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Moisture problem between roof decking and open cell insulation

GBA Editor | Posted in Energy Efficiency and Durability on

I need help with a moisture problem in Southeast LA. A year ago I had a company spray open cell foam underneath the roof, and I have noticed that I have moisture on part of the asphalt shingle roof between the roof deck and the insulation which is constantly dripping into the soffit and the facia board. The rep from the company says that he has never seen this before, and that he dosen’t think the problem is with the sprayed foam, the roofer (roof is 6 months old) checked the roof and sprayed water on it and there was no sign of leaks.

Is this a problem were the warm air from the house or heater unit in the attic, and the cold air outside causing this problem?
How can this be resolved since the two supposedly professioanls don’t have an answer?

Thanks for any ideas that you may have.


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  1. GBA Editor
    Martin Holladay | | #1

    What is the outdoor temperature when this phenomenon occurs?

    Is this a finished attic or an unfinished attic?

    Did you install a vapor retarder on the interior side of the foam?

  2. Riversong | | #2

    The open-cell foam allows water vapor to diffuse through to the cold-at-night roof sheathing where it condenses and runs down, possibly saturating the foam which does hold water.

    Open cell foam needs to be sealed with a vapor retardant paint. If the installer didn't inform you of that, he wasn't doing his job.

  3. homedesign | | #3

    How can you "see" that you have moisture between the foam and the roof deck?
    Sounds like this was an existing home....
    They sprayed the underside of the roof where they could easily reach.
    I think it would be difficult to retrofit a perfect air control layer.
    Perhaps warm moist air has found a shortcut near the soffit area?
    Did you change your furnace to sealed combustion before you buttoned up the attic?
    Do any exhaust fans or dryer vents dump into the attic?

  4. homedesign | | #4

    Vapor retarder paint? in Southeast Louisiana?

  5. Riversong | | #5

    Louisiana? Why not? Open cell foam is an example of a hygrophobic material that is formed into a matrix which is hydrophillic. In high humidity environments, it's going to adsorb moisture and - depending on vapor pressure and temperature differentials - allow it to pass through, possibly to a condensing surface, such as the night-time roof sheathing.

  6. Michael Chandler | | #6

    Open cell foam is hardly hydrophillic. Leave a chunk of it floating in a bucket of water for a couple of days and see how much water it takes on, Hardly any, I've done it.

    I have not floated a wad of cellulose or rock wool or fiberglass insulation in water overnight yet. It would be an interesting experiment to set up 6"x6"x6" samples side by side in a 24 hour float test, weigh them before the test, float 24 hours on cold water, weigh again, set on a rack to dry for 12 hours and weigh again. I'm not saying that this would "prove" anything, only that it would give some interesting insight into the nature of the materials.

  7. Traci Sooter | | #7

    Nick, I am a little worried about my roof deck as well. I had a water leak from ice daming last winter and when we pulled the asphalt shingles in an area that should have been uneffected, the top of the deck was wet and looked like it had been for a while. Anyone have an answer for this?

  8. Riversong | | #8


    Maybe Icynene works as a rubber ducky but the standard test method for water absorption of rigid cellular plastics (ASTM D2842-69), demonstrated a 34% by volume water absorption after 96 hour submersion. And Icynene, Inc interprets this as being hydrophobic because it didn't absorb 100% of its volume in water!!!!!!!!

    If it's installed at 0.5 pcf and it can absorb 34% of its volume in water, that's more than 21 pcf of water absorption potential - or 2½ gallons per cubic foot.

    I've heard of Icynene problems under leaking roofs, in which the foam soaked up water like a sponge.

  9. Nick | | #9

    From what I have been reading is that if you use a Vapor Retarder that is 1 perm or less instead of 30 lb. felt it will keep the cold air on top of your roof and the hotter air in the attic from condensing. The problem I have with this is that the condensation is only happening in a small area, and not the whole roof.

  10. homedesign | | #10

    My question about your furnace was not exactly related to a durabilty concern.
    What is more important is the safety issue.
    I have seen a house where the builder created a conditioned air tight attic and then installed coventional (not sealed combustion) gas waters heaters in the attic...not good.

    If your furnace and water heaters are sealed combustion or all electric then no problem...
    If not... how are you providing make-up air to the furnace?
    Do you have carbon monoxide detectors?

  11. Nick | | #11

    Thanks for your reply, this was also a concern and I have no problems with combustible air for my furnace and water heater. They are both direct vent, and I also have carbon monoxide detectors. My concern right now is with the condensation problem. The temp. today in metro New Orleans is 36 degrees and I have so much condensation that there are a couple of icicles on the soffit. :)

  12. Riversong | | #12


    With spray foam under the roof deck, are you assuming that the soffit drips you see are condensation from the interior?

    If it's below freezing and you're getting icicles on the soffits, it's almost certain that you're experiencing what we northerners know all-too-well as ice dams. Heat from an attic that's full of combustion appliances is getting through the roof in enough quantity to melt the snow into water which then runs down to the cold eaves where it freezes and forms a dam which allows water to pool uphill until it gets under shingles and either into the soffits or into the exterior walls.

