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Old 11-28-2008, 09:03 PM   #1
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Insulate joist bays along with radiant heat, how ?


Gonna be running pex tubing (for radiant heat) soon and would like to know if the following would be a wise way to insulation after.

Joist depth = 11-7/8, spacing = 12 and 16 on center.

"The Plan"
1) Run the pex, staple the heat transfer sheets.
2) Tack in some 1/2 rigid reflective foil insulation leaving about a 2" space between the pex and rigid insulation (a little "heat cushion").
3) Staple some R30 pink-panther under that with the paper facing the basement (reason noted below).

Will moisture be a problem ?
Was thinking of putting some tyvek between the rigid and fiber-glass ??

Whats the best way to insulate this to have the greatest effect on the floor above ?

Because of house taxs, i have to insulate the floor because the basement will be considered unfinished and unheated.


Paper down notes....
The basement under this will be unheated for a year or so, after that it will be a heated work shop (so for that time i cant have fiberglass fibers floating around, im in and out of the area quit a bit now and will continue for the next year while its unheated). The basements construction is roughly 9' high, two 8" poured walls 5-6' below grade and one 2x8 framed wall which will be insulated, the framed wall has a 6' french door, no windows period. In the end the poured walls will be 2x4 framed with 6m plastic and then R13.


Whats the best course of action for this ?
The floor above is the main concern now and in the long run.
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Old 12-08-2008, 01:09 PM   #2
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Insulate joist bays along with radiant heat, how ?


We don't like temporary installations, especially expensive ones that produce a pile of stuff that has to be removed and might not be reusable. Put your time and money where it will do the most good and get that basement insulated and damproofed. This is not as expensive as what you are proposing. Are you quite sure your taxes go up if you insulate the basement? That seems like a backward policy to me. I don't have alot of experience with pex in air, but I think radiant heat is much more effective when it is installed in concrete. You have the headroom (9 ft.) in the basement to do that and you could go with any of the new radiant systems that are now available for the main floor. Get an HVAC person to advise. If your basement wall has not been foamed on the outside you can retrofit polystyrene board to frost depth with a shallow trench. If you insulate inside the concrete wall then you must be certain that wall is bone dry before you close it in, otherwise mildew and then rot. Your 2x8 walkout should insulate easily. Make sure its stemwall or footing is frost protected and drained. If you are talking R30, you are talking superinsulated and you must be absolutely certain you are not trapping water vapor inside your building envelope, walls floor and ceiling. Layers work better than a solid lump of fiberglass batt and superinsulated walls usually include a dead air space or capillary break for moisture control. This helps the piano stay in tune. Even if you do only some of this work now and get your basement to 50 F or better that would help your comfort level in the home considerably.

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Old 12-08-2008, 01:17 PM   #3
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Insulate joist bays along with radiant heat, how ?


We don't like temporary installations, especially expensive ones that produce a pile of stuff that has to be removed and might not be reusable. Put your time and money where it will do the most good and get that basement insulated and damproofed. This is not as expensive as what you are proposing. Are you quite sure your taxes go up if you insulate the basement? That seems like a backward policy to me. I don't have alot of experience with pex in air, but I think radiant heat is much more effective when it is installed in concrete. You have the headroom (9 ft.) in the basement to do that and you could go with any of the new radiant systems that are now available for the main floor. Get an HVAC person to advise. If your basement wall has not been foamed on the outside you can retrofit polystyrene board to frost depth with a shallow trench. If you insulate inside the concrete wall then you must be certain that wall is bone dry before you close it in, otherwise mildew and then rot. Your 2x8 walkout should insulate easily. Make sure its stemwall or footing is frost protected and drained. If you are talking R30, you are talking superinsulated and you must be absolutely certain you are not trapping water vapor inside your building envelope, walls floor and ceiling. Layers work better than a solid lump of fiberglass batt and superinsulated walls usually include a dead air space or capillary break for moisture control. This helps the piano stay in tune. Even if you do only some of this work now and get your basement to 50 F or better that would help your comfort level in the home considerably.
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