Basement wall insulation in Climate Zone 5
I am hoping someone can help me determine the correct way to insulate my basement. After reading many forums, completing a lot of research, and even contacting the builder of my home I am confused more than ever.
I’m located in central Illinois zone 5. The front of basement is fully below grade with poured concrete foundation. The back of the basement has daylight windows with standard 2×6 framing on top of a 3′ foot foundation wall. The 2×6 framing is currently filled with unfaced fiberglass and poly on the interior side. The home was purchased new and was built late 2011.
I contacted the builder and verified that the foundation is not insulated; however he did say they used a vapor barrier on the exterior of the foundation walls. He advised me that when they finish basements in homes almost exactly like mine they do not use foam on the concrete, frame 2×4 walls in front of the concrete and fill them with fiberglass but do not allow the fg to contact the concrete. The explanation for no foam on the concrete was to prevent moisture from getting trapped between the foam and the concrete which could cause mold issues. This advice seems to go against everything I have read so far.
My plan based on much research is to use 2” EPS or XPS adhered to the concrete and continued into the box sills, seal all seams, frame a 2×4 wall tight to the foam, add fg or roxul in the stud bays, no poly, and finish with 1/2 drywall.
Is it the general consensus to use this approach rather than my builders suggestion?
Can I use regular 2” EPS instead of 2” XPS? The EPS is going for $10/sheet vs. $25/sheet for XPS at the local big box store. I’ve read that EPS is actually more environmentally friendly and will not lose R-Value as opposed to XPS, but is that all EPS? Are there different types? The cost savings of EPS over the XPS seems like a no brainer to me to use EPS. The guy at the box store even questioned my approach with using EPS and suggested ‘the pink stuff’ (XPS).
As for the above grade section of the basement I plan on removing the fg and poly. Filling those stud bays with the 2” EPS foam sprayed around the edges, puting the fg back in front of the EPS, no poly, and same 1/2 drywall. Does this sound correct? If I frame the wall in front of the short foundation wall all the way up to the ceiling to avoid the ‘ledge’ on the wall how should I fill the void created between the 2×6 framing and the framed 2×4 wall from floor to ceiling? The edge on top of the short foundation wall is about 4 inches.
Sorry for so many questions. I’ve just ran into a wall (pun intended) on this and really want to get this right and start building asap.
Thanks in advance for any help.
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