GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Audio Play Icon Headphones Icon Plus Icon Minus Icon Check Icon Print Icon Picture icon Single Arrow Icon Double Arrow Icon Hamburger Icon TV Icon Close Icon Sorted Hamburger/Search Icon

Community and Q&A

Zone 6 wall construction – Is Zip R sheathing (R12.6) adequate

Jim Cuhel | Posted in Green Building Techniques on

Hi

A contractor I am considering for a new house build in Fond du Lac Wi (zone 6) is recommending using the foam zip sheathing (2″foam – R12.6) and HD batt. The wall is 2×6 So the total R value is (20+12.6). After reading the articles here on gba for calculating the minimum ridged foam thickness, I’m concerned this isn’t enough because the foam is de-rated at extremes temps. But since the zip foam faces the wall cavity, I wasn’t sure if the dew point being inside is still an issue as long as the wall can dry to the inside by providing the class III vapor barrier. I was thinking of asking the contractor to go back and give me a quote for zip sheathing (non insulated – just osb) and 3″EPS foam over the top of it. What do you recommend?

Another contractor I am considering just uses 1″ridged foam and batt insulation also with 2×6. And no wood sheathing. I think the total r value here is 25. I realize this isn’t nearly as energy effiecent as the first contractors recommendation but would this wall have condensation/moisture issues?

Thanks I appreciate everyone’s perspective.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. Steve Knapp CZ 3A Georgia | | #1

    Jim,

    I think this thread will provide some pros and cons on Zip-R: https://www.greenbuildingadvisor.com/community/forum/green-building-techniques/100998/zip-system-r-sheathing

    Some folks on GBA don't like ZIP-R because they feel the foam is on the wrong side. That may be a valid argument. If you decided to use exterior foam, you would need R-11.25. Three inches of EPS wouldn't get you there, but 2 inches of XPS would be pretty close. See this article for more information: https://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minimum-thickness-rigid-foam-sheathing

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |