questions about XPS for basement walls

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Old 10-18-16, 07:27 AM
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questions about XPS for basement walls

Hi,
I am interested in framing and drywalling the perimeter walls of my basement (1920s home in Massachusetts). I have DriCore on the floor and plan to put down laminate after doing the walls. I am leaving the joists exposed. This is not going to be living space, but primarily a music practice room and small homebrewery. I am a little confused about what I've been reading about XPS and sealing all of the joints. The basement is dry. There are some irregularities (uneven spots) in the concrete walls. Some questions:
1) How do I get the XPS panels (haven't purchased yet) to sit flat on the walls if there are some uneven spots?
2) Do I have to seal all around the XPS panels (such as on the top) if I am leaving the joists exposed?
3) Does this just have to be done on the walls that are outside walls (Two of the walls are actually interior)?

Thank you!

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Old 10-18-16, 07:59 AM
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What joists? Do you mean you're not finishing the ceiling?
 
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Old 10-18-16, 08:23 AM
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That is correct. I had removed an old dropped ceiling and am leaving it off to maximize headroom.
 
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Old 10-18-16, 08:36 AM
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Are you planning to insulate the rim joist?

Why are the walls uneven? Bumps can be ground down.

No, do not insulate interior walls.
 
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Old 10-18-16, 08:49 AM
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Minor variations in the walls will not interfere with the XPS. Any particularly high spots can be ground down or chiseled off as SS says, or you can dig out small areas of the foam to help the panel lie flat.

You must have a fire stop at the top of the walls whether you finish the ceiling or not. The easiest way to do this is to install a strip of 3/4 OSB against the bottoms of the joists that extends from the inside face of the foundation wall plate to the inside edge of the stud wall top plate. You cut and install the OSB first, then attach your top plates (or stand the walls up if you are building the walls flat).

Here is an article on firestopping that demonstrates the idea:

How to Firestop Your Basement | Contractor Kurt

There is no need to insulate interior walls unless one side will be heated/cooled and the other not heated/cooled, or you want to provide some level of noise reduction through the walls (insulation does not help much with that, but it helps a little, a little more if you use a product like Roxul Safe n sound).
 
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