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basement insulation xps with studs already done

pulper11's picture

A good portion of my basement has walls that have wood panelling on them.  These walls have fiberglass batts between the studs.  I'm not a fan of wood panelling, and have read that batts are not good up against below grade foundation walls.  therefore when i do this i plan on removing the wood panelling and the batts, but keeping the studs.  

I also have a laundry room/mechanical room that has open walls (no studs or insulation).  I would like to insulate but the thought of finishing this room with studs and drywall isn't a high priority.

I have a few questions:

1.  For the walls with studs, to insulate with XPS, could I simply cut the XPS to fit between the studs (gluing them to the wall) and then use expanding foam around the edges of the XPS?  Almost everything i read online about using XPS on foundation walls starts with a blank wall and the XPS going up right against the wall, and then building the studs up inside the XPS.  Here I already have the studs.The technique i'm proposing is similar to the technique used for rim joists below:

http://www.finehomebuilding.com/2013/09/...

2.  For the mechanical room, if I use XPS, is drywall required for proper fire rating?

3.  There is efflorescence and water damage on the bottom of my foundation walls in the mechanical room.  I have attached a few pictures taken before I moved in.  The pictures with the black are parts of the wall that will crumble.  It's not a large area but still i have concerns prior to insulating.  I have fixed a number of issues that have been a cause of previous water issues in the basement including the downspouts.  Before I insulate in this area, what kind of expert would you recommend to rectify these issues with the walls (unless this is something an intermediate DIY person can handle).

Thank you for your help!