1. Welcome Hearth.com Guests and Visitors - Please enjoy our forums!
    Hearth.com GOLD Sponsors who help bring the site content to you:
    Hearthstone Soapstone and Cast-Iron stoves( Wood, Gas or Pellet Stoves and Inserts)
    Caluwe - Passion for Fire and Water ( Pellet and Wood Hydronic and Space Heating)

Insulating a basement

Post in 'DIY and General non-hearth advice' started by mithesaint, Jan 17, 2013.

  1. mithesaint

    mithesaint Feeling the Heat

    Joined:
    Nov 1, 2011
    Messages:
    412
    Loc:
    NW Ohio
    I'm in the process of getting started on finishing my basement. I'm going to have approximately 900 sq ft. Foam on the walls, studded walls and unfaced fiberglass between the studs. About 18 inches of the basement wall is above grade outside, and that already has an inch of foam insulation on it.

    I'm in NW Ohio. I plan on heating the basement only when it's being used, and will probably be using some form of electric. I won't be heating the whole thing, as part of it will be a workout room, and both the wifey and I would prefer it cooler in that room. Still gonna insulate that part, but not install any heat in that room.

    What R-value would you go to? How much did you put in your basement, and was it enough?

    Helpful Sponsor Ads!





  2. daveswoodhauler

    daveswoodhauler Minister of Fire

    Joined:
    May 20, 2008
    Messages:
    1,847
    Loc:
    Massachusetts
    Live in Central Mass, and I went with rigid R5 on the interior foundation walls, left about one inch of an airspace, and then framed with 2X4's and used R13 faced in the wall cavity. I added another zone of my boiler with 16 feet of baseboard, and it heats up very quickly and retains the heat well. Only thing I could have done more is some insulation on the floor, as that seems to be the coldest spon in the room. Without heating the area, the lowest temps I see is about 56-57 degrees, so you probably don't need much btu's for heating. (I was going to go electric as well, but found a pretty decent plumber to run the third zone on the cheap)
  3. velvetfoot

    velvetfoot Minister of Fire

    Joined:
    Dec 5, 2005
    Messages:
    6,480
    Loc:
    Sand Lake, NY
    I used glue and furring strips to attach 2 layers of 2" foam and drywall on top of that. Not finished covering yet. We don't really use the basement, so it's somewhat of a waste I suppose. The basement is less stinky in the summertime because of less condensation.
    Don't forget the rim joist area.
    Are you going to do anything on the floor? Insulation? Finish (paint, tile, etc)?
  4. semipro

    semipro Minister of Fire

    Joined:
    Jan 12, 2009
    Messages:
    2,293
    Loc:
    SW Virginia
    I've done this and haven't recorded temps or heating load but I can tell you that you'll feel a significant difference immediately. You'll realize that that the bare concrete walls were sucking the heat out of the room and any warm objects nearby (like you).

    There is a minimum thickness (actually R value) of foam needed against the walls to ensure that condensation doesn't form on the surface of the foam potentially causing problems within the wall. This thickness is dependent upon the min. temps outside the wall and the R value of the wall itself (which is almost nothing for concrete).

    Below grade its likely that 1" XPS board will be enough but it depends on your climate. Above grade you'll probably want more. I'd suggest doubling to at least 2". Bat insulation can not replace the foam in this application as you're trying to create a temp gradient such that the temp at which condensation would occur is located within the foam layer. If this condensation temp point was located within air space of the wall or the batt insulation you could have moisture issues in the wall (e.g. mold).

    You may want to consider doing the floor but getting the walls done is a great start. I'd suggest avoiding any contact between concrete and wood. If you're framing inside the foam and connecting below to the slab and above to floor joists than a foam layer should go between slap and the bottom plates. If found it easier to frame full walls instead of tying only to the wall. It allowed me to ensure that my walls were plumb and straight, which my poured concrete walls were not.

    As you're probably already aware you don't want to put oil-based paint, vinyl wallpaper, or other vapor barriers on the drywall surface.
    Swedishchef and woodgeek like this.
  5. Swedishchef

    Swedishchef Minister of Fire

    Joined:
    Jan 17, 2010
    Messages:
    2,316
    Loc:
    Quebec, Canada
    FWIW, I live in Canada. Quebec to be precise. And we have winter. Real winter :D I am uncertain what your winters are like for weather/temperature.

    I sprayed 1.5 inches of closed fell spray foam directly on my walls and rimjoists. As semipro said, you want to create a thermal barrier preventing the cold from reaching the moist air in the basement. I feel no cold/air on the inside of the foam. On top of my R10 spray foam I placed R14 Roxul Comfortbat between the studs.

    My basement is completely insulated from top to bottom. 3 feet above grade and 5 below. My wood stove is located there and with the great insulation heat rises fast and my entire house is toasty.

    Andrew
  6. mithesaint

    mithesaint Feeling the Heat

    Joined:
    Nov 1, 2011
    Messages:
    412
    Loc:
    NW Ohio
    Thanks for the thoughts guys.

