There are really only two major types of insulation used in the walls and ceilings of Canadian residential construction. They are cellulose and glass fibre. Cellulose is produced from recycled paper and borates. Borates are fire retardant and comprised of two types of chemicals: borax and boric acid. These are the same chemicals commonly found in day-to-day items such as beau­ty products, laundry soap and fertilizers. Glass fibre is comprised of sand, boron, phenol formaldehyde and a percentage of recycled glass product.

Cellulose is a loose-fill, fibrous insulation made from selected paper stock. Each bag displays Environment Canada's "Ecologo", classifying it as an "environmentally friendly" product. Cellulose may be hand poured or applied using a blowing machine. Machine application ensures that the cellulose is prop­erly conditioned and placed at the required design density.

The great advantage of cellulose is that it forms itself to whatever cavity it is injected into. This enables it to fill the cavity with the most consistency and does not allow any voids.

Glass fibre batt is the most widely used type of insulation by contractors because it is cost-effective nature. It is also more environmentally friendly today, as major manufacturers are making formaldehyde-free fibreglass insulation.

Typically it is installed in formed batts for the walls and loose fill for the attic. If not installed properly the product can leave voids, which cause air gaps leading to increased heating/cooling costs. Loose fill product is made from the same material as batts but is left in its fibrous state and must be blown-in using a machine and delivery hose. Glass fibre is fire retardant by nature and will not rot or decay over time. The product is quick and easy to install but offers less thermal value than cellulose.

Cellulose and glass fibre function under very different principles. Cellulose is a paper product and derives its thermal value from the density of the product, which means less air movement. Glass fibre derives its thermal value from the air, which it traps within its fibres.

Spray-in-place

Spray-ins of any type has several other advantages. There is little likelihood of the insulation settling since the fibres are glued to each other and the cavity sides. It forms a uniform covering throughout the cavity and forms a good air seal between electrical wiring, pipes, framing members, and anything else inside the building cavity.

Blown or sprayed loose fibre glass insulation uses roughly the same sort of equipment and adhesive that sprayed cellulose uses, but it doesn't prevent air infiltration as well as sprayed cellulose does.

There are some precautions to take when using sprayed fibre insulation. The chemical fire retardant within the products may corrode metal fasteners, pipes, or structural members that they contact. Unscrupulous installers can also "fluff" blow-in-blanket insulation, installing it at lower density than disclosed to the homeowner. Excessive water content and insufficient drying may promote fungus growth inside building cavities.

Application and cost

Sprayed insulation is most practical for new construction or unfinished spaces with exposed studs. Installations are often messy, since some of the insulation also adheres to unintended surfaces such as floors and windows. However, the adhesive binders are water-soluble so it is easily removed. After application, the stud edges are scraped clean with a special milling tool. As long as the "salvaged" insulation is free of debris it can be sent through the blowing machine again for reuse.

Sprayed insulation also needs time to dry before being enclosed in the building cavity. The drying time for the insulation varies depending on the type of insulation material and its moisture content, the moisture content of the framing members, and conditions such as humidity and temperature. Two (proprietary) techniques for faster drying times is to use rockwool, which does not easily absorb moisture, or netting over the studs to support the insulation, with less water content, as it dries.

Sprayed insulation systems cost more than fibreglass batt insulation - about 40 per cent more. However, it generally is less expensive than sprayed foam, and performs almost as well in many cases.

A foot of blown-in loose-fill cellulose yields an R-value of 45, while a foot of loose-fill mineral fibre would offer an R-33 level, according to a study by the Canadian Construction Materials Centre. A foot of fibreglass batt insulation would deliver about R-46. (Since most batts are 5.5 inches thick, the actual insulation is still a respectable R-21). R-values are compromised with any insulation if does not completely fill the wall cavity.

With thanks to Michael DellaFortuna, a product specialist with Can-Cell Industries Inc., Owens Corning / Johns Manville