GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

UPDATED 6/25/19 @10:07am – Can open cell spray foam in MA cause mold/rotting?

jbritton1979 | Posted in Green Products and Materials on

Good morning GBA,

Thanks for all of the feedback!  This has been hugely helpful.  My plan is as follows.  I’d appreciate any feedback.  The two major changes are:

1. Use Certainteed Membrain on the exterior walls over the insulation to help with water vapor / dampness in walls.
2. Use Intello Plus in the ceiling of the second floor (floor of the attic).

I’m going to follow up with the installers and make sure the product being used will generate the intended R value either by changing the product or changing the number of inches of product. 

I’d appreciate any feedback on my plan.

Thanks Again!

————————————————————————–
Initial question from 6/24/2019

I’ve heard great things about this community!  I’m in the process of building my home.  The house already has been framed, sided (vinyl with Tyvek), windows, etc… Insulation is next.  We are planning on doing open cell insulation in the walls and attic (roof line).  I ran into my cousin who is a builder in Vermont and he informed me that they are not permitted to install open cell insulation in their buildings because it can result (in the winter) in the warm humid air from inside passing partly through the exterior walls and then hitting the dew point somewhere in the middle of the wall resulting in condensation forming and eventual rot of the framing.  I have similar concerns about the roof sheathing.

Is this a concern?  If it is, given that the siding is already installed without a vapor barrier, do I have any options that would allow me to safely proceed with open cell insulation?

Additional information requested in a comment follows.  

The roof will not be vented. It will be a conditioned space. What follows are the areas, the type of spray foam, the depth of the cavities, the planned inches of the spray foam, and the intended R-value.

Under side of roof – VS80 – open cell icynene fl-450 spray foam – 2×8 – 12.25″ of foam – 49 R-Value
All Exterior Walls – VS79 – open cell icynene fl-750 spray foam – 2×6 – 3.75″ of foam – 15 R-Value
Blockers / Rim Joist – VS80 – open cell icynene fl-450 spray foam – 2×10 – 5″ of foam – 20 R-Value
Overhang (2′) – VS80 – open cell icynene fl-450 spray foam – 2×12 – 7.5″ of foam – 30 R-Value
Under side of roof – VS80 – open cell icynene fl-450 spray foam – 2×8 – 12.25″ of foam – 49 R-Value

Thanks,
James

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. GBA Editor
    Brian Pontolilo | | #1

    Hi James,

    In Massachusetts a vapor barrier would be on the inside of the wall, not the outside. We do need to know if your builder intends to install one. As far as the walls are concerned, we also need to know the dimensions of the framing, likely 2x6, and the R-value target, or what your building inspector is requiring.

    Using only open cell spray foam in the roof is more problematic. Again, we need some more info. Will the roof be vented or unvented? What are the rafter dimensions?

    I'm sure you'll get a lot of responses here, but some more info will help us dial in those responses. In the meantime, please read this article: https://www.greenbuildingadvisor.com/article/how-to-build-an-insulated-cathedral-ceiling

    1. jbritton1979 | | #3

      Sorry Brian. The roof will not be vented. It will be a conditioned space. What follows are the areas, the type of spray foam, the depth of the cavities, the planned inches of the spray foam, and the intended R-value.

      Under side of roof - VS80 - open cell icynene fl-450 spray foam - 2x8 - 12.25" of foam - 49 R-Value
      All Exterior Walls - VS79 - open cell icynene fl-750 spray foam - 2x6 - 3.75" of foam - 15 R-Value
      Blockers / Rim Joist - VS80 - open cell icynene fl-450 spray foam - 2x10 - 5" of foam - 20 R-Value
      Overhang (2') - VS80 - open cell icynene fl-450 spray foam - 2x12 - 7.5" of foam - 30 R-Value
      Under side of roof - VS80 - open cell icynene fl-450 spray foam - 2x8 - 12.25" of foam - 49 R-Value

      Don't hesitate to ask for more details and I really appreciate the rapid response!

  2. Jon_R | | #2

    > the warm humid air from inside passing partly through the exterior

    Put MemBrain on the interior side and this won't be a problem. Consider adding strips of polyiso to the studs/joists if you want to increase thermal performance.

