What is the role of vapor retarder membranes?

Vapor retarder membranes are essential to the performance and longevity of buildings. These components allow precise control over the passage of water vapor through the various layers of a building.

Unlike traditional vapor barriers that create an airtight seal, vapor retarder membranes enable a more subtle and dynamic management of moisture flows. This approach is particularly well-suited to the Quebec climate, characterized by significant seasonal variations. Let’s see how these membranes work and why they are important for energy efficiency and the lifespan of buildings.

What is the building envelope?

The building envelope includes all the elements that separate the interior from the exterior: the walls, roof, windows, foundations, and other structural elements. This envelope must serve several important functions: insulating against cold and heat, preventing air leaks, managing moisture, and remaining in good condition over time.

Moisture is one of the biggest challenges for the durability of constructions. If not properly controlled, it can lead to serious problems such as the formation of mold, degradation of materials, and a significant decrease in energy efficiency.

What is a vapor retarder membrane?

A vapor retarder membrane is a material installed within the building’s thermal envelope, usually on the interior side (the warm side). Its role is to slow down the passage of water vapor through the walls, without stopping it completely. It therefore offers an intermediate solution between a traditional vapor barrier (which completely blocks vapor) and a fully permeable membrane (which lets vapor pass freely).

Its main purpose is to allow water vapor to gradually escape while preventing it from turning into liquid water (condensation) inside the walls.

How does a vapor retarder membrane work?

Indoor air in a building contains water vapor from various sources: the respiration of occupants, cooking, showers, and other daily activities. This water vapor naturally moves toward the exterior, where the air is generally colder and less humid. In Quebec winters, this movement becomes particularly pronounced due to the large temperature difference between the heated interior and the cold exterior.

The role of the vapor retarder membrane is to control the movement of moisture. It limits the amount of water vapor that can reach the colder parts of the walls, thereby preventing the vapor from turning into liquid water (condensation). In this way, it helps to:

• Reduce the risk of mold
  
  
• Protect insulation, which loses its effectiveness when wet
  
  
• Prolong the lifespan of the entire building structure
  
  

Some vapor retarders are called hygroregulating. This means that they can change their permeability according to the humidity level of the air: when the air is very humid, the membrane allows more vapor to pass through to help evacuate it; when the air is dry, it allows less vapor through. This capacity for adaptation is particularly useful in Quebec, where climatic conditions change significantly from one season to another.

How to install a vapor retarder membrane

To ensure the effectiveness of a vapor retarder membrane, it must be installed continuously, with perfectly sealed joints around electrical outlets, window frames, and at the junctions between panels.

Typically, the membrane is placed between the interior finish (for example, gypsum board) and the insulating layer. In certain configurations, it can be integrated into prefabricated panels or incorporated into multi-layer systems. It is important to note that the vapor barrier alone is not enough; one must also ensure that the building does not have air leaks. In fact, air leaks through cracks or holes can carry much more moisture than would naturally pass through the materials.

How to protect your building against moisture with SIGA Majvest 200 and SIGA Majrex 200

To optimize the performance of the building envelope, two innovative products from the SIGA range deserve special attention.

1. The first, SIGA Majvest 200, is an exterior windproof and waterproof membrane designed to offer protection against the elements. Its three-layer structure, which is both tear-resistant and easy to install, forms a barrier against wind while allowing water vapor to escape, thereby preventing the accumulation of moisture within the walls. This product is perfectly suited for sealed facades and certain roofing applications. Additionally, thanks to its printed markings that facilitate cutting and gluing, installation is fast, precise, and free of wrinkles.
   
   
2. The second product in the range is the interior membrane, Majrex 200, which optimizes unidirectional moisture management. Equipped with the exclusive Hygrobrid® technology, it enables the efficient evacuation of excess moisture present in the wall cavity while blocking infiltrations from the interior. This mechanism ensures optimal protection of the structure and contributes to the overall tightness of the envelope. Its composition in PE/PP fibers gives it flexibility, stability, and ease of installation. Used in conjunction with a permeable membrane such as Majvest 200, it offers a complete and intelligent solution for high-performance, durable construction adapted to the climatic variations specific to Quebec.

The Additional Benefits of Vapor Retarder Membranes

As we have just seen, vapor retarder membranes are essential for protecting buildings against moisture, as they allow walls to breathe without becoming excessively damp. This results in improved indoor air quality, more consistent thermal comfort, and increased longevity of the buildings.

Planning a renovation or a new construction?

For more details about these membranes and how they can enhance the energy efficiency of your construction projects, please feel free to contact us. Our experts will be happy to advise you and determine how best to integrate the new SIGA products into your project.