remain intact and no water staining is visible on the underside. The FSC certified timber is durable but should not be painted or treated with additional coatings unless specified by the rooflight manufacturer, as this may compromise the seal.
- Complies with UK building regulations for flat roof rooflights
- Inspect seals annually and after severe weather
- Do not paint or treat timber unless manufacturer specifies
- Check for water staining or damp on underside after heavy rain