Hi everyone, As we near completion of our new home in eastern Iowa, I find that I have likely made the worst choice in a general contractor that I could have imagined. Maybe lots of people feel this way as it can be a frustrating process, but I digress. In trying to "make the best of things", I'm looking at the insulation work that was done on our first floor today. This is about a 2000 sq ft ranch with full basement. 2x6 typical construction outer walls with exterior OSB, tyvek wrapped, .046 vinyl siding, with some brick on the front. We've done dense pack fiberglass on the main floor, but I was surprised to see a plastic vapor barrier installed over the dense pack netting. This finish will be tyipcal 1/2" drywall inside. Does this make sense or am I going to wind up with a potential mold issue if I have vapor barrier with visqueen on the inside, and tyvek on the outside??

If I recall correctly, Tyvec IS vapor permeable.

"Tyvek is not a vapor barrier. It is intended to be wrapped around the outside of a building before the siding is installed. It is a water barrier, but allows water vapor to pass to the outside. In almost all areas of the U.S., a vapor barrier will need to be installed on the inside wall, closest to the drywall."

The plastic inside is designed to prevent internal moisture from penetrating the wall and finding someplace cold to condense. Since the OSB and Tyvec should breathe to the outside, You should be fine

Awesome, thanks for the re-assurance. A little googling and I could have solved that one myself :)

If you leave it in place, your risk will be when the AC is on - you could get condensation or mold inducing high %RH on the exterior side of the vapor barrier. You could pretty much eliminate this by maintaining the house at a slight positive pressure when the AC is on.

Eastern Iowa covers both US climate zones 5 & 6, and the solutions vary somewhat.

Find yourself on this map: http://www.greenbuildingadvisor.com/sites/default/files/images/DOE%20climate%20zone%20map.preview.jpg

...or on this map: https://energycode.pnl.gov/EnergyCodeReqs/?state=Iowa

In US climate zone 5 with OSB sheathing and vinyl siding you can skip the interior side vapor retarders completely and still meet code- standard interior latex paint on air-tight wallboard would be good enough.

In US climate zone 6 it would need something more vapor tight than standard latex paint, but half-perm "vapor barrier" latex primer is good enough, but 2-mil nylon (Certainteed MemBrain) has variable vapor retardency, and would allow moisture out more quickly than vapor barrier latex, while having comparable vapor retardency during the winter, when the air is far less humid. Replacing the 4-6 mil polyethylene with 2-mil nylon is pretty cheap insurance, but in zone 5 just getting rid of the polyethylene and paying attention to air-sealing the wallboard is the right way to go.

See section" R702.7.1 Class III Vapor Retarders" : https://up.codes/viewer/int_residential_code_2015/chapter/7#R702.7.1

Your stackup meets the "Vented cladding over wood structural panels" definition allowed for Class III vapor retarders (= latex paint) for zone 5 (but not for zone 6.)

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