Basement insulation

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jjohnston

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I am looking to start finishing my basement here in Minnesota. I have concrete block walls. I read an article by Holmes on Homes about using 2" rigid insulation glued to the walls, then tuct tape the joints. He mentions no need for vapor barrier or fiberglass insulation.

My question is, if I wanted to use fiberglass insulation in addition to the rigid insulation as described above, is that ok, or would that lead to mold problems?
 
If you get water you will get mold. it doesn't really matter how you do it. Out here we build a wall that does not touch the concrete, insulate that and had vapour barrier behind the drywall. If you put up foam and seal it, that is vapour barrier so the other one would not be needed. Either way you still want a fire break at the top of the wall so a fire in that wall does not spread to the floor structure.
 
Got ya. So I wouldn't be harming anything adding the extra fiberglass insulation if I had the rigid board in place too?
 
One of the reasons we build the wall is because the rental forms we use for concrete leave the inside, something less than straight. But with a block wall you could just use enough foam to get the required insulation a glue up the drywall.
 
I'm thinking I'll stud the walls regardless, just so I can run electrical through it easier.
 
Don't bother with the fiberglass. Just add thickness to the foam until you reach the r-value that you want. You can fasten the studs for a wall through the foam, or build a wall in front of the foam. Put your wires in there.
 
OK, I'm going to do the foam glued to the walls, then frame in front of it. Do I need to worry about a fire brake at the top or anything since the studs are right against the foam?
 
I would think so, they want 30 min. burn thru, from the wall to the floor. But they don't take a second look when a hole is cut for a heat duct or plumbing.;)
But it is really not hard to do if you figure where the inner most side (drywall side) of the wall will be and measure back to the sill plate on top of the concrete and just add 1/2" plywood or drywall between to the two.
 
Our house was just built, so per code they drywalled the whole basement ceiling. My thought is, build the wall on the under side of the existing drywall. the XPS will hit the dry-wall, and the top of the wall will hit the drywall. almost like the firebrake is already there. Would that work? then just foam insulate fill any gaps using fire rated foam...
 
Yes, that works. Depending on direction of the floor joist, you may not have anything to nail the top plate to, there is a trick for that if you need it.
 
Yes, that works. Depending on direction of the floor joist, you may not have anything to nail the top plate to, there is a trick for that if you need it.

Waiting...
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Waiting...
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The same trick as when you are adding a wall to but into a finished wall that has no stud to nail to.
In line with the wall placement you cut a hole in the drywall to slip a block behind and screw thru the drywall and when you build the wall you have something to nail to and the wall hides the hole. :trophy:
 
In line with the wall placement you cut a hole in the drywall to slip a block behind and screw thru the drywall and when you build the wall you have something to nail to and the wall hides the hole. :trophy:

...hmmpf...

Did not know that. When I run into a problem like that I just open the drywall and put a stud in. But then I am not a pro framer either.

Thanks for the tip! :beer:
 
OH, so just make a notch in the drywall the same width as a 2x4 for example, then just fasten the studs to the 2x4, once drywall is on, it hides the hole? Sorry, VERY new to all of this.

Also, do I need a fire block at the top of interior walls, or would the header count as the fire block? I'll probably do the same thing, and just build the wall under the drywall, but I'm curious.
 
OH, so just make a notch in the drywall the same width as a 2x4 for example, then just fasten the studs to the 2x4, once drywall is on, it hides the hole? Sorry, VERY new to all of this.

Also, do I need a fire block at the top of interior walls, or would the header count as the fire block? I'll probably do the same thing, and just build the wall under the drywall, but I'm curious.

The drywall you have is firestop and you can just nail thru it if there is solid wood behind it.
If there is nothing to nail to you can just cut a small hole and slide a block behind the drywall, screw that in place and attach the wall to that.
Header is over a door or window in a bearing wall, you should not need that.
If you are talking about top plate, yes.
 
Sorry, another insulation question. So Rigid insulation was put on the outside of my basement walls when the house was built. I can still use rigid insulation on the inside walls like I was looking at doing above right? I just wanted to make sure the sandwich effect wouldn't cause problems.
 
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