basement framing questions

[rundrave]

I am getting ready to start framing up my unfinished basement. It was really cold this last weekend and while I was down there getting measurements I came across this in 2 corners:

Those corners are the SW and SE facing and the parts with the frost are above grade. Is this normal to see when its -15F? I have only noticed them appear when it gets extremely cold and then they go away.

With that said when I start framing these exterior walls. Do I frame them up, add insulation and then put plastic over that? Isn't that going to trap the moisture in between the concrete and the plastic? OR do I put up the the big sheets of foam up against the exterior walls and seal that up? And then frame?

Also the height from concrete floor to the floor joists above is 91". When I purchase the wall studs should I buy the pre-cut studs that are 92 5/8" or buy just the regular 8ft (96") 2x4's?

Lastly is green treated required for the bottom boards with the foam under it that will be in contact with the floor?

[BoxMN]

OR do I put up the the big sheets of foam up against the exterior walls and seal that up? And then frame?

I am not a builder, but this is what my builder did, and told me it is ready for framing INSIDE the foam, and not to use any other insulation or plastic, as mine IS the insulation and vapor barrier. He used foil foam, because I was not going to finish right away and I think that is code for fire reasons. It is also all taped up so no concrete is showing on face or top of blocks. He spray foamed the rim joist area.

Others know more than me of course, but I think this is best way and code, at least in 2008 it was. Good luck!

[EyeChsr]

I'd put 2" Styrofoam (blue or pink) glued to block then frame 2x4 walls. Use green plate and get the nails for green treated wood. Use regular nails for the white wood. Check with local building official to see if they would like to see a vapor barrier. Personally think this is better than using fiberglass batts.

[NoWiser]

You will need green treated on anything that contacts the floor.

I think your best bet would be to use 1 1/2" thermax insulation directly against the foundation walls. Seal the top to the sill plat and the bottom to the floor slab using acoustical sealant. Tape all seams and penetrations. When that is done you can frame your stud wall just inside of the insulation. You do not need to or want to poly or insulate the stud wall.

Another cheaper way to do it is to seal poly to the sill plate and the joint between the slab and foundation wall. Be sure to tape all of the seams. You don't want any holes in the poly. You can then build your energy walls and insulate with fiberglass. This is effective if you are very careful to not damage the plastic, but does not meet code in MN anymore. Some inspectors will allow it on existing houses. Do not put poly over the insulated stud wall if you do this. Only against the foundation.

For studs, I'd get whatever is cheapest, which will probably be the precuts. No need to waste more material than you need to.

Good luck!

[CAMAN]

If you are going to finish the walls right away you can use the standard pink or blue rigid foam boards, if it is going to be left open for an extended time use foil faced. It is a fire code.

Foam on the concrete is what I would do, either spray foam or glue up rigid foam and tape the seams.

[PurpleFloyd]

When I finished ours I used green treated plates and SPF studs. I spaced the wall 1/2 inch from the block so the studs did not contact the concrete blocks and then had the wall spray foamed.They also foamed the joist pockets so that everything was sealed tight.

[nobody05]

if you have the funds spray foam that concrete after the framing is done then cover her up.

[rundrave]

Great info everyone thanks. Can any one chime in about the frost on the wall in the pics? Is that normal or anything to be concerned about?

[Surface Tension]

No the frost isn't normal. Curious what size are those blocks?

Is that a drip line, crack, or joint running vertically off the corners?

Any chance the sill is leaking air and not just in corners?

Could be the whole wall would frost but because the corners don't get the same air movement the surface stays cold. Still this looks odd.

[low277]

I have seen it before and I think it is normal if your basement is heated and if the blocks are not insulated on the outside from the siding to below grade.

The cold will transfer through the exposed block and come in contact with warmer moist air in the basement and condense and frost over.

The insulation and vapor barrier should prevent this from happening in the future.

[soldoncass]

I think it is the result of too little air flow in those corners. I would run a fan aimed there, then when dry, glue foil foam on the walls top to bottom(3/4" minimum), foil tape the seams and tops. Frame walls inside that, with no additional insulation or poly.

Frost shows up where the surface is colder than 32 degrees....no air movement. I don't see any other problem than that.

[Tom7227]

I think the smartest thing you can do is to contact your local building inspectors and find out what they require. Since you live in a city and in SD I suspect that there are inspectors. The 'how do I finish the walls' question comes up in the forum quite often and I am reasonably sure that differing cities and differing inspectors have differing answers. As you deal with the 'how do I insulate' question it also would be wise to find out what the local answer is to things like how to install the electrical and plumbing.

The answers you get here will be all over the place and probably most make sense for that person and their home. What you need to do is make sure you meet current standards for your area and then start to decide how much you want to spend for anything that is above the minimum.

[rundrave]

I think it is the result of too little air flow in those corners.

