My builder is planning to use number 4 and 5 rebar every 32" on center vertical and horizontal. Great soil conditions and low wind no seismic issues in Phoenix, AZ. Is this acceptable? Pay the difference for 18 oc? Thanks Dan.

Fox blocks is great! 32" on center should be fine for horizontal. But vertical should be about 24' oc depending. with fox blocks you would have to go down to 16" oc horizontal due to the web spacing. It all depends on block core size and if there will be any sub grade walls.

Posted By dford on 22 Jul 2013 06:07 PM
My builder is planning to use number 4 and 5 rebar every 32" on center vertical and horizontal. Great soil conditions and low wind no seismic issues in Phoenix, AZ. Is this acceptable? Pay the difference for 18 oc? Thanks Dan.

First I see three major problems:

1 - If the price is increasing because of going from 32" oc to 18" oc, that I find absurd. Rebar is cheap and only pennies on the dollar. Sure there is some labor involved but on a residential wall going from 32" to 18" oc should not cost a measurable amount. We are talking a few hundred dollars for the rebar and labor. On a 3,000 sqft ICF wall, maybe $200-$400 additional.

2 - The 32" oc is against American Concrete Institute (ACI) recommendations.

3 - 32" oc for both vertical and horizontal is unheard of in everything I have read and from ICF installers that I know. 32" oc vertical is completely absurd in my opinion.

How are your roof top plates going to anchor down, are they installing bolts?


If doing the absolute minimum standard as applicable and allowed by law is the standard, why even do ICF?

Did the engineer sign off on this or are they using the Prescriptive Standard Manual?

I am quite aware of Phoenix's building code as it is some of the most lax in the nation. That is why there are so many problems with the homes in Phoenix. If you attempted to build a Phoenix home in other parts of the country, it would fail instantly.

If you are going with ICF, do it right. Sure a 32" oc rebar schedule will probably be OK as long as the mix is a high psi and vibrated to prevent voids but remember concrete is strong in compression but weak in tension without rebar.

I've seen #4 bar at 48" both vertical and horizontal in a 6" wall in Ft. Myers, FL. Was it correct and acceptable? According the engineer who designed and stamped the drawings, yes it was. I've also been subjected to both 12" horizontal and 4" vertical #5 bar, right on the San Andreas fault north of San Francisco myself...because the engineer who designed and stamped the drawings said so.

So to answer your question, what does the engineer who designed and stamped your drawings call for? Follow those, or if an engineer is not required follow the prescriptive code.

Just to put it out there to you, a competent residential engineer (not a commercial guy or bridge builder) will save you money, usually more then his fees, designing YOUR house in YOUR area based on his RESIDENTIAL design experience. Prescriptive code is a blanket and not job site specific...anyone can design out of that, including you and I.

Llbear is correct. That spacing is not allowed by code, and you would have to have an engineered design to suupport it. Call Robert Schulthorpe at FB (ther engineer and a personal friend of mine). He will tell you the same thing. To save time, get ahold of the current building code in AZ, probably the 2009 IRC. Go to Section 611 for prescriptive desgn specifications for ICF walls. No engineer needed. If you call Robert, tell him douglas sent you. DJB