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  1. #1
    Join Date
    May 2013
    Posts
    3

    Unhappy insulating main floor, above basement in 2 story home

    Hello everyone,

    I live in Edmonton, AB, and the winter is quite cold up here. I have a two story home with unfinished basement (only insulated walls).
    Main floor is 9 ft high. 2nd story is warmer always.
    I have close the heating vents for basement, no need to waste heat there.
    However, I was thinking if I can insulate the main floor underneath. Looking from basement I can see the wood structure and openings among joists, and there is not insulation, there are pipes coming, wires, but since basement is not finished, it is not covered with ceiling.

    So my suspicion is that I am losing heat there, cause main floor is cold, since basement is usually 14 C-16 C, we keep temp in home 20C, but main floor feels cold.

    Can I insulate that portion? and would it help to contain the heat in main floor and second floor? Do I need to remove wires or I can cover them in insulation?

    thanks a lot

  2. #2
    Join Date
    Sep 2012
    Location
    Boston
    Posts
    1,004

    Default Re: insulating main floor, above basement in 2 story home

    you can cover the wires in insulation. i assume you would be able to fit R-30 in the floor joist bays in the basement. it will make a big difference. another thing to consider, if it's to your liking, would be to install a ceiling fan or two on the first floor. they make a big difference in helping out with the heat on ceilings that are over 8'-8'6" high.

  3. #3
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,788

    Default Re: insulating main floor, above basement in 2 story home

    Start by caulking the seam between the rim joist and the floor boards. It won't make any difference right now, but if you don't start with that, then the air infiltration there will undo any good that the insulation you install afterwards.

    You could also caulk the seam where the rim joist meets the sill plate, but that won't be as critical. Then insulate the rim joist from the floor boards to the sill plate. This is where most of the heat is lost. Now in theory, this should be enough as air that gets warmed up from the radiation from the floor boards will rise up and get trapped under the floor. Unfortunately in practice with a full basement, air currents in the basement will disturb this layer.

    But that is easily fixed. You only need a small barrier between the basement and the floor cavities now to keep the floor warm. You could use a sheet of plastic attached to the bottoms of the floor joists but that might look a little tacky. You could use the plastic and then some kind of ceiling tiles, like acoustical ceiling tile nailed to the joists instead of using the hangers. You could also use some insulation, but you won't need much. The air gap between the floor boards and the barrier is worth about an R-3 per inch in this application because it is still air that is stratified. You will want anything you use as a barrier to be as close to the bottom of the joists as possible.

    You only get this R-3 from the air space in the floor joists. It does not work that way in wall cavities or the attic because the warm air rises to the tops of those cavities which in an attic is the cold surface. In a wall, one side is cold, the other warm so you end up with air circulating up the inside surface and down the outside surface of the cavity, so the air in an empty wall cavity is only about R-0.75 total.

  4. #4
    Join Date
    May 2013
    Posts
    3

    Default Re: insulating main floor, above basement in 2 story home

    Quote Originally Posted by MLB Construction View Post
    you can cover the wires in insulation. i assume you would be able to fit R-30 in the floor joist bays in the basement. it will make a big difference. another thing to consider, if it's to your liking, would be to install a ceiling fan or two on the first floor. they make a big difference in helping out with the heat on ceilings that are over 8'-8'6" high.
    Installing fan that would be good idea. I pay over I pay over $250/month in gas, usually from Oct to Apr. It is quite costly. The house is close to 2,000 sq ft (2 story), so basement is wide open close to 1,000 sq ft. I can feel the heat as I walk up the stairs. If I close the 3 bdroom doors on 2nd floor, the corridor on 2nd floor becomes very hot.

    I'll try fan.

    thx for the idea

  5. #5
    Join Date
    May 2013
    Posts
    3

    Default Re: insulating main floor, above basement in 2 story home

    Quote Originally Posted by keith3267 View Post
    Start by caulking the seam between the rim joist and the floor boards. It won't make any difference right now, but if you don't start with that, then the air infiltration there will undo any good that the insulation you install afterwards.

    You could also caulk the seam where the rim joist meets the sill plate, but that won't be as critical. Then insulate the rim joist from the floor boards to the sill plate. This is where most of the heat is lost. Now in theory, this should be enough as air that gets warmed up from the radiation from the floor boards will rise up and get trapped under the floor. Unfortunately in practice with a full basement, air currents in the basement will disturb this layer.

    But that is easily fixed. You only need a small barrier between the basement and the floor cavities now to keep the floor warm. You could use a sheet of plastic attached to the bottoms of the floor joists but that might look a little tacky. You could use the plastic and then some kind of ceiling tiles, like acoustical ceiling tile nailed to the joists instead of using the hangers. You could also use some insulation, but you won't need much. The air gap between the floor boards and the barrier is worth about an R-3 per inch in this application because it is still air that is stratified. You will want anything you use as a barrier to be as close to the bottom of the joists as possible.

    You only get this R-3 from the air space in the floor joists. It does not work that way in wall cavities or the attic because the warm air rises to the tops of those cavities which in an attic is the cold surface. In a wall, one side is cold, the other warm so you end up with air circulating up the inside surface and down the outside surface of the cavity, so the air in an empty wall cavity is only about R-0.75 total.
    You think I will get only R-3? Nothing more?

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