Spray Foam Insulation Is Not a Magic Bullet
It’s time for me to bad-mouth something besides batt insulation
In case you haven’t noticed, I’ve been pretty hard on batt insulationInsulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance. in the past. I feel that my complaints and concerns are well justified, but no matter which insulation product is chosen, it has to be installed properly or it just doesn’t work.
Many people mistakenly believe (myself once among them) that spray polyurethane foam (SPF) is the perfect product, is always installed right, and tightens up homes every time.
This is simply not the case. In fact, I am seeing more and more poorly installed SPF than ever before. Demand for SPF has increased, bringing more installers into the market, many without the necessary experience or quality control to provide consistent quality installation. SPF, and open-cell foam in particular, is frequently installed with large gaps where the fast-curing material folds over itself, leaving both exposed and hidden unfilled areas. Mix and temperature problems can affect its ability to adhere to framing. Cured insulation often pulls away from framing members leaving large gaps. Insulation is installed too thin. And finally, installers can miss whole sections, leaving large gaps in the air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. that the insulation is supposed to provide.
Quality control needs help
While there are plenty of installers who have good quality control, in many cases, SPF has become yet another commodity product. Inexperienced contractors don’t understand that installation quality varies, and they often don’t know enough to evaluate the work they get.
I have inspected projects for LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. , EarthCraft, and other certifications where neither the insulation installer nor the contractor realized that the average installed SPF was several inches thinner that specified, had significant gaps, and in some areas, was missing entirely.
When I inspect homes, I stick a metal ruler in the foam to check the depth, pointing out the areas that are insufficient. More often that not, I see ½-pound open-cell SPF installations that average about 4 inches in rooflines and less than 3 inches in exterior walls. With an R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of between 3.5 and 4 per inch, that means the installed R-value doesn’t even meet the energy code minimum.
Not unlike the contractors who install batt insulation, there is far too little supervision or quality control over SPF in the field, and the contractors who are paying for it don’t know enough to evaluate what they are buying.
Is spray foam for lazy people?
While I acknowledge that SPF is often the best solution for some building conditions such as floors over crawlspaces that must be vented, it is a petroleum product full of chemicals with significant environmental impact. I see it used in exterior walls where blown in fiberglass or cellulose, combined with sealing the exterior sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. would work just as well.
Complicated building volumes, particularly vaulted ceilings and cantilevered floors are difficult to insulate and air seal with traditional materials, so builders resort to SPF, when simpler designs would allow them to use less expensive materials.
Even though SPF does solve a lot of problems with other insulation products, it isn’t magic and most of what it does, with some good planning and design, can be done just as well by alternative materials, often at a lower cost.
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