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Basement Insulation

| Posted in Energy, Heating & Insulation on May 26, 2003 06:59am

We are currently trying to refinish a basement in Minnesota that has had previous mold problems.  We have gutted the existing framing and insulation and repaired the grade that we believe was causing the problem.  We have also applied thoroseal product to the interior block.  There is no exterior insulation or internal/external drain tile.  Our question:  what is the best method to insulate & finish?  From our research there are conflicting recommendations.  The use of the vapor barrier directly on the concrete versus on the interior of the wall.  Or, vapor barrier both on the interior & exterior.  Or, no vapor barrier at all – and use of polostyrene glued directly on the concrete.  We are planning on finishing a bedroom, bathroom, and family room and prefer with 1/2 inch sheetrock.  Additionally, in considering air flow – this basement is a walk-out.

Recommendations?

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  1. motek999 | May 26, 2003 09:25pm | #1

    Check out:

     http://www.buildingscience.com/resources/foundations/basement_insulation_systems.pdf

    They seem to have good information on this.

  2. PaulReuter | May 27, 2003 01:39am | #2

    Manitoba Hydro,s (electric company) recommended method is 6 mil poly atteched to the basement wall at grade level then downto the floor, out under the bottom plate, and after all insulating is done, up the face of the studs.  Where the poly is fastened to the wall, it is sealed with acoustic sealent.  I used 1x4 strapping & concrete nails to hold up the poly.

    Normally, you would not use poly on the cold side of the insulation but the purpose of this is to keep any water that comes through the wall out of the insulation & any that there is can drain out along the floor.  In a perfect world with a perfectly sealed foundation and weeping tiles, this wouldn't be necessary.  But, in your case I would recommend it.

    When I did my basement, I used 2x4 studs spaced approx. 3" from basement wall.  After studding & wiring were complete, I laid R12 batts on their edges, brick style, behind the studs & then R12 batts in regular position between the studs, for an R24 wall.

    Before applying the regular vapour barrier, bring the back poly up onto the face of the studs, & seal the vapour barrier to it with acoustic sealent.  Seal all the other edges & laps of vapour barrier with acoustic sealent as well.

    When applying finish surface (drywall, panelling, etc.) keep the bottom edge 1/2" off the floor.  The bottom edge of the vapour barrier can be pulled up in front & then the edge hidden behind the baseboard.  This also helps to protect against moisture.

    Hope this helps.  If I've missed any thing or raised questions, you know where to find me.

    Paul

    1. MG911 | May 27, 2003 08:25am | #5

      Hi Paul, I'm from Sask and appreciate your last post in regards to insulating a basement. I live in a 4 level split and the basement and 3rd level are very uncomfortable during our "mild" winters. I actually had one of those EnerGuide surveys done on my house today - what a surprise - the guy told me insulating the basement would be a big improvement!  I'll keep your tips in mind when it comes time to insulate my basement.

      Looks like I need to get some insulation blown in the attics too...he said they were about an R9 with the current insulation.  (House was built in 1959).

      Mike

  3. tcbudpro | May 27, 2003 01:50am | #3

    living also in minnesota and being in strictly remodeling our firm uses no vapor barrier. most of our houses are 50 -100 yrs old.best bet is let it breathe. leave yourself a 1 to 2 inch gap from framing to block wall.

    insulate with friction fit bats. tore out many basements with vapor barriers that were extremely moldy. moisture needs to go somewhere.

    1. darrel | May 27, 2003 04:37am | #4

      <em>From our research there are conflicting recommendations.</em>

      yep. As you can see from the above two posts, that's still very true.

      We're in MN as well and I spent a bit of time a couple of years ago researching the same thing. Baby came along so things went on hold for a bit, but maybe this summer we'll get at it again.

      Most, of cours, and rightfully so, will tell you that you shouldn't touch a basement unless is is absolutely dry. The problem with MN is that it's so humid in the summer that there is little you can do to keep your basement from being just a bit musty in july.

      Of the various advice I got, the options that I felt had something going for them were to build a floating wall a few inches from the wall, and somehow vent the back into the interior or exterior space. The only draw back to that, IMHO, was that it provided a great, dark, damp at times space for creepy crawlies.

      The option that I'm leaning towards is to do a 2x4 stud wall about 2 feet up from the floor. Above that, glued polystyrene to the concrete, and then 1x1 furring on the outside. Then I'd vent the bottom of the wall (probably with some heater ducts along the baseboard) This will insulate down to the frost line, and allow the bottom to dry out if ever need be.

      I have no idea how viable of an idea that is, but, like you, I've heard so much contradictory advice that I'm pretty sure there is no right answer...other than to plaster the concrete directely, paint it up nice, and pump a little more heat down there in the winter. ;o)

      One thing I did see was a basement system from Owens Corning. It was insulated fabric panels. It was a very interesting idea (completely breathable walls) but incredibly ugly. Looked like a bad 80's office cubicle farm. I am considering something like that, though...namely stained peg-board wainscotting. It's certainly a more 'modern' look, but I've seem some amazing interior spaces done with peg board (and other raw materials like finished particla board) that look quite nice. I may go for the 'modern' (also = CHEAP!) decor of pegboard walls, stained concrete floors, and exposed, stained celing joists.

