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Urethane spray foam on exterior above grade block walls?

dante03 | Posted in GBA Pro Help on

I was talking with a urethane spray foam installer this morning who stated numerous concerns about all other spray foam products but his – more notably open cell products. He says they do not perform in areas such as rim joists, etc. They don’t belong anywhere but in stud cavities on sidewalls. Go figure. He is currently spraying my neighbors’ exterior above grade block wall foundation(in addition to 4-6″ below grade) wall with a closed cell spray foam. He said there was a study that indicated this is as efficient as spraying the main floor 8′ exterior walls. I’m wondering if anyone has any info on this. He has been a spray foam contractor for 40 years, and seemed to know the spray foam argument well. But, I’ve never seen any stats on his particular approach. I live in Iowa, and the house he is working on has 2×4 exterior walls, and was built in the 1960s. I’m unsure of the wall/attic insulation. I’m sure his approach will help but is it as effective as he says?

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  1. GBA Editor
    Martin Holladay | | #1

    Open-cell spray polyurethane foam cannot be used below grade. However, closed-cell spray polyurethane foam is routinely used below grade -- either under slabs or on the exterior of foundation walls.

    Here's a PowerPoint presentation listing uses of spray polyurethane foam:
    Slide 11 shows that one application is below-grade walls.

    Here's information on one type of closed-cell foam, TerraThane, that is specially formulated for below-grade use:

    Here's a sample specification for below-grade spray polyurethane foam:

  2. Riversong | | #2

    What particular approach? You'll need to explain it better. But this guy sounds like a salesman with one answer to every question, not an insulation consultant.

  3. dante03 | | #3

    He is spraying 1-1/2" of closed cell spray foam on the exterior of the above grade foundation, as well as 4-6" below grade, and up to the siding. Somewhere around 20". How effective is this? He is not spraying the rim joist, or insulating anything else.

  4. Riversong | | #4

    Insulating the outside of a masonry foundation leaves the thermal mass where it belongs - on the interior. However, if its an unconditioned basement, then interior mass won't offer much benefit.

    Exterior foam of any kind needs to be protected from physical damage, UV deterioration and insects. It needs to be integrated into the weather-resistant barrier and properly flashed where it meets the siding. If it projects beyond the siding, it presents an aesthetic issue.

    Insulating the exposed foundation without insulating and air-sealing the band joists is a waste of time and money.

    This contractor sounds like a fraud.

  5. dante03 | | #5

    Robert - There is an exterior coating that will be applied. And it is an unconditioned basement. I'm anxious to see how the siding is flashed, etc, as those details are critical. I don't know that the guy is a fraud, but we'll see how serious he is about what he does as the project gets finished.

  6. Riversong | | #6


    Why is he insulating an unconditioned basement? Unless the goal is to redefine the thermal envelope to include the basement, then that's a waste of money and materials.

    And what could he possible mean by "this is as efficient as spraying the main floor 8' exterior walls"? How can adding insulation to a part of the house outside the thermal boundary be comparable to adding insulation to the thermal envelope?

    Am I missing something here or is this guy selling snake oil?

  7. dante03 | | #7

    I'm baffled as to the effectiveness of what he is doing. He gave me some 'fact' about how a crack in your foundation can lower the efficiency of your home by xxx amount. So I think air sealing may what he is trying to accomplish.

    I don't think your missing anything, my take is that he is set in his ways, much like a lot of guys around here. He's been in business for 40 years, so you'd think he's got some tried and true methods?? I don't know where the study he mentioned on the main floor 8' walls came from, but I questioned it as soon as I heard it as well. The basement is not finished, but I'm sure there may be a couple heat runs down there. To me, this doesn't qualify as conditioned - is this accurate?

    I didn't take him to be a crook, but I certainly don't understand the benefit.

  8. GBA Editor
    Martin Holladay | | #8

    Just because a basement isn't finished, doesn't mean it is unconditioned.

    If the basement walls are insulated, and the basement ceiling is not insulated, it's a conditioned basement. Even if all it contains is a furnace and a water heater.

  9. dante03 | | #9

    Martin - I agree. Maybe I'm missing something here. It's seems like a grey area - there are a couple heat runs down there, but there is no insulation on the basement walls or ceiling. Inefficient - yes, conditioned - I'd say no. Do you agree?

  10. GBA Editor
    Martin Holladay | | #10

    If the contractor is spraying the foundation walls with closed-cell spray polyurethane foam, then the basement walls are insulated.

  11. dante03 | | #11

    Martin - he is spraying only the exterior above grade foundation walls - it's about 20" of foam. Do you consider the basement conditioned following this?