    There is already fiberglass in the rim joist spaces, and I've spray foamed the junction between the sill plate and the top of the wall. I haven't 100% decided what I'm doing for the floor yet. I'm probably going to use the Platons and put OSB on top of that, kinda a poor man's DriCore set up. I also considered laying down a layer of foam and putting the OSB on top of that, but I don't think that will let the floor breathe enough. I could put the foam on top of the platons, but I'm afraid that will take away from from overall room height too much. I'm already at 7'8" before I do anything about floor or ceiling, so I don't want to take too much away.

    Yeah, I've read about the condensation issue when warm air hits a cold wall, so I'm trying to avoid that. Not sure how much the wall will actually breathe, as there is some layer of paint that I suspect might be Drylock (previous owner did it) already on the wall. I'm planning on full frame walls. It should allow for a nice flat wall.

    I managed to get about 100 pieces of 14" wide foam, most are 3/4 thick. They were free. Some are imperfect, notches missing, small holes, etc. My plan was to use those as the first layer attached to the wall, and then put a layer of 1" foam over top of those, giving a R value of approx 8.5 or so. Then I'll frame the wall out and insulate that with fiberglass. I've noticed that it's actually cheaper to buy the R-19 at Menards vs the R-13. That would give me a R value of 27.5 or so for the entire wall, and since I already have a inch of foam (R-5) above grade on the outside, I'll have basement walls that are R-32.5 above grade. That sounds a bit insane to me. Is it?

    Should be pretty cheap to heat though.

    Thanks for the heads up on the vinyl stuff. Had wanted to put a nice vinyl floor in the wife's workout area, but had to rethink that plan.
  7. mithesaint

    mithesaint Feeling the Heat

    Joined:
    Nov 1, 2011
    Messages:
    412
    Loc:
    NW Ohio
    Tell me more about the spray foam. What system did you use? How easy was it? How much did it cost?
  8. billb3

    billb3 Minister of Fire

    Joined:
    Dec 14, 2007
    Messages:
    3,471
    Loc:
    SE Mass
    If you can lower the moisture content of the soil immediately outside those basement walls that will help with heat loss via concrete as well.
    semipro likes this.
  9. Swedishchef

    Swedishchef Minister of Fire

    Joined:
    Jan 17, 2010
    Messages:
    2,316
    Loc:
    Quebec, Canada
    Mit: I had my entire basement done as well as rim joists. There is only one company that install spray foam within 150 miles of my house and the company is 150 miles away from me. lol. They do lots of work around this part as we have local shipyards that build big fishing vessels and the sprayfoam is used to insulate the water holds. And lots of people have started using their services for insulating basements, crawl spaces, walls, etc.

    For 1.5 inches of closed cell foam you get an approximate R valule of 10. THe cost for the entire basement wall including the rim joists was $3781 taxes inc. It was a little on the expensive side. Why did I chose to do it? Simple. I did the math. To get R10 with foam I would have needed to install 2 inches of blueboard. I would have needed to purchased SEVERAL tubes of foam board glue, several foam board anchors and washers as well as rolls of tape. I would have needed to try and smooth some of the little imperfections on the wall to ensure no air would remain behind the boards. Then I needed to do everything myself which would have taken me a week. And then there's always the rim joists with are a PITA. These guys came in, covered what little items were in my basement and within 2.5 hours were done. I had calculated that with foam boards it would have cost me $2500 in materials. The perimeter of my house is 160 feet and my basement walls are 8 feet high and they added 1 foot for the rim joists. So I had approximately 1440sq ft of coverage. It worked out to be $2.62/sq ft.

    And where I live it is currently -25. I put my hand on the foam and it feels mildly cool but far from cold. It created an air tight layer inside my basement. Extremely air tight. I love it.

    Andrew
  10. velvetfoot

    velvetfoot Minister of Fire

    Joined:
    Dec 5, 2005
    Messages:
    6,480
    Loc:
    Sand Lake, NY
    As far as floor, I'm uncertain myself. Screwing down osb onto foam is a lot of screws into the concrete floor. Then, if there ever is a leak, you'd still probably have to remove the osb, I imagine. Then too, it'd be nice to have one floor in the house where you don't have to worry about getting hot, etc. Then again, it'd be nice to have non-cold floor. Then again....
  11. semipro

    semipro Minister of Fire

    Joined:
    Jan 12, 2009
    Messages:
    2,293
    Loc:
    SW Virginia
    Regarding foam costs and the floor:
    I put a cost comparison of all DIY foams into a spreadsheet and foam board was the least expensive per volume with home center spray foam cans coming in second and DIY foaming systems 3rd. I did not compare the costs of contracted foam installation or do the evaluation with R values instead of volume. Sorry, I can't find the numbers right now but remember the outcome.

    I haven't gotten to insulating the floor in my basement but have made provision to do so with wall and door heights. My plan right now is to go with a floating floor system where poly sheeting is laid first followed by XPS foam (taped and sealed) and then a waterproof laminate.
  12. Swedishchef

    Swedishchef Minister of Fire

    Joined:
    Jan 17, 2010
    Messages:
    2,316
    Loc:
    Quebec, Canada
    You guys are hardcore! Since I plan on selling me house I simply put 15mm laminate down on poly with a 2mm thick foam backing. I didn't lose head clearance and the floors are OK. My next house will have 9 foot high foundation walls to allow for a properly insulated foam floor (the foam should be put under the slab).

