DIY Doctor

Condensation in stud wall.

Postby rhr802 » Sun May 29, 2011 1:36 am

I live in the Northeast where winters are cold. I recently built a 2 story garage where the first story is built into a bank with 3 concrete walls and the open wall (with the garage doors) is 2 x 6 construction. The concrete walls used the foam block form system so they are covered with 2” of foam both inside and outside the wall. The second story is open to grade on the back side and is all 2 x 6 construction. The roof is a truss system.

The 2x6 walls are 2 x 6 studs 16" OC with 1/2" CDX plywood, Typar house wrap and Certainteed Cement board clapboard siding. The exterior has all been caulked and painted. 6" unfaced fibergalss insulation with a 4mill poly VB on the inside. The insulating was done in the fall with 50 degree temps before winter arrived. This is how the buildin has been since October and through the winter (it’s now late march). During the winter the interior was heated to a temp of 50 and of course the exterior temp was colder. The truss roof system has a 4mil VB applied to the bottom of the trusses and 14" of cellulose in the attic space. Heating the space was no problem with a hot water baseboard system.

It's now summer and the temp inside and outside are identical. We've had a VERY rainy spring with lots of flooding, thunderstorms and torrential rain. Almost everyday. Lots of moisture in the air. I have not experienced a flood where I live but the ground is saturated with water….We’ve had much more water and rain than normal.

I'm getting ready to sheetrock a portion (the office) and OSB the remaining interior walls (the workshop). While setting up to do this i noticed a small amount of condensation on the VB. I thought I should investigate before covering it up. I pulled the poly off a wall and found the top (from the top plate down) 12-18" of the wall cavity very wet in some places. Wet to the point of water droplets dripping from the plate. The exterior plywood is also wet. The siding from the outside of the building is dry to the touch. From the pattern of the water it's clear the moisture is near the outside of the wall and it works its way to the interior. Typically the first 2-3" of the top plate are wet but the final 2" to the interior is dry. The insulation feels dry except for the area that touches the plate. It's wet there because the plate is wet....VERY wet. This is happening on all 4 walls and I don't have water leaks. What's very odd, one stud bay will be VERY wet yet the adjacent stud bay will be completely dry.

I'm not exactly sure what is causing this moisture issue? My builder says to pull the poly and insulation. let the space dry out then re insulate and poly and cover with sheetrock and OSB as desired. Then paint the interior of both the OSB and Sheetrock and it will be OK. He says the covering of the VB and the paint will help keep the moisture out of the cavity. I'm thinking the moisture is coming from the outside in not the inside out.

I don't want to go through all the time and expense of re insulating, repolying and covering the walls only to find out 5 years down the road I have a building infested with mold.

Can anyone give me some advice as to where all this moisture is coming from and how to solve the problem? My house is constructed in exactly the same way and it's completely fine?

I'm so frustrated with this. I mean I've hired a very good reputable builder, we have used quality materials and are following very common construction practices.
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