AVCL: THE IMPORTANCE OF AN AIR AND VAPOUR CONTROL LAYER IN YOUR BITUMINOUS ROOFING SYSTEM

As its name already makes clear, an air and vapour control layer (AVCL) controls the movement of air and water vapour. A crucial part of the roof build-up, this sheet or film prevents warm, humid indoor air from condensing, by keeping it from touching the cooler outer layer.

AN AVCL PREVENTS MOISTURE PROBLEMS

Having a well-insulated building not only depends on the quality of the insulation material used. The AVCL must be of equal quality and correctly installed, as insulation material that gets damp loses a great deal of its insulation value. Applying a moisture-regulating layer underneath the insulation on a roof rules out condensation and, hence, moisture and mould problems.

PERFORMANCE GOES HAND IN HAND WITH APPLICATION

An AVCL only does what it is supposed to if applied correctly. The head lap must overlap by a minimum of 100 mm and the side lap by a minimum of 75 mm, and the overlaps must be neatly sealed.

BS 5250: 2021 on the “Management of moisture in buildings” recommends not only an AVCL on the warm side of the insulation, but also an air gap of at least 50 mm between the thermal insulation and the cold deck. This ensures ventilation or the circulation (rather than condensation) of warm, indoor air that rises.

The choice of membrane depends on the temperature and humidity conditions within the building. A single-layer reinforced bitumen membrane (RBM) can act as a vapour check, but where a high level of vapour resistance is required, it might be necessary to provide a two-layer air and vapour control layer or to use a proprietary foil laminated bitumen membrane.

Finally, once it is applied, remember to never pierce an air and vapour control layer to allow for pipes or cables.

HIGH-QUALITY AVCL’S FROM SOPREMA

Soprema offers a wide range of reliable and durable AVCL products designed to meet your specific building envelope needs. Our AVCL solutions provide superior performance, ensuring the longevity and energy efficiency of your construction project.

1.     SOPRAVAP STICK ALU ACTIVA 2

SOPRAVAP STICK ALU ACTIVA 2 is composed of SBS modified bitumen with a composite aluminium reinforcement. The upper and lower surfaces have SBS lanes that alternate with non-stick lanes. This means the AVCL is quick to install and adhesive is not required for the insulation sheets.

2.     SOPRAVAP STICK ALU S 16

SOPRAVAP STICK ALU S 16 is a self-adhesive modified bitumen membrane with an aluminium foil and non-woven polyester reinforcement. The upper surface has a sand finish. The lower surface is protected by a silicone release sheet. This air and vapour control layer is cold-applied and therefore suitable where a flame-free application is required on steel, timber and concrete decks.

3.     SOPRAVAP STICK ALU TS DUO 3MM

Made from elastomer-modified bitumen and reinforced with a composite aluminium layer, SOPRAVAP STICK ALU TS DUO 3MM serves as an effective air and vapour control layer for structures with substantial moisture generation, such as those with steel decks or concrete substrates. It provides reliable protection against moisture infiltration in challenging building environments.

4.     SOPRAVAP EVA 35

SOPRAVAP EVA 35 is a high-performance AVCL made from SBS modified bitumen and fortified with a composite aluminium and fiberglass reinforcement. It is specially designed to function as an air and vapour control layer in structures with high moisture levels. The top layer has a talcum-and-sand finish, while the bottom surface is safeguarded by a thermofusible film. Even in the most demanding applications, SOPRAVAP EVA 35 ensures effective and durable moisture control.

5.     SOPRAVAP STICK A 07

Finally, SOPRAVAP STICK A 07 is a high vapour resistant, self-adhesive membrane featuring elastomer-modified bitumen and an aluminium complex. This premium AVCL is designed for steel deck applications in buildings with elevated moisture levels. The lower surface is shielded by a silicone release film, ensuring excellent moisture management and protection.

6.     A COMPLETE SOPREMA SYSTEM

Not sure which air and vapour control layer best suits your project? Our technical sales team are there to ensure you get the right product specification within your waterproofing system. We offer design consultations, standard details and drawings, site surveys and much more.

For more information on AVCL: THE IMPORTANCE OF AN AIR AND VAPOUR CONTROL LAYER IN YOUR BITUMINOUS ROOFING SYSTEM talk to SOPREMA UK