An Air Barrier Insulation employee spray foaming a school

Insulation Explained

Insulation and Air Sealing

“The “house as a system” principle reminds us that even if you are investing in new heating and cooling equipment or new windows and doors, you cannot optimize the energy performance of your house if you are not keeping heat in during the winter and out during summer.

In Canada, there is a large variety of choices when it comes to insulation materials and installation methods for walls, attics, basements, floors and ceilings.

Insulation upgrades coupled with air sealing are among the most cost-effective home retrofits. This simple home improvement sometimes pays for itself in less than a year.”


Natural Resources Canada, Government of Canada website 


The process of drawing fluid or gas into a porous material, such as a sponge soaking up water.


Acoustical treatment

Application of absorbing insulation for sound control.


Air barrier

A layer of material resistant to air flow. A material which is applied in conjunction with a building component (such as a wall, ceiling or sill plate) to prevent the movement of air through that component. Air barriers control air leakage into and out of the building envelope.



Device to maintain a ventilation space between the insulation and roof deck, assuring air flow from the eave/soffit vents to ridge vent or other roof vents provided in attics and cathedral ceilings.



Pre-cut pieces of fiber glass or mineral fibre insulation.


Bottom Plate (Sole Plate)

The lowest horizontal member of a wall which rests on the sub-floor to which the studding is nailed.


Building Envelope

The building envelope (or building enclosure) is the physical separator between the interior and the exterior environments of a building. It serves as the outer shell to help maintain the indoor environment (together with the mechanical conditioning systems) and facilitate its climate control. Building envelope design is a specialized area of architectural and engineering practice that draws from all areas of building science and indoor climate control.



The empty space between studs or joists typically filled with insulation.

Closed-cell polyurethane foam (also called high-density or two-pound foam)

Closed-cell foam is sprayed onto surfaces in layers not more than 50 mm (2 in.) thick at each pass (if greater thicknesses are desired), where it hardens in seconds. A 24-hr curing and off-gassing period is required before occupancy can resume.

The foam can expand 28 to 35 times its initial volume and should not be used in enclosed cavities. This product can be used as an air barrier. When applied to a thickness of 50 mm (2 in.), it can sometimes act as a vapour barrier. It can be used below grade and it bonds well to clean cement and masonry where it also makes a good moisture barrier. Though high-density foam is a premium, material with a soft chalky texture. When poured or injected into cavities by a trained installer, it has the consistency of shaving cream and may require some drying out time. This insulation can be used as an air barrier but not a vapour barrier.


Collar Beam

A horizontal member between two rafters and is very common in domestic roof construction. Often a collar is structural but they may be used simply to frame a ceiling.



The change of the physical state of matter from gas phase to liquid phase and is the reverse of vaporization. It can also be defined as the change in the state of water vapor to liquid water when in contact with any surface.


Crawlspace Vents

An opening to allow the passage of air through the unfinished area  under a first floor. There should be at least two vents per crawlspace.


Cross Bridging

Small wood pieces placed at angles so that they extend from the bottom of one floor joist to the top of the adjacent joist to add stability to the structural members.


Cross Ventilation

Placement of vent openings so that air flows in one vent, over insulated space, and out the other. In attics, a combination of eaves and ridge or high gable vents is best for cross-ventilation, because this takes advantage of natural convection.



Weight divided by volume typically expressed as pounds per cubic foot.


Eave Vents

Vent openings located in the soffit under the eaves of a house to allow the passage of air through the attic and out the roof vents.


Fibre Glass Insulation

An effective resistor of heat flow that is spun from molten sand and recycled glass into fibres.


Gable End Walls

The triangular end of an exterior wall above the eaves.


Gable Vents

A louver vent mounted in the top of the gable to allow the passage of air through the attic.


Ground Cover

Polyethylene sheeting used on the dirt floor of crawl spaces to prevent ground moisture from being drawn up into the house.


Heat Loss

Heat that is lost from a building through air leakage, conduction and radiation. To maintain a steady interior temperature, heat losses must be offset by a combination of heat gains and heat contributed by a heating system.



Acronym for Heating, Ventilation and Air-Conditioning systems.