    If that's the case, you either need to increase the roof insulation and eliminate the thermal bridging of the rafters or ventilate the roof above the thermal layer by building a secondary roof deck on sleepers.

  13. GBA Editor
    Martin Holladay | | #13

    Is there any chance that the spray foam has shrunk away from the rafters, leaving cracks that permit warm humid air to contact the cold roof sheathing?

    Perhaps the moisture transport mechanism isn't diffusion -- perhaps it's air movement.

  14. Nick | | #14

    I took off the soffit vents, and you can see the condensation dripping between the roof decking and the insulation. The Temp in New Orleans today is a cold 36 degrees wich is very cold for us, but we rarely get any snow. Martin has a good point since it got colder last night and today I have more condensation since the icicles. Like Martin I'm begining to believe that somehow the warm attic air is coming in contact with the cold roof decking and that may be the problem.

  15. Michael Chandler | | #15

    Spray foam can cause a lot of damage if it gets loose on finished siding, concrete etc by working its way through the soffits so some spray foam outfits have gone to using food service film to stop up the rafter bays at the exterior walls. Of course this keeps the foam from sealing the wiring and plumbing penetrations in the top plate and allows the stack effect to run humid air up into the soffits where it can condense and cause the problem you are seeing.

    Some of the foam operators have also given up on "picture framing" application technique (where they spray up the side of one rafter and down the side of the opposing rafter and only then fill between the rafters.) If they take a short cut and just switch to a #3 wide spray tip they can run one wide bead of foam slow and thick up the center of the rafter bay and it will expand and "crown out" to the point that it touches the rafter a couple of inches away from the roof decking creating a little tunnel void between the top of the rafter and the roof decking.

    I'd go into your soffit and check to see if the foam has completely covered and sealed the top of the wall plate and I would cut a small plug out of the foam in the roof adjacent to a rafter or two to determine if the bay is truly filled with foam and if that foam is making a good airtight seal to the sides of the rafters. If you have issues in these two locations you have a bad installation. I've seen foam applicators inject foam into the tunnels to fill them but I really don't know what the fix is for the food wrap on the top plate problem other than remove all the soffits and seal from the outside.

    So much of this stuff is about caring enough about the building science to get the details right the first time. Spray foam is "hot" and there are a lot of get rich quick types going into green building with little care for quality or integrity. Meanwhile even those of us with high ethical standards are caught up in our disagreements about what is "the right way to do it" and "green enough" etc.

    Robert, I really respect your knowledge of green building and the industry but I hardly think a 96 hour submersion test is a reasonable way to test an insulation material, while it may be the standard in that sector of material testing, if you hold my house underwater for 96 hours the state of the insulation is the least of my problems. Having lived through several hurricanes I think a twelve hour dripping sink test replicating a hole punched in the roof by a falling tree (or a plumbing leak) would be a more sensible test for water absorption of an insulation material, which is why I spray foam in my roofs rather than cellulose. A big part of this is regional and climatic differences. What is right in Vermont may be different than what is right in North Carolina or New Orleans.

  16. Riversong | | #16


    The fact is, Icynene does not have to be submerged for it to get saturated. There are many examples of open-cell foam in walls and roofs that has become so wet from vapor diffusion alone that it could be wrung out like a sponge. It is simply incorrect to call such an open-matrix vapor permeable material hydrophobic, as the manufacturer and all the installers do, or to claim that it allows water to drain through and does not hold it.

    The Moffit house here in Warren was one such example. The Icynene (with no vapor barrier and T&G boarding inside) was so thoroughly saturated from diffused moisture that the plywood roof sheathing was delaminating and buckling and the sidewall studs were black with mold (EDU vol 25 #7).

    An anecdotal report on a blog told of Icynene in a basement ceiling under a bath that developed a leak. When the foam was pulled, the subfloor was black with mold and there were mushrooms growing in the foam.

    From EDU vol 25 #4:

    "Clyde Potts, a builder in Big Fork, Montana, had Icynene installed in the cathedral ceilings of his own home. Believing that Icynene did not require a vapor retarder, Potts used tongue-and-groove boards as his finished ceiling. Within a few months, moisture accumulation in the roof assembly was causing problems. The ceiling boards absorbed so much moisture that they swelled, popped their nails, and bowed out towards the living space. “The 1x6s started buckling,” Potts told EDU.
    “Water was getting through the foam. The water hit the roof sheathing and had nowhere to go. In one section, it popped the tongue-and-groove boards completely off the rafters..."

    Open-cell foam adsorbs water by both vapor diffusion and bulk leakage and holds it long enough to cause serious structural and health problems. I suspect the problem that Nick describes is due to vapor diffusion and condensation.

  17. Michael Chandler | | #17

    Robert, I know that I'm not going to dissuade you from your aversion to open cell spray foam, but I do remember reading those EDU articles, which I think were written by Martin, and they both had complicating factors involving high indoor humidity levels.

