Insulating concrete block foundation
A client has asked me to insulate and finish part of her concrete block basement here in Northern VT. Liquid moisture doesn’t seem to be a problem, –we regraded around her house 2 years ago and there’s been no liquid water in her basement since then.
Nevertheless, I’m concerned about water vapor coming through the block and its joints, and also the possibility that insulating this wall will reduce the ground temps outside and perhaps subject the wall to frost action.
My plan is 2″ of EPS glued directly against the interior side of the block, taping the seams and sealing around all sides of the perimeter. Then I would build a 2×4 stud wall spaced slightly off of the EPS, and sheetrock this.
Any thoughts on this plan?
Thanks, –Brian Abbott
Replies
Nothing wrong with that approach. BTW, 2" foam allows you to use 2" deep electrical handy boxes glued and screwed to the block. You can drop cable down to them through the cores of the block and use junction boxes above the wall.
No alarms raised for you regarding my concern about the insulation creating a frost situation in the soil which the block won't handle well?
Sorry, I didn't remember you were going to build a 2x4 wall too. As Piffin said, that is really not necessary. We have done dozens of basements without constructing another wall. I think it's just a waste of money and space to do it that way.
Never, ever had problems with frost harming the block.
Actually, we use treated 2x2s with a healthy strip of PL Premium on the back and shoot them in to the block with a special nailer that shoots a hardened pin.
We use all block basements, so we do a lot of this. That's one of the benefits of having a nice flat straight surface to work with.
Edited 7/9/2009 6:57 pm ET by BoJangles
That is how I would do it - or run tapcons thru strapping to the block instead of devoting a whole 4" to a full framed wall.
If the frost action will destroy the wall, there are other problems with poorly built wall or bad soils backfilling this. The right soils and perimeter drain will not retain enough moisture to be a problem.
If the insulation does this, then the trouble exists and will eventuall show up I think, just sooner with the insulative layer.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
Just a couple thoughts from the great north.
Consider insulating from the rim joist down the wall below grade on the outside of the wall. with 2 inch Ground contact SM to 2 ft below grade. then place 2 ft wide by 2 inch thick horizontil to the piece coming down the wall with a little slope away from the house. Back fill 12 inches top soil and you have a nice flower bed.2 things This prevents the most heat loss from the basement and provides a rain screen as a bonus. In high clay soils it also slow water migration from under the slab.I have built a few on grade slabs and instead of putting foam under the whole slab. Insulate the perimeter. An engineer had no problem with this system. Cold is lazy and in most houses the most heat is lost through the top 2 feet of the basement and rim joists.Then finish the interior with 2x4 and fiberglass. Leave a gap as mentioned.