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Old 01-15-2009, 04:56 PM   #1
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Frost in Basement Wall Corners


Awhile back I posted about mold on my basement walls. They have been dry so I was at a loss of where the water was coming from.

We have had a couple of days of -20 weather and I now notice that I have quite a bit of frost in the corners of my exposed basement and even the sub floor above is a bit wet. This is all above grade, brick exterior.

In one corner the wooden beam that sits upon the foundation wall has even rotted somewhat and when I pull a few pieces away there is quite a bit of frost in there.

Ideas?

Is there something in the roof that is causing moisture to come down the wall? I have read about insulation plugging breathing holes? Or is it not insulated?

I have to stop this frost and associated mositure as I would like insulate everthing down here again.

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Old 01-15-2009, 05:23 PM   #2
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Frost in Basement Wall Corners


Woody:

Concrete, and all masonary materials are very poor insulators. The frost is forming in the corners because that's where you find the coolest concrete; not because the ground is coldest there, but because the concrete can lose heat in two directions at once there, so it cools down to the ground temperature first in the corners.

You say you have "rot" on the joists? that sit on the basement wall? The Serpula Lacrymans fungus (the wood rot fungus) won't be active in sub zero temperatures. Dig a screw driver into the wood of that joist where you think it's rotted. If the screw driver penetrates into the wood, then you actually do have rot. If it doesn't, then you're looking at mildew, which is harmless to wood. Clean it off with some bleach diluted with 10 parts water.

If you have lots of frost between the joists, a good way of insulating between the joists is to stuff rectangles of fiberglass insulation into appropriately sized plastic bags and stuff those between the joists. You get insulation and a vapour barrier at the same time.

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Old 01-15-2009, 05:34 PM   #3
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Frost in Basement Wall Corners


Is this a poured wall and not a block wall?

More common with poured because of the conductance and lack of cores.

Is there any exterior insulation OR coarse, permeable gravel backfill?

The more moisture retained in the backfill, the more heat loss.

Dick
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Old 01-15-2009, 06:57 PM   #4
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Frost in Basement Wall Corners


Pictures say a thousand words and after you see them you will now why I am ripping things apart.

First, the house is built in 1952, brick veneer with a poured concrete wall. The pictures you will see are are all at the top of the basement wall which is about 2 ft above grade which is why I am baffled.



This is the corner at the bottom of my stairs to the basement. Nice orange walls I found underneath. On top of the foundation wall sits a 2X8. You can see it more to the left of the picture. For the past month that corner has been very wet and you can see wet on the subfloor in the corner. Above this is a cold closet. I poked holes in the wall which was plaster, insulation, exterior type drywall with tarpaper and then brick. I can't get at the actual corners without taking the joists out of the wall but I didn't want to go that far rightaway. The brick does not seem to be wet though.



This is another corner. Same thing. Frosty but has not been wet as far as I can tell. This was the first time I saw any frost but it has obviously been historically wet because that 2x8 is rotted and I have pulled a good piece of it out. There is frost again on the subfloor and you can see it between the two joists.



This is the 2X8 in that corner. Actually the 2x8 is rotted and I have pulled about a foot of it out and what you are looking at it frost and ice on the first row of concrete of the exterior wall which again is 2 ft above grade.

When I took the basement apart there is mold and dirt and guck on the walls and all of it right in these areas. The frost ect must build up and then melt and then sit in there.

I just want to clean it up and re insulate etc.
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Old 01-17-2009, 08:06 AM   #5
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Frost in Basement Wall Corners


Looks like your sill plate has rotted but the rim or ring joist looks relatively intact. Rather than seal it since it's near a corner I think you'll want to look at cutting out the rot and replacing it. If you just foam over it the moisture problem won't go away and the rot may travel up into the joist above so you want to stop the frost from entering.
I have a similar issue where my slab porch meets my ring joist. Melting snow and rain has seeped in and rotted the bottom of the ring from the outside in. Without realizing it I foamed the bottom edge of the cavity trapping the moisture and perhaps made it worse. So because its the joist I have some serious planning to do.
If you can stop the cause you may be able to cut back the sill and replace a section of it. I don't think you want to put this off for too long especially near a corner.
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Old 01-18-2009, 08:38 PM   #6
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Frost in Basement Wall Corners


Reading your answers has already helped me understand what's happening in my house. Thank you! I have the same problem as Woody10. There is no frost in the two corners that adjoin the attached garage, but frost in the corner where the daylight section of the basement starts.

