I think the point of the Ufer ground was to increase the contact area significantly beyond that normally had by a thin conductor rod. IE: Dry soil isn't as conductive typically so the CC puts you in contact with significantly more of the soil to achieve an acceptable resistance to earth ground. Putting a plastic insulator in between CC and soil would not be a good thing I think. That letter I linked to talked about removing some of the plastic to mitigate this insulation effect of a stay in place plastic form...

The Ufer ground was first invented to provide a good ground in a location where the soil in the vicinity of the building structure was essentially an insulator (i.e., a non-conductor). As such, I am thinking that isolating even good conducting soil with non-conducting plastic sheet might not significantly increase the Ufer ground impedance. As I am sure you know, one can create a good ground without even being in contact with the ground...it's all about material properties, surface area and the power frequencies...think spacecraft.

Not at all sure about that. The house ground must get back to the grid ground. You cannot have a ground that is isolated from the "ground" The concrete would just be a storage devise of some sort which of course doesn't happen. Strays must make it back to the real "earth."

A space ship has its own power supply and as such is a complete system.

"The NEC defines the term “grounding electrode” as “a conducting object through which a direct connection to earth is established.” The 2005 NEC first defined the term, and the definition has been subsequently revised to describe how electrodes function and to apply to conductive objects or materials that qualify as grounding electrodes. An important feature of this definition is that the electrode is in direct contact with the earth, making a connection. It is important to remember that, without a connection to the earth, there is no grounding. Let’s take a closer look at what constitutes a concrete-encased electrode (Ufer), when it is required, and the installation techniques.
"

http://www.ecmag.com/section/codes-standards/what-ufer-ground

I don’t believe NEC code will provide the required clarity to answer this question. This gets more into the science and theory of AC grounding.

If you took a basic electronics course, you know that capacitors are created by sandwiching an insulator between two conducting plates. Capacitors won’t pass DC at all (because their resistance is extremely high), however they will readily pass AC...the amount of current allowed to pass being dependent on the reactance (which is the AC analog to DC resistance) which for a capacitor is the inverse of the power frequency times the capacitance. So higher power frequency and larger capacitance will result in lower reactance and lower impedance (which is essentially the combination of DC resistance and AC reactance).

The theory of Ufer grounding is based on the amazingly simple principal that if you wire a lot of resistors in parallel, you will end up with a very low total resistance. The earth can be considered as trillions of parallel resistors which is called a sheet resistance. The Ufer ground is also a sheet resistance, although one of much smaller size. The resulting Ufer concrete structure forms one plate of a capacitor and the earth forms the other plate. The capacitance of this capacitor is extremely large and hence the reactance and impedance is extremely low.

So it isn’t at all obvious to me that the presence of another insulator between the two plates created by the Ufer grounding method would significantly alter the low impedance. After all, this is why the Ufer ground was first invented...the ground in the vicinity of the building structure was already an insulator (i.e., a non-conductor).

FBBP: I agree and also find:

Note: Concrete installed with insulation, vapor barriers, films or similar items separating the concrete from the earth is not considered to be in direct contact with the earth.

Not surprising considering that a device shorting to ground might contain a rectifier.

Any pics of the ICF footings and dowels in place?

Lots of photos and examples of ICF footings with dowels in place here: http://www.fab-form.com/fastfoot/fa...onials.php

Here's are some more photos showing the footing key way, 12" spaced dowels and thermally isolated overhead garage door apron. These 12" thick x 36" wide footings with (4) #4 rebar in bottom section were poured on top of an engineered pad and later back-filled after the electrical/plumbing and footing drainage were accomplished. The 5" thick hydronic radiant concrete slabs float on pea gravel and 4" thick EPS insulation.

Apron...

Posted By sailawayrb on 13 Jul 2016 08:31 PM
Lbear, actual schedule depends on the actual engineering, but four (4) #4 rebar is pretty common for the 36” wide footing.

On a 30" wide footing. Is it common practice to have 2 - #4's on the bottom and then 2- #4's on top? I always thought it would be just one row of horizontal rebar.

My understanding is that a 30" wide footing would see 3 - #4's sitting on rebar chairs and then the verticals every 16" oc

Rebar placed top and bottom in the footing would indicate to me a footing designed to deal with forces other than gravity pushing the wall down into the soil(heaving/unstable soil possibly).

