Insulation
An insulating material slows the rate of heat flow from a warmer to a cooler area. Building envelopes generally consist of several components that act in different ways to slow heat flow. These materials are usually comprised of one or more of the following:
• Most insulation materials block heat flow by radiation. They may be “opaque” to radiation much as dark glass is opaque to light transfer, or they may act to reflect back the heat as with reflective foil sheeting.
• The material (typically) contains tiny pockets of air or other gas(es) that reduce the conduction of heat.
• The air or gas pockets should be small enough and separated so that the possibility of heat flow via convection is reduced.
Some common types of insulation are:
Batt Insulation: Made from glass or mineral fibers. These fibrous materials are suitable for interior use, specifically inside exterior walls, as well as in ceilings and joist cavities. The performance of Batt-type insulation products is directly related to installation practices. Gaps and compression around wiring and plumbing must be prevented, and batt materials must fill cavities completely and evenly. Failure to do so results in a dramatic drop in the effectiveness of the insulation.
Loose Fill: Glass fibre, mineral wool and cellulose insulations are available as loose fill insulation. Loose fill insulation is generally chopped, mixed with air, and blown into place using special machinery. It can be used in attics and inside above-grade exterior walls.
Loose fill materials require the installation of a mesh or other material over the face of the wall to contain the insulation material prior to the installation of the finished wallboard. It must be applied at the correct density to get good performance.
Cellulose fibre insulation is made from recycled newsprint. The raw material is shredded and treated with chemicals to control flammability, to prevent the growth of moulds and fungi, and to keep rodents from nesting in the material.
As with any chemically treated substance, this may affect the indoor air quality of the house. A precaution, cellulose fibre insulation used on the outside of the air barrier should greatly reduce any problems.
Rigid Insulation: rigid insulation come (typically) in sheets, and is classified by a type # from 1-4, the higher the number the more dense the insulation is.
• Expanded Polystyrene (EPS) is made by expanding polystyrene beads in a mould using ozone safe and non-toxic gases. To make board stock, large blocks of expanded polystyrene are cut into sheets of various thicknesses using hot wires.
• Extruded Polystyrene (XPS) is manufactured by extruding a hot mass of polystyrene through a slit using refrigerant gases with low ozone depleting potential. At atmospheric pressure it expands, creating a closed-cell foam material. This product is available as type II, III and IV insulation and is suitable for use in all the applications listed for type ii.
Type II or higher will withstand fairly high pressures and is suitable for below grade applications. Both (eps and xps) types of rigid insulation can be used on the interior of the house, but because of its flammability must be covered with 12.7mm drywall as a minimum.
Spray Foam: Three different spray-type insulations are available to the residential construction industry.
• Spray cellulose insulation is available in a variety of formulations to suit specific applications. The material is applied using special applicators that mix the insulation material with water-based adhesives, allowing it to hold together and adhere to the surface to which it is applied. Wet spray materials are gaining broader market acceptance because they offer thorough cavity coverage, reducing envelope air leakage. Some spray-applied materials require the installation of a mesh over the face of the wall to contain the insulation material prior to the installation of the finished wallboard.
• Two-Component isocyanurate foam is best suited for use in exterior stud wall cavities and in perimeter joist spaces. Special applicators are used which mix the chemicals in the correct proportions. This is the common material used in manufactured insulated panels.
• Polyurethane formulations are available for use in a variety of spray applications. For large applications, the material is mixed on site using special foaming equipment. Some products are more environmentally benign, using water-based blowing agents.
• For small applications, single-component polyurethane foam is available in cans with “gun type” dispensers or in 4.5 kg (10 lb.) Canisters for sealing shim spaces around windows and doors. Application must consider the expansion characteristic of the foams, taking care to minimize pressures on frames, which could result in binding of window and door units or could void the window manufacturer’s warranty.