Achieving Net-Zero Insulation Levels Without Foam
I’m sure this has been asked a dozen times so I apologize for asking again but I can’t find – or maybe can’t understand – what the best framing approach would be for Net Zero.
Our aim is to design a Net-Zero home while balancing cost vs performance. I’m in Ontario, Canada climate zone 6. My understanding is that the recommended insulation levels here for net zero is R40. So the question is how best to achieve this. The debate about what level of insulation aside, let’s assume we want to achieve R40 or close to it. For background our original plan was to go with ICF R30 to the roof for a 2 storey house. But after speaking to a few engineers I’ve been advised that although possible, it may not be the best solution as some of our 2nd story walls don’t line up with the 1st storey. So we’d have to introduce a lot of steel beams to hold the ICF etc. Again debate aside, let’s assume we’re now going with ICF for the foundation and stick frame above grade. I don’t want to use spray foam so our options seem to be:
1. Double studded walls with no exterior insulation. I’m not a fan of this as from everything I’ve read external insulation is the best approach. I know I can do double studded + external but then the cost gets very high.
2. 2×6 @ 24″ on centre framing with Rockwool. If I’m calculating correctly Rockwool at 2×6 24″ is R23. And their Comfortboard 80 for external is R4.2 per inch. So with 3″ of external insulation it would only gets me to a total of R35.6.
3. The third option is to go 2×8 24″ on centre. Again if I’m calculating this correctly 2×8 @ 24″ is R30. Plus 2″ of external at R4.2 per inch would be a total of R38.4. Still not reaching that R40 recommendation.
So now the question is even though the 2×6 model has a lower R value, would it not be better having that extra inch of external insulation vs thicker internal walls? I’m also trying to balance cost so I would think the 2×8 studs would be more expensive as a total system. Would the 2×6 @24″ centre with 3″ of external insulation achieve the Net Zero I’m looking for even though I’m not reaching R40? I know I can keep adding insulation but again I’m trying to balance cost vs performance and I want to stay away from spray foam.
Appreciate any advice.
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