  3. Expert Member
    AKOS TOTH | | #4

    You are mostly good except for your roof. Open cell with unvented roofs can cause issues:
    https://www.greenbuildingadvisor.com/article/open-cell-spray-foam-and-damp-roof-sheathing

    For your roof, your best bet is enough closed cell foam for condensation control (I think it is around 3" in MA) and fill the rest with open cell.

    If you can vent from eave to ridge, it is probably cheaper to go add in vent channels, you can than fill with open cell without problems.

    Your walls are ok, I'm just wondering why only 3.75" of foam in the 2x6 wall.

    1. jbritton1979 | | #5

      Thanks! My guess is the insulation guys chose the bare minimum to keep the cost down. In your opinion, would it be better to target more like 20 R-value (5")?

      1. Expert Member
        AKOS TOTH | | #6

        The sad reality is the extra insulation is not worth it. It will take a long time to recoup the cost from energy savings.

        None the less, I would have a hard time not building the highest R value wall, it would bother me too much. Even putting some 2" fiberglass in there feels better than leaving it empty.

  4. Expert Member
    Dana Dorsett | | #7

    All of Massachusetts is in US climate zone 5A. With vinyl siding open cell foam is just fine in the walls without an interior vapor retarder tighter than latex paint on gypsum, per the IRC prescriptive, per the "Vented cladding over wood structural panels." exception in R702.7.1:

    https://up.codes/viewer/wyoming/irc-2015/chapter/7/wall-covering#R702.7.1

    Fill the stud bays completely with open cell foam. Don't use closed cell in the walls- it's a complete waste of money, buying next to nothing on thermal performance, and lowering the overall drying capacity of the assembly. R20 of open cell foam at 5.5" depth will outperform R21 of HFO blown closed cell foam at 3", due to the higher R thermal bridging. See:

    https://www.finehomebuilding.com/2017/07/10/closed-cell-foam-studs-waste

    Using MemBrain or other "smart" vapor retarder behind the gypsum board is optional, but would be cheap insurance if you ever decided to maintain high indoor humidity levels in winter.

    The unvented roof is still a problem with open-cell only, but you may be able to get away with it using Intello Plus as the interior side vapor retarder.

  5. Expert Member
    Dana Dorsett | | #8

    I'm a bit confused about the foam vendor you're actually using in your specifications, eg "icynene fl-450".

    FL 450 is a ~half-pound open cell foam product from Lapolla, not Icycene.

    https://lapolla.com/spray-foam-insulation/open-cell-foam/foam-lok-450/

    https://lapolla.com/wp-content/uploads/2018/08/FL-450-TDS-08.20.18.pdf

    It tests 22 perms and R3.7 @ 1", so 12.25" would be about (22/12.25"= ) 1.8 perms and (3.7 x 12.25=) R45. At 1.8 perms it's not super vapor open, but still about twice what is considered generally safe in zone 5 unvented roofs.

    Similarly fl-750 spray foam is ~0.7lb product from Lapolla, not Icynene:

    https://lapolla.com/spray-foam-insulation/open-cell-foam/foam-lok-750/

    https://lapolla.com/wp-content/uploads/2018/09/FL-750-TDS-09.13.18.pdf

    It runs ~ R4 @ 1" and 20.7 perms @ 2", and would be a better choice for the roof foam. At (R49/R4=) 12.25" it would hit R49, and (20.7 x 2"/12.25'= ) 3.3 perms. Not sufficiently vapor tight, but it at least hits code-min.

    Is in fact the description outlining which product goes where being flipped around a bit, with FL75o under the roof decks, FL450 going in the walls and band joist?

    At 3.75" the FL750 foam does indeed hit R15, but R15 is well shy of code minimum in Massachusetts, which requires R20 minimum. That can be met in 2x6 framing with 5.5" of the lower density FL450 product.

    A full 5.5" of FL750 would be R22, which is 10% higher than code-min on an R-value basis, but barely moves the needle on "whole wall R", not necessarily worth paying extra for.

