Air By-Passes…

19 01 2011

Ambrose, one of our DER gurus checking out the sidewall for bypasses

While you’ve got to have good air for your human lungs to breathe in a house, you don’t want to have uncontrolled holes letting air in and out, and giving an easy ride for lots of heat to exit and enter.  Air by-passes, thermal bridging and moisture penetration are anathema to a deep energy retrofit.  You’d think that with a superinsulated retrofit, we wouldn’t have an air bypass problem, but we did—because of the structure of the house. The rafters were sitting on 2×10’s laid flat across joists that protrude outboard from the sidewalls like the fins on a motorcycle engine (wierd metaphor, but that’s what they reminded me of).  Needless to say–a “chainsaw” retrofit–to keep a continuous air and water plane, became out of the question.

Joists above the southeast sidewall

Rafters and joists with structural plate in between

"Motorcycle fin" joists above southeast sidewall

"Crenellating" the rigid foam around each joist--2 layers worth...

Yes, we could have boxed everything in–but that didn’t happen. Instead, we spray-foamed the ____ out of all the air-bypasses at the joists (at least I hope we did…). And then used some nano-paint to try to “assuage” the conductive heat loss. I’m not sure the strategy really worked. An infrared scan will let us know soon enough.

Spray foam (closed cell) at the soffit joists

Nanopaint at joists but not at "joist-tails" that are just extending the roof eaves visually.

How we might have dealt with air bypasses and thermal bridging from the inside--if the attic sprayfoam had gone according to plan--see next post...




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