does a water proof membrain effect ufer grnd

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acrwc10

acrwc10

Master Code Professional
Location
CA
Occupation
Building inspector
I have worked on alot of houses with basements that a 12' under the finish grade, these basements have a rubberized membrain that is completely sepperating the concrete from the soil. there are no penitrations through this to earth, What I was wondering is does this make a significant impact on the effectiveness of the ufer ground that is in the foundation.It is not something I have ever heard questioned.
 
Concrete-Encased Electrode. An electrode encased
by at least 50 mm (2 in.) of concrete, located within and
near the bottom of a concrete foundation or footing that is
in direct contact with the earth
Click to expand...


Are you saying the membrane extends under the footing? If so, i would say it does not qualify as a CEE.
 
petersonra said:
Are you saying the membrane extends under the footing? If so, i would say it does not qualify as a CEE.
Click to expand...

Yes, The footing is the wall of the basement,and the basement floor space is about 2500sq ft. There is no direct contact with the soil as far as I can tell. I know a CEE must be in contact with earth. What I am questioning is, is it possible there is something I am not taking into acount before I bring this to the attention of the GC. Has anyone had this issue come up in the past,and would an ohms to ground test be an accurate test or could the reading be faulse because of a small breach in the membrain, such as a small wire or steel that would conduct but not be an exceptible path to earth. I hope my explenation is clear enough to understand what I am questioning.
 
acrwc10 said:
Yes, The footing is the wall of the basement,and the basement floor space is about 2500sq ft. There is no direct contact with the soil as far as I can tell. I know a CEE must be in contact with earth. What I am questioning is, is it possible there is something I am not taking into acount before I bring this to the attention of the GC. Has anyone had this issue come up in the past,and would an ohms to ground test be an accurate test or could the reading be faulse because of a small breach in the membrain, such as a small wire or steel that would conduct but not be an exceptible path to earth. I hope my explenation is clear enough to understand what I am questioning.
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The size of the basement does not matter. What matters is if the footing has direct contact with earth. The floor is not part of the footing. The wall is not part of the footing. Only the footing matters. if the footing has no direct contact with earth, it does not qualify as a CEE, IMO.
 
How would you guys feel if a 20' section of the vapor barrier/membrane is removed in the footing exposing that section of concrete to the soil. Would that satisfy the CEE requirement? (Assume no building code violations are created.)
 
One question

One question

The original question states: "does a water proof membrain effect ufer grnd"

I thought a ufer grnd must be in contact with the soil, "in relation to moisture and the soil doping" if you have a water proof membrain between the concrete and the soil how can the ufer grnd function?
 
bphgravity said:
How would you guys feel if a 20' section of the vapor barrier/membrane is removed in the footing exposing that section of concrete to the soil. Would that satisfy the CEE requirement? (Assume no building code violations are created.)
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I think that would satisfy the CEE requirement, but I think it would also make the water membrane useless. Wouldn't that be like putting a hole in the bottom of a boat?

I think you are back to the two ground rods and water pipe for grounding the service. But IMO, that leaves a dangerous situation. That is, the whole concrete basement, walls, footings, etc. are ungrounded. What if the concrete is somehow energized (say a short to a piece of rebar sticking out somewhere). That leaves the homeowners walking around on a slab at 120V. They won't find out the slab is hot until they touch a grounded appliance.

The code requires bonding for metal systems likely to be energized. But there is no requirement for bonding concrete slabs that are insulated from the earth. I am wondering if a new requirement should be added for these situations. Require a CEE in insulated slabs to keep the potential of the slab at zero.
 
The usual practice in residential basement construction is to pour the footings first; directly on the dirt. Then, pour the foundation wall on the footing.

The floor is poured last, usually after the foundation has had a chance to settle. A membrane is usually placed under the floor only.

It is not structurally possible (practical) to construct a floor that will withstand water pressure from the bottom. The buoyancy is 62.4 pounds per square foot for one foot of water pressure. That is 150% of the usual design live load on the floor of a residence. Those loads over the large spans will crack the floor.

The usual practice is to put drains around the footings, and pump or drain the water depending on available elevations.

Unless I saw the plans and construction in progress, I would doubt that the membrane passes under the footing.
 
Bob NH said:
It is not structurally possible (practical) to construct a floor that will withstand water pressure from the bottom. The buoyancy is 62.4 pounds per square foot for one foot of water pressure. That is 150% of the usual design live load on the floor of a residence. Those loads over the large spans will crack the floor.
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Unless the floor is completely porous, there will be bouyance from any ground water beneath the floor. Head is head, a leaky floor (or walls) doesn't make the head go away completely -- the head is still the distance between the top of the water and the bottom of the (very wet) basement.

You can see this in a boat with a hole in the bottom -- the boat remains afloat until the weight of the boat out of the water (displacement) exceeds the unflooded volume inside the boat below the lowest non-watertight opening.

So, it's possible the house is designed as described.

(Edited to add ...)

Obviously, at some point sufficient head can result where the upward forces, uniformly distributed under the floor, exceed the structural limitations of the floor, but this can also occur when the floor is less porous than needed to result in equilibrium between the groundwater level and the (very wet) basement level.
 
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bphgravity said:
How would you guys feel if a 20' section of the vapor barrier/membrane is removed in the footing exposing that section of concrete to the soil. Would that satisfy the CEE requirement? (Assume no building code violations are created.)
Click to expand...
Other posters have stated they remove a section of the vapor barrier.
 
bphgravity said:
How would you guys feel if a 20' section of the vapor barrier/membrane is removed in the footing exposing that section of concrete to the soil. Would that satisfy the CEE requirement? (Assume no building code violations are created.)
Click to expand...

