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Advantages and applications of vapour barriers

Flat roofs are a common architectural feature in modern construction, offering a sleek and practical design. However, they also present unique challenges, particularly when it comes to managing moisture. Vapour barrier membranes play a crucial role in addressing these challenges by providing an effective solution for restricting the movement of water vapour through the building.

A vapour barrier, or vapour control layer (or VCL) is designed to block the passage of water vapour through the roof assembly. As this phenomenon goes in the direction from a high humidity to a low humidity, it mostly goes from inside the building to outside. By controlling moisture, vapour control membranes help enhance the longevity of the roof and prevent issues like mold growth and structural damage. In the context of flat roofs, these membranes are usually installed directly over the roof structure and under the insulation layer (at its warm side). 

Properly installed Vapour barriers also contribute to the overall energy efficiency of a building. By reducing the risk of condensation within the roof assembly, they help maintain the insulation's thermal performance. This, in turn, ensures that the building's heating and cooling systems operate more efficiently, leading to lower energy consumption and reduced utility costs.

Although it’s generally advised to always include a vapour control membrane on flat roofs, its presence is crucial in regions with varying climates, especially in areas prone to heavy rainfall or high humidity, as temperature fluctuations can lead to condensation within the roofing system. Many building codes and regulations require the installation of Vapour barriers in certain climate zones or specific building types. 

The type of building is also crucial to evaluate the need for a VCL and which kind. Buildings where a  high relative humidity may be expected (laundries, indoor swimming pools, office buildings, etc.) will need a VCL for a sustainable, proper functioning of the roof.

Vapour barrier membranes are commonly used on new build flat roofs. In the case of renovation or retrofitting, adding a Vapour barrier membrane is a cost-effective way to enhance the moisture resistance of the existing structure. This is particularly important when upgrading the insulation or installing a new waterproofing membrane.

There are many different types of Vapour barrier membrane available in the market, each designed with specific characteristics to suit varying applications and environmental conditions. Below are some of the most common ones for flat roofs:

  • Polyethylene (PE) vapour barriers: made from plastic material, they are available in various thicknesses and are suitable when a low migration of humidity is to be expected.
  • Bituminous vapour barriers: made from bitumen, they offer excellent waterproofing properties and are often self-adhering, making installation easier. Commonly used on flat roofs, they provide effective moisture protection and are compatible with various roofing materials.
  • Aluminum-foil Vapour barriers: they have an aluminum-facing layer for enhanced vapour resistance and durability. They are suitable for all types of climates and all types of building, including the building with very high internal humidity such as swimming pools.

Choosing the appropriate Vapour barrier membrane depends on factors such as climate, function of the building (the potential future destination of the building must be also considered), intended application, and the specific requirements of the building envelope. Consulting with construction professionals and considering local building codes can help ensure the proper selection and installation of Vapour barrier membranes for optimal performance.

Discover here Elevate’s range of vapour control membranes, specifically designed to enhance the performance of flat roofing systems.