Many new state code books have the rebar schedules in them and can be checked out at a library. Follow the code or have an architect design it. Asking someone online that you have no background of or they don't have responsibility for is not a good idea on some thing as expensive as your house or life.

Thanks.

Montana has not yet updated those codes for use with ICF's yet; all they have is a link to the 2018 IRC, unfortunately. The only data available is from the ICF manufacturers themselves (albeit drafted by an engineer).

Have you priced 4500 PSI concrete mix with a low water ratio for the wall below grade? It is much more water resistant than 3500.

I am talking strictly about increasing the below-grade concrete wall's resistance to water. However, the architect or engineer might consider adjusting the rebar schedule based upon the projected 28-day PSI of the concrete. The following link explains what can happen to a mix that has a high water/cement ratio. https://en.wikipedia.org/wiki/Water%E2%80%93cement_ratio

The documents you list are outdated.
Montana has adopted the 2018 IRC.
The 2018 IRC itself allows you to use an alternative method of ICF rebar - the document is called PCA-100 and is free to download.
It is a larger more elaborate version of the tables found in IRC.
Forget the manufacturer's rebar tables - most of them dense up the rebar to fit their blocks etc.
Ignore the extra 500psi you think you will get.
Your horizontal rebar for basement walls (and in most cases for above grade walls) is more or less useless. It is temperature reinforcement that controls cracking. Cracking is not a structural but a looks issue especially for plywood formed concrete walls where cracks can be seen. It is also used on shear walls which I doubt you need.
In my opinion, #3 horizontals at 12" o/c is an overkill. I'd rather see #3 at 24".
Vertical rebar is what studs are to a wall. Look at your wall height, backfill height, wall thickness, backfill pressure and select accordingly. PCA-100 will give you something like #6 at 35" o/c. Use the table 2.3 (in PCA-100) to alternate this to lower rebar grade, or smaller bar diameter with larger/smaller spacing etc.
Or use simple proportion math. #6 has a cross section area of 0.44 inches squared. Spaced at 35" o/c. You'd like to see the spacing for #4 bar (0.2 inches squared) of the same grade (grade 60).
Spacing for #4 bar = (35 x 0.2)/0.44 = 15.9" o/c. And so on. By the way #5 has a cross section area of 0.31. #3 is 0.11.

Thanks so much, Baldwin. Your info is super helpful!

I fully concur with Baldwin's math and mindset... A good structural PE can design ICF for whatever you need. I think we were D1 here in southern Oregon, but our structural PE designed for a 9.2 event. It wasn't a significant construction cost addition to do so either. Beefier concrete and rebar, and using sliding plates and such so floor slab, walls and ceiling trusses could move and flex within some limits.

Posted By schulace on 08 Mar 2021 07:48 PM
Thanks.

Montana has not yet updated those codes for use with ICF's yet; all they have is a link to the 2018 IRC, unfortunately. The only data available is from the ICF manufacturers themselves (albeit drafted by an engineer).

Really? I thought Montana updated these codes a while ago! Thank you for sharing this info.

Posted By sailawayrb on 11 Mar 2021 04:37 PM
I fully concur with Baldwin's math and mindset... A good structural PE can design ICF for whatever you need. I think we were D1 here in southern Oregon, but our structural PE designed for a 9.2 event. It wasn't a significant construction cost addition to do so either. Beefier concrete and rebar, and using sliding plates and such so floor slab, walls and ceiling trusses could move and flex within some limits.

You are totally right. A good structural PE not only works for designing a ICF but also to eco-build in the most effective manner.