    Andrew
  13. RSNovi

    RSNovi Feeling the Heat

    Joined:
    May 12, 2010
    Messages:
    261
    Loc:
    Michigan
    I have been having good luck with Dricore flooring.
  14. semipro

    semipro Minister of Fire

    Joined:
    Jan 12, 2009
    Messages:
    2,293
    Loc:
    SW Virginia
    i was considering using the TrafficMaster Allure from HD.
  15. velvetfoot

    velvetfoot Minister of Fire

    Joined:
    Dec 5, 2005
    Messages:
    6,480
    Loc:
    Sand Lake, NY
    1" XPS? Will the laminate play nice with the flex of the foam?
  16. semipro

    semipro Minister of Fire

    Joined:
    Jan 12, 2009
    Messages:
    2,293
    Loc:
    SW Virginia
    Yes. The floor in the room I'm in as I type is built like this. It has endured lots of traffic including large dogs and a rolling office chair for about 6 years without problem. Its a relatively inexpensive laminate also. The Allure I hope to use in the basement is much more pliable and forgiving.
  17. Seasoned Oak

    Seasoned Oak Minister of Fire

    Joined:
    Oct 17, 2008
    Messages:
    3,641
    Loc:
    Eastern Central PA
    I used this several times and i like it very much. I put it in bathrooms and kitchens where i need a waterproof floor,too many time people use laminate in their kitchens only to have the dishwasher/sink/ref ect. dripping on it for weeks before they know it the laminate is all ruined. Im planning to put some directly over the concrete in my basement with possibly a layer of plastic down first. It does FLEX quite a bit ,great for uneven and moving floors. So far the first bathroom i put this in is about 6 years old and its holding up great.
  18. mithesaint

    mithesaint Feeling the Heat

    Joined:
    Nov 1, 2011
    Messages:
    412
    Loc:
    NW Ohio
    Poly sheeting on the floor? I was under the impression that the floor needed treated the same way as the walls in terms of allowing the concrete to breathe. The poly sheeting will trap moisture and lead to mold, right? That was my understanding of the situation.
  19. semipro

    semipro Minister of Fire

    Joined:
    Jan 12, 2009
    Messages:
    2,293
    Loc:
    SW Virginia
    Good point.
    I think whether you would us poly sheeting depends upon what's above it. In most cases where I've seen poly recommended its because there was going to be a flooring substrate such as plywood or OSB above it which would serve as a growth substrate for mold if moisture was to come up through the slab.
    Mold requires not just moisture but a growth substrate to propagate. If moisture coming through the floor is stopped by the poly I"m not sure how mold would grow there as its trapped between slab and poly.
    I'm not sure why the same rules don't apply to the walls but the only cases where I've seen poly recommended on walls is where water is actively leaking in.
    Perhaps its because water is always moving upwards though the slab and flooring?
    In my situation it may be better to let it breath as I don't think mold would grow on the Allure. I may post over at GreenBuildingAdvisor to get some clarification unless someone here knows.
  20. semipro

    semipro Minister of Fire

    Joined:
    Jan 12, 2009
    Messages:
    2,293
    Loc:
    SW Virginia
    Thanks for the insight.
    Have you ever installed it over XPS?
  21. velvetfoot

    velvetfoot Minister of Fire

    Joined:
    Dec 5, 2005
    Messages:
    6,480
    Loc:
    Sand Lake, NY
    Not that the foam on my wall has only recently been covered by sheet rock after 4 years or so, but no "worries" about the allure not being having adequate fire resistance?
  22. semipro

    semipro Minister of Fire

    Joined:
    Jan 12, 2009
    Messages:
    2,293
    Loc:
    SW Virginia
    Are you thinking of coals from a stove or house fires, or both?
    Its an "approved' flooring product for interior use so I'd assume it meets code as far a fire resistance.
    I've always wondered if fire resistance was as important on floors as walls and ceilings. Seems it wouldn't be and that many common flooring products are combustible (e.g. wood, bamboo, carpet).

    I know what you're talking about on finally getting around to covering your foam walls with drywall. I'm doing the same in some attic storage space.
  23. semipro

    semipro Minister of Fire

    Joined:
    Jan 12, 2009
    Messages:
    2,293
    Loc:
    SW Virginia
  24. Seasoned Oak

    Seasoned Oak Minister of Fire

    Joined:
    Oct 17, 2008
    Messages:
    3,641
    Loc:
    Eastern Central PA
    No just old hardwood floors But it is rated to go directly over concrete such as in a basement. I would not put it too close to a wood stove though as its kind of a vinyl/rubber type product and you would get burn marks on it from stray embers. I plan to put slate under the stove and at least 2 feet in front of the stove as well.
  25. semipro

    semipro Minister of Fire

    Joined:
    Jan 12, 2009
    Messages:
    2,293
    Loc:
    SW Virginia

Share This Page