Condensation between Roxul and Vapor Barrier

[dsl_mech]

This weekend for the first time I found a substantial amount of condensation inside my walls against the vapor barrier. Enough to run down and make the framing visibly wet with pooling water. This was never a issue until the hot sun started coming out here. I have been watching it and narrowed it down to happening only on the walls that the hot sun is on. First thing in the morning it starts to appear on the east wall and by afternoon when the sun moves to the west wall it starts there. Never anything on the north or south walls and the sun never touches those walls. I spent alot of time in there this winter and this was never an issue. This weekend it was 85-95F outside and the temperature in the shop was alot cooler at 60F. Humidity inside the shop has been staying around 70-80%. My belief is that that the hot heat from the hot sun is warming up the walls and that warm air meats the cold side of the vapor barrier and causes the condensation. Someone has told me that once I have a finish on my walls, it will help keep the cooler inside air off the vapor barrier and stop the condensation. Obviously I am concerned because once the finish is up I cant monitor and see if it continue to be an issue. Anybody have any thoughts and what should I do to stop this?

 

[rancherbill]

I would consult stores in your area and Govt of BC sites to see the correct way to install this stuff in your area.

 

[dsl_mech]

I have zero concern whether the product is installed correctly. I passed an insulation inspection and the inspector commented it looks nicer then some installs he sees done by the professionals and he was impressed I even used the correct blue tape. Now maybe it's possible he lied to me but I do not think this is an installation issue. If you can see a specific fault with the installation I'm all ears.

 

[Fav Onefour]

This tool is pretty slick.

Dew Point Calculator

Dew Point Calculator is a web resource created by the Image Permanence Institute to help express and visualize the relationship between temperature, relative humidity and dew point.

www.dpcalc.org

Move the temp slider around and it will show you why the sun side has condensation vs cooler side.

The insulation vapor barrier setup looks like a standard cold climate sequence. Your cold side has moved to the inside wall with the season changing to warm.
The amount of condensation is considerable. It looks consistent all the way. That is sorta good news because it doesn't indicate air leaks.

The idea of stopping condensation with an inner finish is partially true. It will slow the contrast in temps. The reality is that lower humidity is the best answer. Your current indoor humidity is pretty high. How often do you see that kind of level with environment air? Not sure how long the wall has been closed? If it had moisture during the build, it takes time to dry down. That only happens with drier air. I've had wet buildings that took months to dry down the walls. I'd be curious to see your RH levels behind the vapor barrier.

 

[dfiler2]

Is this a new building? New buildings can take a while to dry out, I've seen new homes almost rain on the inside for a couple of months. It appears that moisture is on the back side of your moisture barrier so may be from moisture that is trapped in the wall.

 

[mepstein]

I would open up the vapor barrier until you figure it out.
I used rock wool in my workshop. I used a cheap house wrap to cover it, inside the building. It’s a water barrier but not a vapor barrier. I’m also running a mini-split to keep the humidity low.

 

[mepstein]

Is this a new building? New buildings can take a while to dry out, I've seen new homes almost rain on the inside for a couple of months. It appears that moisture is on the back side of your moisture barrier so may be from moisture that is trapped in the wall.

Sounds very possible. Maybe the warmth is bringing the moisture to the surface of the lumber. In any case, open up the plastic and let things dry out.

 

[billconner]

What is exterior of wall? Metal? Sheathing and siding? Other? I theory, this wall should dry to exterior. I also agree theres a lot of moisture in new construction materials.

 

[kbs2244]

this an example of why the vapor barrier goes on the warm side of a wall
(vapor barrier behind the drywall and moisture barrier behind the siding is the normal construction)
the sun is making the outside the warm side of the wall and the heat is pulling the moisture into the wall to condense on the cooler vapor barrier
(the vapor will follow the heat)
the moisture barrier is keeping out liquid water but letting vaporthrough

the first thing I would try is to vent the wall to the outside

try venting the space between the siding and the moisture barrier first
that should keep the vapor from getting through the moisture barrier

otherwise you are going to have to vent every stud space

 

[PCMusicGuy]

If you are in a predominately cold climate vs warm, you choose the appropriate side for the vapor barrier. If you have some unusually hot or cold weather not typical to your area, you have to remove the humidity right?