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Why are vapour barriers used?

by | Feb 8, 2024 | Roofing Questions

Vapour Barrier Guide and Options

Vapour barriers, sometimes referred to as vapour control layers or VCL, are essential roofing materials in the construction industry. Vapour barriers help to prevent mould in buildings by managing moisture levels. This article explores why vapour barriers are important components to consider when working on a project. The following information is useful for architects and builders, so that they can make informed decisions to ensure the long-term health of a building.


Vapour Barriers are used to prevent the movement of water vapour into the flat roof system.

The process of water vapour passing through structures, such as concrete and timber, is especially increased in winter. As the water vapour passes through the structures, water ingress can damage the weatherproofing system.

Frost can also get through roofing structures. Then, as temperatures rise in the summer, the frost melts, causing leaks in ceiling slabs (see demonstration below).

Vapour Barrier Demonstration
Vapour Barrier Demonstration

When a structure has no vapour control, thermal insulations can become damp from the inside of the building. Stone wool insulation becomes less effective, leading to the structure freezing, and the load-bearing slabs to become damp. Algee and moss growth may then occur.

Therefore, a vapour barrier should be installed so that structures can remain watertight.

SA VB 600
WonderBuilds Self-Adhesive Vapour Barrier (SA VB 600)

A great option is the WonderBuilds Self-Adhesive Vapour Barrier (SA VB 600).

SA VB 600 is perfect for use in areas that are likely to have high temperatures and moisture levels (for example, gyms, factories, and swimming pools).

The self-adhesive area at the bottom of the membrane is protected with siliconised film which can be easily released, and the top surface is covered with aluminium foil.

This product has been specifically developed for use on all substrates.

It is durable, mechanically resistant and has high repairability.

It has superior tensile strength and can therefore withstand foot traffic.

Application is quick and simple.

This product is of a self-adhesive application and can be used in risk of flame exclusion zones.



Click here to see more information about SA VB 600, including the technical data sheet.

Click here to view WonderBuilds SA Primer, including the technical data sheet.


In conclusion, vapour barriers are vital components of many construction projects. They are utilised in projects to manage humidity levels, which results in durable and energy efficient buildings. Vapour barriers prevent mould growth and structural issues caused by high humidity levels. They also prevent materials in buildings from rotting. The use of vapour barriers ensures resilient and sustainable buildings are created. Vapour barriers prevent higher energy bills, as excess moisture can make buildings warmer in summer, and colder in winter. They can also prevent unnecessary repair costs further down the line.


Built-up roofing systems incorporating SA VB
Built-up roofing systems incorporating SA VB 600 vapour barrier can be seen above on a timber deck, metal deck, and concrete deck.

Please find our contact details below and do not hesitate to contact us for more information:

WonderBuilds Team


p:  0208 208 2121



a:  16 Hampden Gurney Street, London, W1H 5AL

Dina Vaisman

Dina Vaisman

Co-founder and Director · WONDERBUILDS

MSc International Financial Management