by Rick Duncan, PhD, PE
A high-performance building envelope material, sprayed polyurethane foam (SPF) is increasingly used in commercial structures as an insulation and air barrier. Sprayfoam is playing a growing role in sustainable new construction, energy-enhancing retrofits, and even the net-zero energy movement.
The material acts as a single-source solution for thermal, air, and moisture control, providing architects and builders with the ability to seal the building enclosure via one product and eliminating the need to specify numerous additional products to accomplish the same performance. Used in all climate zones, the material is durable, versatile, and light. It tenaciously adheres to nearly every construction substrate, expands in place, and remains there without settling, providing consistent performance over the structure’s life.
SPF is offered in a range of densities, classified into three categories:
- open-cell (or low-density) foams consisting of 8 to 22-kg/m3 (0.5 to 1.4-pcf) density with an open-cell structure;
- closed-cell (or medium-density) foams of 24 to 37-kg/m3 (1.5 to 2.3-pcf) density with a closed-cell structure containing an insulating gas; and
- roofing (or high-density) closed-cell foams of 40 to 56-kg/m3 (2.5 to 3.5-pcf) density.
Regardless of density, all sprayfoam options perform as insulation and air barriers. However, the density and cell structure affects the product performance characteristics and should be a key consideration when specifying SPF for different building assemblies. Understanding the variations and fundamental pros and cons between the categories of SPF helps ease the specification process for new or retrofit commercial facilities.
Open-cell SPF is relatively soft to the touch, with the material’s structure providing flexibility to the foam. Offering excellent thermal insulation and air-sealing capabilities, it is ideal for filling interior walls and ceilings where there is no risk of water contact. Impermeable to air movement, it helps reduce the escape of conditioned air, which, in turn, lowers energy demands and operating costs.
An important distinction of open-cell SPF is its vapor permeability, which allows it to absorb and release moisture vapor more freely than closed-cell foams. This characteristic alone makes the low-density material ideal for interior applications rather than exterior ones where water contact is possible.
Open-cell SPF may also better accommodate the seasonal movement of some structures than its closed-cell counterpart. (For example, special design considerations may be needed in the installation of closed-cell SPF beneath large roof structures.) The material also performs better than the other sprayfoam classes in the area of sound attenuation because it is a softer material that absorbs sound better than more rigid closed-cell foams. Open-cell SPF tends to be the lower installed cost option because of higher yield (at the same R-value) and lower total labor costs, since open-cell foams can be installed to required thickness in a single pass.