DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   Insulation (
-   -   Condensation (water) in wall cavity (

rhr802 05-28-2011 08:03 PM

Condensation (water) in wall cavity
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 seconds story 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. 6" unfaced fibergalss insulation with a 4mill poly VB on the inside. This is how the garage has been for almost one year. 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.

I'm getting ready to sheetrock a portion and OSB the remaining interior walls. 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. From the pattern of the water it's clear the moisture is near the outside of the wall and it works it's 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 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.

AllanJ 05-29-2011 08:10 AM

Are you sure you didn't have ice dam problems over the winter? Did you notice snow extra thick on the roof at the eaves?

Maybe you should delay the remodeling a few weeks, pull away the wall insulation, let things dry out, and see if you get it wet again from roof leaking from rain.

rhr802 05-29-2011 02:03 PM

Hi Allan J

Nope, no problem with ice damning and that wouldn't effect the gable ends anyway ;) Also no ice damning to me would say that everything is insulated correctly (no heat loss to make the ice)

I have everything opened up. Have fans and a dehumidifier running (it's about 80 in the space. Rained all night and no water inside. in fact its drying out nicely so I'm very confident there are no leaks. It must just be a moisture a problem from the inside. The real question, how to resolve it so I can close these walls up with confidence.?

Gary in WA 05-30-2011 10:01 PM

1.How many HDD or where are you located?

2. Typar? or Tyvek?

3. Moisture behind the poly but no drywall air-sealing it?

4. How long did the framing have to dry before the poly install?

5. Was the framing ever wet during construction?


rhr802 05-30-2011 10:32 PM

I'm in VT


Correct. I didn't have time or money to drywall before winter so the space was insulated polyed and heated. My builder says no drywall or some sort of wall covering is part of the problem.

The building was up about 45 days before the insulation was installed. I was painting caulking the outside.

We had a very rainy summer last year as well so the framing did get wet a few times before it was dried in.

Here's my game plan. I've run fans and a dehumidifier in the space. Everything is 100% dry. Any area where mildew had formed I bleached with 100% straight bleach. I also threw away any insulation that was even slightly wet and replaced with new.

I'm going to reinsulate and poly everything again. I'm then going to sheetrock the office portion of the space and OSB the workshop portion of the space. I'll paint the sheetrock and caulk the OSB joints and paint that as well. I'll actually be working in the office portion of the space so the computer equipment should help keep it warm and dry. The heat will also be at 70 rather than 45-50. I'll Keep a dehumidifier in there as well to regulate the humidity.

In the workshop space I'll have a dehumidifier on guard to control the moisture level and also set the heat to 60 or so rather than 45-50. Also, all winter I was keeping a small Kubota tractor in the workshop space that I use to snowblow. The snow would melt onto the floor and I'd sweep the water out once the tractor had thawed. I'm thinking this in conjunction with the typical extra 1st year moisture put way to much moisture into the space and with nothing over the poly to buffer it it was more than it could handle. My fault really.

After running the dehumidifier for just one day I'm amazed at how much drier the space is.

I'll let it go like this until next spring. At that point I'll pull a sheet of the OSB and check the wall cavities for excessive moisture. I'll also cut a hole in the sheetrock and test a bay there. If all is good then I'm home free. If it's wet like it was this year I'll pull the OSB (screwed on so that will be easy) and the sheetrock (that will suck but it's only 3 small walls). Pull the fiberglass, let it dry out again and then just foam the walls and that should solve any problems. Fingers crossed all is fine next spring but if not at least it's still savable. It will just require more work?

Gary in WA 05-30-2011 11:19 PM

VT is Zone 6:

Type 1 or 2:

I would have used faced batts. The framing got wet, sucked up the water like a sponge, now it’s coming out. At the top of the wall because that’s the warmest (driest) as heat rises in the air permeable insulation--- fiberglass, due to convective loops;

The type of heating system added more interior moisture. It went through the wall trying to get out because the poly wasn’t air-tight, sealed with caulking as you should do to the drywall:

What type of siding?

Any rain-screen?

OSB? On outside and inside?

OSB and foam is not good:

It takes way longer to dry:

Optimum drying range- - 18-25 perms;
Tyvek= 58 perm.
Typar= 16 perm. = below minimum.

Painting the backs is a waste of time/money. You would need an oil-base or v.b. primer for the face, but pull the poly off if not required by your local AHJ.

BTW- straight bleach is not as effective as 10% beach solution or a mold fighting solution without bleach.


All times are GMT -5. The time now is 04:18 PM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Search Engine Friendly URLs by vBSEO 3.6.1