Thank you for your question regarding the grounding of metal buildings. It is our pleasure to help.
You must have some excellent building inspectors where you are at, as it is rare to see them bother with grounding a building that has no electrical service. It is of course the right thing to do. Since your building does not have an electrical service, the grounding requirements are not under the National Electrical Code NFPA 70. While there may be some other code that governs grounding of buildings with-out electrical service, we are not aware of it. As such, whatever satisfy’s your inspector is probably all that you are legally required to do.
E&S recommend 10-ft ground rods, as this allows you to have 8-ft of the rod below the 1.5-ft mark, and still have 6-inches of the ground rod above grade for bonding purposes. The National Electrical Code (NEC) now requires two (2) of these rods (unless you can measure the rod and prove it is below 25-ohms resistance-to-ground) be installed at least 6-ft apart. You may want to install two (2) rods, one each at opposite corners of the building. Bond the steel frame directly to the ground rods using a solid #6 copper wire (or larger). And yes, ideally the rebar in the concrete should be bonded to the metal frame of the building. We recommend at the 4 corners. Please see the NEC 2011 Handbook for illustrations detailing the bonding requirements of rebar and the steel frames of buildings, as well as how to properly install a ground rod.
We hope you find this information useful. Feel free to contact us again in the future if you should have any further questions.
The Engineering Team at E&S Grounding Solutions