Double stud retrofit with T1-11 existing siding (perm ok?)
(Zone 6a, Maine)
I’m going to be insulting a garage, which is currently 2×4’s open to the inside with t1-11 siding painted red on the exterior. Nothing else in the assembly currently.
My plan is to build an inner 2×4 wall to make it a double stud assembly, resembling the ‘Lstiburek’s ideal double stud wall’ but likely with intello plus in place of the sheathing on the ‘exterior of the interior wall.’ ala 475
For clarity, the plan is, from inside to exterior:
-tongue and groove (or shiplap) pine running horizontal (its a shop so I want to be able to hang stuff anywhere)
-2×4 non load bearing wall with batt (roxul?) insulation and acting as service cavity
-smart vapor retarder and air barrier (intello +?) attached to exterior of interior wall. must allow cellulose blow in.
-space between framing (2-4″) filled with dense pack cellulose
-2×4 wall (existing) with a continuation of the dense pack (one blow)
– t1-11 sheathing (existing)
– rain screen gap?
– cedar shingles?
I have a few questions.
1) Most generally, does this assembly seem like a good choice to retrofit a garage for heat given that I want a high performance wall at a low price point (labor will be done by me, i.e. free).
2) Will the T1-11, being painted (unknown type of paint), cause any issues with permanence/ drying potential? I am not 100% set on it, but I think I will add shingles to match house, in which case would a WRB installed over the T1-11 (with a rain screen) be the best route?)
3) I am debating the size of the wall gap. Do I need to be concerned with some ratio of where the air/vapor barrier is in the wall (I read something of a 30 to 70 ratio, 30 percent of wall inside to 70 percent outside of barrier). I don’t remember where I read that and can’t find detailed articles discussing it.
4) Any reason I should use DB+ vs intello+ vs membrain? (Can blow behind membrain?)
5) I will be installing foam on exterior of slab/stem walls. The t1-11 currently comes closer to the ground than I would like. Any reason not to cut away 6″ or so of the t1-11 and then extend the foam that much higher up the wall for better splash protection? I suppose I would loose the connection to the sill plate if I did that… Perhaps foam extending over the t1-11?
Lots of questions, I know. thanks for any help!
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