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Closed-cell foam vs. open-cell foam

dbach | Posted in General Questions on


I am sure his topic has been discussed in detail, but I just received FHB magazine today and read article by Martin Holladay. a few years back I did a remodel and expansion of our house. I did remove much of the drywall on walls, but not 100%. The company I hired to do CLOSED cell foam was a bit new and maybe I did get a price break. But when I compared to Open Cell foam it was about 75%. This was with Icynene open cell. I have been happy with the closed cell. Also I thought closed cell has the advantage of making a tigher home vs the open cell. The one area I knew open cell was better is sound deadening which is always a plus.

We do plan on building a new home in the next few years and have been looking at much of the FHB and will use this website to review recommendations. It seems to be a bit difficult to get others to understand and / or use the new recommended techniques. Even with the closed cell 5 years ago, when the inspectors came, he had no idea if it was ok or not. He said he needed data on the product etc. After his 3rd time back, he said you are the homeowner, I am not sure what it is exactly but if you are ok with it, I will approve. Recently I had some hail damage on roof, not sure I want to replace myself and insurance covered so I had a few estimates. A few companies would not take the job because of no venting on the roof, this was event by one of the big box stores.

I will have to read more about the different products on this website, but it surprised me a bit in the article where it stated closed cell costs more, where it was 75% of what the open cell people wanted. I have been happy with the closed cell. I did have one roof leak and it was a bit more difficult tracking it down. It ended up being where I added additional roof support a nail curved up and penetrated outside. A bit of sealant fixed that luckily.

It sounds like he was recommending open cell over closed cell in all aspects. If so, I guess I need to find out before I build new home 🙂

Before I put drywall on, I used an infrared thermometer on the walls. One day when it was about 15 degrees F outside, I pointed it on a wall with various thickness of closed cell. (yes, I agree closed cell is a pain to scrape, and to get even ) At about 1″ wall temp was 64, at 2″ about 66, and 3.5″ thick was about 68 while inside temp was 68-70. So to pay the 2x price to go from 2″ to 3.5, likely not worth it. Seemed like average of 2″ was fine. It is definitely better than the old fiberglass batts that it replaced. Home is much quieter and dont feel any drafts.

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  1. Expert Member
    Dana Dorsett | | #1

    Closed cell foam isn't particularly tighter than open cell foam. Even at 3" half pound open cell foam is as air-tight as half-inch wallboard or 2" of closed cell, and it seals as tightly to wood framing as closed cell.

    In my area half pound open cell foam costs about 30 cents per board foot, closed cell runs a buck.
    That's 30% the cost per unit volume.

    Just about any spray foam or higher density fiber is going to work a heluva lot better than old low density fiberglass batts.

    See also:

  2. Stockwell | | #2

    Unit volume is not a good way to compare(board foot being one square foot, one inch thick) as one will give you R-3.6 and one will give you R-6.5 to 7. On an R-value basis, open cell foam is approximately 54 to 58% of the cost of closed cell foam.

  3. GBA Editor
    Martin Holladay | | #3

    Closed-cell spray foam works. Almost always, however, it costs more than open-cell spray foam, and many brands of closed-cell spray foam use a blowing agent with a high global warming potential. If you are a green builder, you want to avoid that kind of blowing agent.

  4. Expert Member
    Dana Dorsett | | #4

    Kevin- The significance of center cavity R value isn't what it seems. When installed between thermally bridging framing the framing robs substantially more performance from high-R foam than from lower-R foam. You're looking at less than an R2 difference in "whole-wall R" in a 2x6 framed house between R20-ish open cell and R30-ish closed cell foam filling (or nearly filling) the cavities.

    Martin shows the math for that in this blog:

    Or just look at his summary table:

    That's an R10+ increase in center-cavity R, but less than an R1.7 improvement in the wall's performance. It's a ridiculously expensive R1.7 to boot- performance that can been had much more cheaply (and more greenly) with 3/8" XPS fan -fold siding underlayment to the open-cell filled cavity. (Not that I'm recommending XPS fan fold- just sayin'...)

    It's not just the blowing agent- using having 3-4x the polymer in the wall cavities compared to 0.5lb or 0.7lb open cell foam is a real environmental footprint issue too.

    The bottom line:

    Save the high-performance foam budget for continuous insulating sheathing, where the full benefit of the higher R can be reaped.

  5. dbach | | #5

    The reason I went with the closed cell was the total cost was $17,000 and the Icynene (open cell ) was $21,000+. The closed cell was sprayed 3-5 inches thick depending where. As I stated, it was a bit of a start up business with a local person. Perhaps he did not know his costs well yet, and trying to establish his business. I did give a few referrals as I was happy with the install. It could also be the other estimate was a bit higher than it should have been.

    When I do next project, I will still be "Open" minded and consider both products. But I do like the one note Martin stated in his article that rigid board on the outside maybe the way to go.

