We have already explained that the exterior walls, floors, ceilings, and roofs comprise the solid layer of the house. This solid layer is also known as the building envelope in professional terms.
The thermal envelope on the other hand is composed of insulation and air & vapour barrier systems. These air barriers prevent the unwanted outside air from entering the house. They also prevent any air leakage of the indoor conditioned air.
An exterior air barrier can consist of any solid material. This barrier will prevent the flow of air between conditioned and not conditioned spaces. Some examples of air barrier systems controlling the flow of air are:
- rigid foam insulation or
- flexible air barriers (house wrap)
An effective air barrier needs to be continuous for yielding the best performance and energy efficiency. Building Codes dictate that exterior and interior air barrier systems must be fully aligned with the home’s layer of insulation.
An air barrier needs to be continuous. For that, you need to air seal any seams between the structural sheathing, joints, vapor barrier, and the transition membrane.
Where Should An Air Barrier Be Installed?
The air barrier may be installed on the outer side of the inner side of the insulation. That depends on the materials comprising the building and the weather of the location.
The air barrier in walls should be positioned on the outer vertical surface of the insulation. That is valid for every type of weather, including Toronto.
For the floors also the air barrier needs to be positioned on the outer vertical surface of the insulation. There are cases where the floor stands above an area with no conditioned air. In this case, the subfloor needs to be aligned with the inner horizontal surface of the insulation.
The insulation layer of the building can be easily seen by everyone. But it might be difficult on the other hand to determine what comprises the air barrier of a building. This can be especially true where building components meet each-other.
This might be problematic. For the air barrier to be effective, it needs to be continuous around the entire building envelope. You have to anticipate that since the design stage.
Take a copy of your residential home or commercial building drawings. In that, you can highlight all the parts that will form the air barrier on each floor.
Movement in Air Pressure Resulting in Infiltration and Exfiltration
Movement in air pressure on your home is caused by three main forces:
- Pressure caused from the Wind
- Stack pressure or the chimney effect
- HVAC system pressure
Pressure Caused from the Wind
Wind pressure can have a really big impact on the building’s energy efficiency. It affects the air leakage and the moisture conditions of the building.
Wind puts a positive pressure when hitting the facade of the building. But as the wind slips the surface and reaches the corners of the building, it creates a cavity. At this point the wind moves very quickly, resulting in strong negative pressure at the corners. The pressure is less strong on the rest of the building such as walls and roofs.
Stack Pressure or the Chimney Effect
The difference in temperature between the top and the bottom of a building creates different atmospheric pressure. This difference in atmospheric pressure is called the stack pressure, or the chimney effect. That in itself puts a different weight on the indoor and outdoor air columns in the winter.
The stack pressure in winter results in air infiltrations at the bottom of the building and air infiltration at the top of it. The opposite is valid during the warm season and when air conditioning is used.
HVAC System Pressure
The HVAC system can cause the so-called Fan Pressure. This system puts positive pressure on the inside of the building. That works perfectly for the warm weather season. But it can create serious enclosure problems towards the wind and stack pressures.
HVAC technicians use the Fan Pressure to block air and outdoor pollutants infiltrations. Recent estimates put the percentage of additional energy needed to heat and cool buildings due to air infiltration and exfiltration between 10% in cold climates and up to 42% in hot climates.
Eco Spray Insulation to the Rescue
Are you planning on insulating your home? Want to know if your home requires an air barrier or a vapor barrier? Do you have any questions regarding spray foam insulation products, cost, and prices?
Are you in between closed cell and open cell insulation? Do you need the opinion of an insulation contractor?