  12. Riversong | | #12


    Generally a space is considered conditioned if there is an active source of heat (or coolth), such as a radiator or supply register (or air conditioner) sufficient for the space. An insulated space with some incidental heat, such as a duct runs or a water heater, might more accurately be called "semi-conditioned", particularly if its equilibrium temperature is somewhere between indoor set-point and outdoors.

    The IECC is ambivalent about these terms. It considers everything within the thermal envelope to be conditioned space. But section R408 states that an unvented crawlspace must be insulated to Table 402.1 levels and either mechanically vented or conditioned. So here, the code language refers to an insulated space that may or may not be conditioned.

  13. Riversong | | #13

    As to whether the basement is now "conditioned" space, I'd say it's no more conditioned than it was before, but it's now partially insulated, leaving the greatest heat loss area - the rim joists - uninsulated.

    Most heat loss from a basement is to the air, but unless the walls are insulated down to the frost penetration level (and ideally down to the footings), it can't be said to be fully insulated.

  14. Riversong | | #14

    And, being in business for 40 years only means that this contractor has either sufficiently satisfied his customers' expectations or manipulated those expectations with pablum in order to keep business coming. It sounds like a mix of the two with this guy.

    With more than 40 years in various trades, I've found that technicians either learn and improve over time or simply repeat the same techniques and assumptions ad infinitum - typically whatever they were taught by the last guy who learned from hearsay and habit.

    A "pro" can be successful either by offering a quality product that meets customers needs or by convincing customers that they need what he is selling. Unfortunately, most marketing falls into the latter category, ever since Freud's nephew, Edward Bernays, published "Propaganda" in 1928 after convincing half the US population (the women) that they would be more modern and liberated if they smoked cigarettes. The term "propaganda" at that time was synonymous with "information" but his approach to manipulating people based on their unconscious desires, mob psychology and conditioning techniques, was the start of the public relations (advertising) industry.

    He also was hired by Pres. Wilson to convince the American people to support our involvement in WWI (Americans have never wanted to go to war without manipulation), by the meat and poultry industry to convince Americans that bacon and eggs was the All-American breakfast, and by Alcoa Aluminum to sell the crazy idea of flouridating our water supplies (flouride is a waste product of the aluminum, fertilizer and nuclear industries).

    The damnable thing about Bernay's techniques of salesmanship is that they work, and many in the spray foam industry act as if they've read his book.

  15. BobHr | | #15


    I would like to see how he is going to finish it off so it looks astheclly pleasing.

    Con men are typically charming andhave an air of confidence about them. They sound convincing in what they say but when you look behind the curtain you will see half truths and lies. It sounds much like this guy.

    To me this is not a cost effective approach. What is the frost depth in your area.

  16. dante03 | | #16

    He finished it yesterday, and it looks good (minus the flashing between the siding and the foam). Matched the roof color (dark brown). I really don't think he is con man, depends on your definition of the word. I guess if he's selling something that doesn't work as he says, you'd call him that. But, I think he is 100% sold that his product is the best, and he is selling it accordingly. I talked with the homeowner yesterday, the contractor quoted spraying the rim, but she turned it down since she would have had to sheetrock the basement lid for fire code. I could see some validity in what he was doing if he sprayed the rim as well, but then it becomes an argument as to whether he should do it at all, or continue to do as the customer requested him to.
    Thanks for all the info.

    Frost depth is 42" here.

  17. Riversong | | #17


    Any insulator who would sell a partial job like you describe is a charlatan at best. If he had any integrity, he would have turned down the job if the homeowner wasn't willing to do it correctly.

    If, as you suggest, he's 100% convinced his product is the best thing since sliced bread, then he's a salesman and not an insulation professional who understands the pros and cons of each material and system and explains them to the client.

    As I've noted many times on this forum, there seems to be an epidemic of such scoundrels in the spray foam industry. Many of the foam installers who've posted here have demonstrated a profound ignorance of building science, and merely repeat the rhetoric they were taught by their supplier.

  18. user-659915 | | #18

    Reminds me of the old joke about the drunk looking for his keys under a streetlight - it's not where he dropped them but he could see better there. I'm guessing the foundation wall treatment was easier and cheaper than any treatment that could actually be expected to improve the home's energy performance, and it was what the homeowner could afford. To a man with a spraygun, everything looks like a foam job.

  19. BobHr | | #19

    So the frost line is 36-38 inches lower than the bottom of the insulation. The foundation is still going to suck the heat from the basement. The homeowner would have been better off installing a foil face foam board.

    Unless the contractor can show me proof that this will have a positive beneift then I will continue to believe that the homeowner was taken for ride.

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