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Community and Q&A

Open Cell Spray Foam—Bubble Repair

user-958947 | Posted in Energy Efficiency and Durability on

I’m building a new 1 1/2 story home in a HH climate (2B). Insulation is ocspf—6″ in walls and roof (i.e. semi-conditioned attic).

The insulation is complete, but there are just a few small areas that aren’t well done. There are some areas (corners mostly) that have fist-sized holes in the insulation. It appears that there is enough foam to seal to the outside, but not full thickness because of a bubble. The contractor and the manufacturer both advised that I should just fill these up with canned window foam.

1) Window foam is closed cell. If I spray this in the holes, I am concerned about creating a vapor barrier where I don’t want one. Would I create a condensing surface in the wall? Is a small area like this a problem, or would any condensate just sort of dry around the repair ball of foam? The walls are wood frame, plywood sheathing, and tar paper WB. The first floor is brick facade with air gap; second floor is fiber-cement siding with no gap. Roof is metal with polymer under-layment and plywood deck. So the roof must dry to the inside and the walls can dry from both sides.
2) I have some scrap chunks of the foam. Since the bubble areas appear to be sealed to the plywood sheathing, why couldn’t I just put a chunk of insulation into the bubble? The manufacturer didn’t like this option–something about the edges of the repair chunk wouldn’t be sealed. So what?
3) There are some areas (gaps) that were too narrow to spray with a foam rig. Such as the gap (1/4″ or so) between a roof rafter and the adjacent plywood sheathing in a dormer-type room. Would this be best sealed with window foam or should I just caulk the gap? Either one is vapor impermeable.
4) The manufacturer mentioned a 2-part ocspf kit (like propane bottle size) available from the big box stores, but not from him. But he said it was difficult to use. Any thoughts on this. I do have one larger spot on the roof I just discovered that I’ll have to either fix with this, or get the contractor back with his rig.

I would appreciate any comments on this.

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  1. GBA Editor
    Martin Holladay | | #1

    1. I think the question of the vapor permeance of any type of foam used to make this repair is irrelevant. Closed-cell foam or open-cell foam -- it doesn't matter which you use.

    2. The contractor who installed the foam should be responsible for the repairs, not you. I would insist that the contractor return to the site to fix the problems.

    3. It's a bad idea to try to fill a "bubble" with a chunk of cured foam. You need to spray foam in the voids to do any good.

    4. The cracks that are too narrow to seal with spray foam should be caulked. These are potential air leakage areas.

    5. The roofer specified the wrong type of underlayment for your roof. You describe your underlayment as "polymer underlayment." Almost all synthetic roofing underlayments can only be installed over ventilated roofs. Manufacturers do not allow these underlayments to be installed over unvented insulated roofs.

  2. user-958947 | | #2

    Thanks for your response. I have a few follow-up questions. Please accept this in the spirit of educating me and not of questioning your knowledge.

    1) It seems that vapor permeability would be quite important in a HH climate---thus the use of oc vs cc. Are you saying it doesn't matter because its a small area or that it doesn't matter period. i.e. I could have specified cc for the entire house?
    2) Yes, I need to get the contractor back out here, but he's going to want to just pump it full of window foam. I want to understand the science behind why that's ok for my climate and my situation before I let him do that.
    3) I thought poking a wad of scrap into the bubble hole would be akin to "flash and batt". I've since read some about the controversy over this type of system, and assume that is the basis of your concern. Right?
    4) Yep, the roof underlayment is "synthetic felt" ---looks like house wrap. I just looked it up on their website. It states that it is for installing above "properly ventilated spaces" and is considered to be a "vapor barrier". Ouch! What are the consequences--what problems could I expect? Will the open cell foam allow sufficient drying to the inside to avert any problems? Also, note that the metal roof is installed flat on the deck (no external venting). The metal roof is already a vapor barrier in itself, so how is another vapor barrier (the synthetic felt) just under it a problem? It's essentially two vapor barriers stacked on top of each other. What's the science behind this?

