How and where to use guide
VELUX Underfelt Collar 78x98cm BFX MK04 1000
Typical applications and where to use
This underfelt collar is used in timber frame roof construction to seal the junction where the roof structure meets the timber frame end. It is essential in exposed roof conditions where weather protection is critical. The standard 78cm x 98cm size suits most conventional timber frame roof applications, making it suitable for both new build and renovation projects where timber frame roofs are being installed or replaced.
- Sealing timber frame roof junctions in new build construction
- Protecting frame ends from wind-driven rain and moisture penetration
- Maintaining thermal efficiency at the roof-to-frame interface
- Renovation and repair work on existing timber frame roofs
- Applications requiring weather-tight seals in exposed roof conditions
Installation and usage
The collar is designed for straightforward installation over timber frame ends. Position the underfelt collar to cover the frame end completely, ensuring it creates a snug fit around the timber structure. The smooth finish of the felted underfelt material allows for easy positioning and adjustment during installation. The collar should be secured firmly in place to maintain its weather-tight seal and prevent movement or displacement during roof construction and weathering.
- Position collar over the timber frame end before roof covering is installed
- Ensure complete coverage of the frame end for maximum weather protection
- Secure firmly to prevent movement during construction and in service
- Check that the collar sits snugly against the timber frame
- Install before applying roof coverings or external finishes
Performance and maintenance
The felted underfelt material is engineered for durability and long-term performance in exposed roof conditions. Once installed, the collar requires minimal maintenance but should be inspected periodically to ensure it remains in place and undamaged. Check that the seal remains intact and that no gaps have developed around the frame junction, particularly after severe weather or seasonal changes. The smooth finish helps shed water effectively and resists degradation from UV exposure and weathering.
- Inspect collar periodically to ensure seal integrity
- Check for gaps or displacement around the frame junction
- Verify that water is shedding effectively from the collar surface
- Replace if damage or deterioration is observed
- Ensure no debris accumulation that could compromise the seal
Limitations and important considerations
This collar is sized at 78cm x 98cm and is designed for standard timber frame dimensions. Verify that your timber frame end dimensions match these specifications before ordering. The collar provides weather-tight sealing at the frame junction but must be used as part of a complete roof weatherproofing system that includes appropriate roof coverings and flashings. It is not suitable for non-timber frame applications or where frame dimensions exceed the standard size. Proper installation is essential to achieve the intended weather protection and thermal efficiency benefits.
- Confirm timber frame dimensions match 78cm x 98cm size before installation
- Use only in timber frame roof construction applications
- Must be part of a complete weatherproofing system with appropriate roof coverings
- Not suitable for oversized or non-standard frame dimensions
- Proper installation is critical to achieve weather-tight performance