Moisture Behind Vapor Barrier in Basement with Spray Foam

[flipside82]

I am in the process of finishing our basement in our 4 year old house. While putting up some drywall nailers, I noticed moisture behind the plastic vapor barrier between the plastic and spray foam insulation. The moisture is only near the floor joists and not down the rest of the wall and only spreads about 4 ft. The rest of the wall with the vapor barrier is completely dry. The wall is an exterior wall and sits on top of a 4ft cement wall to make a daylight basement. Directly above the spot with the moisture is our dining room and sliding door to the deck. The spray foam between the floor joists is completely dry and is not covered with plastic. There seems to be some grayish mildew on the studs where the moisture was in vapor barrier. I’m not sure what is causing the moisture. Should there be a vapor barrier over spray foam? If there was a leak from the outside, wouldn’t the floor joist cavity also be wet or moisture further down the wall? I am worried about this before I put drywall up on the wall. Looking for ideas, suggestions, answers that might help me solve this. Thanks in advance.

 

[nealtw]

There should be no poly under the floor joists. If fire stopping is applied there should be blocking between the top of the wall and the floor system .
How is the wall constructed and insulated?

 

[flipside82]

There is no poly on the floor joists. The wall is an exterior wall in a daylight basement and constructed of 2x4 with open-cell spray foam. The poly covers the wall stud wall only and not the concrete wall below and not the joist cavity on the wall. The moisture is only in a 4’ x 2’ section of the wall. This wall is about 30’ long and 9’ high, including the partial cement wall.

 

[nealtw]

There is no poly on the floor joists. The wall is an exterior wall in a daylight basement and constructed of 2x4 with open-cell spray foam. The poly covers the wall stud wall only and not the concrete wall below and not the joist cavity on the wall. The moisture is only in a 4’ x 2’ section of the wall. This wall is about 30’ long and 9’ high, including the partial cement wall.

Can you post a photo.

 

[flipside82]

Here is a photo of the section of wall with the moisture.

 

[nealtw]

Was this done when the house was new, when the lumber or some of the lumber still had a high water content?

 

[flipside82]

The plastic was put up in May 2015 right before we moved in and was put up by the contractor. I’m sure there was moisture down there and possibly in the wood because there was snow down there for most of the build. They melted the snow with heaters in March and then poured the concrete floor in late March/ early April. I’m wondering if I could take down the poly vapor barrier and put up the mold/mildew resistant drywall and paint with a vapor barrier primer.

 

[nealtw]

The idea is to have a dry wall system and not allow warm moist air from the house to get to a cold surface of the outside.
So the question is where did the moisture come from. wet wood maybe. leak from the outside, maybe , warm moist air from inside getting in there and condensing on cool studs.

We seal all edges of the poly with Acoustic sealer and in the US they use Quad, so right now I don't think you can rule anything out.
I think, if it has dried out I would seal it back up as tight as I could and leave it for the winter and see if it comes back.

Coloured paper on the front of drywall will not stop it from getting wet from the back.

 

[flipside82]

Agreed. I will also note that the vapor barrier was put up without any seal tape anywhere. Just stapled. I’ve removed the poly vapor barrier last night and the poly dried up but the foam insulation is still a bit wet.

 

[flipside82]

Update - I cut out a chunk of the foam insulation as still felt wet after removing the plastic vapor barrier. What I found was not great the OSB sheathing behind the foam insulation was damp and had signs of mold spreading. I checked a few more spots and they were all dry. The mold only appears to be in 2 stud cavities and just near the top of the wall. I’m guess the moisture is coming from outside, but unsure how to locate.

 

[nealtw]

Update - I cut out a chunk of the foam insulation as still felt wet after removing the plastic vapor barrier. What I found was not great the OSB sheathing behind the foam insulation was damp and had signs of mold spreading. I checked a few more spots and they were all dry. The mold only appears to be in 2 stud cavities and just near the top of the wall. I’m guess the moisture is coming from outside, but unsure how to locate.

What kind of siding? What's above this outside?

 

[flipside82]

It is vinyl siding. Above the spot with the moisture is a deck and sliding door. I do see they put a z channel between the deck and the house to keep water from getting behind the ledger board. But I noticed there is a gap in the ledger board since they couldn’t put a single board to cover the length. There is also a small gap between the j channel and the ledger board where you can see the house wrap.

 

[nealtw]

It is vinyl siding. Above the spot with the moisture is a deck and sliding door. I do see they put a z channel between the deck and the house to keep water from getting behind the ledger board. But I noticed there is a gap in the ledger board since they couldn’t put a single board to cover the length. There is also a small gap between the j channel and the ledger board where you can see the house wrap.

Post a picture of that and from under, where you should be able to see the flashing.

 

[flipside82]

Hopefully this helps see what I see under the deck. I don’t have a pic of under the slider yet.

 

[nealtw]

Hopefully this helps see what I see under the deck. I don’t have a pic of under the slider yet.

That looks fine, do you know if you have house wrap behind the siding?

 

[flipside82]

Yup, there is house wrap under the siding. Not sure on the brand or anything.

 

[nealtw]

Yup, there is house wrap under the siding. Not sure on the brand or anything.

I think I would remove more foam and see just how much you have there.

 

[flipside82]

Here’s what I found... the 2x6 is pretty rotted on the edge. Plus there are rusted nails coming through the OSB. The OSB is pretty rotted as well.

 

[nealtw]

With a zip tool you can open the siding and inspect from the outside. I would keep digging out foam until you get to good wood.

https://www.homedepot.ca/en/home/p.siding-removal-tool.1000681016.html

 

[John Loesch]

Is it possible that the sliding door above is leaking and that's the source of water? I believe the threshold of a door is supposed to sit on top of flashing that directs any water to the outside. This flashing may be hidden by a trim board between the door threshold and the deck.