Vapour Barriers

What is a Vapour Barrier? 

A vapour barrier is a sheet, typically made of polythene, placed on the warm side of a structure between the cavity insulation and inner masonry skin.

The vapour barrier prevents the warm air or water vapour from penetrating through the wall to where it might reach its dew point – when it turns back into a liquid. This, in turn, lowers your risk of internalised condensation and damp damage.

A vapour barrier can be used for:

• Timber frame constructions
• Roof and floor constructions
• High-humidity buildings such as swimming pools and factories.

Using a vapour barrier could also improve the overall thermal performance of your building, as it can improve airtightness.

Some types of rigid foam insulation have a foil bonded to their surface, acting as a vapour barrier. However, care must still be taken to ensure that joints and edges are properly sealed with the right vapour barrier products.

Different Types of Vapour Barriers

We stock various vapour barrier products to suit a range of jobs, including: 

Vapour Barrier

As stated above, a vapour barrier is used to prevent warm, internal air from passing through the walls and reaching its dew point.

A vapour barrier is commonly used in timber frame housing as well as commercial buildings.

Vapour Check

A vapour check is very similar to a vapour barrier in that it’s used to reduce the risk of interstitial condensation within a structure. However, unlike a vapour barrier, a vapour check (also known as a vapour control layer) is designed to slow the flow of air without stopping it entirely.

Vapour / Joining Tape

Vapour tape is not in itself a vapour barrier but does have mostly the same qualities. Vapour tape is designed to be used alongside a vapour barrier to improve the overall airtightness of a building.

Does My Project Need a Vapour Barrier?

When insulating a building from the inside, you will always need a vapour barrier. The only exception to this is when your insulation of choice already has a vapour-resistant layer. In this case, you should seal the gaps and seams with vapour tape to ensure that the vapour still can’t get through.

Depending on where you live, the vapour barrier will either go on the inner surface of the insulation (if you live in a cold climate) or the outer surface of the insulation (if you live in a hot climate).

It’s safe to say that a vapour barrier will be needed for almost all projects. All that changes is where the barrier is placed and what kind you intend to use.

Shop our high-quality vapour barrier products to keep your builds damp-free. For anything else your project needs, see our extensive range of building supplies.