      As a plus, any future owner could still easily 'finish' it a step further if they really wanted the sheetrock and drop ceilings.

    2. MDavies | May 27, 2003 02:15pm | #6

      I found MN building code it reads that you need R10 min if insulating foundation wall, you need vapor barrier between Ins. and concrete, but also reads vapor barrier on the warm side of the wall.  Have you had any problems with the Building inspectors?  I have been leaning toward no vapor barrier as well.  It obviously   never worked when the previous owner finished the basement.

      1. darrel | May 27, 2003 08:27pm | #7

        I'm just a homeowner...not a professional builder of any sorts, but I can say that I've found local building codes to be rather random.

        I've been on a few home tours in St. Paul of finished basements. Several of them had vapor barriers up (walls + floor) for the specific purpose that 'sometimes, we just get too much water and it leaks'. That just seems like a great way to trap water.

        From my limited amateur research, I'd be fairly confident in saying that 90% of all basements will leak someday (with exceptions going to some new foundations that install proper draintiles and insulate and waterproof the exterior), and, at least in MN, 100% of basements will be humid in the summer. So, it seems that if you live in MN, at least, you will have some sort of wetness in your basement at some point. Might as well let the walls be prepared for it.

        1. darrel | May 29, 2003 04:44am | #8

          TCBUDPRO:

          I noticed that you state that you don't use Vapor barriers, but another post mentioned that MN requires them.

          How do you go about getting around the code? I also want to finish off our basement this year and really don't want to use a vapor barrier. Is it just a matter of don't ask/don't tell? Or is there some justification that can be presented to inspector? (Maybe a $20 bill? ;o)

  4. User avater
    DanMorrison | May 31, 2003 04:05am | #9

    There's alot of viewpoints here, and they're not all as conflicting as they seem. Paul says two layers of vapor barrier -- down one side and up the other. Others say none at all.

    Building Science Corporation will give excellent advice. In fact, I'm working with Joe Lstiburek an an article for FHB right now -- it's his top ten list of dumb things to do to a house. Guess what the first item is? Yup-- Vapor Bartriers on basement walls. Why? because walls need to dry to at least one side, and below-grade walls can't dry to the exterior. That means that they need to dry to the interior right? Right.

    What about all the moisture flowing through the foundation wall? it'll pass right through into your interior living space. So, Paul is right sort of. He's saying you need to keep the water out of the wall assembly, but he's not taking active enough measures to keep the water out of the inside of your house.

    Yes, you should have your foundation sealed from the outside with drain tile along the perimeter. But it's a pretty fat chance that you'll hire a backhoe to dig it up and do it right? Right. I doubt if I would either. So what's the next best thing? Seal the interior from water. Rigid Foam insulation is wonderful for this. Glue the stuff to the foundation and seal it with some sort of hyper-sealant, then build your stud walls wherever the heck you want them. Better yet, spray the inside of the basement walls with polyurethane foam. Water-sealing and insulation in one shot.

    I edited an article in FHB issue # 153 by Larry Janesky called Sealing a Crawlspace. He outlines an excellent strategy for waterproofing a crawlspace (which is a mini-basement, only messier) wich should be useful to you.

    Hope that helps,

    Dan

    1. poorsh | May 31, 2003 08:52am | #11

      Hi Dan

      Loved your reasoning. We live in Vancouver, BC Canada and have just gone through horendous leaky condo syndrome. Everyone is passing the buck. Simple thought, if it can't dry out our local Botany Lab would like the spores for experimentation. We also have cold (relatively) wet and dry season, similar to Seattle. Energy efficiency was all the rage at the expense of circulation.

      Chhers

      Mac

  5. wrick2003 | May 31, 2003 05:52am | #10

    another minnesotans .02:

          yes, the MN energy code is confusing. more often than not, it's the inspector who determines for you just how close you need to be to the letter of the code.

    in a small suburb of St. Paul, i did a basement where we used 6 mil poly against the foundation wall, after cleaning it with a strong bleach solution, and friction fitted several 1 1/2" sheets of rigid insulation against the poly.  then we prebuilt and fit into place 2x2 partitions against the insulation and attached them to the block.  

    after the electrician was done, we added 1 1/2" rigid foam between the 2x2 studs, and covered it all with sheetrock.  a bit of trim and we were done. the inspector for this little burb was very happy with this arrangement and wondered to me why everyone didn't do it that way.

    the next basement in minneapolis was going to be built the same way, but the inspector would have none of that. she preferred to have bare 2x2 studs attached to the walls, rigid foam between the studs, and poly on top of that, then the rock.

    good luck     rg

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