Minnesota code requirements with CEI – GreenBuildingAdvisor

Hello all,

Building a house in central MN.  I had come across a good deal of use 1″ XPS, and had gotten sign-off to wrap in 1″ foam from local building inspector.  However, was later able to get more, and after doing research here saw the ideal thickness would create r-11.25, and so was planning to wrap in 2 layers + another 1/2″ layer for a total of 2.5″ inches and r-13.

Challenge right now is that my building inspector is not at all familiar with this and right now is telling me that the code only allows 1″:

“only 1” is allowed on the exterior of the structure per code at this moment in time, due to exterior fasteners for the siding and their sheer strength. Any other designs outside of the provisions of the code have to be engineered and signed off, unfortunately it comes down to the overall thickness of your build up prior to siding.”

Is this really what is specified in code?  I’m limited by fasteners?  I have asked for clarification, but he’s not super prompt, so looking for any other insight here to help things along.  I have not found reference to this in my initial researches, but I am by no means an expert.  Is an engineer required for this sort of thing?

My wall assembly proposal inside out:

Drwyall

ClassIII Vapor Retarder

2×6 Stud wall with r-19 or r-21 batt

7/16″ OSB

Tyvek Commercial Housewrap

2 layers of 2″ XPS, staggered seams

1/2″ layer of XPS, taped seams

1×4 furring strips

budget housewrap

Ascend Siding (composite that looks like insulated vinyl)

I recall reading an article here about fasteners required for furring strips, and that it’s kind of nebulous, but seemed like screws 24″ o.c. would be fine.  The siding company has signed off that my system would be fine as it would allow 3/4″ fastener penetration into the furring strips for the siding.