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Finishing a room in basement with sketchy poured concrete foundation and related questions…

Jesse P | Posted in General Questions on

Hi. I own a bungalow in Minneapolis, MN built 1921 with a poured concrete foundation. I am finishing 1/2 of this basement as a legal bedroom, and wish to put in drywall walls and ceiling. My wife and I have lived here for seven years, and have had nary a drop of water leak through the foundation and into our basement. No mold or mildew problems, either, though it can get humid down there in the warmer months, for which we use a dehumidifier.

The room we are finishing was your typical Midwest basement bar when we moved in, and the walls were nothing more than 1/4″ thick cedar closet board tacked to furring strips attached to the concrete foundation with masonry nails.

I just finished tearing out the last of this stuff and am noticing that there is one corner of the basement where the concrete walls seem pretty soft, to the point where I was able to scrape a 2″ gouge into it with the claw of a hammer without too much trouble. The walls are also rather damp at the very bottom, to about 1.5′ up, for a length of about 3′. I want to clean these walls up so that I can attach 2″ XPS board all the way around as an insulated vapor barrier, and understand that these need to be attached to the concrete with construction adhesive (PL400 or something similar). This wall also had a sacrificial layer of concrete skim-coated across the lower two thirds to make it look pretty, and I’ve already scraped off all of the loose stuff (i.e. nearly all of it.), as well as any efflorescence/surface blisters.

I of course need to make sure that the adhesive will hold, which means I can’t be attaching them to a dusty, crumbly surface. I realize there are concrete sealers and hardeners out there (Drylok, SaniTred, RadonSeal) to help stabilize the concrete and keep moisture at bay, but I know that anything applied to an interior, without waterproofing the exterior, with only last for 5-20 years depending on the product. Waterproofing or wrapping the exterior of our foundation is not an option at this time (we spent a lot of money already on the egress window for this basement room and other home improvements this year), so I need to figure out something for the interior.

Once the insulation board is up, I want to hang the drywall on furring strips that are attached to it, so I can’t run the risk of the insulation board separating from the foundation eventually.

So…what is my best course of action with this foundation issue?

Thanks for your time and suggestions!

*UPDATE*

So, here’s something crazy: Looks like I’m not going to insulate the basement at all. As it turns out (according to Minneapolis code, anyway), insulation is not required for refinishing an existing basement into habitable space. It’s not that I don’t want to, though. It just seems that I shouldn’t. Check this out (from the City of MPLS website):

“Cover a northern quadrant of the interior bare basement wall (floor to sill plate) with clear 6-mil. polyethylene such that the polyethylene extends at least 10 ft along each wall away from the corner. Seal the polyethylene edges only to the wall, sill plate and floor with appropriate sealing tape or construction adhesive….observe the polyethylene for a period of at least 2 weeks. If the wall surface becomes wet or any condensate that has collected on the interior surface of the polyethylene does not evaporate or drain away, then the wall is by definition wet and interior insulation of any kind should not be installed on the walls of that basement.”

I know for a fact that the bottom 2-3 feet along the west and north wall had areas where they were consistently damp to the touch, even though most of it has now been parged over with a thin layer of masonry concrete and Drylok (which I only used on the lower half of the wall). While it’s too cold now to do a soak test (where you soak the ground next to the foundation for awhile to see if and how it penetrates the foundation wall), I feel like I shouldn’t even take the chance with insulation, especially because the rest of the basement isn’t insulated. I mean, the basement never really gets that cold, anyway, and is always comfy and cooler in the summer (though I do have to have a dehumidifier running constantly to keep it between 50-55% humidity, otherwise it’s around 75%. BTW, I’ve done everything I can on the exterior to make sure rainwater drains away from the foundation. I should also add that exterior insulation on my foundation is not an option.

Basically, there’s no way in hell I’m going to take a chance with a potential mold problem.

Two additional questions, then. First, should I use treated wood studs in addition to treated wood for the sill plate because I’m putting a wall over uninsulated concrete? Also, should I use regular sheetrock or the water and mildew resistant stuff with the green paper backing?

Anything else I should do before building these walls over my uninsulated foundation walls?

Again, many thanks.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Jesse,
    If the basement wall is that crumbly, the best insulation for your walls is probably closed-cell spray polyurethane foam. If you frame a stud wall with a 2-inch air gap between the back of the studs and the concrete, you can spray 3 inches of spray foam behind and around the studs.

    By the way, in climate zone 6, the 2006 IRC calls for a minimum of R-15 basement wall insulation, not R-10.

  2. Jesse P | | #2

    ...

  3. Scorched Earth, 3B | | #3

    That update halfway through the original post is hard to spot up there.

    Somebody please advise this fine gentleman before he finishes his basement uninsulated in 2012.

  4. GBA Editor
    Martin Holladay | | #4

    Jesse P,
    It's true that it's important to fix any moisture problems before insulating.

    Unfortunately, completely fixing moisture problems in an old basement often requires excavation of the soil at the exterior perimeter of the building, down to the footings, to install footing drains and an exterior waterproofing system. That's not cheap, but it's often the right way to proceed.

  5. Jesse P | | #5

    Martin-

    Thanks for your response. I understand that, but an exterior waterproofing system just isn't going to happen. We're already paying down a small loan we took out to do a bunch of other work on our house, and exterior waterproofing is not financially an option, especially in light of the fact that I'd have to tear out and replace a lot of landscaping to do it. Meanwhile, my permit is nearly expired and I need to get this buttoned up.

    So. Any further discussion of this needs to be based on how to proceed WITHOUT doing exterior waterproofing. Thanks.

  6. Scorched Earth, 3B | | #6

    How close are your plantings to your house where you're noticing wet walls, and how deeply are you watering there?

  7. Scorched Earth, 3B | | #7

    P.S. in my experience, Minneapolis city inspectors have been fairly understanding when it comes to timing of closing out permits.

  8. Aj Builder, Upstate NY Zone 6a | | #8

    Wet cellar. Use all PT wood. And of course use paperless drywall.

    To save money and not trap mold, your best bet would be to finish the concrete wall as is or w a cement coating made to look like a stucco finish of your choice. And concrete can be finished to be similar to drywall smooth.

  9. J Chesnut | | #9

    The best advice may be not to create a bedroom in these conditions.

    I've met some contractors that I found very knowledgeable on these matters that seemed to had success with closed cell spray foam even on basement walls that show signs of deterioration. Martin describes this method in comment #1.

    Insulating the basement bedroom would increase comfort and decrease the amount of heating fuel you use to heat your home. Closed cell spray foam has a relatively greater environmental impact than most insulation products. A not so easy question to answer is how much energy needs to be saved in order to overcome the impact of the spray foam application. Also, only insulating a portion of your basement is different then retrofitting your home to have a proper thermal envelope and therefore the energy savings potential of your proposed work is difficult to estimate.

    Here is a link to a blog that includes an excellent description of how a well thought out basement insulation retrofit was executed -
    http://blog.energysmiths.com/.

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