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autojoe 07-07-2013 06:59 PM

exterior question
bought old house years ago....been gutting inside and ready to install vinyl siding on outside.I had lots of problems with rot/carpenter ants over years.I tore off the dolly varden ship lap siding years ago and poor so had to paint the 7/8 inch t&g sheeting.
I was planning on installing a 1/4 inch fanfold and house wrap and vinyl.I have been told that the owens corning xps does not need house wrap.use fanfold or housewrap not both.I have seen contractors put housewrap under and over top of the insulation panels.the surface is not perfectly flat that is why I wanted to use xps.Should I use 1/2 inch panels instead of the 1/4 inch fanfold?since the sheeting is painted would that interfere with the insulation board and moisture trapped?I am confused on what to do?Also I have a 4 mil vapor barrier on walss and ceiling of entire house and r-13 in 2x4 walls walls and r-19 in 2x8 joists and r19 across joists.I was also told that a 4 mil plastic vapor barrier is old school and not needed now traps moisture.what is correct?need some clarification.....thanks in advance

WindowsonWashington 07-09-2013 06:29 AM

Fanfold is typically used as a leveling agent and not so much as a WRB.

I like WRB for the seamless nature of them and the ability to cover the entire house making for fewer seams.

Where is the home located?

Drywallinfo 07-09-2013 07:21 AM

I thing the vapor barrier is still something you want in cold climates. In cold climates, the plastic needs to be directly under the drywall. The moisture will stay in the drywall and can escape back into the interior and will be prevented from migrating to the colder portions of your walls (under siding or in cold spots of wall interiors) where it might condense.

Note: If the plastic is on the exterior right under your siding, it will trap moisture inside your walls, rotting your entire home frame and basically destroying your home (happened to some homes around here). So never do this in cold climates!

If you are using expanding foam insulation that seals walls tight, I think you can forgo the plastic since the foam itself will serve as a vapor barrier.

WindowsonWashington 07-09-2013 04:27 PM

open cell SPF is not a vapor barrier.

It is very vapor open but it does seal up the air leakage which is usually much more responsible for the vapor migration than is pure diffusion.

autojoe 07-09-2013 06:59 PM

thanks for located in southwestern pennsylvania

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