The Importance of Air & Vapour Barriers
Vapour barriers (also known as vapour diffusion retarders), air retarders and air/vapour retarders all relate to the interaction of temperature and moisture in and out of a building. A vapour barrier is a material that is used to reduce the rate of water vapour at which it can move through a material. Its ability to retard the diffusion of water vapour is measured in units, known as permeability.
Although both, vapour barriers and air barriers are extremely important components of high-performance building, you must know that the two are not the same. With their different functions to perform in the building assembly, understanding differences between them are paramount to building high performing homes.
Vapour barriers can help control moisture in:
- Crawl spaces
- Slab on grade foundations
In addition, to have a more effective moisture control in these areas and throughout, the building must also include air sealing gaps. It cannot be just the use of vapour barriers. However, if your home needs a vapour barrier or not, it depends on the climate and the construction of the property.
What is an air barrier & a vapour barrier?
Air barriers are systems designed and constructed to control airflow. This control is done between a conditioned indoor space and an unconditioned outdoor space. They can be mechanically fastened building wraps, fluid-applied materials, poured concrete, non-insulating board stock, insulating board stock, metal, glass and many more materials. Keep in mind that there are two types of air barriers, interior and exterior. While both serve similar purposes, each complements and enhances the effectiveness of the other.
Interior air barriers:
- Control leakage of interior air into the wall cavity and attic.
- Limit the ability of moist indoor air entering the wall.
- Limit convection losses within walls.
Exterior air barriers:
- Control infiltration of exterior air into the wall cavity and attic.
- Limit the ability of moist outdoor air entering the wall.
- Prevent wind washing of wall insulation.
Vapour barriers as we earlier mentioned, are materials used to slow or reduce the movement of water vapour through a material. They are installed on the warm side of the insulation in a building assembly. As determined by climate conditions, in warm climates it will be on the exterior and in cold climates on the interior. A vapour barrier can be a mechanically fastened sheet material, fluid-applied materials, insulation board stock or spray polyurethane foam. Whether it is a vapour barrier or not depends on the thickness of the material./p>
What can I use as a vapour barrier?
There is a wide range of materials that can be used to create an effective vapour barrier. Here are some examples:
- Elastomeric coatings
- Aluminum foil
- Polyethylene plastic sheet
- Metallized film
- Exterior grade plywood
- Sheet-type roofing membranes
- Glass and metal sheets
Combination of Air Barriers/Vapour Barriers
An air barrier/vapour barrier aims to achieve water vapour diffusion and air movement control with one material. This type of material usually is the most appropriate for southern climates. It keeps humid outdoor air from entering the building cavities.
Mostly, this combination of air barriers/vapour barriers consist of one or more of the following materials:
- Polyethylene plastic sheets
- Builder's foil
- Foam board insulation
- Other exterior sheathings
Air barriers/vapour barriers mostly are placed around the perimeter of the building, under the exterior finish. The key to making it work effectively is to seal all of the seams and penetrations, including around windows, doors, plumbing stacks, electrical outlets and vent fans.
If there are any missing gaps of any size, apart from the fact that it will increase the energy use, it also can increase the risk of moisture damage to the house. An air barrier/vapour barrier should also be carefully inspected after installation before other work covers it. If there are any small holes, it's recommended to repair them with caulk or polyethylene or foil tape. Remember that patches should always be large enough to cover all the damage and overlap any adjacent wood farming.
Why do those barriers really matter?
Now that we got to understand the difference between air barriers and vapour barriers, the important question is why do they really matter? This question is asked by many architects, contractors and engineers, and the answers vary.
Firstly, air pressure and moisture control in the building are a very important element in constructing a durable and energy-efficient structure. Air leaks can cause damage because air not only short circuits insulation but it is also a carrier for unwanted elements inside a home, such as dust, vapour, noise, heat, cold etc. There is an increased risk for building failure especially when there is uncontrolled air movement from outside to inside and visa versa. Moisture can also be a hazard to a building no matter its state (vapour, liquid, solid).
Airflow must be controlled! - In order to build a safe, healthy, durable, comfortable and economical building. Airflow carries moisture that impacts a building material’s performance:
- Integrity and durability
- Behaviour in fire
- Indoor air quality
- Thermal energy
The key strategy to control the airflow is the use of air barriers. By effectively wrapping the building shell, air barriers ensure that the building is protected from the effects of airflow and leakage. Here are some of the most important benefits of air barriers and vapour barriers:
- Preventing the loss of conditioned air
For consumers the most important reason to use air barriers and vapour barriers is comfort. Usually, when moisture is in crawl spaces it affects the temperature in the house, making it either too hot or too cold. This happens because the moisture will absorb all the warmth from your house. A crawl space vapour barrier system and a proper air sealing help reduce uncomfortable temperature fluctuations and often allows for smaller, more efficient HVAC equipment.
- Saving on energy
Maintaining conditioned air means less energy is needed. Saving energy means lower utility bills. Since all building systems must perform well together to optimize energy efficiency, the savings can add up. Electricity bills rise because more electricity is being used to keep heating appliances working. By installing a vapour barrier and air barrier, you’ll keep your energy costs down.
- Preventing moisture and mold growth
One of the most common problems in cases of missing a vapour barrier system is that crawl spaces create high moisture levels, which may result in mold growth. Wherever air moves, water vapour can follow, therefore, it is important to have a proper air sealing. It will reduce the risk of water vapour moving into the wall, which can cause structural damage or even health problems.
- Improved indoor air quality
An air barrier will help you keep out pollutants such as suspended particles, dust, allergens, insects, odours and more. Now it’s no time to question if you should use a barrier system, but how to design and install high-performance barriers that will stand the test of time.
- Protecting your crawl space pipes
Vapour barrier systems can help you prevent your crawl spaces pipes from bursting. Most likely your crawl spaces contain different pipes that supply the water and power to your home. If moisture gets to these pipes, they’ll start rotting which can lead to bursting or breaking them. Installing a crawl space vapour barrier means fewer repair costs to worry about.
EcoStar’s insulation team strives to provide the best quality products and the highest standard of expertise. Our professionalism and experience goal is that you never have to worry about anything less than thorough and complete workmanship. Our professionals will guide you from the consultation to the execution stage. Contact us for your free estimate.