Basement Insulation

[MattPKC]

Hey everyone here’s the issue I’m dealing with. I had a contractor install insulation in my walkout basement walls above grade. They first picture framed the stud cavities with spray foam and then put in the blow in blanket system with fiberglass. The issue I’m wondering about is I’ve had issues in the past with condensation forming on these walls behind unfaced batts in the winter. So since this is already done, is there a way I can not have condensation form in the winter behind this blow in blanket system? I’m just guessing it might happen since fiberglass is air permeable....I thought about using the membrain product from certainteed...Any suggestions would be great, thanks!

 

[John Galt]

The spray foam is your vapor and air barrier if it is at least one inch thick closed cell and covers the entire exterior wall. This is all you should need. The gap between the foundation and the wood wall should be sealed as well. They probably put down a thin foam strip, sill sealer, that is designed for this but a good bead of caulk along that edge will help. Around the window should be foamed from a can. The rim board in the ceiling should be well insulated and the pipe penetrations can foamed too.

 

[MattPKC]

John,
Thanks for the response. That’s the thing, they did not spray foam the entire wall, they only picture framed in the cavity. So at this point I have the blow in blanket up against the house wrap/siding. I feel this will not stop interior moisture From condensing against a cold wall in the winter. Is there any remedies I can do now since the work in done to stop vapor from passing through the fiber glass and to the wall? Thanks again

 

[gggvan]

We had our basement, below grade, spray foamed with 2" close cell in between the stud openings. The blow in thing they did in your case sounded odd, but I figured it was due to you being above grade.

 

[MattPKC]

Gggvan,
Well those walls are above grade for the walkout portion of the basement. I just know that this past winter, all I had were unfaced fiberglass batts in there against the house wrap/siding (builder grade) and it condensed. I’m trying to take care of a potential issue now before it gets cold here in Missouri and I run into the same problem possibly. The contractor stated the blow in blanket system reduces airflow to to 70% but my issue is the vapor passing through. My wife didn’t want spray foam due to the smell (don’t ask) haha Any ideas?

 

[brenndatomu]

My wife didn’t want spray foam due to the smell

No smell foam...

Home | Airkrete - All Green Light Weight Cement Insulation!

The most environmentally safe, the only fireproof insulation on the planet, gives off zero noxious gases and odors, and is 100% pest and mold resistant!

www.airkrete.com

 

[gggvan]

Gggvan,
Well those walls are above grade for the walkout portion of the basement. I just know that this past winter, all I had were unfaced fiberglass batts in there against the house wrap/siding (builder grade) and it condensed. I’m trying to take care of a potential issue now before it gets cold here in Missouri and I run into the same problem possibly. The contractor stated the blow in blanket system reduces airflow to to 70% but my issue is the vapor passing through. My wife didn’t want spray foam due to the smell (don’t ask) haha Any ideas?

The sf should be your vapor barrier. I'm just not sure right now whether open or closed is best for below grade. My main objective was to keep heat in the space, since I have an insert down there.

 

[John Galt]

The wall has to be able to dry either to the inside or outside. That is the important thing to remember. Since the foam is not continuous, the vapor barrier has to be the plastic now. It will need to be sealed with tape at all seams and penetrations including outlets. This is assuming you are in a cold climate, you don't want the warm moist air to go through the wall and condense on the exterior sheathing. The problems occur when the walls are built to a semi tight standard. Either build it tight and control the air mechanically or build it crappy and let the air flow freely through the walls, rooms, and attic accepting that your heating bills will be much higher.

 

[semipro]

The wall has to be able to dry either to the inside or outside. That is the important thing to remember. Since the foam is not continuous, the vapor barrier has to be the plastic now. It will need to be sealed with tape at all seams and penetrations including outlets. This is assuming you are in a cold climate, you don't want the warm moist air to go through the wall and condense on the exterior sheathing. The problems occur when the walls are built to a semi tight standard. Either build it tight and control the air mechanically or build it crappy and let the air flow freely through the walls, rooms, and attic accepting that your heating bills will be much higher.

Well said. It's the semi-tight installations that are really tough to deal with.
Unfortunately, I don't think Missouri is a cold enough climate to allow the use of poly on the inside of the studs. Moisture will likely occur on the backside of the poly in warm weather.

The options for the OP to me seem to be:

1. Leave it be and monitor closely to see if problems (i.e., condensation, mold) arise.
2. Yank the blown-in FG and do the insulation/sealing correctly: install enough panel or sprayed foam to move the condensation temp point so that it lies within the foam insulation. Install more insulation of your choice beside the foam.

Personally, I'd go with the first option. There's theoretical and there's real life. The combination of conditions that result in enough condensation to cause mold problems may never actually occur, especially if you're controlling your basement air conditions with HVAC or dehumidifiers.

 

[gzecc]

Are you aware of the humidity level in the basement year round. If you have excessive humidity no amount of insulation or type will matter.

 

[DickRussell]

It's hard to tell from the picture if the FG is blown behind a sheet of plastic or just a tight mesh fabric. If it's plastic, tape shut all the openings made for the blowing tube, as well as any other openings that allow air flow between interior air and the back of the sheathing. A plastic sheet will provide a vapor barrier to keep winter interior humidity from diffusing through the porous FG to the sheathing. However, a poly sheet also will provide a condensing surface for summer humidity (serious in your climate) diffusing inward from outside. If that covering for the fiberglass is a fabric mesh, you can cover it with Certainteed's MemBrain or another "smart vapor retarder" product, or you can cover everything with sheetrock and put a couple coats of latex paint on it. That would give you a class II vapor retarder, which will allow slow diffusion in either direction when needed. In any case, be careful about running interior AC colder than outside air dew point.