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Minimum Thickness Rigid Foam Sheathing in Zone 4A

brad17 | Posted in General Questions on

This article

specifies a minimum of R3.75 exterior rigid insulation for a 2×6 wall in climate zone 4-Marine to prevent interior condensation. I am in Zone 4A (mixed humid) and NOT “marine”. Does anyone know if this number still applies? And if not, where do I find a more relevant R value?


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  1. brad17 | | #1

    Ok, I found a resource for this.

    "2021 IBC includes all of Zone 4" - so not just Marine.

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