There is also condensation on the concrete below the framing of the daylight wall. There is also condensation on the fuse box, which is placed in the daylight wall.

This house is only four years old. The basement is poured. The daylight wall has fiberglass insulation and is drywalled. I put in pea gravel 4" deep and 18" wide along the exterior of the daylight wall section. I can't make it deeper without adding window wells.

Will insulating the basement with foam board provide enough insulation, and enough of a vapor barrier? What's a good way to insulate the fuse box?
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Old 01-18-2009, 09:55 PM   #7
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Frost in Basement Wall Corners


What is the answer? I still don't know where this moisture is coming from?????
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Old 01-18-2009, 10:12 PM   #8
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Frost in Basement Wall Corners


I've been reading a document published by the U.S. Dept. of Energy which I found at www.buildingscience.com called Basement Insulation Systems. This document, and others on building are evidently also available at www.buildingamerica.gov

It seems the moisture comes from the interior air in the winter time. The way to prevent it condensing on the cold concrete is to insulate it. The document I read recommends insulating the rim joist area with foil-faced polyisocyanurate or XPS, and insulating the walls with 2" extruded polystyrene (I think that's the blue or pink foam sheets).

Now I need to figure out how to insulate the fuse box. The only thing I can think of is a cabinet with foam insulation inside it.
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Old 01-18-2009, 10:34 PM   #9
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Frost in Basement Wall Corners


The warm interior air coming in contact with the cold basement concrete, sill plate, and rim joist is causing your condensation. You have a big problem that needs fixing ASAP. Your sill plate should have been a treated piece of lumber, if it is not it is only a matter of time until it rots away. Any wood coming in contact with concrete needs to be PT because concrete is like a giant sponge. This is true regardless of whether you have old or new concrete or whether it is tarred on the outside.
Back to your problem I might mention that you might or might not have to replace part of your sill plate or even your rim joist if they are rotten to the point that they won't provide support. A little degradation isn't serious but if you don't fix this you will have lots of work to do in the future.
Don't use fiberglass! Fiberglass insulation is a no no in a rim joist area. The insulation that you need is foam. They have spray kits that you can now purchase that work great. They are for this application. Otherwise you can just cut blocks of 2" styrofoam to size and then seal around the four edges with cans of spray foam.
I have seen whole sills rotted out just like yours and replaced them as well. The air leaks in the sill need to be airtight and fiberglass, even in bags, won't do that. In addition, fiberglass will allow air movement and does not have the R-value that you need.
To deal with this problem in cold climates, builders now offset the rim joist to allow for an exterior placement of foam insulation and then insulate with fiberglass on the inside.
I would also recommend walking around the basement and filling any voids that you have in the concrete that are causing airleaks.
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Old 10-28-2010, 12:52 AM   #10
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Frost in Basement Wall Corners


1st Your problem is definitly caused in part by vapor from the inside air being sucked out of your house in the cracks between the rim joist and sill plate and condensing once it reaches those cold surfaces. To replace sill plate you must first support all floor joists between both cuts carrying that load to basement floor.

2nd No insulation nor vapor barrier to prevent this.

Here goes...
-start by controlling relative humidity levels below 50% mechanically(dehumidifier winter, air conditionning in summer)
-repair sill plate
-make sure totally dry before insulating
-insulate with 2'' extruded polyethylene rigid foam concrete walls and spray foam rim joist(at least R12 for basement concrete walls and R20 for rim joist check local building codes) or if budget on high end spray foam every thing. I would advise against the double vapor barrier as this has led to failure in basement walls in less then a year!!

Good luck and do it soon before carpenter ants nest in there...
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Old 10-28-2010, 04:53 AM   #11
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Frost in Basement Wall Corners


The best place to insulate is on the outside, using XPS (yes, blue or pink board). Any way to do that? If not, then do it inside, and use the airtight drywall approach to keep air (and therefor moisture) from getting to the blocks. Yes, S-can the fiberglass; use foam as suggested. And you MUST repair the wood asap, or sooner. Glad you read on buildingscience.com. Greenbuildingadvisor.com is another great site. Science, coupled with good experience, makes for good reading. Good luck; you have a huge task before you.

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