Fixing and buying guide

What this product is and who it is for

The underfelt collar is a structural timber component that bridges the gap between your rooflight aperture and the roof deck. It provides the critical interface where the rooflight frame meets the underfelt layer, ensuring water cannot penetrate around the installation. This product is essential for anyone installing a skylight or rooflight into a flat roof and is particularly important in conversions, extensions, and new build projects where building regulation compliance is required.

Sizing and compatibility

This collar is sized for 134x98cm rooflight apertures. Before ordering, measure your rooflight opening carefully to confirm it matches these dimensions. The collar is designed specifically for flat roof installations and works with standard VELUX rooflight frames. Check your rooflight documentation to verify compatibility with your specific model.

What you are getting and pre-installation checks

• One FSC certified timber collar frame measuring 134x98cm
• Inspect the timber for any damage or warping before installation
• Ensure your roof aperture is cut to the correct dimensions and is square
• Confirm underfelt and roofing materials are ready for installation
• Check that the rooflight frame is compatible with this collar size

Installation and building regulations

The collar must be positioned between the rooflight frame and the underfelt layer to create a weather-tight seal. It is engineered to comply with UK building regulations for rooflight installations. The FSC certified timber construction ensures durability and environmental responsibility. Proper installation is critical for weather-tightness, so follow the rooflight manufacturer's installation instructions carefully and ensure the collar sits flush and level within the aperture.