Sweating Walkout Wall

the catfish

I built a house in 04' in missouri with a 2x6 walkout wall, osb and tyvek w/vinyl siding on the outside. The inside was insulated but no vapor barrier was installed by the insulation contractor, last winter I went to install a plastic barrier and noticed the inside of the osb was sweating and had caused almost the entire walkout wall to mold between the osb and insulation. I bleached the mold and painted the wall with kilz and it seemed to remedy my situation. I installed the vapor barrier in all but a small portion of the wall. Recentely I pulled back the insulation on the part with no barrier and it was sweating behind the insulation again. Is this because there was no plastic barrier or could something else be causing this sweating problem?

Chris Johnson

What is the finish on the outside of the house? Are all windows, doors, penetrations (light fixtures, hose bibs, etc) caulked?

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Chris

house bldr

more than likely its the lack of a vapor barrior causing it. The vapor barrior is what keeps the moisture inside your house from migrating through the walls and condensing on the cold outer wall. And basements are especially humid.

MVH

Yep, warm, moist basement air meeting cold exterior wall. Put in a proper vapor barrier.

Mike

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Mont Vista Company, LLC
Alpine, Apache Junction, Gold Canyon, and Mesa, Arizona
Apache Junction Builder
Gold Canyon Builder

the catfish

The outside of the house is vinyl siding, no fixtures or hose bibs anywhere close. I figured it was the vapor barrier, just seemed odd to me, will install and keep an eye on it. Thanx

Floordude

Control the dew point(ambient conditions), and you will control the moisture that is condensing on the cooler surface. Dehumidification on the side condensing, this will lower the dew point.

If this area of the home is sealed off, door and windows closed and no conditioning or air movement, to lower the humidity, YOUR CREATING A GREENHOUSE.

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woodmagman

By sealing the OSB on the back side with a paint like KILZ, you have
essentially created a VB on the cold side of the wall and when you install a VB on the inside you will create a locked cavity. The problem that you first had of no VB is now doubled.
You can correct this by Sanding off the paint or using a stripper..

woodmagman

When the VB is on the warm side of the wall the moisture is coming from the exterior and control is not required. The problem was the OSB has VB qualities and gave a place as you suggested for the interior moist air to condensate. By putting the VB on the interior the problem will be corrected.

mxim

thats a case and point example as to why cutting a corner never pays off. why the guy never installed vapor barrier is a mystery.

the catfish

I am curious though, what is the difference between the walkout wall sweating due to the lack of a vapor barrier and for instance when you have a canteliever with an osb bottom with vinyl soffit bottom, and insulation stuffed into the floor joist on top, there is never any type of barrier between the joist space and the basement, and with heat rising, would'nt this be even warmer air?

woodmagman

The canilever is outside the basement and the floor of the canilever is acting as the VB or you likely have a VB install on the warm side of the subfloor between it and possiblely the underlay. Some plyoods do have products in them that give them some VB qualities

Floordude

The surface that is condensing moisture, is below dew point temperature. Just like a glass of water does on a hot humid day. The water in the glass makes the outside surface cooler, below dew point, and moisture vapor(humidity) condenses on the cooler surface.

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andyj12

I had the same issue in the house I just built. I installed a 6 mil plastic vapor barrier on the inside and it took care of the issue. I made sure to tape all the seams so that no air could get behind the barrier and cause the problem again. My only question is: how do you insulate between the floor and the sill plate along the outside of the house? I have read that you have to put insulation inside each cavity between the joists but I noticed condensation after doing that.

woodmagman

You need to install a VB between each joist aswell. Tape it to the sides of the joist too.

andyj12

Thanks for the advice. I was hoping there was something less time consuming, though! I looked at a lot of web sites that had articles and videos on how to insulate a basement and none of them, including insulation manufacturers, said anything about a vapor barrier between the joists.

the catfish

Iv'e worked in thousands of houses through the years and have never saw a vapor barrier between floor joists or above cantilivered cielings