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Wall and insulation

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Youstina

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Jul 15, 2022
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Hello, im building my home in hermitage, TN, 37076, davidson county, i need to use the 2×4 walls because i have a limited budget so what type of insulation can fit in 2×4 walls to comply with 2018 IECC guidelines and pass the inspection , climate zone 4 and it requires R20 or R 13+5
 
Are you sure it is required? The amendment online says local code adopts 2018 IECC but deletes R401.1 through R406.6.5 in their entirety.
 
Closed cell spray foam would get your there, either to the required thickness or maybe flashed with R15 high density batt. I think the amendments simply remove one & two family dwellings from the IECC in favor of using IRC ch. 11. The requirements are the same. But, there are other methods that may be available other than the prescriptive route which might provide a different path.

BTW, I used to live in Hermitage, considering returning to the area in a few years.
 
Thank you all, does it worth to go with the 2×4 and the extra insulation, will it save money or should i upgrade to 2×6
 
This analysis compares three options - closed cell foam, an added insulation board, and 2x6 framing. 2x6 framing was the least expensive in their situation.

www.mich-energy.com

A Surprising Financial Study of 2x6 Construction

Does 2x6 construction makes financial sense? Can you pass the energy code with 2x4 construction? You will be surprised at both answers!
www.mich-energy.com www.mich-energy.com
 
Inspector Gadget said:
R12 batt insulation plus shiplap XPS foam (2") on the exterior would get you to R20 effective.
Click to expand...
The IECC is similar to ASHRAE 90 in that they prescribe nominal insulation values rather than effective like our code. The R13 + 5 means R13 in the wall cavity and R5 continuous insulation.
 
tmurray said:
The IECC is similar to ASHRAE 90 in that they prescribe nominal insulation values rather than effective like our code. The R13 + 5 means R13 in the wall cavity and R5 continuous insulation.
Click to expand...
Hmm. Interesting to know. From my point of view, if you're not taking into account thermal bridging, you're not getting a full picture of the energy efficiency.

(FWIW, at my own build, I went with 2x6 @16 with batt insulation; 1" boards, R5 shiplap foam, 1" air gap, wood siding. Once all the air films, vapour barriers and other dark magic is included ... the wall is pushing R27. Code is always a minimum standard.)
 
Try ResCheck. I uses to have a developer that used 2x4 walls with R13 with extra insulation in the attic, very efficient windows and HVAC and it worked with ResCheck. But that was back with the 2006 codes.
 
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