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2021 IRC Insulation requirements

alaskajoe

alaskajoe

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Joined
May 22, 2019
Messages
53
Location
Alaska
How is everyone dealing with the requirements for insulation when it comes to the R value of 20 + 5ci in the stud cavity. Adding that 5ci is putting a big cost on construction. If you use rock wool at 5.5" it is just R-23
 
Climate zone 5 - Its required either R-20 + 5ci or R-13 + 10ci.

How else am I supposed to deal with that? They can certainly provide compliance through section 406.
 
alaskajoe said:
How is everyone dealing with the requirements for insulation when it comes to the R value of 20 + 5ci in the stud cavity. Adding that 5ci is putting a big cost on construction. If you use rock wool at 5.5" it is just R-23
Click to expand...
So, will the R-value Zip sheathing get you there? I personally prefer the R-9, but they make an R-6 also.

I like it a lot, not sure how simple that is to get in your neck of the woods but works great IMO, cost is not really that bad in my neck of the woods.

https://www.huberwood.com/zip-system/insulated-r-sheathing#products
 
You have to add 1" foam exterior insulation and use much longer nails for your siding. If you use wood siding it has to have an air space behind it or it will warp badly. I found that out the hard way on a house I built in the late 70s.
 
I wonder if the ZIP R9 - which is an actual R9.6 - is accepted for the CI in zone 6.

Does wood warp on ZIP - since it's basically OSB and house wrap?
 
Staggered studs on an oversized plate works also. The idea of the code is to eliminate (greatly reduce) thermal bridging. With framing making up to 25% of the exterior wall it is one of the IECC requirements that makes sense.
 
Zip-R6 is cheaper to install than exter. foam because you would still need a WRB, and trim out all the windows to be flush with the protruding insul.
Downside is the stuff (ZIP-R6) has lousy shear values. Needs to be fastened at 4" OC to get any shear at all.
 
joecode said:
Zip-R6 is cheaper to install than exter. foam because you would still need a WRB, and trim out all the windows to be flush with the protruding insul.
Downside is the stuff (ZIP-R6) has lousy shear values. Needs to be fastened at 4" OC to get any shear at all.
Click to expand...
And you have to buck out all the windows for nailing and deck ledgers get weird with ZipR...And you can't do IRC portal frames
 
steveray said:
And you have to buck out all the windows for nailing and deck ledgers get weird with ZipR...And you can't do IRC portal frames
Click to expand...
Yeah you need to break it at the ledger, I copied one of the manuf's details- didn't seem too terrible, we will see how it holds up. The contractor is the one who pushed for the ZIP-R so it must be easier/cheaper. Some struct. engineers are insisting on a layer of sheathing against the studs, then ZIP-R over that. That's how crap it is in shear. (Saw this for Colorado-high wind area)
 
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