Is Using Closed-Cell Foam Worth the Trade-Offs?
This insulation material is popular for its high R-value and good air-sealing and vapor-blocking properties, but cost, health, and environmental concerns cause some builders to have second thoughts.
Synopsis: Contributing editor Michael Maines takes a detailed look at closed-cell spray foam, which is growing in popularity as an insulation material. Maines identifies its advantages—a high R-value per inch, a capacity for air-sealing and for blocking water-vapor movement, and its enhancement of the framing-to-sheathing connection. He then discusses its disadvantages—including high cost, messiness and potential health risks, and the fact that it can’t be used in many transitional areas where air leakage is high. But Maines focuses primarily on closed-cell foam as a contributor to global warming because of the blowing agent that is used in most closed-cell foams, which is over a thousand times worse than carbon dioxide.
Closed-cell polyurethane spray foam is amazing stuff. It’s a great insulator, with a higher R-value per inch than almost any other commonly available material. (Polyisocyanurate foam can be equivalent, but it varies with product and temperature.) When installed at least an inch or two thick, it essentially blocks water vapor and air movement. It even has some structural benefits: It’s good at adhering sheathing to framing, and it also enhances racking resistance. Thanks to these qualities and more, including strong marketing from the industry, foam is only getting more popular. Unfortunately, it also has some serious issues that aren’t typically discussed outside of greenbuilding circles. Understanding these drawbacks may convince you to limit its use to those special situations in which it makes the most sense, or even to avoid it entirely.
Polyurethane foam starts as two containers of liquid chemicals, referred to as the “A” side (isocyanates, the primary component of the solid foam) and the “B” side (a blend of resins, catalysts, a blowing agent, a flame retardant, and other compounds). When combined at installation, the chemicals react to create a polymer filled with tiny bubbles. The bubbles, or cells, are filled with a blowing agent and provide the insulating value, while the polymer forms the cell walls.
The ingredient that makes closed-cell foam special is the blowing agent—typically HFC245fa—but that’s also its biggest drawback.
HFC245fa is a hydrofluorocarbon refrigerant and a persistent greenhouse gas; it goes up into the atmosphere and stays there, preventing heat from escaping the earth. Carbon dioxide is commonly used as a measure of the damage a greenhouse gas can do, and HFC245fa is considered 1030 times worse than CO2. The only common building product more potent is the blowing agent in conventional XPS rigid foam. According to the Environmental Protection Agency, “Although [HFCs] represent a small fraction of the current total volume of [greenhouse gas] emissions, their warming impact is very strong. HFC emissions are projected to increase substantially over the next several decades if left unregulated” (from EPA Rule 21 Fact Sheet).
Insulating valuePro
Con
Air-sealingPro
Con
Environmental impactPro
Con
Vapor blockingPro
Con
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SafetyPro
Con
Sticky and structuralPro
Con
ExpensePro
Con
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More about spray-foam insulation:
- Spray-Foam Problems
- Spray Foam for the Rest of Us
- What’s the Difference: Open-cell vs. closed-cell polyurethane-foam insulation
There's this guy at the University of Alabama, Huntsville, who runs NASA's satellite remote temperature sensing program. I know he's not a contractor, but he swears there has been no increase in atmospheric temperatures. Another guy--not a contractor--was professor emeritus in atmospheric sciences at M.I.T. for 40 years. He says that we really shouldn't panic over a 2 degree projected temperature change in 100 years. Take that with a grain of salt, because, like I said, he's not a contractor.
I'm eagerly awaiting a paper written by Princeton physicist whatshisname on the proper way to flash chimneys when using metal tiles.
I am frustrated that the article doesn't address the foams that are out there that use a different blowing agent. I don't have any experience with them but I have heard about them (probably from FHB and the podcast) multiple times. Is nobody using them? Are they not really available?
... (pause, use Google)
After some quick research, including a story from Green Building Adviser almost 2 years old, there are closed cell foams with other blowing agents out there including a generally available product from honeywell with a Ozone score of 1, same as CO2. After 5 minutes of web research this posting sounds more like a ill informed opinion than the type of information FHB usually publishes.
Closed cell has been my only choice since using on a mid 90's project. I'm a serial remodeler -- often very old (1810/ 1870) or unusual buildings (fire house/church). Foam allows a coating in very tight or thin areas when space does not allow 6" of another material -- or even 4". Even 1" of close cell is amazing stuff for both insulation and air sealing. Foam transformed my drafty, inefficient and more importantly uncomfortable cape at the beach a few years ago. A few inches on my 1810 federal in the city 20+ years ago ... a full 4+ inches on my new project expanding a Pa stone building. Also, lived though a fire w/ foam -- the fire cut through the wood rafters and broke through the windows before burning through any foam. The foam eliminated any passage for the fire (and smoke) to find it's way through the structure. I can't comment on the environmental aspect -- except to say structures use smaller HVAC equipment and are energy efficient.