Fixing and buying guide

What this product is and who it is for

Twin and combination flashings are metal or composite components that seal the joints where two roof planes meet or where a roof meets a vertical surface. This VELUX product is designed for pitched roof installations where standard single flashings are insufficient. It suits builders, roofers, and experienced DIY customers undertaking roof repairs, extensions, or new builds where complex roof angles require dual coverage to ensure complete weather protection.

Size and compatibility

This flashing measures 55×118cm (21.6×46.1 inches) and is graded EKW CK06 S0312. Before ordering, confirm that your roof junction dimensions and pitch angles align with this standard size. Check that the flashing will cover the full width of the junction and extend sufficiently up both roof planes. Verify compatibility with your existing roof covering material and any adjacent VELUX components or flashings already installed.

Pre-installation checks and preparation

Inspect the roof structure and junction area for damage, rot, or deterioration before fitting. Ensure the roof surface is clean, dry, and free from debris, moss, or old sealant. Check that roof timbers are sound and properly supported. Confirm adequate ventilation around the flashing installation to prevent condensation issues. Have all necessary fixings, sealants, and roofing materials to hand before starting work.

• Verify roof pitch and junction angles match the flashing design
• Clean and prepare the roof surface thoroughly
• Check structural integrity of roof timbers and supports
• Gather all fixings, sealants, and roofing materials in advance
• Ensure safe access and working conditions on the pitched roof

Installation and fixing

Twin and combination flashings must be fitted to create a continuous watertight seal across the roof junction. Position the flashing to overlap existing roof covering correctly and extend up both roof planes. Secure according to VELUX instructions using appropriate fixings for your roof type. Apply approved sealant to all joints and edges to prevent wind-driven rain penetration. Ensure the flashing sits flush against the roof surface with no gaps or lifting edges. Work should be carried out in dry conditions for optimal sealant performance.