A basement for my double wall dream house, second try
I've now pretty well settled that a poured concrete basement with exterior insulation and aligned under the inner main floor wall which carry s the roof load is the simplest and most " buildable" if the floor framing is simply extended (cantilevered) beyond the basement . With the floor truss extension, if I don't use a classical rim board but use blocking located under the upper wall's inner face and insulate between the joists with the same 'stuff' (r45 cavity, r1.3 sheathing and r0.63 plywood) I'll use in the double stud walls the the r of the joist area alone is r40.4, almost no worse than the wall above. Good enough! Now onto the real problem. How to get " outsulation on those concrete basement walls at reasonable cost. The TF system 'Transform system looks interesting, it can be had with 5 1/2" foam on the outside and 3/4" inside an r value of 25+ and it has plastic studs 16" OC on the inside and plastic flanges covered by 1 1/2" foam on the outside for mounting cladding. Well it was interesting till I got a quote, they are really proud of that stuff!! About 4x my budget! So here is my alternative that fits the budget for materials.
Basically surround a classic poured wall basement with a non structural (except for soil pressure) wood basement. But do it with 2 layers of 2x4, wood basement pressure treated, framing. The inner is vertical 16" OC and attached at the bottom to 2x4 bottom plate sitting on the same footing as the poured walls and attached to the concrete about 2' below the cantilever floor above with angles and tapcons. These studs upper end is trimmed to land 14 1/2" below the floor truss's bottom plane. The cavities, including the horizontal one above the studs, are filled with r15 bats Then a horizontal " strapping layer is created with horizontal 2x4 s, the upper most screwed to the bottom of the floor truss s, the rest to the vertical studs, 16" OC for the top 3 spaces then switching to 12" OC for he bottom 4'. After filling the spaces with more r15 1/2" wood basement plywood is attached to the horizontal framing. After seam sealing and waterproofing as if it was a wood basement it's back filled following the wood basement rules.
An r28+ ,7 1/2" thick basement insulator for under $3.50/wall sq ft. excluding labor (I work cheap). Your thoughts?
Posted Wed, 03/20/2013 - 18:01
Edited Wed, 03/20/2013 - 18:22
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