  3. GBA Editor
    Martin Holladay | | #3

    1. I disagree with your conclusion that only open-cell spray foam can be used in your climate. Closed-cell foam would also work fine. In general, open-cell spray foams are associated with more moisture accumulation problems than closed-cell foams. Fortunately for you, these problems with open-cell spray foam are generally in cold climates.

    2. As far as I know, canned window foam will work for a repair, as long as the foam has access to the atmosphere. Single-component foams are moisture-cured foams; they won't cure properly unless they can draw moisture from the atmosphere. Two-component foams can cure in the absence of atmospheric moisture.

    3. Flash-and-batt insulation systems only work if all voids are completely filled with insulation, leaving no air pockets, and only if the insulation is enclosed on all sides by an air barrier. Stuffing a piece of cured foam into a hole in the wall won't work.

    4. The main consequence of choosing the wrong roofing underlayment is that the manufacturer won't provide any warranty. Your roof will probably perform fine. However, next time you build this kind of roof, use asphalt felt.

  4. user-958947 | | #4

    1) It seems from reading the web site that oc vs cc in a HH climate is controversial. I chose oc (right or wrong) on the basis of allowing drying in both directions in the walls. I chose it for the roof so I could tell immediately if (and where) a roof leak occurred, and to allow drying to at least the one side. I may have misinterpreted this, but I thought drying to both sides ( or to at least one side), and not installing a vapor barrier was a basic philosophy of much of the BSC literature for HH climates. Is not the cc foam a vapor barrier? Anyway, having adopted that philosophy, I had concerns about now introducing small areas of vapor barriers into a system that otherwise had none. Could mixing and matching create a problem that wouldn't exist with a one-system installation?
    2) My roofer sold me the "synthetic felt" as an upgrade. Looks like I paid extra for the wrong stuff. By the way, if you do use asphalt felt as an underlayment, is ice & water shield ok in the valleys? It seems like it would be impermeable. What's actually at risk with the "synthetic felt" in my case---is it the "synthetic felt" or is it something else--like the metal roof or whatever?

  5. GBA Editor
    Martin Holladay | | #5

    Q. "I chose open-cell foam (right or wrong) on the basis of allowing drying in both directions in the walls."

    A. You're right that open-cell foam allows drying in both directions. It also allows wetting in both directions, since it is open to vapor transfusion. That's a double-edged sword -- but not a problem in your climate.

    Q. "if you do use asphalt felt as an underlayment, is Ice & Water Shield OK in the valleys?"

    A. Yes.

    Q. "What's actually at risk with the synthetic felt in my case---is it the synthetic felt or is it something else--like the metal roof or whatever?"

    A. The synthetic underlayment limits drying of the roof sheathing to the exterior. If you have traditional screw-down metal roofing with ribs and channels, roofing underlayment can dry upwards because of air movement through the channels. If you have standing-seam roofing, less upward drying is possible, and the choice of underlayment becomes moot.

    Final point: your roofer should not have charged you extra for installing a product in violation of the manufacturer's instructions. You could take your roofer to small claims court if you wanted to recover the upcharge -- or just let the issue go as the cost of your construction education.

  6. user-1103036 | | #6

    You should be fine to seal up the holes with can foam, provided they aren't too large. Looking at the data sheets can foam seems closer to open cell than closed. Of course no one lists the perm rating of their can foam, that I've seen.

    More importantly, to me, is the open cell roof leak stuff. This just seems like such a red herring to me. In my experience all bulk insulations can conceal roof leaks for quite some time. Roof leaks are also rarely as cut and dried as water spot below = roof leak directly above. When they're that simple you'll see the hole in your roof. If we're choosing our insulations based on the ability to locate leaks then we should be using batts so we can just pull them out and look. I have no issue with the OC foam, but the roof leak thing really shouldn't be a factor in one's insulation choice.

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