I do not feel the code says anything about 20 feet of the footer being exposed to earth. It only requires 20 feet of rebar. Nothing says the rebar has to span the length of the footer at all. It could be bent so it all fits in a 1 foot long segment of the footer.

IMO, you are code legal if any part of the footer is exposed near where the electrode is located. I think it is also code legal for the exposure to earth to be on the side of the footer, as well as the bottom of the footer, since it is not specified.

(3) Concrete-Encased Electrode. An electrode encased
by at least 50 mm (2 in.) of concrete, located within and
near the bottom of a concrete foundation or footing that is
in direct contact with the earth, consisting of at least 6.0 m
(20 ft) of one or more bare or zinc galvanized or other
electrically conductive coated steel reinforcing bars or rods
of not less than 13 mm (? in.) in diameter, or consisting of
at least 6.0 m (20 ft) of bare copper conductor not smaller
than 4 AWG. Reinforcing bars shall be permitted to be
bonded together by the usual steel tie wires or other effective
means.
Click to expand...
 
Good afternoon. Bob is right about the 20 feet not necessarily being 20 linear feet of concrete. I'd have reservations myself about the integrity of the foundation or footing if someone was to remove the vapor barrier, because I don't think you could achieve the soil compaction originally made between the concrete and the earth. This could lead to the footing or foundation sagging until the compaction equalized with the building weight bearing on that disturbed concrete.

Regards,

Dan
 
why not just add a ground ring under the barrier, then connect it to the steel? still connected to earth, still bonded to the steel, and no leaky barrier
 
Last time I had this same problem we drove 2 10' rods before the membrane, and had them seal the #4 solid conductor coming up, then treated it as a ufer from there. It is a quandry though- aint it. Our local code requires a ufer for any new > 20' foundation - both in the electrical, and building code... No real exceptions to it....
 
Bob NH said:
The usual practice in residential basement construction is to pour the footings first; directly on the dirt. Then, pour the foundation wall on the footing.

The floor is poured last, usually after the foundation has had a chance to settle. A membrane is usually placed under the floor only.

It is not structurally possible (practical) to construct a floor that will withstand water pressure from the bottom. The buoyancy is 62.4 pounds per square foot for one foot of water pressure. That is 150% of the usual design live load on the floor of a residence. Those loads over the large spans will crack the floor.

The usual practice is to put drains around the footings, and pump or drain the water depending on available elevations.

Unless I saw the plans and construction in progress, I would doubt that the membrane passes under the footing.
Click to expand...

Well time to lay doubt aside, the houses here have a membrain under the whole thing, They start by digging a hole about 12' deep lay down a special water proof membrain that is sealed together at the seams,then they put down the steel and pour the floor/footing over it after the slab cures they form the walls and pour those using rebar coming out of the slab to tye the walls to floor.the membrain is run up to the top above grade and sealed to the concrete.It is like a giant boat. there is a drainage system with sump pumps both above and beneath the water proof membrain. the ground water table in this area is not so high that it would lift the house due to hydrostatic pressure.
What I did find out today is there is a part of the garage that has no basement under it and the footing is in contact with the earth for about 40ft.The problem is the UFER was run up at the oppisite end of the house and the garage footing was poured at a later time even though the steel was left 30'' out to tye into the garage I don't know how well the rebar was tyed in.So is it UFFER or is it just some rebar that looks like a Uffer??????
 
Bryan brought up opening a section of the barrier for the ufer.Well that is what they do here.Under the footer steel the vapor barrier is cut like a long opening under the footer steel.Since almost all slabs here are monolithic They are poured integral with the footer and slab together

I know the grounding system is not to be used as a grounded system.But one would think that in the event of a poco or other failure of the grounded system,that the grounding system would at least eliminate the unwanted voltage that results from a lost neutral.Since the grounded and grounding conductors are together at one point.I`ve seen lost neutrals reek havoc in a structure with a ufer system.But have also seen a 2 ground rod system keep the unwanted voltage from frying everything plugged in.

Now I`m sure there are some that will say if that was the case the slab/building steel etc would be energized.But from what I have encountered is that when a poco or service neutral is lost and the 2 groundrod system supplements it and creates a grounding conductor in place of a grounded conductor there are tell tale signs.Like every light that is turned on dims the other light on.TV`s drop out and within a little bit of time a call is made to an EC to find out WHATS GOING ON !!!!!

This is just my opinion....Ok now you can throw stones :)
 
allenwayne,
But one would think that in the event of a poco or other failure of the grounded system,that the grounding system would at least eliminate the unwanted voltage that results from a lost neutral.Since the grounded and grounding conductors are together at one point.I`ve seen lost neutrals reek havoc in a structure with a ufer system.But have also seen a 2 ground rod system keep the unwanted voltage from frying everything plugged in.
Click to expand...
It is a rare case where any grounding electrode system other than a common metal underground water pipe system provides enough protection from an open neutral on the service to prevent equipment damage.
Now I`m sure there are some that will say if that was the case the slab/building steel etc would be energized.
Click to expand...
That is the case for all conductive objects connected to the electrical system under open neutral or ground fault conditions. The voltage on the system under ground fault conditions will only exist until the OCPD clears the fault. In the case of the open neutral it will be there until the load is removed or the neutral is repaired. If everything is bonded together there is no shock hazard as you are like a bird on the wire, but if some things are bonded and others are at "earth" potential, there is a shock hazard.
Don
 
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