What the heck to do with basement walls !?!?!


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Old 10-20-12, 10:02 AM
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What the heck to do with basement walls !?!?!

I have read posts and building science and etc. for so many hours I am about to go nuts and still haven't really decided what is best in regards to finishing basement walls.

I am adding in a couple bedrooms in my basement. Walls are completely finished over a poured foundation that was done in about 1987. No cracks or water leakage issues that I have ever encountered in 4 years of living there.

In the process of taking down some of the finished interior framing to put in an egress window I have run into some concerns. The current finish is 2x2's directly on the concrete walls with styrofoam fitted in between. Plastic vapor barrier then drywall.

I am not finding any mold or anything but the 2x2's are moist in some places starting on the concrete side.

Basically I am planning on leaving most of the basement alone but inside the two new rooms tearing out all of the exterior finished walls and redoing them.

Trouble is I cannot find a great recommendation that everyone agrees on. The best I can decide is dryloc paint the concrete 1" of XPS with sealed seams of caulking or something. Then frame out with unfaced batt insulation, no vapor barrier and drywall.

Thoughts?

I just need to feel comfortable with what I am doing and get started. The more I read the more worried I am about mold and whatnot. There are just a thousand different opinions on the vapor barrier and etc.

Thanks
 
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Old 10-20-12, 10:31 AM
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Hi DeereDoc and welcome to the forum,
I can get you started, but saying "this" is the way to do it has become almost impossible, as you have discovered.

What does that moisture on the 2x2's tell you? Moisture is passing through the foundation walls in the form of a vapor. Because there is a vapor barrier, it can go no further and accumulates until the moisture inside is the same as the outside. Moisture on wood will be a problem eventually. Will drylock solve the moisture movement or just force the moisture to accumulate just behind it? It will accumulate just behind the drylock. If you omit both the drylock and the vapor barrier, then the moisture will dry to the inside, assuming any rigid foam used has sufficient permeability.

If you opt to dry to the inside, then you will need to take care of that moisture. Heating in the winter and ac in the summer or perhaps a dehumidifier.

I realize you are not having a terrible problem with moisture in the basement, however, any extra steps you can take to divert surface water from the outside well away from the foundation can't hurt.

Let's see what others say.
Bud
 
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Old 10-20-12, 10:31 AM
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Basically I am proposing this




But include or skip the poly behind the drywall???


Should note this is in Southeast Iowa and that the top 2 feet of the concrete is exposed externally.
 
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Old 10-20-12, 08:27 PM
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Im currently looking into a sump system because I *do* have moisture issues in my basement.

I asked one of the quoting companies what they suggest for wall finishing once a system is installed and their advice was a gap of 1/2 to 1" between anything (studs, insulation, etc) and foundation walls. Then rigid foam (preferably the stuff with aluminum on each side), then insulation of your choice for between the studs.

I think the key is spacing it off the foundation wall. As you can see your biggest issue is moisture getting to the studs since they are right on the wall. I know some of the rigid foam products can "breathe" but Ive never looked into exactly how well, and in my case letting any moisture thru the walls is OK as long as it can roll down the walls to the sump system (not saying this would ever happen anymore, but Id rather give it a nice path than my insulation soaking it up). Rigid foam directly on the foundation would prevent that from happening and who knows where it would end up.
 
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Old 10-21-12, 06:25 AM
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I don't want to drift on the op's thread, but an air gap can allow convection to carry moisture from below up to an extremely cold concrete surface above. And the foil faced foam is a vapor barrier, ok if that is what is needed. Where drying to the inside is necessary to prevent moisture accumulation from the outside, no vb.

DD, your illustration is great (add a credit if needed) but note the slope on the surface and the drainage system around the foundation. Modern versions of that cross section would include a water resistant barrier on the outside and not just moisture proofing, which is never perfect.

Bud
 
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Old 10-21-12, 09:02 AM
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If an air gap is a bad idea, what would be the suggested approach? Looking at my imperfect concrete foundation walls (i.e. not perfectly smooth) I think it would be impossible to get something bonded directly to it without air gaps. Its an existing finished basement but because of water issues Im taking down a wall (the drywall itself got wet, but Im finding some moisture behind the fiberglass insulation, presumbaly just because of the gap between foundation and fiberglass).

I wanted to prevent any insulation from building up moisture if some ever got there. Ill be having an interior french drain installed, if there is still some moisture from the walls obviously it would have to be because of landscaping, but looking at what I have now nothing is pitched towards the house....I could maybe use a little more pitch away from the house but with the setup of our land vs our neighbors that would be hard/impossible to do.
 
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Old 10-21-12, 09:36 AM
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Hi Chris,
It doesn't require a gap for moisture to accumulate, the gap would just help the moisture vapor move from low to a colder region above where it could condense. Two different animals, water and water vapor. Check this link, especially "Water Vapor or Vapor Emissions". Their discussion is about concrete slabs, but also relates to concrete walls.
Moisture In Concrete

They make specific covering for concrete walls when drainage is behind it is necessary. As for the rough surface, an angle grinder will take off the seams and bumps. They also make a diamond surface cup for the angle grinder, but a bit pricey. In most cases the less expensive grinding wheels will do just fine. Eye protection and vent to outside.

An adhesive may work as well and can also help to block air circulation in places where the rigid foam isn't making good contact.

BuildingScience.com has a lot of information on basements.

Bud
 
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Old 10-21-12, 04:03 PM
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Thanks for that info, Bud. Very helpful.

Looking at their "Renovating your basement" document, they show that, even with a wall that occasionally gets water on it, XPS foam should be applied directly to the wall as long as an interior drain setup is installed. So that seems to be my case *after* the sump system is installed. The only reason I questioned that is because there will be Mira-drain installed where the wall meets the footer and it will be brought up above the level of the slab. If the XPS is in the way, any water wouldnt get to the miradrain....I assumed its purpose was to catch any water that might flow down the wall. Am I wrong in that assumption?

Im not changing how the floor is insulated, though (currently have DriCore installed). Hopefully that doesnt disrupt the wall insulation.

Now my only question is if I should pull ALL of the drywall and insulation down to redo it the right way (the other 2 walls have 2x3s and kraft faced fiberglass insulation between them, set a little bit off the wall in most areas)
 
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Old 10-22-12, 09:21 AM
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I'm curious what the "magic bullet" is as well. I have a cottage with a block basement under part of it. I recently bought it so I have no personal history with it but it feels a little damp down there. Looks to be recently painted but I can see where paneling had been stripped off the walls so maybe there were moisture issues before. I want to insulate & make it suitable for bedrooms but I don't want to start a mold colony. My downspouts all go into underground pipes & exit far away & the soil surrounding the house is sand (lakefront). My biggest fear is the water could come from ground springs rather than rain. Time will tell...
I don't plan to start any basement remodeling until I know what the issues are.
 
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Old 10-22-12, 12:03 PM
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This is the document I was referring to on buildingscience.com:

http://www.buildingscience.com/docum...g-your-basment

Its actually quite interesting because its the only document Ive seen actually give recommended solutions for walls that may get wet (even after installing a sump system). Instead they suggest ways you can still insulate/finish a basement area while providing for the wall to dry out if it ever does get wet.
 
 

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