For more normal soil conditions, I would only expect it to be near the bottom on chairs or CC block pieces(busted-up CC pavers) as you describe.

For a 30" footing I would also expect shorter rebar pieces(approx. 25" long for a 30" footing) running perpendicular to the long pieces at intervals probably not more than 4'. CC is great in compression, not so hot in tension. You put a 6" CC wall in the center of a footing, that footing would want to bow down at the center which would put the top of the footing in compression, and the bottom of the footing in tension. The short pieces of rebar near the bottom running perpendicular to the wall help keep the footing from trying to turn into a taco...

3-#4's. The dowels in the footing should match the vertical rebar schedule as per the PM

Posted By smartwall on 01 Aug 2016 05:41 PM
3-#4's. The dowels in the footing should match the vertical rebar schedule as per the PM

So 3 - #4 bars in a 30" wide footing is common practice

We usually use small pieces to tie the rebar together to keep them separated

Posted By Lbear on 02 Aug 2016 01:52 AM

Posted By smartwall on 01 Aug 2016 05:41 PM
3-#4's. The dowels in the footing should match the vertical rebar schedule as per the PM

So 3 - #4 bars in a 30" wide footing is common practice

For a 30" footing, Yes, 3EA #4 or #5 rebar in the bottom "continuous"(overlapped X number of bar diameters for bar size and grade). One near the center, one down each side of the form, spaced an appropriate distance from the bottom/sides of the form for concrete in direct contact with the earth(3"?).

Posted By Lbear on 01 Aug 2016 02:20 PM

Posted By sailawayrb on 13 Jul 2016 08:31 PM
Lbear, actual schedule depends on the actual engineering, but four (4) #4 rebar is pretty common for the 36” wide footing.

On a 30" wide footing. Is it common practice to have 2 - #4's on the bottom and then 2- #4's on top? I always thought it would be just one row of horizontal rebar.

My understanding is that a 30" wide footing would see 3 - #4's sitting on rebar chairs and then the verticals every 16" oc

Yes, (3) #4 located near bottom is common for a 30" footing. There is normally no need for footing rebar in the middle or top sections.

The dowel spacing can depend on the actual ICF used, specifically the spacing between the webs. Most ICF would use a multiple of 8" with a 16" dowel spacing being common. Some ICF (e.g., BuildBlock) would use a multiple of 6" with 12" or 18" being common. The actual dowel spacing is normally called out by the specific prescription or specific engineering, and considering the actual ICF that will be used.

I hate to disagree but the dowel spacing should mirror the rebar spacing as per the PM or engineering specs and has really nothing to do with the web spacing in the form being used. If the specs call for a #4 every 14" then that's the dowel specs regardless of the web spacing in the form used.

I don’t think we are really disagreeing Smartwall... At least I hope not, I have learned much from you about ICF over the years!

Just like the dowel spacing can be a multiple of the specific ICF web spacing, the vertical rebar schedule can also be a multiple of or the same as the dowel spacing. If the engineer’s load analysis software calls for a minimum of 14” or 17” vertical rebar, you can use a dowel and vertical rebar spacing of 12” or 16” for 6” web ICF or 8” web ICF respectively. Yes, you may use a little more rebar, but you will be locating all your rebar in the center of the ICF cores....certainly not required, but a nice thing and less chance of having any interference with the webs. We also like to drop 1” lengths of appropriate diameter PVC pipe over the dowels and use these to capture the bottom ends of the vertical rebar (i.e., essentially tying the vertical rebar to the dowels without actually having to do any tying here). This certainly isn’t required either, but it makes for a stronger structure without expending much effort/expense.

I guess my advice or message here is to consider engaging your engineer early and to have him/her consider the parameters of the ICF that will actually be used BEFORE calling out the ICF dowel/vertical rebar schedule on the construction drawings. This is also important for the horizontal rebar schedule. You certainly would not want to have the construction drawings call out a 16” horizontal rebar schedule if you are using Nudura ICF or call out a 18” horizontal rebar schedule if you are using BuildBlock ICF.

I have to admit that I'm a reformed dowler. As I stated previously I haven't installed a dowel in over 12 years. So I should probably leave the conversation to others.

Reformed dowler...LOL! I suspect that you may have only forgotten more than what most ICF people know... Thanks again for all your help with the BuildBlock ICF parameters...we really love this block and we will be using it again soon for another project.