Insulating and remodeling 1970’s basement
Hi Martin/Dana/GBA Community:
Thanks for all your prior help, particularly Dana. Based on GBA articles and feedback, last year I replaced an aging, dirty oil furnace and HW heater with clean, efficient heat pumps. My whole house is not only more comfortable in the winter but now also in the summer. All at a running cost less than oil was for just one floor.
I am now focused on remodeling my basement for my 88 year old father to live in. I’ve read all the articles I can find on GBA and would really appreciate a sanity check on my plan as well as get guidance where I am not so sure. The house is in southern NH and built in the 1970’s. It’s a walkout basement in back with half below grade up front. All basement walls are full height poured concrete except the front and corners which are half poured, half stud wall. The prior owner finished it with drywall+paneling over 2×4 stud wall with interior faced F-13 fiberglass. The studs are ¼-1/2” off foundation, no poly or insulation on foundation walls nor under slab. Basement is dry and has no water issues, tho smells musty and has mold on bottom of walls probably bc it has no moisture barrier/retard under slab or on walls, was carpeted and old drywall contacts slab. House above is 2×4 construction with inner faced R-13. There’s currently no exterior insulation and I have no current plan or budget to reside and add insulation.
My plan for the basement remodel is to:
1) Remove perimeter stud walls to Insulate+tape rim joist, foundation, half height stud wall in front and all door/window surrounds with 1” ISO. Then put perimeter stud wall back, replacing 40+ year old drywall with new. I hope to re-use existing R-13 faced fiberglass from existing wall and will add more fiber around rim, filling any holes with canned spray foam. Questions:
a) This results in near R-20 wall insulation and moisture retarding, within code for climate zone, correct?
b) Do I need to keep drywall ½” off floor if insulating floor with foam and OSB subfloor?
c) I’m remodeling a bath that has tub and surround against back full foundation wall. I need 2-3” more space in bath to meet code. Current wall uses 6+” from foundation. Can 3 layers of 1” ISO be used: 1 on foundation then 2 interior layers ‘cut and cobble’ between 2”x2”’s for attaching cement board?
2) Insulate floor with 1” EPS with foil facing up and subfloor on top before putting laminate down.
a) This results in near R-5 floor insulation and moisture retarding, within code for climate zone, correct?
b) Is caulk needed/worthwhile between EPS if I’m taping?
c) Can I float two layers 1/2’” OSB instead of one ¾”? I’d prefer to float subfloor and not to drill+screw into slab but with 7’6” clearance I am limited on height.
d) Do walls, particularly perimeter ones, need to rest on ESP+OSB subfloor? If so what type/density/psi will I need? If not, do I caulk and tape to wall sole plates?
e) For bathroom, what type/density/psi EPS or XPS do I need under tub and file floor?
f) For utility/mechanical room that has floor drain, can I leave slab bare? What are pro/con’s?
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