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Old 03-06-2009, 09:36 PM   #1
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Question about Insulation of unheated basement ceiling


My contractor friend just replaced all the floor joists and posts in our mother's unheated basement. When replacing the fiberglass insulation, he put kraft paper face down. He told me that this was OK. I'd like some comment from those who might know why manufacturers instruct the kraft paper to be placed face toward the underside of the floor (there is no subfloor in this house) AND if it is OK to face the paper the opposite direction. Will this be a problem in the future? What is wrong with placing the paper toward the basement floor (down)?

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Old 03-06-2009, 11:10 PM   #2
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Question about Insulation of unheated basement ceiling


Where are you located?

How warm does the basement stay?
Paper usually faces the warm side of the wall/floor

It's easier to install with paper facing towards you so you can staple it up

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Old 03-06-2009, 11:31 PM   #3
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Question about Insulation of unheated basement ceiling


Usually, in northern climes, a vapor barrier is stapled on the bottom of the subfloor between the joists. Unfaced insulation is friction fitted between the joists and then is held in place with strapping, screening or chicken wire!
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Old 03-07-2009, 12:22 AM   #4
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Question about Insulation of unheated basement ceiling


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Originally Posted by Scuba_Dave View Post
Where are you located?

How warm does the basement stay?
Paper usually faces the warm side of the wall/floor

It's easier to install with paper facing towards you so you can staple it up
Home is on the shore of Puget Sound, Washington (near Seattle). Contractor tells me there is so little heat differential between the floor above and the basement that moisture won't be a problem from heated floor above. Basement stays cool, maybe 30 - 50 degrees.
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Old 03-07-2009, 08:50 AM   #5
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Question about Insulation of unheated basement ceiling


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Originally Posted by dpdolstad View Post
Home is on the shore of Puget Sound, Washington (near Seattle). Contractor tells me there is so little heat differential between the floor above and the basement that moisture won't be a problem from heated floor above. Basement stays cool, maybe 30 - 50 degrees.
That may be so and maybe it won't! If the vapor barrier is above, then there will be no more guessing!
Its a lot more work to staple up a vapor barrier, install the insulation and then support it, so that it stays in place!
Is there any chance of mice getting into the insulation? If so, it should supported with a screen, rather than chicken wire!
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Old 03-09-2009, 01:05 PM   #6
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Question about Insulation of unheated basement ceiling


i don't think we really got a clear answer on the cold/heat temperature difference issue here. Lets say the basement gets down to 50 degrees in the winter, and the room above is 70 degrees. would 20 degree difference cause a condensation issue? (i don't know). If the answer is yes then the kraft facing has to be on the warm side, if no condensation issue then the paper can be on the basement side. Is this correct? i think alot of homeowers would prefer the paper on the basement (cool) side so they don't have to worry about being rained on fiberglass when they go down there.

I'm curious about the temp difference though since my laundry room is under my kitchen and would love to insulate the joists.
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Old 03-09-2009, 01:20 PM   #7
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Question about Insulation of unheated basement ceiling


I did some more checking with local insulation contractors. The upshot is that, in this climate, it probably won't make a difference. Many installers now use unfaced insulation and install a fire retardant barrier on the side facing the basement floor. Another consideration is where the moisture is. If in the basement, the barrier would be better facing down. Otherwise, up. As for me, because my sister is upset with the installation, I'll either remove the vapor barrier or take out the batts and reinstall with the facing UP. Thanks for all your comments
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Old 03-09-2009, 01:27 PM   #8
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Question about Insulation of unheated basement ceiling


I think that it would depend on if you are in Florida or in Michigan!
In Florida with an outside temperature of 100F and 70F inside when the a/c is running, the v/b should be under-neath.
In Michigan, when the air outside is 20F and the inside is 70F the v/b should be up on top, against the sub-floor!

I have noticed in my basement, when the air temperature is in the 80's that condensate occurs on contact with the water lines, whose temperature is 55/60F. From this I would assume that this much differential would cause condensate to occur in insulation also!
I suspect that if moisture laden air drops even one degree that it would give up a certain amount of water. And ther lower that it drops, more water would be given up.
Sort of like sqeazing a sponge! I little squeeze brings out a little water. A big squeeze, big water!
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Old 03-09-2009, 01:29 PM   #9
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Question about Insulation of unheated basement ceiling


Don't forget that kraft paper is flammable. My local codes prohibit having the barrier side exposed.
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Old 03-10-2009, 12:49 PM   #10
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Question about Insulation of unheated basement ceiling


Great point Mr Giant,

Therefore i will not have my paper side exposed in the mechanical room.

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