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Insulating the inside of concrete basement walls?

Post in 'DIY and General non-hearth advice' started by Knots, Mar 13, 2013.

  1. woodgeek

    woodgeek Minister of Fire

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    Sorry...missed that. Is that stackup really cheaper than 2-4" recycled polyiso on the outside with 2x6 studs and cellulose? If you weren't in a monosyllabic state I would give you a hard time about the foil backed drywall (a vapor barrier). In Maine, I will stay mum. ::P
    SmokeyTheBear likes this.

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  2. Swedishchef

    Swedishchef Minister of Fire

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    lol...what is wrong with monosyllabic states? I gotta admit, I have never seen drywall with foil...
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  3. Coog

    Coog Burning Hunk

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    I second foam on the outside wall continuous. Much thermal loss is through the stud. Not as bad a steel studs but still. Foam on the outside provides a nice thermal break.

    Of course the other major thermal loss is through the windows. You may spend as much attention to the insulation of your windows as you do the walls. Add brick as exterior facade and you will add some thermal mass to the structure as well. Now we are talking.
  4. jdp1152

    jdp1152 Minister of Fire

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    Too late to consider ICFs?
  5. Knots

    Knots Feeling the Heat

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    I was unaware of the effect of monosyllabism on insulation...
    SmokeyTheBear likes this.
  6. velvetfoot

    velvetfoot Minister of Fire

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    With the exterior you have to protect the foam from damage while making it look good as well as be concerned about carpenter ants. I can definitley see the foam under the concrete floor slab because then you wouldn't have put something on the concrete like I might; it'll be strong enough so can you drive cars on it and stuff, right?

    I've noticed less stinkiness in the basement since I put the 4" of foam on the walls.

    Are you sure about the stove heat setup? I'm sitting here by the insert and it got toasty quick after putting in some splits, nice looking flames, etc...value added, not totally just heat. It might take a while with the basement setup and you have to have grates, keep the basement door open etc. Are you going to be down in the basement a lot? Conserving wood, and dollars and time, can't be a bad thing.What kind of backup heat will you be using? Maybe you can tie something into that, but the indoor gasifier route seems expensive, especially for a not too big house.
  7. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    Sort of like PA say??
  8. Knots

    Knots Feeling the Heat

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    It seems like an equal number of pluses and minuses to putting the foam on the inside or outside. I'm definitely going to pursue putting foam under the slabs.

    When you say "gasifier" do you mean a wood stove with secondaries? I'm not familiar with the term.

    I will be in the basement a lot and it will be heating the two bays under some of time.

    Back-up heat will be LP.
  9. velvetfoot

    velvetfoot Minister of Fire

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    I meant like a boiler or furnace that uses gasification technology (see the boiler forum). I was just saying that you'll probably have to have it cranking in the basement to heat the upstairs, and you could tie something in to your central LP fired backup. That game could get expensive though.
  10. Knots

    Knots Feeling the Heat

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    I'm going with a Jotul F55 in the basement. Water will be on-demand LP. Back-up heat will be direct vent wall units - one in the basement - one upstairs.
  11. velvetfoot

    velvetfoot Minister of Fire

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    Sounds great!
  12. peakbagger

    peakbagger Minister of Fire

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    For some illustration of why foam on the outside is not a great idea in rural Maine

    Attached Files:

  13. Knots

    Knots Feeling the Heat

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    Whoa! Can you tell me any more about that?
  14. Swedishchef

    Swedishchef Minister of Fire

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    Looks like ants to me..
  15. Knots

    Knots Feeling the Heat

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    Yes - but was it completely below grade? What brand of foam was it? How long was it installed?

    This really makes me reconsider having it on the outside.
  16. sheetmetaldan

    sheetmetaldan New Member

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    I just found this thread lots of very good informative posts. I would not do the foam on the outside for fear of Carpenter ants. I added a 25`X23` ft addittion to my home a few years ago and did not use any foam on exterior of my foundation just tar painted on concrete for water protection. I have seen some high end homes use a black plastic material like a bubble wrap with a black felt cover, you would place the bubble side against the foundation (foundation is painted with tar or similar material) and felt side facing soil water passes through and runs down to french drains keeps basement dry inside. I wish I knew the name of this stuff maybe others will know what I am talking about and chime in. The french drains definatley keep my basement dry I highly recomend having them!

    One day I will finish my basement. I am thinking of using metal studs with a 1 inch gap off the foundation wall and putting astro foil between stud wall and foundation or sprayfoam between studs and foundation, not sure which way to go yet. The floor I am thinking of using 2" high density interlocking foam and a floating type finish laminate floor on top of that.
  17. peakbagger

    peakbagger Minister of Fire

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    For those who wonder, that shot was taken from some foam above grade in a dry location, actually inside the house. One end was butted up tight to a nail hole running through a rim joist to the outdoors. The hole lined up with some of the more serious tunnelling on the exterior of the house. The exterior foam on my walls has a paint on stucco so the tunnels are not as obvious from the outside. How I originally discovered they were in the above grade foam with the coating on it was just a few small holes with some frass usually on edges where the stuuco was thin or nonexistent (sawdust and ant waste) falling out of it. I had been having yearly infestations up on my second floor in some foam and couldnt figure out how they were getting in. One day I took a knife and cut out the area around one of the holes and found the tunneling.

    I am not the only one, a friend in Millinocket had Iso board foam on the exterior of his house under the siding. He had serious annual ant issues until he brought in a pro who tracked the ants. They ripped off the vinyl siding and found one whole wall of foam tunneled out and loaded with ants. He doesnt think it was moist.

    This is contrary to the advise that with wood, if you see carpenter ants they are just following wet/rotten wood. I have heard references to bug proof foam but have yet to find any boards or contractors who spray it. I expect Borate might work but dont know how it would affect the foam as it usually has a polyethylen glycol carrier. Great Stuff canned foam advertises a bug proof foam but I have never seen it at a store.
    Knots likes this.
  18. sheetmetaldan

    sheetmetaldan New Member

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    I think termites can do this type of damage as well! I think I recall my father telling me stories of this happening to places in Florida
  19. Knots

    Knots Feeling the Heat

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    Yikes! I know a guy who has continuous foam from his footings all the way up the side of the house. I'm going to do him a favor and NOT show him that picture. Ignorance, bliss, and all that...
  20. jdp1152

    jdp1152 Minister of Fire

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    Thanks for posting this. I've been going going back and forth on insulation upgrades. We went ahead and spray foamed our three attics, garage ceiling, and rim joist. The results have been outstanding, so I've been looking into what I want to do with walls. Rebuilding the window boxes and using exterior foam boards was the direction I was leaning, but given the amount of carpenter ants we have in this area, I think I'll reconsider and caulk the heck out of all my board seams when I reside the house this spring.

    I imagine their infestation on those boards was largely just hunkering down for winter and not seeking out a food source.

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