Posted By jacktca on 20 Mar 2012 08:50 PM
Get over this frying pan business.  You're going to pack the ICF's with steel rebar anyway.   So what does it matter if their connectors are made of steel?

As mentioned, steel that runs parallel becomes a thermal bridge. When someone builds a "Larsen" wood wall, it is done to stop the thermal bridge the wood creates. The same with good windows, they have thermal breaks. If an ICF from has metal to metal webbing on each end of the EPS, this does create a thermal bridge.

I would like to see thermal imaging of an ICF block that has steel webbing in it. If I were a betting man, there would be visible thermal bridging within the webs. This same issue is common in some SCIPs that have steel trusses within their forms. The steel trusses create a thermal bridge. Some SCIPs manufacturers are using different technology to combat this issue.

 

Polycrete Big Block's steel reinforcement and steel cross ties are made from 4mm steel wire. It is embedded 1" - 1-1/2" deep within the EPS foam panel, and there is no evidence of thermal bridging. Thanks.

> absolutely zero problem in the industry in shipping or availability

if cost is no object

> For residential, a 6" core is the standard. Using 4" cores is OK for maybe a garage or something but residential should be 6".

I have talked to people who built using 4" ICF walls and lived in the places they built.    They said 4" is way more than enough.  Overkill.  Much stronger than 2x4's at any rate.

The guy who is doing my bracing doesn't have a problem with 4" and has built schools with it in our area (Los Angeles County) before.  He only has an issue with the limited space.   I bought a ton of #5 rebar.  He told me that for the vertical we need to go with #4 due to limited space.

>  If you are in a seismic area, 6" concrete core is the standard

Hogwash!   The only thing that is standard about 6" core and seismic zones is that people open their mouths or write about it but when it comes down to it just can't come up with any definitive and clear specifications written down anywhere that support their claims.    Case in point I was on the phone one day with an executive from Reward blocks.   He said it is in his documentation for sure somewhere, he would get back to me.   A day or two later he admitted that while Reward blocks are certified for D1 and D2 he cannot come up with any documentation which will clear up the matter of what core size is required.  

> #4 or #5 rebar every 16" or 18" on center

I'm using #5 every 14" horizontal #4 every 16" vertical.

I have to say that I have been in many earthquakes.  I have seen concrete/brick walls next to me wiggle and wave.   I would rather be in an earthquake with a 4" wall next to me than a 6" wall.   As long as it has styrofoam around it to cushion the blow I'm good.

I'm using #5 every 14" vertical #4 every 16" horizontal.   Oops, sorry.

Oh and one more thing.   Good luck trying to figure out for 100% sure if your house is in seismic zone C, D1, or D2.    The place I'm building is 1 mile from the San Andreas fault but if my life depended on it I couldn't prove I'm in D2.  

Well I built on/next to the San Andreas fault for over 5 years, if we were below grade it was 6, 8, 10, or 12", above grade never less than 6", everything is required to be design by an engineer and never once did I find one who would allow 4" anywhere in that State.

I even had one engineer design a 12" wall for above grade!!! I even called him on it and he would not change his spec.

Posted By Chris Johnson on 22 Mar 2012 07:44 AM
Well I built on/next to the San Andreas fault for over 5 years, if we were below grade it was 6, 8, 10, or 12", above grade never less than 6", everything is required to be design by an engineer and never once did I find one who would allow 4" anywhere in that State.

I even had one engineer design a 12" wall for above grade!!! I even called him on it and he would not change his spec.

I am no engineer but from all my research I agree that 6" of concrete in a seismic zone would be minimum for a residential ICF wall. The problem with a 4" core is not the shear strength/in-plane or the bearing strength/vertical but the out-of-plane strength.

As per an engineer:

"Anyways, there are many design scenarios where you will need to go to 8". I am sitting here in my office engineering one right now. And don't even ask me about 4" unless it's for the family dog"  

The problem is that the stiffness (deflection out of plane) is based upon this distance cubed and the strength (bending out of plane) is based upon this distance squared.  So, ROUGHLY, the stiffness is 4^3 or 64 vrs 3^3 or 9, so a 8" wall is 7 times stiffer than a 6" wall.  Also, strength in bending is 16 vrs 9, so a 8" wall is about twice as 'strong' as a 6" wall for out of plane loads.

ICF Concrete Thickness

The concrete costs involved from going 4" to 6" is not really that much more money. What a 6" form allows is better consolidation, especially with all the rebar involved. Stuffing rebar in a 4" space and then trying to get concrete to consolidate within there will be a lot harder than if a 6" or 8" form was used.

Building on the above comments. I read an article claiming that 4" is sufficient for residential walls but some engineers disagree vehemently that 4" concrete cores are sufficient for residential use, especially in seismic areas. As noted in the above statement and article.

I think another issue with 4" cores is the rebar schedule and concrete consolidation (concrete voids). Concrete must be 4" of thickness (minimum) in order to achieve strength. In an ICF form the margin of error for concrete is very much there and in a 4" form, losing an 1" of concrete can cause problems within the wall.

In the end the cost of the actual concrete used in the 6" core or the 4" core is negligible. The cost of a 4" ICF block vs. a 6" ICF block is identical. So why the push for a 4" core?

I agree with everyone in this forum, your installer is what’s really going to make the biggest difference in your cost and development of any ICF product. Our company Forming Solutions Inc. is based out of Dana Point California. We are Southern California’s largest ICF distributor and have many contractors that are certified to be installers with a verity of developments to show their qualifications. We are authorized to sell more than one brand of ICF since we have been through the mill of them since the last 14 years. Fox blocks are our favorite just because of the internal relations and dedication to technical advancements, but that’s just our opinion. Pick what you like as long as you have the most authorized installers to perform the best of the blocks performance in the field. If anyone has any questions on block pricing, design questions or references for installers in the area don’t hesitate to call or shoot us an email.

(714)412-0133
www.forminggreen.com