    I am happy to find this site and from from a few magazines I subscribe to, I hope to pickup knowledge before contracting the work out. I am a home owner, not a builder, but viewing much of the work of some, I tend to do some of my own work when I can. With some knowledge, I hope to be able to select a good contractor. The one technique that seems popular is putting rigid foam under the slab (done correct), but many builders I talk to think that is waste of money, just gravel with layer of poly, many never heard of doing such. Many say you will never get your money back on it, well comfort is something too :)

    Thanks for your replies and I will continue reading articles such as form MARTIN.

  6. Expert Member
    Dana Dorsett | | #6

    The rigid foam under the slab is more than comfort, it's a mold-hazard mitigation issue in many areas.

    Deep subsoil temperatures are often well below average summertime outdoor dew points, so the film of air nearest the slab can have extremely high relative humidity in the summer, even with vapor barriers under the slab. But an inch or three of rigid EPS makes the temperature of the slab track the room temperature more closely, resulting in much lower relative humidity in the proximate air film.

    If you use reclaimed EPS (or XPS, but not polyisocyanurate) from building material salvage yards or foam reclaimers for under-slab insulation it can pay back in cash savings too, since the cost of the EPS is typically 1/4-1/3 the cost of virgin-stock EPS. Using reclaimed foam (including polyisocyanurate) for the exterior of framed walls & roofs is pretty cheap performance too. Any reclaimed foam is greener than sprayed foam, since no new polymer or blowing agent is used- it only enhances the benefit side of the lifecyle cost ^ benefit balance.

  7. Jon_R | | #7

    My bare un-insulated basement floor is nowhere close to deep subsoil temperatures - it's 2F less than the room temperature, causing a 4% RH increase at the floor. 3F less under thick rugs.

    Foam under my slab would cause a small % decrease in my dehumidification and heating bills. No mold either way.

  8. Expert Member
    Dana Dorsett | | #8

    Most rooms will have stratification with the floor at least 2F cooler than the average room temp, even above-grade floors. Are you storing spent nuclear fuel under your slab or something? :-)

  9. Expert Member
    Dana Dorsett | | #9

    The deep subsoil temperatures in my area are in the low 50s F, and my basement slab is not insulated.

    On Saturday I took a few minutes to wander the basement with an IR thermometer in hand. The slab temperatures ranged from about 58F in the coolest room (wall temperatures 4' from the floor ~64-65F) to a high of 63F in one the warmer rooms (wall temps ~66-67F). The subfloor of the rooms above ranged from 68F to 72F as measured from below. The coldest room has insulation in the ceiling keeping it from being warmed by the rooms above. (The insulation is there for the radiant floor heating in the room above.)

    In one of the warmer rooms the slab next to an pen plastic storage bin (not a very high-R object) was 62F, but when the bin was moved the temperature of the slab at the center of where the bin had been was 58F.

    The average outdoor dew point on that day was 62F, but the average for July in most years is about 65F.

    Clearly any moisture susceptible materials resting on the slab would take on moisture on the bottom side. But with even a modest amount of insulation under the slab it would be at least a handful of degrees warmer, and the room stratification would be diminished as well, and the mold risk would be substantially lower.

  10. RobInNorCal | | #10

    Returning to the original question... in a new house construction, even in a moderately cold climate, does it make economic sense to use either open or closed cell foam as the interior wall insulation? Wouldn't dense packed cellulose (maybe with a flash layer of closed cell), and an inch or more of foam board on the exterior to break the thermal bridge, be more cost effective? [I'm in the same situation as David, starting a new house build soon and trying to make sense of all the great information on this site!]

  11. Jon_R | | #11

    True, I measured not far above the floor to exclude some stratification.

    When considering under slab foam, look primarily at two issues. What the energy modeling/payback shows for the climate and Winter comfort (I'd consider radiant heat). Any potential mold issues can be addressed with a little more dehumidification.

  12. Expert Member
    Dana Dorsett | | #12

    Dense packed cellulose is usually more expensive as cavity-fill in my neighborhood, at about the same performance point. Sometimes even damp-sprayed cellulose is more expensive than half-pound open cell foam. But it varies by market. A perfectionist batt-insulation contractor good with a caulking gun is often the most economic for cavity fill.

    But to be most cost effective, save the expensive high R/inch foam budget for continuous exterior insulating sheathing, using only cheaper stuff between the studs.

    The flash of closed cell approach is sometimes the best economics in a retrofit, where the existing siding and window flashing are not going to be touched. In new construction that's almost never the case- you get more bang/buck out of putting that money into the insulating sheathing.

  13. GBA Editor
    Martin Holladay | | #13

    I suggest you read this article: How to Design a Wall.

  14. RobInNorCal | | #14

    Thanks, Martin
    I had actually read that article (and probably a dozen other discussions here about building a pretty good, passive, airtight, appropriately insulated, water-resistant, vapor-tolerant (or managed, or self-drying) wall. It's clear and comprehensive, like most of the articles on this site - but, of course, there are so many options for different circumstances that one question inevitably leads to another....

    I just signed up for the site so I can attach my questions to the discussions about the building topics II need to learn about so I can build myself a Good Enough house next year.

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