    1. jbritton1979 | | #9

      Ok, I've updated based on the latest discussions with my insulation provider. Looks like he did have it backwards and the fl-750 is for exterior walls. The information follows.

      under side of roof - VS80 open cellicynene fl-450, 2x8, 12.25", R 49
      exterior walls - VS79 open cellicynene fl-750, 2x6, 5", R20
      blocks / rim joist- VS80 open cellicynene fl-450, 2x10, 5", R20
      over hang - VS80 - open cellicynene fl-450, 2x12, 7.5", R30

      I also spoke with him about the attic and he indicated he would be applying a special paint which will serve as a thermal barrier as our attic will contain air handles powered by external multi-zone Mitsubishi air based heat pumps.

      Thoughts? Will the paint serve the purpose of a vapor barrier or otherwise remedy the issue in the attic?

      1. Jon_R | | #11

        > Will the paint serve the purpose of a vapor barrier

        Some paint can be a Class II retarder. If that remains true when sprayed on open cell foam is a good question (substrate has a large effect and they test it with none).

  6. Expert Member
    Dana Dorsett | | #10

    Dude- though Icynene and Lapolla have gotten into bed it's not Icynene (tm) open cell foam (LD-R-50, etc) The product designations you are using are Lapolla's Foam-Lok series open cell foam, which are similar but not identical to Icynene products. The comparable Icynene products would be "Icynene Classic Plus" or "Classic Ultra" or LD-C-50:

    https://www.icynene.com/sites/default/files/US%20content%20uploads/TDS/Classic%20Plus%20-%20USA%20Technical%20Data%20Sheet%20Mar%202018.pdf

    https://www.icynene.com/sites/default/files/US%20content%20uploads/TDS/Classic%20Ultra%20TDS%204.26.19.pdf

    https://icynene.com/sites/default/files/US%20content%20uploads/TDS/Classic%20-%20USA%20Technical%20Data%20Sheet%20May%202018.pdf

    >"under side of roof - VS80 open cellicynene fl-450, 2x8, 12.25", R 49"

    No it isn't. The half-pound foam is only R45 @ 12.25"

    >exterior walls - VS79 open cellicynene fl-750, 2x6, 5", R20

    Yes, 5" is R20 (= code minimum). But note that 5.0" of 0.7lb foam is more expensive than 5.5"/R20 of half pound foam, and the shorter 5" path through the framing means it will slightly underperform R20 half pound foam.

    >blocks / rim joist- VS80 open cellicynene fl-450, 2x10, 5", R20

    Rong. At 5.0" the FL450 is only ~R18.5 It nees to be FL750 to hit that at 5", but it'll be cheaper to just go with 5.5" of FL450.

    >over hang - VS80 - open cellicynene fl-450, 2x12, 7.5", R30

    Rong agin. At 7.5" the FL450 is ~R28, not R30. It takes 8.1" of FL450 to hit R30.

    Read the datasheets:

    https://lapolla.com/wp-content/uploads/2018/08/FL-450-TDS-08.20.18.pdf

    https://lapolla.com/wp-content/uploads/2018/09/FL-750-TDS-09.13.18.pdf

  7. jbritton1979 | | #12

    Perhaps I wasn't clear. I am not an expert in this area. I am trying to make sure that the planned insulation being utilized is done correctly. I am seeking advise in this regard on this forum. I greatly appreciate the pointers. Especially as the insulation is supposed to go in next week :). I have relayed your points to the insulation guys. I'm guessing they marked down the wrong type, but that likely would've resulted in them using the wrong type too.

    1. MattJF | | #13

      Remember the foam guys are going to be running a moderately difficult chemical reaction based manufacturing process out of a truck in your driveway. You really only want this done by guys who know every line of the spec sheets and application manuals by heart for every product they use. This is why there is some concern about confusing product information.

      You need a clear statement of what they are putting in. You should check with the manufacture of that product to confirm they are an approved installer of that product. You should confirm the day of the install that what they said they would use is what is being mixed on the truck (look at the barrels).

      1. jbritton1979 | | #14

        All excellent points. Thank you!

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |