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Community and Q&A

Mold Growth on Tremco Enviro-Dri (WRB) Walls

Chip Keim | Posted in General Questions on

Could really use some help from the experts here on the next recommended steps to take to find a solution to the mold growth in my basement. I have a one year old home in Tennessee that was built using Tremco Enviro-Dri and Tuff & Dri products. About 2 months ago, I pulled back the insulation to began to run electric in the basement and found the sheathing and insulation to be damp and mold starting to grow. It appears to be a condensation problem as it was fairly universal across all the exposed framed basement walls, but is worse on the north facing walls. I have never seen any sign of the water penetrating from outside. The builder has installed an return air duct and dehumidifier in the basement to help solve the problem, but the dehumidifier has been running 24-7 for over a month and has never been able to drop the RH below 50-55%. The basement outer wall is framed with 2×6 walls with R19 unbacked insulation. We are wanting to finish the basement but obviously want to solve this problem first. The builder and local distribution rep think the drywall and paint will help but I am not so sure. What would you recommend our next steps should be? Unfortunately, with warmer weather approaching I am not sure we can prove we have it solved with the humidifier solution and not real happy about the costs associated with running it non-stop.

Thanks for your help-

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  1. Torsten Hansen | | #1


    You are talking about framed outer walls in your basement. Do you have a wood foundation below grade or is it a combination of traditional block/poured foundation and some above grade framed walls? Either way, the humidity level is high. Assuming a temperature of 70 degrees, 55% RH air has a dew point of around 53 degrees. Your walls are insulated with fiberglass but otherwise uncovered. The fiberglass lowers the temperature of the sheathing and does nothing to stop the humid basement air from reaching it. I would say that condensation issues are unavoidable.

    How to fix it? Well, that depends on the specifics of your situation. For now, I would remove the fiberglass to raise the sheathing temperature and reduce the risk of condensation. Whatever you do, don't drywall and do not put up any plastic vapor barriers. Priority number one is to dry things out and vapor barriers trap moisture. I recommend "Understanding Basements", which you can find on Building Science Corporation's web site.

  2. GBA Editor
    Martin Holladay | | #2

    The situation you describe is common. The problem is that you installed fiberglass insulation (an air-permeable insulation) without an interior air barrier.

    The air in your basement is warmer and more humid than outdoor air. Your wall sheathing is cold, because it's winter. You have no barrier to prevent the warm, humid indoor air from reaching your cold wall sheathing, so of course the moisture in the air is condensing on your cold sheathing, leading to mold.

    Fiberglass batts perform worse than any other insulation because they are permeable to air. The best insulation in a basement is spray polyurethane foam. If you don't want to invest in spray foam, it's best to keep your basement dry and wait for warm weather. Once your sheathing is dry, you can insulate your stud bays with fiberglass batts if you want (although almost any other type of insulation would be better). Then immediately install drywall or tile backerboard, following the Airtight Drywall Approach.

    Make sure that all of your electrical boxes are airtight boxes, and use gaskets or caulk when installing the drywall.

  3. Bruce Miller | | #3

    What happens if a foundation wall leaks with spray foam? I posted a question a couple of weeks ago about XPS foam that went unanswered. I know the obvious response - make sure your foundation does not leak. However, I'm being realistic that a foundation leak via hairline crack or concrete tie is always possible.

  4. GBA Editor
    Martin Holladay | | #4

    It's never good to have water enter your basement through the foundation wall. Before anyone considers insulating a basement wall, potential water entry must be addressed -- no matter what type of insulation you choose.

    If you're building a new home, it's usually possible to keep a basement dry by installing good footing drains leading to daylight, installing a layer of crushed stone under the slab, installing a waterproofing system against the exterior of the foundation walls, and backfilling with clean, porous material.

    If you want to insulate the walls of an existing house, your job is trickier. If you think that water entry is an issue, you may need to install an interior French drain at the perimeter of your basement slab; the French drain should lead to a sump equipped with a sump pump. You can then install rigid dimple-mat material on the walls, followed by a moisture barrier, followed by insulation -- ideally spray polyurethane foam.

  5. Randy Langer | | #5

    Mr. Holliday,
    I was stunned to read this post/letter [from Chip Keim] requesting help/advice.

    We're experiencing the very same problem/issue using Tremco Enviro-Dri here in our Berlin, MA condo development. We are a Green Community and have built the development to qualify as such. So far three units have been ID'd with severe mold growth, one of which also has a severe termite infestation. The units in question are less than three years old.

    I run my dehumidifier continuously, day and night and I still have moisture issues in my basement. A vapor barrier was installed, I removed it to dry
    out the soaked sheathing and batt insulation. As with Chip's comment, all three units have zero exterior water penetration, however all three units are
    Southerly facing and are shaded.

    My sheathing is rotting from the inside-out. It's as if my basement was drowning in it's own sweat. That leads me to one and only one conclusion,
    the Tremco Enviro-Dri, product is sealing off my basement preventing it from doing what it should be allowed to do, which is breathe, as a Tyvek product would allow.

    We've brought the issue to the attention of the State's Green Building Rep, they are suggesting installing ventilation systems to circulate air
    continuously though the basements to alleviate the moisture. Seems counter productive to me. If we're looking for energy efficiency with tighter homes
    using products like Tremco Enviro-Dri, why are we dealing with excessive moisture issues and running ventilation?

    My thoughts.


  6. GBA Editor
    Martin Holladay | | #6

    The first question that needs to be answered in any moisture or mold investigation is: "What is the source of the water?"

    You wrote, "I still have moisture issues in my basement." However, I have no idea how your basement was constructed, so it's impossible for me to know where the moisture is coming from.

    You wrote, "A vapor barrier was installed, I removed it to dry out the soaked sheathing and batt insulation." Basement walls should never include a polyethylene vapor barrier, so this may be part of the problem.

    In short, unless you can tell us how your basement was built, it won't be possible for us to guess where the moisture is coming from.

  7. Flitch Plate | | #7

    More analysis and diagnosis needed here before prescribing solutions or spending money:

    What kind of mold?

    I am assuming this is NOT a pressure treated wood foundation as no mold will grow on it?

    Did your Tuff-n-Dri include the Drain Star? And very important, was the underside of the slab water proofed? And how was the basement slab to basement wall joint sealed?

    And what about this: Tremco says do the following as well; and expect a drying period:

    Moisture through a slab or concrete wall is not in liquid form (usually, hopefully in a new building), it is vapor. Depending on season, as it moves indoors, it will pass through the FG insulation and condense when it hits the dew point or continue as vapor to rise and condense when it hits to cool sheathing, plates and eventually the underside of roof decks.

    Did you use OSB in the basement?

    How long did you, or even did you, allow the house to dry out before finishing the basement?

    Do you have working gutters and drains taking water downhill?

    Do you have surface water flowing on the lawn uphill, carried towards the house?

    Post some photos of the situation.

    Get a moisture meter and the check concrete slab and walls:

    But it’s hard to test this without drying out the building first.

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