Heat Recovery Ventilation Systems (HRV)

A mechanical ventilation system that recovers energy from exhausted indoor air and transfers it to incoming air. This system usually incorporates an air-to-heat exchanger which transfers the heat from exhaust air to the  incoming air or vice versa.



(Hydrochlorofluorocarbons) are compounds containing carbon, hydrogen, chlorine and fluorine. They have shorter atmospheric lifetimes than CFCs and deliver less reactive chlorine to the stratosphere where the “ozone layer” is found.



A humidity sensitive control device that signals the ventilation system to operate if the humidity goes above a preset limit.



Horizontal framing member set from wall to wall to support the floor or ceiling.


Knee Walls

Walls of varying length. Used to provide additional support to roof rafters with a wide span or to finish off an attic.


Loose Fill Insulation

Particulate insulation, made from either fiber glass or cellulose that is blown into a home using a motor and hose. Loose-fill insulation is suitable for walls and floors and excellent in attics and enclosed spaces, such as roofs, where the space between the joists may be irregular or cluttered with obstacles. You can use it to top up existing insulation in attics and accessible enclosed wall cavities and to fill in cracks and small or uneven spaces. It is not appropriate for below-grade application.


Material Safety Data Sheet (MSDS)

A standard formatted information sheet prepared by a material manufacturer describing the potential hazards, physical properties and procedures for safe use of a material.


Mineral Wool

A broad term used to refer to rock wool and slag wool.


Open-cell polyurethane foam

(also known as low-density or half-pound foam) is made from a combination of isocyanurate resins and catalysts,

resulting in an open-celled, spongy semi-flexible material. With a very high expansion rate – up to 100 times its initial volume – and its lower comparative cost, this product is more effective than closed-cell foam for filling larger cavities. It can be used as an air barrier but not a vapour barrier.


Perimeter Insulation

Insulation installed on the sidewalls of a crawl space to reduce heat loss. Also protects plumbing in the space from freezing temperatures. Perimeter insulation should only be used at the express approval of your utility.



The transfer of heat by direct rays traveling through space to a solid substance, but without heating the air (similar to light rays). Your body loses heat through radiation to cold windows and to cold uninsulated walls, ceilings, and floors. If walls themselves are cold, your house may be uncomfortable, even though the air temperature is as high as 75 or 80°.



A slope framing member that supports a pitched roof.


Recessed Fixture

Specialty lighting or exhaust fans installed flush with the ceiling, so that the back of the fixture extends into the attic. Recessed fixtures require special treatment in ceiling insulation. To avoid fire hazard, insulation must not come within 3 inches of the fixture.



The modification of an existing building or facility to include new systems or components.


Ridge Vents

A vent mounted along the entire ridge line of the roof to allow the passage of air through the attic.



Measure of resistance to heat flow. The ability of insulation to slow the transfer of heat is measured in R-values. The higher the R-value, the better the insulation material’s ability to resist the flow of heat through it.


Spray-foam insulation

Spray-foam insulation is made of plastic resin and a catalyst, which is prepared and applied on the job site. Spray kits for this type of insulation are available to the consumer, but employing a certified installer who is trained in the application

of the specific product will ensure the best results. The liquid foam is sprayed directly onto the building surface or poured into enclosed cavities with a pump-driven applicator. The foam expands in place and sets in seconds.



A vertical framing member used in both exterior and interior walls.



The structural material that spans across floor joists. It serves as a working platform during construction and provides a base for the finished floor.


Thermal Barrier

A material applied over combustible plastic insulation to slow the temperature rise of the plastic insulation during a fire so as to delay its involvement in the fire.


Thermal Bridge

A thermally conductive material which penetrates or bypasses an insulation system such as a metal fastener or stud.



 A building energy diagnostic technique using an infrared camera for locating areas of temperature differential in a building.


Top Plate

The horizontal member nailed to the top of the studding of a wall.


Vapour Barrier

A layer of moisture resistant material usually controls moisture diffusion to prevent moisture build up in walls, ceilings and floors.


Volatile Organic Compounds (VOC)

Any compound containing carbon and hydrogen or containing carbon and hydrogen in combination with other elements.

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