Sorry to go over old ground… I searched some in the archives but didn’t come up with all of the answers I was looking for.
I am about to finish half of my basement for a laundry room. I am considering the XPS insulation against the slab and walls for reasons stated in other posts and in the FHB of a couple of months ago.
However, I am worried about two things:
1) walls are 1922 vintage block with sloppy mortar. They are not flat and not plumb anymore. So I wouldn’t be able to attach XPS directly and neatly like you can with a new poured concrete foundation.
2) Walls and slab leak. I don’t get puddles on the floor, but I do get damp spots when it rains heavily. Pretty sure this is weeping through the walls and not condensation on cold surfaces. Worried about trapping moisture behind XPS.
Seems that trying to keep those spaces dried out with ventilation is better than letting moisture build up in there. But then I would be sending air whose dewpoint is above the slab temperature, causing condensation…
I am planning to improve the drainage around one of the outside walls to reduce weeping through the wall, but not sure what to do about the floor.
Thanks for any suggestions.
Replies
AlecS, try this link from building science - good article on finish/insulating walls in basement: http://www.buildingscience.com/resources/foundations/renovating_your_basement.pdf
Regards
I don't have any thoughts on the moisture problem.
For the uneven walls use Great Stuff foam. I just did this in a basement with pour concrete foundation. The foundation had crack and the top moved in 4". This had all been repaired with I-beam support and epoxy grout. But the wall was far from plumb or flat.
In most of the area there was already and existing ceiling. So I ran the XPS from floor to ceiling. Used a small amount of pannel adhesive to against part of the wall to hold it in place. Then after all of them where cut and set I used the Great Stuff to seal them top, bottom and edge to edge.
In the bathroom area therem was no ceiling. So I just stopped the foam a few inches from the top of the foundation. Then again used Great Stuff to seal the top of the foam pannels to the walls.
Then build plumb walls in front of the foam.
Bill, thanks for the info.
Just so I understand you correctly, you only used the great stuff to seal around the edges. Does it matter then, that there will be gaps behind the XPS where the wall is not flat?
Where will the water that leaks through the block wall go? Do I need a drainage provision like some sort of trough at the bottom of the wall?
Thanks again
Alec
I don't think that I can really address you moisture issues. I don't really have enough experience to give you much guidance on this, nor to judge how bad it is.
Since you said that you also have a problem with water coming up from the floor (or at least dampness) it might be worth it to install and interior drain system and sump.
But I think that you should address the exterior drainage issues first and see how much that affects both the walls and the floor.
You might check with neighbors and see what kind of problems that they have and if they sumps and if so how much they run.
If you have a high water table then drains and sumps are the only fix.
But if you have problems with surface water getting in around the foundation then you are going to have damp walls and the water will pond at the bottom of the foundation untill it can leach away and thus you will have damp floors.