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  1. #1
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    Jan 2010
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    Default Basement Insulation Question

    I have a New house less 1 yr old. We are going to finish the basement.
    It is dry...
    and I put a 6in X6 in pc of plastic taped on all 4 sides and sealed to the wall ( poured 8 in thick) and Floor for 2 weeks and had no moisture what so ever on inside of plastic ... now My question is How should I build the walls on inside of the basement wall? I am not going to paint or Drylock the walls due to being dry. For a vapor barrier I put up 3 mil plastic all around the walls on the inside of the basement walls. the sill plate is sealed and fiberglass insulation is between the joists above the poured wall. Now can I put up my 2x4 walls and put fiberglass insulation between the studs and put up dry wall over Everything?
    being that it is dry is it ok to put the vapor barrier( 3 mil plastic sheeting) between poured wall and 2x4 studs??? the basement is somewhat warm and has heat 2 registers down there
    we live on MI /Ohio state line so it gets cold in winter

    some people have said to put 2x4 studs against the basement wall an put in insulation between studs the put plastic over everything then put up dry wall

    what are my options
    Last edited by opus8844; 01-03-2010 at 11:57 PM.

  2. #2
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    Mar 2009
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    Default Re: Basement Insulation Question

    Howdy i would stud the walls leaving at least an inch between the foundation wall and the studs to allow moisture not to transfer to the studs.If you can afford it then have stray foam insulation installed on the foundation wall then dry wall.

  3. #3
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    Aug 2009
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    Default Re: Basement Insulation Question

    The main this old house site has a great video and walk through of how to do it. The only modification I would make is I'd use 2x4 studs instead of 2x3. In part because I'd do 2x4 studs I'd do this process.

    1" thick foam board covering all of the walls (adhered with foam board adhesive) with vapor tape sealing the joints. Build the 2x4 stud wall and anchor the sill plate to the floor using bolts anchored in to the concrete slab as well as anchoring the header to the joists using screws (putting perpendicular 2x4"s between the joists for any basement wall that ran parallel and between the joists and then tie the header in to those perpendicular 2x4"s). Then fiberglass R13 insulation in the cavities, electrical/plumbing and drywall over.

    For the floor I'd also do 1" foam board directly on the floor adhering it down the same as the walls, vapor tape and then 1/2" plywood or OSB over the foam board using concrete screws and adhesive to hold it down to the foamboard/slab.
    -Matt

  4. #4
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    Default Re: Basement Insulation Question

    Quote Originally Posted by Timothy Miller View Post
    Howdy i would stud the walls leaving at least an inch between the foundation wall and the studs to allow moisture not to transfer to the studs.If you can afford it then have stray foam insulation installed on the foundation wall then dry wall.
    Unless you insulate that gap don't do this.

    By leaving that 1 inch uninsulated gap you have an air space that allows air movement within the wall --- that creates all kinds of negative issues including potential condensation and mold as well reducing the insulation performance.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  5. #5
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    Default Re: Basement Insulation Question

    The method posted by Matt is an excellent system.
    Glad that someone else posted it ---- I'm sure folks are sick of me always doing so.




    Quote Originally Posted by opus8844 View Post

    the sill plate is sealed and fiberglass insulation is between the joists above the poured wall.
    Excellent start.
    This is a critical area that often gets over looked ---- well done.





    For a vapor barrier I put up 3 mil plastic all around the walls on the inside of the basement walls.

    Now can I put up my 2x4 walls and put fiberglass insulation between the studs and put up dry wall over Everything?
    being that it is dry is it ok to put the vapor barrier( 3 mil plastic sheeting) between poured wall and 2x4 studs???
    Here is a problem that I see.
    This is a vapour barrier and should be on the warm side of the insulation since the main source and concern will be vapour from the heated space --- not from the concrete.

    By having the vapour barrier on the cold concrete wall behind the insulation will allow moisture that enters the wall to condense on the cold plastic ----- allowing that moisture to be trapped.

    A proper method and is required by many codes to isolate the wood studs from the concrete. However, using the plastic is not the way to do it----- instead apply either tar ( felt ) paper or house wrap. House wrap is a better choice since it won't deteriorate like tar paper can when exposed to moisture.
    By applying these materials they provide the isolation between the wood and concrete except the house wrap breathes and won't trap moisture.

    You will also need to provide isolation between the concrete floor and the bottom plate of the wall frame. This can either be the house wrap or sill seal --- which is a thin foam sheet the width of a 2x4 and comes in 50 & 100 foot rolls.




    some people have said to put 2x4 studs against the basement wall an put in insulation between studs the put plastic over everything then put up dry wall
    what are my options
    Once the above things have been taken care of then build out the walls ---- properly install the insulation ----- properly install the vapour barrier then apply your wall finish.

    The vapour barrier needs to be well sealed. This means it should also cover the insulation you installed in the cavities of the floor joists and the rim board.
    Ideally use acoustic caulk along the bottom plate --- vertically along each stud ---- along the top plate ---- along the seams up in the floor joist cavities.

    Make sure to overlap seams at least 6 - 12 inches and seal them with house wrap tape.

    Electrical boxes ---- cut a 12 inch square of plastic --- put the box in the middle ---- attach the box. When you wrap the wall with plastic and cut openings for the boxes ---- reach in and pull out the plastic from behind and open it out on top . Then tape that to the outside covering to provide an air tight seal.

    Bottom line ---- the vapour barrier should be a well sealed monolythic envelope.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  6. #6
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    Default Re: Basement Insulation Question

    Quote Originally Posted by jkirk View Post

    another option is something the electrician can provide, there are electrical boxes that are plastic and have a gasket built right into them so when the drywall is installed the vapor barrier is drawn tight into the gasket and seals it
    yep ---- just got to make sure the poly is sealed to the electrical boxes.
    .
    not too sure about the laying of foam on the floor then putting plywood over it while omitting sleepers, ive tried the method described and it can be a bastard of a job to get the fasteners to hold in the slab without installing sleepers
    no problems here ---- try longer tapcons
    "" an ounce of perception -- a pound of obscure "
    - Rush

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