    I have submerged both Demelec and Icenene (and Biobased) foam underwater overnight to force them to become saturated with water and then left them out in the air to drain. The Icenene did dry more quickly than the others but all dried very quickly in keeping with my experience with roof leaks in homes with open cell foam. I've seen water damage in walls insulated with cellulose (black osb and studs) as well as fiberglass and would not be surprised to see water damage in walls insulated with foam.

    I don't think your concern with foam and those of us who use it is unwarranted, It's still a relatively new material and we are finding out about problems in the application with spray pattern, mix consistency and temperature regulation, and we may yet discover health effects that have not come to light at present, but water in walls causes damage regardless of the insulation material.

    Bottom line, I'm betting that the issue with this home in Louisiana is related to bulk air movement due to installer error and not to moisture diffusion through the open cell foam.

  18. Nick | | #18

    Michael and Robert,
    Thanks for your ideas.

  19. bill jr | | #19

    i did not use the spray because if the wood is not dry it wont stick!!! the only way to do it is in ridged foam i bought 500 sheets if 2" blue foam for 23.00$ a sheet and installed it in the rafters giving me a r 30 but make sure you use good caulk . then i installed a cold roof with 2 by3s every 16" . i then installed 1" blue board foam on the out side walls i heat my 3000sq house from 1926 with the smallest pellet stove and its 70 or more in the winter and nice and cool in the summer.i only use 4 ton of pellets thats pretty good if you ask me. billjr from buffalo,new york. not a drop of ice at all . ps do not use the open cell at all because the gas comes out in 8 to 10 yrs the only pay off is that you will get your money back right away then after the years go by you will see the difference. do not use the foil faced foam either always the blue or pink its the same stuff just different company its always been for years. i to was going to spray the foam in but not for 9000$ i only spent 4500$ and did it my self

  20. adkjac upstateny | | #20

    My experience with Icynene as posted here in other threads has been wonderful. I am more than happy. Super. And... the home I used it on... has a seasonally wet basement.

    The home is dry dry dry as a bone!

    The homes Robert mentions must have swimming pools in them. Showers taken for hours with no fan... water boiled for dinner daily with no tops on the pots... humidifiers running continuously trying to attain 65% hmidity like one of my customers tried after being advised to do so for their sinus issues!

    I would like to see Robert's problem homes in person... if someone has addresses

  21. Nick | | #21


    If you read my threat you can see that I live in New orleans, La. The climate here is always hot and humid, last week when the temperature was 28 degrees the humidity was 70 percent. The problem is defenitely the warm attic air coming in contact with the cold roof decking, thus the condensation , and not the things you mention above, because we don't have humidifiers, boil water and we do have exaust fans on the bathrooms.


  22. adkjac upstateny | | #22

    Nick... I bet you find out that open cell foam is not the problem.

    air leaks of some nature like others have said... most likely.

  23. Daniel Morrison | | #23

    Can you send me a photo of the icicles?
    [email protected]

  24. adkjac upstateny | | #24

    definite air leaks in Dans pic

  25. Rich Bev | | #25

    I would look for a crack in the condensation line from the A/C in the attic that is contributing to the water/humidity content first. Sincen it wasn't as great a problem when it was colder (no A/C is on) it may be just a direct leak from the A/C to a poorly installed spot in the insulation.

  26. Matt Spina | | #26

    Is the duct for the vent shown in your photo still in place? If yes, what is that duct made of and does it penetrate the foam insulation so that it is exposed to the warm moist air in the attic?

    If this is the case then obviously the cold outside air would cause that duct material to be cooler than the air in the attic. This would cause the moisture in the attic air to condense on the outside of that duct wall in the attic space. Once there it would simply drip down onto the open cell foam and soak in. Open cell foam, although great for use as an air barrier, sucks as a moisture barrier. The open cells in that foam would act like a sponge distributing that condensation water over the large area you describe.

    In any event, I think the penetration of the vent end-cap into the soffit at that point has something to do with your problem.

  27. Audie | | #27

    This stuff is pretty complicated. Can someone recommend a professional in or near High Point, North Carolina, who does good work with this becuase we have a 1923 home with basically no insulation, but a walk up attic with board flooring. We use if for storage, but I'm sure all of our HVAC is going straight out the roof. Thanks.

  28. Michael Chandler | | #28

    Audie I would contact someone from Southern Energy Management to do an evaluation of the building and recommend the most high priority solutions. 919-836-0330 Either Andrew Nicola or Rachel Della Valle would be great to give you recommendations. A duct blaster and blower door test along with basic inspection would be the place to start. they have partnered with Chad Ray and NC Energy Savers, (919) 389-4832, to provide the repairs which can include foam and sheet rock as well as duct sealing and crawlspace sealing.

  29. Danny Kelly | | #29

    Audie - you are correct - weatherization of existing homes can get extremely complicated especially when using some of the newer materials around. It is important to find a contractor that has some "house as a system" building science training. Both the Building Performance Institute (BPI) and RESNET will have some contractor locators on their website.

    We are based in Charlotte but would be willing to make the trip to High Point if you cannot find someone that you feel comfortable with.
    Good Luck.

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