Rigid foam underneath pier and beam house
Josh_Dillingham
| Posted in Energy Efficiency and Durability on
I’m building a house on piers with 2×12 floor joists dense packed with cellulose. To eliminate thermal bridging from the floor joists (and to air seal underneath) I plan on using zip R sheathing underneath the house. In terms of eliminating thermal bridging is it worth it to pay extra for R-6 sheathing or would R-3 be sufficient?
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It's hard to say; it depends on your climate zone and your specific conditions. Vapor drive is usually lower in floors than in walls or roofs, so the ratio of vapor-closed insulation to vapor-open insulation is not as important as it is at other locations. Foam has high levels of embodied carbon so it's good to use as little as possible. But the more you use, the safer the assembly will be. More info here: https://www.greenbuildingadvisor.com/article/insulating-a-wood-framed-floor-assembly.