Simulated performance model – underinsulating homes
A number of home builders in our area use a simulated performance model to pass residential energy code. The current code is based on 2015 IECC. But instead of following the insulation requirements, they run a software simulation that somehow demonstrates that despite using lower insulation than required by 2015 IECC, they outperform a “standard” home built to 2015 IECC specs.
Using this software somehow allows them to use R11 in basements, R13 in walls, and R38 in attics despite this being below 2015 IECC requirements. No insulation under the basement slab. No exterior insulation.
I would think the only way this would happen is to beat the code somewhere else. The only thing I see them beating is ACH50. They enter 3 into the software and code is 4.
How his this possible?
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I'm going to go out on a limb and guess that they're using spray foam insulation, there's been a lot written about spray foam sellers using "equivalent insulation" or similar arguments to justify underinsulating.
There are other tricks you can do like reducing the framing fraction. Without seeing the calculations it's hard to know.
It's all 2x4 framing with fiberglass batts
Is it 24" centers?