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Not sure if my vapour barrier is done right or in the right spot. Can you tell me what is right?

GBA Editor | Posted in Energy Efficiency and Durability on

I live in Alberta, Canada (great white north). I built a new house myself and wanted extra insulation. I purchased 1″ styrofoam that has foil on both side which passes as a vapour barrier (P2000 is the manufacturer).

I built a normal 2×6 wall with 3/8″ OSB for sheathing. I put the 1″ styrofoam over top the sheathing from the footings right up to the eave. My house has a cement basement with a walkout which that portion is wood and is a storey and half. I put R-20 batts in the wall then drywall with no vapour barrier on the inside as per what the guys told me even though I questioned this many times but they said not to double vapour, even though I know it should be to the inside.

The ceiling has 1″ styrofoam on the bottom side of the rafters then strapped with 1×4’s then drywall or tongue-and-groove fir.

I noticed frost building up on a wall that had no drywall on it yet, so I questioned the P2000 guy. The guy said because air could get to the batts it was causing the frost, as soon as I covered it with poly it was OK.

I have a test hole on the main floor ( I was mad about the frost and punched a hole in the wall, now covered with tuck tape and a picture) and I checked it this winter and the OSB had frost on it. I phoned and questioned this and they said that was normal, but I don’t believe them.

Can anyone give me advice or guidance for this situation? I was trying to get a better insulated house but not sure if I did because there is no air gap on the outside walls. I was doing what they said because they have done it this way on several houses, but now their literature shows it differently.

Please help.

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  1. GBA Editor
    Martin Holladay | | #1

    Up in Alberta, I assume you are in Climate Zone 7 (using the DOE Climate Zones developed for the U.S.) If you use rigid foam sheathing on the exterior side of your OSB, and if you have 2x6 framing filled with insulation, your rigid foam needs a minimum R-value of R-15.

    Unfortunately, your 1-inch-thick foam from P2000 is made of expanded polystyrene (EPS) and has an R-value of only R-4. (P2000 has been in legal trouble in several U.S. states and Canadian provinces for exaggerating the R-value of its insulation; but trust me, it is 1 inch of EPS, and its R-value is about R-4.)

    Your OSB sheathing gets cold during the winter, and it becomes a condensing surface that allows moisture and frost to accumulate. Eventually, your OSB is in danger of rotting.

    There are two ways to solve this problem. Either:
    1. Strip the siding and upgrade your exterior foam to a minimum of R-15, or
    2. Demo the drywall and the insulation between your studs and install spray foam insulation between your stud bays.

  2. Riversong | | #2


    Frost on the inside of your sheathing is hardly "normal", but evidence of a significant problem.

    The problem is less likely to be vapor diffusion as it is air movement into the thermal envelope from the interior. Poly works mostly by stopping air movement, though in extreme cold climates vapor diffusion can also be problematic and interior vapor barriers are generally recommended. But you're correct that you should not have a double vapor barrier as that would trap moisture in the wall cavities.

    Your mistakes were several:

    As Martin suggested, you would need far more exterior R-val1ue to keep the sheathing above the dew point in your extreme climate. Depending on your local heating degree days, you may need as much as 50%-75% of the total R-value exterior to the sheathing.

    You should not have used exterior vapor-impermeable materials.

    You should have used cavity insulation that prevents air movement, unlike the fiberglass I assume you installed.

    You should have detailed a very air-tight interior, such as with the Air-Tight Drywall Approach developed in Canada.

    You should take precautions to keep winter-time indoor relative humidity down to 30%.

    And you should have used at least double the insulation for effective thermal performance.

  3. oMovBMjK2B | | #3

    I wanted to say that I checked my walls again this year and I still have frost/ wet OSB when I opened up my "check holes". I have been trying to get answers from P2000 since June but am having no luck. I am worried that they will do nothing about the problem. The guys that sold the product in Alberta are no longer listed on their website or the regional manager from Saskatchewan. Like I said previously, that I installed it the way they told me even though I researched and questioned them often before I built. I don't want to have a rotten house but I believe they probably won't do nothing about it but I can't afford to tear my house apart and do it right. Any suggestions or help in my situation would be greatly appreciated. I don't have the money to take them to court. I just got a blower door test down and energy audit done but don't have the results back yet.

  4. Riversong | | #4


    The only thing that's under your control at this point is to keep the indoor relative humidity below 35% by using bath and kitchen exhaust fans and whole house ventilation (and not introducing unnecessary moisture into the house).

  5. jklingel | | #5

    Adam: I think we all hurt for you, as you tried, and actually knew more than the cats "helping". Were this my place, I'd do what was suggested about, come spring. Thicker outside insulation, tear out the sheet rock, install better insulation, and use the ADA. I am a rookie here, but I'd follow the advice they are giving, even though it means a little dodging and weaving when there are minor disagreements in the options provided.

  6. Adam | | #6

    Thanks, right now the inside humidity is 30% and that's with a couple of portable humidifiers going because we use a wood fireplace insert 24 hours a day, trying to keep all the wood from drying out( ceiling, baseboards and trim). I do have a HRV installed. I don't know what the ADA is?

