UFER Grounding and Vapor Barriers

J

Jim Follett

Member
Location
Houston, Texas
Occupation
Estimator / Project Manger / Designer
We have been trying to get a proper method of applying the UFER ground in new construction where there is a complete vapor barrier between the concrete slab, and earth. In these installations, the slab is not actually in contact with the earth. I have been telling our crews to install a properly sized, bare grounding conductor, at least 30' long. Connecting one end to an exposed slab rebar, then 20' away, connecting to another rebar in the same slab. The section of bare copper conductor installed between these two rebar connections, is installed below the vapor barrier, in direct contact with the earth. The remaining end of this conductor is connected to the main service ground connection. This is usually installed in the main service tap enclosure, main service wireway, or the main service OCP device. This depends on the particular service design. The AHJ's across the state require we install the UFER grounds, in all new construction. NEC 250.52 (3) "Informational Note" states "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. So, essentially all we are doing here is bonding the slab back to the service ground. I don't have a problem with this installation, but want to know if anyone sees an issue with this.
 
What you've described (if I'm understanding it) is not code compliant as a CEE. You're installing the bare copper below the vapor barrier which does not meet the prescribed methods of creating a CEE in Article 250.

Welcome to the Forum. :)
 
Jim Follett said:
We have been trying to get a proper method of applying the UFER ground in new construction where there is a complete vapor barrier between the concrete slab, and earth. In these installations, the slab is not actually in contact with the earth.
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The slab is irrelevant; only the proper rebar or wire in the footing qualifies.
 
Jim Follett said:
We have been trying to get a proper method of applying the UFER ground in new construction where there is a complete vapor barrier between the concrete slab, and earth. In these installations, the slab is not actually in contact with the earth. I have been telling our crews to install a properly sized, bare grounding conductor, at least 30' long. Connecting one end to an exposed slab rebar, then 20' away, connecting to another rebar in the same slab. The section of bare copper conductor installed between these two rebar connections, is installed below the vapor barrier, in direct contact with the earth. The remaining end of this conductor is connected to the main service ground connection. This is usually installed in the main service tap enclosure, main service wireway, or the main service OCP device. This depends on the particular service design. The AHJ's across the state require we install the UFER grounds, in all new construction. NEC 250.52 (3) "Informational Note" states "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. So, essentially all we are doing here is bonding the slab back to the service ground. I don't have a problem with this installation, but want to know if anyone sees an issue with this.
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You do not actually have a CEE (Ufer) if there is a vapor barrier between the footing or foundation and the dirt.

If the vapor barrier is only under the slab it does not matter since whatever rebar is in the slab is not part of the CEE.

The rebar that is in the foundation or footing is the CEE.
 
Jim Follett said:
...The AHJ's across the state require we install the UFER grounds, in all new construction. NEC 250.52 (3) "Informational Note" states "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. ....
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This is a contradiction that has developed in recent years, it seems. 20-30 years ago, vapor bariers were not required and some AHJs were in the habit of requiring installation of a CEE when new foundation is poured. Now other codes call for vapor barriers and if that barrier is sufficiently complete then there can be no CEE. So the AHJ ought to take their pick. If they want to enforce vapor barrier requirements then they can't require a CEE. If they require a CEE then they're telling you that you can't have complete vapor barrier (whether that was a design choice or required by another code).

Installing a random length of bare conductor in the earth that isn't concrete encased is not a valid NEC electrode, unless it's "encircling the building or structure" so as to be a ground ring.
 
This is an issue I have observed and brought up to my company and my area of Florida. If I had the power, I would refuse to install a bond to the rebar in a footer that is surrounded by a moisture barrier and make it come to a head. (I don't have that power in my company). I wonder how many houses there are out there right now where they don't have proper bonding to earth because of this issue.
 
Since the vapor barrier negates the use of a CEE why not just use another method of making an electrode like two ground rods or a plate electrode?
 
Be careful how hard you push this, or someone will decide that you need to use _conductive_ polyethylene as your vapor barrier. Making a conductive vapor barrier is no big deal; you just add carbon to the film and $$$ to the price.

To the OP: Don't try to paint the lily; you recognize that with the electrically insulating vapor barrier you don't have a proper Ufer electrode. Don't try to make something new up to overcome this issue; instead just install one of the code accepted grounding electrodes, and move on. Two ground rods is a very common approach, but plates, ground rings, etc. are other options.

If the local AHJ continues to require connecting to rebar, just call it 'locally required bonding' and move on.

Ufer type ground electrodes are great, but unless you are handling explosives in the basement I'd put the money into better corrosion protection for the rebar, and just use the minimum required grounding electrodes.
 
