Fixing and buying guide

What this product is and who needs it

A recessed flashing is a weatherproofing component that sits around the perimeter of windows, doors, and roof openings to prevent water penetration at the junction between the frame and the building fabric. This VELUX flashing is intended for builders, contractors, and experienced DIY installers working on pitched roof installations and wall openings in timber-framed or dry-lined constructions. It is suitable for both new builds and renovation projects where reliable weather protection is essential.

Compatibility and sizing

This flashing is sized at 78×118cm and is designed for standard window and door applications. It is compatible with timber grades F16, F24, and F36 only. Before purchase, verify that your opening dimensions fall within the coverage of this size and that your structural timber meets one of these grades. If your project uses different timber grades or requires a non-standard opening size, you will need a different flashing product.

• Size: 78 × 118cm (30.7 × 46.1 inches)
• Compatible timber grades: F16, F24, F36
• Suitable for timber and dry lining constructions
• Designed for domestic and commercial projects

Material and durability

The flashing is manufactured from durable plastic with UV stabilisation, which protects it from degradation caused by prolonged sun exposure. This treatment ensures the material remains flexible and watertight throughout its service life, even in exposed roof and wall positions. The plastic construction is lightweight and resistant to rot, making it a long-lasting alternative to traditional materials.

• UV-stabilised plastic resists weathering and UV damage
• Lightweight and rot-resistant
• Maintains flexibility and watertight performance over time

Pre-installation checks and preparation

Before fixing, inspect the flashing for any damage sustained during delivery and confirm the dimensions match your opening size. Check that the surrounding timber or dry lining is sound, dry, and free from rot or damage. Ensure the opening is square and level, and that any existing sealants or old flashings are removed. Have appropriate fixings and sealants ready—consult the installation instructions or your architect's specification for the correct fastening method and sealant type for your application.

• Inspect flashing for transport damage
• Verify opening dimensions and timber grade compatibility
• Remove old flashings and sealants
• Ensure opening is square, level, and dry
• Prepare fixings and sealants as specified in installation guidance