[Hoey]

Moisture in the air - was my first thought. The warm, moist air in that corner is being cooled by the wall below the air dewpoint. This results in condensate/moisture, not a lot, but enough to make the surface damp. Then the interior surface is being cooled through a thermal bridge through the wall to a point of frost. So a combination of air flow and wall insulation in the area and reduced overall moisture level of the air are the key variables to change.

[delcecchi]

My thought was, if the temperature of one side of a block is -20, what is the temperature of the other side? Seems it could easily be below 32.

[soldoncass]

It looks to me like those walls may be poured concrete(not blocks),and if so the cold transfers inside very well. Concrete blocks have open cores that ,at least, slow the transfer down....solid concrete does nothing at all in that regard. Good insulation is definitely needed.

I saw a chart one time comparing different products, and the thicknesses required to obtain equal r value. It was an eye opener for me: for R-13 it was 9 inches solid wood and 9 FEET of concrete or brick. Any air pockets help, but solid items , cold transfers straight through.

Makes me think your basement is quite cool?

[crothmeier]

Set a fan in your basement blowing on the corners, moving air across that surface will take care of the frost and dry the walls out. I had this issue in my basement on a block walkout wall. I studded the wall with 2x4 leaving a 1/2" gap between the block and the 2x4, and then spray-foamed the cavities. This is the best way to remedy your situation. you can either hire it done, or buy the "Froth-pak" at a lumberyard. I bought the 600sqft kit (figured at 1" thick) and sprayed it on twice, achieving 2.5-3 inches total thickness. Costs more, but in the end having to tear out your sheetrock and insulation 5 years from now and remove mold would be even more expensive.

[BoxMN]

(aside question) - Hey Crothmeier, is the Froth Pak from lumberyard the same as the the spray foam the big M store has? I was going to get that to do around my rim joists in my old house, as I have big M gift cards to use. I think about $350 for two cans and gun. Thanks for any info!

[crothmeier]

Should be, there are a few different brands out there. Make sure and read the specs on it to see if it qualifies for vapor barrier and at what thickness. Also temperature makes a HUGE impact wen spraying, not only the "tank" temp, but the substrate you're applying it to.

I set mine in front of the heat register before I sprayed it, and it comes out way better.

[PurpleFloyd]

How does the cost/sf compare to having it done professionally? When we did out basement about 8 years ago the DIY kits came out to cost the same as having a Pro do it. Maybe that has changed now.

[crothmeier]

Depends on the amount you are looking to do. Typically there is a minimum from a pro. Around here its usually $750, well you can buy a 600sqft do it yourself kit for less, but any more than that and you might as well have someone do it. Small jobs they spend more time setting up, tearing down, and cleaning than what its worth.

[YiGGiN4SLoBS]

Theres nothing abnormal about that frost on the concrete inside the basement when its that cold. You don't have your energy walls built yet so that cold concrete is directly contacting the warm air in your basement creating condensation. Once your energy walls are built there won't be any frost on the foundation behind the wall.

There are lots of different ways to do energy walls. Like people have already said- Use green treated on anything that contacts concrete and i would always leave a 1/2" air gap in-between your energy wall and foundation.

Ive seen people use waterproofing paint on the inside of the foundation, seen insulation applied directly to block or concrete, you can also use typar or tyvek to wrap the back of your energy wall to deal with moisture issues.

Spray foam is going to be at least double the price of fiberglass if not more. There is nothing wrong with fiberglass bats, especially when 3/4 of your basement is already insulated by earth! But if you want to spend the money and have it to spend go spray foam

[soldoncass]

I did the service calls on the houses we built.....and I can tell you that ALL the problems, we were seeing, went away, as soon as we started gluing foil foam on the block foundations. Before that, code required poly on the block, then a stud wall with fiberglass batts, and vapor barrier poly on that. That created MANY problems related to moisture, I advise NOBODY use fiberglass.(unless they want moisture/mold problems in the future).

Spray foam may work, but I don't have first hand experience with that. I know foil foam, one inch thick(or more), will work well, so that is my recommendation.

[Archtek]

I did the service calls on the houses we built.....and I can tell you that ALL the problems, we were seeing, went away, as soon as we started gluing foil foam on the block foundations. Before that, code required poly on the block, then a stud wall with fiberglass batts, and vapor barrier poly on that. That created MANY problems related to moisture, I advise NOBODY use fiberglass.(unless they want moisture/mold problems in the future).

Spray foam may work, but I don't have first hand experience with that. I know foil foam, one inch thick(or more), will work well, so that is my recommendation.

I find that very interesting that you say there were all kinds of problems associated with the 2 layers of poly with a stud wall. Quite a few years ago I got into quite a "discussion" with the local building inspector about that system. I just couldn't imagine that system working at all. It went against everything I was aver taught in school or in continuing education classes. Fortunately I ended up not finishing off the space, so I always wondered how it would have worked or not worked. Now I know it was full of problems, just like I suspected it would be.

[YiGGiN4SLoBS]

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