Most spray-foam insulation is installed correctly, but as an industry consultant I’ve inspected SPF projects that have left me scratching my head in wonder. Sometimes the foam is cracked or delaminated, indicating an improper mix or poor substrate preparation; in other cases, there’s too much overspray. Occasionally the foam is properly installed but applied in the wrong place or at the wrong thickness; sometimes there is a vapor retarder when one isn’t required, or a required one is missing.
A decade ago, most SPF problems could be traced back to equipment issues. But with the recent expansion of the spray-foam industry, I’m also seeing a growing number of application defects made by inexperienced or poorly trained installers. Faced with job competition, some installers may be trying to cut costs by taking shortcuts, or they may be trying to extend the window of application into risky climatic conditions in order to squeeze in more jobs.
Since a poor foam job can sabotage building-envelope performance, general contractors should know what can go wrong and learn how to evaluate the quality of their installer’s work.
There are two main types of spray foam used for interior insulation: 1/2-pound open-cell SPF and 2-pound closed-cell SPF. Thanks to ASTM and industry-wide standards, different foams from different manufacturers within these two categories have roughly similar physical properties, such as R-value and the amount of closed- and open-cell content.
A few companies also offer 1.2-pound SPF, a kind of hybrid that shares some of the characteristics of both open-cell and closed-cell foam. But with no current industry standards or general code criteria for this type of foam available, installers will need to consult the manufacturers’ literature, case studies, and ICC evaluation reports carefully to compare various products’ physical properties and determine which is suitable for the application and meets local code requirements.
Stored in liquid form, SPF insulation consists of a petroleum-based “A” side (primarily methylene diphenyl diisocyanate) and a “B” side consisting of polyols, catalysts, fire retardants, blowing agents, and other chemicals.
Half-pound low-density open-cell SPF. Water is the blowing agent in low-density foam, which weighs between 0.4 and 0.6 pound per cubic foot of reacted material and expands to 100 to 150 times its liquid volume. This foam has an R-value range of 3.5 to 3.8 per inch and a vapor permeance of between 6 and 10 perms at a 3-inch application, which — according to current ICC building codes — qualifies it as a Class III vapor retarder.
Two-pound medium-density closed-cell SPF. Proprietary blends of HFC-245fa and water are the current blowing-agent packages used in medium-density foam, which weighs between 1.5 and 2 pounds per cubic foot of reacted material and expands to about 30 times its original volume. The foam has an R-value range of 5.8 to 6.8 per inch (depending on the blowing-agent formula) and a vapor permeance of less than 1 perm at 2 inches or more, qualifying it as a Class II vapor retarder. Unlike open-cell foam, 2-pound closed-cell foam is water-resistant and accepted by FEMA as a severe-flood-zone approved material.
Vapor retarder. Whether or not foam insulation requires an additional vapor retarder depends on the foam being used and its thickness, the climate, and local building codes. Closed-cell foam has a permeance averaging about 1.5 per inch, so as the average temperature goes down, more foam thickness is needed to keep the temperature inside the wall or ceiling cavity above the dewpoint and minimize the potential for condensation inside the assembly. The IRC allows a Class III interior vapor retarder — that is, latex or enamel paint — when at least R-15 of closed-cell foam is used in a 2x6 wall in climate zones 7 and 8. (For specific requirements for other climate zones, see 2009 IRC Table R601.3.1.)
With an open-cell content of over 80 percent, which allows liquid water to enter the foam, 1/2-pound SPF is considered a Class III vapor retarder. So, with a few exceptions, the IRC requires an additional Class II vapor retarder, such as the kraft-paper facing on batt insulation, on the warm-in-winter side of open-cell foam installed in climate zones 5, 6, 7, 8, and Marine 4.