How and where to use guide
VELUX Vapour Barrier 134x140cm BBX UK08 0000
Typical applications
This vapour barrier is designed for loft conversions, roof insulation projects, and any roof space where moisture control is required. It works effectively in standard pitched roof construction with rafter spacing that accommodates the 134×140cm sheet size. The product is particularly suited to UK08 VELUX window installations where moisture management around the opening is critical.
- Loft conversions with insulation between rafters
- Roof insulation upgrades in existing properties
- New roof construction with thermal insulation
- Moisture control around VELUX UK08 window openings
Installation and positioning
Install the vapour barrier on the warm side of insulation, which means between the insulation and the internal plasterboard or finish. This positioning allows water vapour from the interior to be controlled before it reaches the cold outer layers where condensation would form. Ensure the membrane is continuous and overlaps are sealed with appropriate tape to create an effective moisture barrier. Position the sheet to align with your rafter spacing and secure it with staples or battens, taking care not to puncture the membrane.
- Position between insulation and internal plasterboard
- Ensure continuous coverage with sealed overlaps
- Secure with staples or battens without puncturing
- Align with standard rafter spacing for secure fixing
Maintenance and on-site tips
Once installed, the vapour barrier requires no ongoing maintenance but must remain intact to function effectively. During installation, avoid unnecessary movement or damage to the membrane. Store the product in dry conditions before use and handle carefully to prevent tears or punctures. If the barrier is damaged during installation, repair immediately with appropriate tape to maintain its moisture control properties. Ensure adequate ventilation in the roof space above the barrier to allow any moisture that does penetrate to escape safely.
- Inspect for damage before and after installation
- Repair any tears or punctures with vapour barrier tape
- Maintain roof ventilation above the barrier
- Keep stored dry until ready to install
Limitations and important considerations
This vapour barrier is sized specifically for UK08 VELUX window openings and standard rafter spacing. It is not suitable for applications outside these dimensions without modification. The product must be used as part of a complete insulation and ventilation strategy—it is not a standalone solution. Ensure your roof design includes adequate ventilation above the barrier to prevent moisture accumulation. Do not install on the cold side of insulation, as this will trap moisture within the structure and cause damage.
- Sized for UK08 openings and standard rafter spacing only
- Must be part of a complete insulation system
- Requires adequate roof ventilation above the barrier
- Never install on the cold side of insulation