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Vapor Barrier Between Floors


zoom38's Avatar
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05-18-14, 03:50 PM   #1  
Vapor Barrier Between Floors

I have a two floor home. A few years back I added the second floor and when I did that I installed r30 insulation under the second floor with vapor barrier against the second floor with radiant floor heat above. I never removed my first floor ceiling r19 vapor barrier thinking I should not have issues between the two floors. Others agreed this to be the case. I am now doing some renovations to my first floor and have access to about 60 to 65% of the first floor ceiling insulation. Would I be better off leaving the vapor barrier or removing it knowing if i removed it there still will be a double vapor barrier over 35 to 40% of the first floor.

Thanks
Gary

 
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Bud9051's Avatar
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05-18-14, 06:04 PM   #2  
I don't entirely understand what you have, but vapor barriers between floors are not necessary. Perhaps a radiant barrier below some radiant floor heat could be justified, but based upon moisture movement and temperatures, a typical VB would probably be a mute point. That said, I would not want two regardless. But I don't have a scenario where that would create a problem.

Bud

 
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05-18-14, 06:21 PM   #3  
As long as temperatures are warm enough on both sides of the insulation to preclude a dew point temperature from being a factor, you should be fine with the multiple vapor retarders.

In reality I would say that unless you have a very humid house and have significant temperature differences between the levels it is ok to leave them in place.

 
zoom38's Avatar
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05-18-14, 07:24 PM   #4  
Thank you both for the quick reply. One last question, would I do more harm than good if I did remove the lower vapor barrier over the 60 to 65%? I planned on getting rid of the insulation and replacing it because of some electric and plumbing I will be doing between floors. I did not want to re-use the old insulation because I HATE fiberglass. I was going to replace the fiberglass with something else like roxul. Hence the question, if I did replace the insulation, should I install a vapor barrier knowing there will still be a barrier over about 35-40% of the ceiling. I know its a waste of money but thats what I wanted to do.

Gary

 
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05-19-14, 04:03 AM   #5  
Removing the va would not be bad. Omitting a new one would be better than having 2.

The only example of "why not 2" I could come up with is when my daughter tripped over the tub of water she was soaking her feet in, second floor bed room. She ran to get some towels to soak it up but when she got back it was all gone . So she thought she was ok and didn't tell anyone. Next day the dinning room ceiling directly below began to drip and I panicked thinking I had water leak in one of the pipes. She finally stopped me and confessed. I smiled and we had a good laugh.

But a spill that gets between two vapor barriers could take a long time to dry and possible be a problem. I have run into old nasty water in flex ducts and it can be bad.

Roxul is good and no vb is needed.

Bud

 
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05-19-14, 04:55 PM   #6  
I probably will be removing that vapor barrier from that 60 to 65%.

Thanks Again
Gary

 
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