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-   -   Attic vapor barrier plastic sheeting - becomes brittle due to heat? (http://www.diychatroom.com/f19/attic-vapor-barrier-plastic-sheeting-becomes-brittle-due-heat-126616/)

rrr1 12-14-2011 01:39 PM

Attic vapor barrier plastic sheeting - becomes brittle due to heat?
 
I plan to put a vapor barrier down on the unfinished floor in my attic, then add unfaced fiberglas batts (I have free unfaced batts avail).

Thinking of using the basic 6mil clear plastic sheeting, but I'm worried about it drying out and cracking to pieces due to the heat (gets hot up there in the summer!).

Will this plastic get brittle and crack to pieces in, say, 10yrs?

thanks

hyunelan2 12-14-2011 01:41 PM

Heat tends to make things more pliable, not brittle. Your attic would have to get impossibly hot to start changing the structure of plastic (melting).

titanoman 12-14-2011 02:03 PM

Quote:

Originally Posted by hyunelan2
Heat tends to make things more pliable, not brittle. Your attic would have to get impossibly hot to start changing the structure of plastic (melting).

Lay a piece of plastic out on the sun for awhile. Heat is very determental to plastic sheeting.
Edit: or maybe it's the UV rays that break it down, now that I think about it.

Sent from a Samsung Galaxy S2

Ron6519 12-14-2011 02:15 PM

Left undisturbed, I don't see a problem.

SPS-1 12-14-2011 07:55 PM

So you will have ( bottom to top ) first your interior ceiling, which is perhaps 5/8" drywall, then the vapor barrier, then a whole bunch of insulation. The vapor barrier should be roughly the same temperature as your interior ceiling, which is roughly the same temperature as your living area.

Gary in WA 12-15-2011 09:26 PM

The v.b. should not be on the attic floor. If in a heating climate= next to the ceiling, cooling climate= above the insulation.

Gary

jklingel 12-15-2011 10:11 PM

There are also better plastics than standard "visqueen". Google vapor barriers, and look for Swedish or German ones. There is also MemBrain. All of these should last longer. NOW.... are you sure you NEED a vapor barrier, and not good air sealing and a vapor retarder? Are you ever going to run air conditioning? If you are in a colder place, it is recommended by some to blow cellulose over those marginal fb batts to "seal" them; better, anyway.


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