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

Condensation on floor around exterior walls

C Rouse | Posted in Energy Efficiency and Durability on

-House built 1.5yrs ago,
-open cell spray foam insulation on roof/walls
-Exterior walls: cement stucco/30#build felt/plywood sheathing/1/2″ gypsum board
-Interior walls: 1/2 gypsum board, sound batt insulation (no problems on interior walls)
-Location: Southwest Georgia
-Mold/Mildew throughout house, very bad along north & east walls
-Wife having severe asthma.
-2-1/2 ton a/c unit (does not run very much this time of year)

Do not believe the insulation was sealed. Any ideas on solutions?
I have a mold/mildew contractor coming over tomorrow. Thanks!

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.


  1. Peter Smith | | #1

    Can we assume the only ventilation/fresh air admission in these rooms occurs when the a/c unit is operating?

  2. C Rouse | | #2

    Yes sir, that is correct. There are roof vents in the attic space that are supposed
    to vent, however.

  3. Robert Hronek | | #3

    Is there a basement or crawl space? wast the home blower door tested? Do you have a mechanical ventalation system?

  4. David Meiland | | #4

    What is a mold/mildew contractor?

    I would start by taking moisture meter readings all over the interior of the house, and measuring the humidity in all rooms as well.

  5. C Rouse | | #5

    @Robert: It is on a slab, not sure about blower door testing, & no mech. ventilation

    @David: Hopefully one who will remediate?? What moisture meters do you recommend?

  6. GBA Editor
    Martin Holladay | | #6

    C. Rouse,
    If your house doesn't have a mechanical ventilation system, that's almost certainly part of the problem.

    You need to buy a humidity meter and check you indoor relative humidity. It would probably be useful to identify the sources of interior moisture and find ways to control the moisture. In hot humid climates, tight houses sometimes benefit from the installation of a stand-alone dehumidifier, although ventilation alone should address high indoor humidity during the winter months.

    To learn more about your ventilation options, you might want to read Designing a Good Ventilation System.

    Oh, and one more observation: the perimeter of your slab is probably cold. Did your contractor forget to install perimeter slab insulation?

  7. David Meiland | | #7

    I think ultimately you are going to want an energy auditor to test your house. If you have a lot of foam insulation you might well need mechanical ventilation, which could be as simple as running a bath fan on a schedule (if not 24x7). The problems you are having might be the result of interior humidity build-up that is not being adequately ventilated. The cause can be occupant load (people living and breathing), moisture coming from or up through the slab, or other things. You might also have an issue with water leakage from the exterior, or exterior humidity condensing in your wall cavities. Or, you might have some combination.

    Hopefully you can find someone who knows how to chase down all of the possible issues. If the contractor that comes out simply tells you how they are going to wipe up the mildew, get another opinion. Find a person who does enough diagnostics to clearly locate the source(s).

    There are a lot of moisture meters on the market, and I am not familiar with all of them. I use a Tramex Moisture Encounter Plus most of the time if I need to check drywall and I can't make any holes in it. Another is the Protimeter Surveymaster. I don't think you want to buy these, I think you want to bring in someone skilled who has them already and also has other tools like a blower door and possibly infrared.

  8. C Rouse | | #8

    @Martin: Thanks Martin, that was very helpful. He installed sill seal or something like that below the
    perimeter. I will look into the mech. ventalition system.

    My concern was the unsealed open cell insulation sweating and running down the back of the drywall.

  9. C Rouse | | #9

    Thanks for the info David. I will update in case something interesting is found.

  10. GBA Editor
    Martin Holladay | | #10

    C Rouse,
    You are confusing air sealing and insulation. Sill seal is an air sealing measure, not insulation.

    Slab foundations need to be insulated with vertical rigid foam insulation on the exterior of the slab. The foam is usually protected by a layer of stucco. If you live in a termite-infested region, other measures may be necessary.

  11. Dick Russell | | #11

    Aside from the obvious concern about lack of control of interior humidity, already covered well, I wonder if the wetting problem might be something as fundamental as a poor roofing job, with leakage wicking down through the roof foam (sprayed under the roof deck?) and down the walls until it hits the slab. CR, can we read anything into those "roof vents" and your mold being worst on the north and east walls? If not, perhaps those two walls just get a lot less solar warming to drive out moisture in them. Without a lot more info, we can only speculate, although by now we've collectively covered a lot of possibilities.

  12. David Meiland | | #12

    I have a mold/mildew contractor coming over tomorrow

    All right... what'd he say?

  13. C Rouse | | #13

    2 issues:
    1) Humidity was at 68% inside the house. Need dehumidifyer on HVAC system.
    2) Cold turndown on slab (uninsulated as Martin pointed out probably causing dew point and moisture on perimeter.
    Suggestion was to install vapor barrier and flooring material over stained concrete floor.
    Drywall was dryer than he usually sees, so the issue is coming from the turndown.
    Question: I have 3part cement stucco with continuous weep hole a couple of inches below the finish floor height. Think I should install z flashing below weep hole to make sure moisture (morning dew) making its way past the turndown? (Stud is aligned w/ turndown) Or install backer rod to remove this potential problem?

    Not sure how to install the exterior rigid insulation in this condition without blocking this weep hole.

    Thanks folks for all the help on this.

  14. GBA Editor
    Martin Holladay | | #14

    C Rouse,
    Start with ventilation, not dehumidification.

    A vapor barrier and finish flooring is not insulation.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |