Moisture is one of the biggest enemies of a healthy, efficient building. It can lead to mould growth, degrade insulation, and damage wall finishes. That’s why knowing when to use vapour-resistant wallboards is essential.
At CB Building Products, we regularly advise builders, developers, and homeowners on managing moisture in both new and existing properties. In this guide, we explain what vapour-resistant wallboards are, when to use them, and how they contribute to long-term building performance.
What Are Vapour-Resistant Wallboards?
Vapour-resistant wallboards (sometimes called vapour check plasterboards) are designed to slow the movement of moisture-laden air through wall and ceiling structures. They feature a vapour control layer, typically a foil backing, that reduces the risk of condensation inside the wall build-up.
These boards look similar to standard plasterboard but offer much greater protection in rooms prone to humidity or temperature changes.
Why Moisture Control Matters
Warm indoor air holds moisture. When that air hits a cold surface – like the back of insulation or an external wall – it condenses.
This can cause:
- Damp spots on walls and ceilings.
- Mould and mildew growth.
- Degraded insulation performance.
- Plasterboard softening and failure.
Installing a plasterboard with vapour barrier helps prevent this problem by stopping warm air from reaching cold surfaces inside the structure.
When to Use Vapour-Resistant Wallboards
1. Lofts and Attics
Roof spaces are naturally colder and often poorly ventilated. If you’re converting a loft into a living space, vapour-resistant plasterboard helps prevent warm indoor air from entering the roof void.
2. Bathrooms and En-suites
Although moisture-resistant plasterboard is often used, in some cases, adding a vapour barrier board gives extra protection behind tiles and cladding.
3. Kitchens
Cooking releases significant moisture into the air. Vapour-resistant boards help maintain internal wall condition and prevent damp patches.
4. External Walls with Insulated Studwork
If you’re using internal insulation (e.g. PIR boards or mineral wool), it’s vital to prevent moist air reaching the cold side. Vapour control boards protect insulation and stop interstitial condensation.
5. Utility Rooms and Laundries
Rooms with tumble dryers or water cylinders produce humid air. Vapour check wallboards reduce long-term issues in these environments.
Vapour Control vs Moisture Resistance: What’s the Difference?
Many people confuse moisture-resistant plasterboard with vapour-resistant wallboard.
| Feature | Moisture-Resistant Board | Vapour-Resistant Wallboard |
|---|---|---|
| Resists surface damp | Yes | Not directly |
| Slows moisture movement | No | Yes |
| Use in tiled wet zones | Yes | Sometimes |
| Use in insulated wall build-up | No | Yes |
The two are often used together – moisture-resistant in wet zones, vapour-resistant in surrounding or backing areas.
Installation Tips for Vapour-Resistant Boards
- Always install with the foil side facing the warm room.
- Seal all joints with foil tape or vapour control-compatible compound.
- Avoid puncturing the foil layer with excess fixings.
- Ensure airtightness at perimeters and around services.
Following these tips ensures the board performs as intended and contributes to your SAP or Part L energy compliance.
Compliance and Energy Efficiency
Using the correct vapour-resistant plasterboard applications supports:
- Part L (Conservation of Fuel and Power).
- Reduced heating costs.
- Better long-term performance of wall insulation.
These boards are especially valuable in renovation projects, where internal insulation is added and cold bridging is a risk.
CB Building Products: Smart Drylining for Smarter Buildings
With so many types of wallboard available, it’s easy to make the wrong choice. That’s why we guide customers through product selection, ensuring performance and compliance come first.
If you’re unsure when to use vapour-resistant wallboards, our team is here to advise. We stock high-quality options from trusted brands, ready for fast delivery across the UK.
FAQs
1. Can I use vapour-resistant wallboards behind tiles?
It depends. In high splash zones, moisture-resistant boards are better. Use vapour boards in adjacent or backing walls.
2. Do I still need a separate vapour barrier?
Not if using foil-backed wallboard correctly. But check U-value calculations or regulations for confirmation.
3. Do I need these boards in newbuild homes?
Often, yes – especially in well-insulated homes with little air leakage.
4. How do I know if I need vapour control?
If warm, humid air could reach a cold surface behind the wall, vapour control is required.
Talk to the Experts
Need help choosing the right wallboard?
For guidance on wallboard for condensation control, installation best practice, or U-value solutions, get in touch.
Email: info@cbbuildingproducts.co.uk
Call: 01527 359 047