I have a question regarding a not-so-common construction setup for a house. In this situation, the concrete slab is "floating"/insulated with a rigid insulation underneath. I understand the slab is not grounded and there's a risk for static charge build up. Here's a picture of this setup:

enter image description here (Source: https://www.buildingscience.com/documents/insights/bsi-059-slab-happy)

If my understanding is correct, what would be the best way to ground this floating slab? One idea I had was to have a wire mesh inside the slab (if standard reinforcement is not enough) and ground that mesh on the perimeter of the slab (to the ground wire(s) from electric wiring already setup).

  • $\begingroup$ I'm not convinced that the slab will be a container of static charge in the first place, Nor that static on chunks of concrete would conduct away to the ground anyway (analogy: put a rug on the slab. You can generate static charge in the rug but that won't bleed into the slab) $\endgroup$ Jun 23 '21 at 11:59
  • $\begingroup$ Thanks for the comment Carl. Maybe the real experiment is: 1) Have that rug on the concrete and generate static charge on it 2) Grab a door handle or even a light switch on the wall (should get a shock) 3) Do 1) again but this time before 2), just step onto the concrete. No? My assumption here is that the charge will dissipate in #3, you won't get a shock. $\endgroup$
    – lpezet
    Jun 26 '21 at 19:56

I have used a similar construction method and have never seen any issues with static build up. It was just for thermal storage in a residential home. Like Carl mentioned in the comments the rug and pad would either isolate it or conduct to the surroundings. However, if this design is to be used in an electronics or pyrotechnics manufacturing facility you will indeed want to take some extra precautions.

To ground the internal floor to the foundation I would recommend running 6 gauge copper wire (mainly for flexibility and durability) from a ground clamp on rebar in the foundation to a ground clamp on the floating floor structural remesh. The structural remesh will be sufficient. That will certainly address any static issues, but it is always a good idea to check the NEC (NFPA 70) and your local electrical codes before a construction project. Even if grounding was not required by code, they may require any grounding you add to be installed by an electrician (if not your personal home).

Another option is to install a dedicated ground rod or rods in or below the floating floor. Might be easier than messing with connections to the foundation.

If this is for a static sensitive application you will need to consult with a company that specializes in this. They will help specify conductive flooring, facility grounding, low static generating materials, HVAC systems and controls, garment specifications, etc.


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