Optimizing a fixed depth wall assembly?
Hello GBA community! I’m a nerdy engineer working with my builder in Zone 6 (Southwestern Ontario) on a wall assembly for an addition to a 100+ year old house.
The lot size doesn’t allow much space to work with and the current design is a compromise of aesthetics and efficiency. We don’t have much space to work with for the wall assembly, but I wanted to make it as efficient as possible. Constraints always limit possible solutions 🙂
* Drywall interior.
* Certainteed membrain smart vapor barrier to meet inspection in zone 6 and to avoid double-barrier problems.
* 2×6 16″ OC, using T-studs (thermally broken R-19 studs).
* ccSPF to fill the bays (means we don’t _need_ an interior vapor barrier, but I have a spec’d a smart vapor barrior to avoid failing inspection)
* 1/2″ plywood sheathing.
* WRB on the outside with taped seams.
* Vinyl siding.
The plywood can dry to the outside. The vinyl siding is well ventilated and doesn’t need a rainscreen.
I have about 1″ of extra space on the outside I could use in the assembly if needed.
I may fail to get T-studs due to availability.
– What can I do with the 1″ of extra space to optimize the wall assembly for energy efficiency?
– Would switching to ZIP R6 sheathing help? Is that the only optimization left?
– What if I have to use normal 2×6 studs?
– Adding more exterior insulation is not possible. For the 2×6 wall assembly I would need a lot of insulation on the outside to keep the sheathing below the dew point and I don’t have that space. Therefore I’m stuck putting all the insulation on the inside.
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