How to Insulate a Basement and Which Insulation to Use
I am struggling with what is the best or preferred way to insulate the inside of my basement walls. In order of priority, I am interested in air quality first and cost last – while meeting code. Apologies for the essay.
– 1920s house with poured concrete basement (dry with no water/dampness issues).
– A few miles west of Boston (zone 6). Looks like the current code for my area is R 15/19 (which I think means continuous R15, R 19 cavity, or R13 cavity + R5 continuous).
– Approx. 43′ x 34′ unfinished basement
– Rim joists have already been insulated with 2″ iso. using local MassSave program.
– To save money, I am planning on doing the insulation and framing myself and will sub out electrical and drywall. I will probably use metal studs but have not decided yet.
– I will be pulling permits. The final finished space will be considered ‘finished storage’ rather than ‘finished living space’ as it is just under the height requirement.
So, it seems like I have several options to meet code:
– 3″ of XPS (R 5/inch) stuck to wall
– 4″ of EPS (R4/inch) stuck to the wall
– Some combination of XPS or EPS stuck to the wall (min. 2 ” as a vapor barrier?) + R15 mineral wool in the cavity (R15 seems to be most common in local box store)
– Sprayfoam a little over 2″ to the wall (R7/inch)
– Ball park costs of each seem to be in the region of $2-3K (using new materials). I would consider them fairly comparable in terms of the overall project cost and it would not sway me one way or another.
(I’m not considering fiberglass batt because of potential mold issues.)
– Are my assumptions/options correct and am I missing any?
– Which one should I do and are there any pros/cons to each?
– The spray foam is the easiest option as I write the check and it is ready for framing, but I am concerned about air quality (first) and environmental impact (second). Are there any greener spray foam options available now?
– The XPS is an easy DIY option and there is a local place to buy used/seconds which reduces the environmental impact. But are there long term air quality issues to consider about XPS and any concerns about buying ‘used’?
– How much XPS or EPS would I need to stick to the wall so that it is acceptable as a vapor barrier? I think 2″ but wanted to check.
– I need to look into EPS more as I think this is the most air quality and environmentally friendly option. Are there issues with water wicking with EPS? The need to put 4″ on the wall is also giving me cause as it pushes out the wall the most.
– The EPS/XPS mineral wool option is bottom of my list just because it is (slightly) more work but it pushes out the wall the least. Should I give it more thought?
– I have not looked into poly iso. Maybe that is a better option that I have missed?
Thanks to anyone that read this far!!
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