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Community and Q&A

Wall Assembly Question with Zip R in Zone 6

JonSuj1 | Posted in Energy Efficiency and Durability on
I am building a new home and I am looking for a suggested wall composition. I am in climate zone 6 (Milwaukee, WI) and would like to have a well insulated wall. I have 2×6 studs. I am considering 3 options: 
A) Zip R-6 Sheathing with R23 mineral wool
B) Zip R-6 Sheathing with 3″ closed cell spray foam   
C) Zip R-6 Sheathing with 5.5″ open cell spray foam   
I understand I selected the wrong thickness foam (1″) for my climate, however the windows and doors had to be ordered at the start of the project and can no longer be adjusted to accommodate 2″ of foam.  
Should I eliminate the zip sheathing? Will there be too much condensation in my wall with option A? Should I pony up the $ and go with an open or closed cell foam interior? or consider a different option?

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  1. Jon_R | | #1

    Add the option of a Class II/III smart retarder on the interior side with cellulose fill. Or plywood on the exterior with some interior side foam.

  2. walta100 | | #2

    My opinion large amounts of spray foam in new construction, is a red flag for poor planning and or laziness.

    With some good planning it is almost always possible to find a lower cost, higher R value options than spray foam.

    Option A is good.

    Consider this option on the outsides 2 inches of reclaimed foam board then standard zip and fill the walls with wet spray cellulose insulation. My guess is this wall will cost less per square foot for more Rs.


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