I fully understand that we do not have a UFER ground, this is what we have been trying to figure out, the best way to achieve this, with 100% vapor barrier
jaggedben said:
This is a contradiction that has developed in recent years, it seems. 20-30 years ago, vapor barriers were not required and some AHJs were in the habit of requiring installation of a CEE when new foundation is poured. Now other codes call for vapor barriers and if that barrier is sufficiently complete then there can be no CEE. So the AHJ ought to take their pick. If they want to enforce vapor barrier requirements then they can't require a CEE. If they require a CEE then they're telling you that you can't have complete vapor barrier (whether that was a design choice or required by another code).

Installing a random length of bare conductor in the earth that isn't concrete encased is not a valid NEC electrode, unless it's "encircling the building or structure" so as to be a ground ring.
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What are we gaining by installing the conductor in concrete, other than it meets the wording in Article 250?
 
Jim Follett said:
I fully understand that we do not have a UFER ground, this is what we have been trying to figure out, the best way to achieve this, with 100% vapor barrier

What are we gaining by installing the conductor in concrete, other than it meets the wording in Article 250?
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You're gaining all of the mass of the entire concrete footing which is in contact with the earth. If you want to bury a bare copper conductor you can make a ground ring but you would need to follow the requirements for a ground ring electrode.
 
winnie said:
Be careful how hard you push this, or someone will decide that you need to use _conductive_ polyethylene as your vapor barrier. Making a conductive vapor barrier is no big deal; you just add carbon to the film and $$$ to the price.

To the OP: Don't try to paint the lily; you recognize that with the electrically insulating vapor barrier you don't have a proper Ufer electrode. Don't try to make something new up to overcome this issue; instead just install one of the code accepted grounding electrodes, and move on. Two ground rods is a very common approach, but plates, ground rings, etc. are other options.

If the local AHJ continues to require connecting to rebar, just call it 'locally required bonding' and move on.

Ufer type ground electrodes are great, but unless you are handling explosives in the basement I'd put the money into better corrosion protection for the rebar, and just use the minimum required grounding electrodes.
Click to expand...
I have no intention or trying to get changes made to structural requirements on projects, and, I'm fully aware of the need for the vapor barrier. No, my question was looking for a solution to the slab based Ufer, as per AHJ requirements, which we cannot do. I agree with 'locally required bonding', because that is all it is. The footing is the best solution, as per 250-52 (A) (2).
 
If the footing counts as a CEE, then I agree, use that. However what if the footing also has a vapor barrier?

And, as I said, if you really _want_ to use a CEE, and really _should_ have a vapor barrier, then you certainly can have electrically conductive vapor barrier material.
 
Jim Follett said:
I have no intention or trying to get changes made to structural requirements on projects, and, I'm fully aware of the need for the vapor barrier. No, my question was looking for a solution to the slab based Ufer, as per AHJ requirements, which we cannot do. I agree with 'locally required bonding', because that is all it is. The footing is the best solution, as per 250-52 (A) (2).
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winnie said:
If the footing counts as a CEE, then I agree, use that. However what if the footing also has a vapor barrier?

And, as I said, if you really _want_ to use a CEE, and really _should_ have a vapor barrier, then you certainly can have electrically conductive vapor barrier material.
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I have never seen a footing with a vapor barrier. I like the footing application, no AHJ can complain about not having enough earth contact area.
 
jaggedben said:
This is a contradiction that has developed in recent years, it seems. 20-30 years ago, vapor bariers were not required and some AHJs were in the habit of requiring installation of a CEE when new foundation is poured. Now other codes call for vapor barriers and if that barrier is sufficiently complete then there can be no CEE. So the AHJ ought to take their pick. If they want to enforce vapor barrier requirements then they can't require a CEE. If they require a CEE then they're telling you that you can't have complete vapor barrier (whether that was a design choice or required by another code).

Installing a random length of bare conductor in the earth that isn't concrete encased is not a valid NEC electrode, unless it's "encircling the building or structure" so as to be a ground ring.
Click to expand...
Is more of electrical code and building code clashing and is complicated even more when there is separate entities involved with enforcement of each code. If the electrical code is non amended NEC, it shouldn't be a problem though if the electrical AHJ interprets NEC correctly. NEC clearly doesn't consider a footing with vapor barrier between it and the earth as a qualifying CEE, and doesn't require connecting to a CEE if one is not present.
 
winnie said:
If the footing counts as a CEE, then I agree, use that. However what if the footing also has a vapor barrier?

And, as I said, if you really _want_ to use a CEE, and really _should_ have a vapor barrier, then you certainly can have electrically conductive vapor barrier material.
Click to expand...
I'd go out on a limb and say you might still have less impedance in a large footing with vapor barrier than you may have with a pair of ground rods, it will just have some impedance on the capacitive side of things.
 
Jim Follett said:
I have never seen a footing with a vapor barrier. I like the footing application, no AHJ can complain about not having enough earth contact area.
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I haven't either, but have seen foamboard on exterior side of the concrete for thermal barrier purposes. I still connected to those, I figured there is still plenty of contact with earth between the bottom and other side that it is still rather effective CEE.
 
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