Air barriers, moisture, and HVAC
Both kinds of SPF can form a continuous seal that acts as an air barrier, which is essential to creating a comfortable energy-efficient space. Open-cell SPF—described as 8 kg/m3 (1/2 pcf)—is typically associated with residential applications in Canada. It is commonly used to fill cavities in interior spaces or to insulate unvented attics. It is particularly good at deadening sound when used in interior partitions. Generally, open-cell foam has an 0.65 RSI at 25.4 mm (between an R-3 and R-4 per inch of thickness ).
Open-cell SPF is moisture-vapour-permeable, and usually requires a properly designed and installed vapour retarder in Canada’s climate. Closed-cell SPF has relatively low moisture permeability, so it rarely requires an additional vapour retarder. An exception to closed-cell SPF not needing a vapour retarder may apply in areas with high interior relative humidity (RH). A qualified spray foam contractor can help a building owner make these decisions.
Both types of SPF meet the requirements of an air barrier material at typically installed thicknesses of 25.4 mm (1 in.). When installed with other materials in a building assembly, they provide an effective continuous air barrier. The SPF materials adhere to the substrate and allow for easy monolithic installation around irregular shapes and penetrations. The material is applied as a liquid and then expands into foam in any nook and cranny in the enclosure to provide a seal. This provides superior energy performance and occupant comfort.
Closed-cell SPF—also known as medium-density or 32 kg/m3 (2 pcf)—is the dominant SPF material for commercial construction. Closed-cell SPF has a higher R-value than open-cell, typically an R-value of around 1.2 RSI at 25.4 mm (between R-6 and R-7 per inch of thickness). With its low permeability, a vapour retarder is not needed for this foam.
In Canada, it is more common to see this type of SPF in commercial or institutional buildings, especially as an air barrier and thermal insulation system applied on the building’s exterior. Closed-cell foam is also used as foundation and slab insulation. Not only does the foam provide thermal properties, but it also provides an effective capillary break and helps keep below-grade spaces warm and dry.
Regardless of the project type, it is critical to understand SPF during the design process so its impact on the energy performance of the building envelope can be taken into account. For example, using SPF typically requires the use of a smaller HVAC system. According to the Canadian Urethane Foam Contractors Association (CUFCA), HVAC sizing could be reduced by up to 35 per cent without compromising occupant comfort. Those savings could help offset some of the cost of the SPF. Given SPF’s ability to air-seal, it is necessary to design proper air distribution systems to control moisture from cooking and bathing.
While SPF is most often associated with its energy-saving properties, it has numerous other benefits, including dampening sounds travelling through the air, such as a loud television in an adjoining room or a snow blower outside. SPF is effective at reducing noises because it seals gaps and openings that would allow sound waves travelling through the air to enter the building. In commercial buildings, open-cell foams are typically used in interior partitions for sound control. It is also effective in sealing between dwelling units in multi-family structures.
Many of the properties that make SPF effective for interior insulation also make it attractive for flat roofing applications. SPF roofing is high-density closed-cell foam, frequently described as 48 kg/m3 (3 pcf). Like SPF insulation, it can form a monolithic insulation barrier atop a roof deck. Since SPF roofing is rigid and has neither seams nor joints, it forms an impermeable surface.
Additionally, SPF roofing offers insulation benefits. As it is fully adhered to the substrate, the rigid foam provides uplift resistance during wind storms. A properly maintained SPF roof with regular recoats of the exterior membrane can last for decades.
According to the Spray Polyurethane Foam Alliance (SPFA), some SPF roofs have lasted effectively for more than 30 years. With such a long service life, they are an example of a sustainable roof system.
Due to the unique insulation properties of an SPF roof, heat from the interior of the building will be slow to melt the snow on a roof. Maintaining snow on the roof may significantly increase its thermal performance. Roof colour and slope choices are important factors in calculating the snow load for SPF roofing.
Most building owners are setting a goal of reducing the environmental impact of the built environment. SPF gets high marks for energy efficiency, building durability, and comfort. SPF’s superior performance and durability help building designers meet the demand to deliver low-energy buildings with minimal environmental impact.
While there are several types of SPF with varied applications and a numerous benefits, it is worthwhile for architects, specifiers, and builders to gain a deeper understanding of the product. It has the ability to fill in cavities that could otherwise pose challenges, and allows for more creative design. It can reduce air infiltration and outdoor particles such as dust and pollen that come with it, making spaces more comfortable.
Also, its use as a roofing material can provide an impermeable surface that insulates and can strengthen a structure. The better a designer or builder understands SPF and its uses, the more projects and clients will benefit.
Peter Davis is president and CEO of Gaco Western, and chair of the Spray Foam Coalition at the Center for the Polyurethanes Industry (CPI). He serves on the executive committee of the Spray Polyurethane Foam Alliance. Davis can be contacted at firstname.lastname@example.org.