basement framing questions

[Tom7227]

Isn't just as likely that moisture would form between the block and the poly during the summer? If done before the house had sat and cured for a while I would think it very likely that moisture would form within that space. As for older homes I guess that I don't know but I wouldn't be surprised if there was at least some small amount of liquid getting through a wall in the summer. Just a guess on my part as I am not involved in the trade at all.

[Archtek]

sounds to me like the poly on the block was causing the problem, not the fiberglass. Never had any problems with any fiberglass I've installed

Putting a vapor barrier on the COLD side of an insulated wall is never a good idea

The double vapor barrier was mostly what I was arguing about. The system I wanted to use was the same as what I designed for use in commercial buildings I designed. Long story, but it was a polystyrene insulation that had slots in it for steel channels and the steel channels were then mechanically attached to the block. So basically what is done today with the foil-faced polyiso, except it was mechanically attached; then I was intending to build a wood frame wall with fiberglass insulation in front of that. Building inspector didn't care that it was an accepted method of construction for commercial, he wouldn't accept it on residential.

[Pinusbanksiana]

I think the frost is there due to really poor construction and insulation of the rim joist in the corners of the house. I think cold air is pouring through the framing, being pulled down along the block and condensing on the cold block wall. Go down there when it is cold, put a step ladder up and reach into that corner of rim joist. I bet you feel a rush of cold air coming in.

I agree with everyone else who says avoid the poly and glue exp to the walls. But first, exp and great foam the rim joists and along the block wall to seal the rush of cold air.

[NoWiser]

Poly and fiberglass WILL work fine, but you NEED to make sure that the poly is completely sealed. And, a vapor barrier on the inside of the energy wall is a big no no. That should never be done. I am building energy walls in my own basement this weekend and will be using the poly/fiberglass method. I have no worries about it whatsoever. But, that said, the foam applied directly to the foundation is probably a better method. It's just more money than I want to spend.

[delcecchi]

I'm sorry for being a little slow on this. Don't you always want a vapor barrier on the warm side of the insulation?

I get that if there is foam on the wall then there really isn't much of a warm side, since basically both sides are warm.

[Pinusbanksiana]

EXP is a vapor barrier if seams are taped. No Wiser method is old school and probably will work but I wouldn't do it. I glued and taped EXP on my basement walls only after I had sealed the rim and the top of the block along with the bottom plate and cavities between joists. So, basically I now have an airtight continuous insulation from the top to the bottom. Now my next step is to insulate the walls I am framing with fiber batt but I don't need or want another vapor barrier, just batting since I am already ok in that regard. I don't even really have to put batting in but I will because it is not that expensive. Wiser, if I were you I would reconsider, especially if you plan on living in the home long term.

[Pinusbanksiana]

I cant emphasis enough that rolled batting and a vapor barrier will only work if you have totally sealed the outside air from getting through the insulation and to the vapor barrier. If you don't, moisture will hit the poly and sit there causing mold. The absolute best thing to do, (which hardly anybody actually can when remodeling) is to put EXP on the OUTSIDE of the home, taped and sealed so no air can be exchanged. If I ever build a new home, it will be stick framed 2x4 with 2 inches thick EXP seam sealed on the outside, eliminating any thermal bridging. Couple this with spray foamed interior and ceiling, you will have an airtight warm house, easy to heat and no chance of mold or rot.

[YiGGiN4SLoBS]

I think the frost is there due to really poor construction and insulation of the rim joist in the corners of the house. I think cold air is pouring through the framing, being pulled down along the block and condensing on the cold block wall.

+1 This is the most likely source of the frost

[YiGGiN4SLoBS]

Personally id rather have an air gap between my energy wall and the foundation. I don't really like the idea of putting anything directly on the foundation from the inside. (Unless its waterproofing paint) Just seems like a good way to trap moisture. If water or moisture would ever penetrate through from the outside it can dry and not be trapped and never comes in contact with any material.

Just my opinion. Not saying anyone is wrong or i am right

[NoWiser]

Wiser, if I were you I would reconsider, especially if you plan on living in the home long term.

I should have noted that if I was hiring someone to do the work, I'd also go with the foil faced foam directly on the block. But, I am doing the work myself and can be 100% sure that I do it right. For this reason I have zero worries doing it my way. I will admit that your way is better, though. Unfortunately the cost is significantly more when I priced everything out.

[Down Deep]

Why not have an architect who has a background in insulation take a look at it. I think it would be worth a couple hundred bucks to get a expert opinion and a solution to your problem. You have a moisture problem. You need to find out if it is coming in from the inside or out. Better to solve the problem up front rather than having to go back and rip out perfectly good work.

The net is full of basement insulation information and vids. One thing I learned from contractor buddy of mine was to tape and caulk all seams and joints. I also learned that converting a basement in to year round liviable space cost a lot more than I initially figured by the time I was done with egress windows, insulation, heating, lighting and finishing.

[crothmeier]

Architect.. Ha, pretty picture drawer. As to the talk about the cold coming from the rim, if that block is exposed on the exterior (above grade) it will transfer cold from the exterior all way to the interior and once it hits warm condensate. Concrete is not a thermal barrier. The idea is to create a thermal "break" in the right spot to eliminate condensation issues which will create mold. The above grade areas are more critical than well below grade. In a perfect world a 100% sealed thermal break from the top of your rim to the floor is the best thing. Glued foam or spray foam is the easiest way to achieve this. Any break in your thermal barrier will cause moisture. Happened in my parents house with the stud and fiberglass idea after 5-6 years. We had to tear it all back out and it was black with mold.

[Pinusbanksiana]

Couple hundred dollars would by you about 300 square feet of 1 1/2 inch exp, that is money better spent than on a picture drawer. Now a structural engineer that understands insulation may be different.

[NoWiser]

Couple hundred dollars would by you about 300 square feet of 1 1/2 inch exp, that is money better spent than on a picture drawer. Now a structural engineer that understands insulation may be different.

What he said. My experience with architects who do residential work has not been very impressive. They are good at drawing pretty houses, I will give them that.