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ABOUT SPRAY FOAM
SPF stands for Sprayed Polyurethane Foam commonly referred to as “spray foam”. Spray foam is a two component system consisting of Isocyanate (A side) and a resin (B side). When these two components are mixed together at a 1:1 ratio the resulting product quickly expands into the product we commonly know as spray foam.
Spray foam is the leading material used in the construction and renovation industry due to its ability to effectively insulate and impede air movement within the building envelope. Typically Spray foam comes in two forms, Open and Closed cell. Open cell foam typically has a density of 0.5 Lbs per cubic foot while closed cell foam typically has a density of 2.0 Lbs per cubic foot.
Open Vs closed Cell Foam
Both open and closed cell foam have there own benefits and areas in which they excel. Open cell foam is typically less expensive then closed cell foam and is ideal for attics and sound barrier insulation while closed cell is typically more expensive although has a (higher R-value per inch) then open cell and is used for basements, crawlspaces, main floor, garages, and commercial and industrial applications. When closed cell insulation is applied at a thickness of 2'' or greater, it acts as both an air barrier and vapour barrier and there is no need to poly over the insulation. Open cell foam no matter hoe thick of an application still needs to be covered by poly to achieve a vapour barrier.
THE TRUTH ABOUT R-VALUE
While R-value has been the standard measurement of insulation for the past many years, it only addresses one method of heat transfer “conduction”. The three methods of heat transfer include conduction, convection and radiation. Conduction deals with physical heat transfer from one medium to another while convection deals with heat transfer due to movement of air.
Within a building insulated traditionally with fiberglass or cellulose insulation, the majority of the heat loss is attributed to convection (movement of air from one place to another). Even though a typical fiberglass insulated wall may have an R-value of 20, due to convection currents it only has a thermal efficiency or heat retention of around 30%. The greater the differential in temperature between the outside and inside temperature the greater the convection current becomes thus removing the heat faster from the house.
The same wall applied with spray foam insulation at a thickness of 2’’ would have a thermal efficiency of around 87% due to its ability to impede air movement and greatly reduce convection currents within the walls and ceilings. Applied at a thickness of 3'' the wall would have a thermal efficiency of around 96%. When comparing different methods of insulation it is therefore impossible to compare using R-value and the comparison should always be made using thermal efficiency.
Typical convection currents in a traditionally insulated building
Added Benefits Of Spray Foam
Closed cell spray foam in addition to its insulating properties can also provide benefits in various forms including increased structural integrity of up to 300%, vapour barrier with closed cell foam when applied at a thickness of 2’’ or greater, resistance to mould and mildew, rodent resistant.