  7. JR | | #7

    You are a good candidate for "Holmes on Homes" Canadian TV series. The show specializes in correcting cases like yours.

  8. Riversong | | #8


    A new house in the great white north should not need humidifiers. The house is dry because you're sucking in way too much outside air, and you're sucking in outside air because you're running a woodstove that's not direct-coupled to an outside combustion air intake. And your house is probably way too leaky.

    You need to get an outside combustion air kit for that woodstove (or replace it with one that offers that), and do a blower door test to see where the house can be tightened up. Make sure there's no air leakage up the chimney.

    You're drying out the house by warming up outside air and then pumping moisture into that air which is ending up in the walls because you have the vapor barrier on the wrong side.

    Fix the stove and tighten up the house, get rid of the humidifiers and make sure there's at least a vapor retarder primer on all insulated walls and ceilings.

  9. Adam | | #9

    Hi Robert
    Just so you know, its a fireplace insert with a 6" fresh intake directly outside and a 4" connected to the double insulated pipe to help keep it cool. The outside humidity is 75% and inside is 30% with the humidifiers running, without the humidifiers it would be around 20%. This is very common in everyones house in Alberta, most people use one in the winter. Like I was saying, I did a blower door test but don't have the actual results back yet, it didn't suck any smoke out of the fireplace so I am pretty sure it is airtight. We could feel the pressure difference in a matter of a couple of minutes. I am pretty sure we are very airtight besides the microwave exhaust fan, dryer, and HRV ducts.

  10. Riversong | | #10

    That's good that you have a sealed combustion woodstove and an apparently tight chimney. I'll be interested in hearing about the results of the blower door test, but I suspect you have a relatively leaky house. It's certainly under-insulated for that climate. What part of Alberta are you in and what are your heating degree days?

  11. Mr. Greenguy | | #11

    Water Vapor moves with the air and the heat, from the inside out. As the temperature of the vapor and air decreases, it reaches it's dew point. It now turns to water, where ever it is. If this dew point is inside a cavity that isn't vented, it's trapped and you have a problem.

  12. Adam | | #12

    Hi Robert
    I live in central Alberta, near Red Deer. Most houses here are just a 2x6 wall with R-20 batts. I have that plus the 1" thick p2000 foam on the outside of the house from the footings up to the eave. The ceiling is at least R-40 and some spots R-48 plus the 1" styrofoam on the bottom side of the rafters. You can read how I built it in "Post #1". The P2000 is supposed to be vapor tight and every seam was taped so it shouldn't be leaky. I'm not sure of the heating days.

  13. GBA Editor
    Martin Holladay | | #13

    Several people have suggested that the P2000 foam is inappropriate because it is too thin to prevent moisture from accumulating in your sheathing.

    You are worried about the possibility of wet OSB; in fact you have "check holes" in your wall. So why are you running humidifiers?

    Look, it's your house. But it sounds like you are destroying it. Disconnect the humidifiers !

  14. Adam | | #14

    I'll disconnect them, just that in the past without running them it got very dry, but I don't want to make things worse.

  15. Adam | | #15

    Hi Robert
    Just got the results of my house and it scored an 82 on the new home energy guide. I had to ask him but the blower door test scored a 1.72ACH @ 50 Kpa.

  16. Adam | | #16

    Would applying a vapor barrier primer to the inside of the exterior walls fix my problem. I got told to do it now when the humidity in the house is less than 20%. Is this going to help my situation or cause more problems down the road?

  17. GBA Editor
    Martin Holladay | | #17

    Painting your interior walls with a new coat of primer won't hurt anything, but it is unlikely to help.

    It would be far better to tighten up air leaks in your walls, especially at the crack between the finish flooring and your baseboards, as well as at electrical outlets and other penetrations.

  18. homedesign | | #18

    1.72 ACH50 is not-So-bad
    Odd that the house is SO Dry

    The Air Tightness Skin AND The Vapor Tightness Skin are on the wrong side.
    maybe the wall assembly is acting like a passive dehumidifier?
    Collecting the H20 in AND on the OSB

  19. Riversong | | #19

    The air tightness of the house is largely irrelevant, since it was "purchased" at the expense of perpetual moisture problems and premature building failure.

    P2000 foam is a high-density EPS core wrapped with a mylar membrane. It is a near perfect vapor barrier and it is on the wrong side of your walls. The company that made it, Prime Materials Corp, has gone out of business.

    The only way to correct your problem is to remove the P2000 and install it on the inside where it belongs, with furring between it and the drywall to get the radiant barrier benefit.

    If anyone would like to watch the most perfect example of misleading and scientifically inaccurate sales propaganda, check out this 7 minute video infomercial on P2000:

  20. user-1065387 | | #20

    It looks like Prime Materials Corp. referenced above was a supplier of orthopedic materials.

  21. GBA Editor
    Martin Holladay | | #21

    The company that manufactures P2000 has changed hands several times. Among the names used by the manufacturer of this product (or important distributors) are the following:

    R. R. & D. Enterprises
    Royalty’s Research & Development
    Polar Industries
    Proactive Technology
    Perka Building Frames
    American Supply

    Some of these companies have been cited for using marketing materials that exaggerate the performance of EPS foam.

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