Balloon framing and stone walls
We just learned that some of the walls in our 1950s Cape are ballon framed (sort of). I’ve read GBA and Googled, and I haven’t seen anything that mirrors our exact construction. An open gap runs behind the plaster from the crawl space to the top of the first floor, where 2×4 horizontal blocks are present. At the first floor eaves, these blocks rest 18″ from the top of the studs (there is no top plate). On the gable ends, the studs appear to continue to the top attic, where the same setup appears (2×4 horizontal blocks 18″ from the top of the studs, no top plates). So there is not technically an open cavity from crawl to attic, but the studs do seem to run top to bottom at the the gable ends.
The insulators rigid foamed and sealed all of the basement rim joists, but did not block the bottom of the vertical bay behind the rim joist (as we didn’t know these were balloon framed). Similarly, the tops of the 2×4 blocks at the eaves and in the attic were sealed, although not nearly as well as the basement. No action was taken at the first/second floor transition, where the top of the stone wall meets the bottom of the siding. From the photos I took with my boroscope, it appears our first floor walls are R3: stone>furring strips>plaster. The second story walls appear to be insulated with 3-4″ of rockwool.
1. Given the well-sealed rim joist areas and somewhat sealed tops of 2×4 blocks, is it worth undoing/redoing the air sealing at top and bottom of the balloon frame vertical bays? This would be somewhat labor intensive (eg, redo the rim joist areas) but we’re willing to consider.
2. What kind of air sealing results might we expect with grain bag approach in bays at top of first floor/stone wall transition at gable ends (ie, insulating from inside)?
All experience-based suggestions welcome.
Otherwise, our plan is to move to the internal air barrier and air seal the heck out of the baseboards, outlets, and so forth. In terms of insulation, rather than risk moisture problems in walls (or tear our house apart to spray foam the stone), we are creating a few double-thermal barriers to increase comfort, eg placing batts at floor in newly encapsulated crawl space.
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