We are installing a satellite dish and HDTV antenna on our flat membrane roof and need to ground the antennas and the coax cables. There is a steel beam supporting a roof overhang a few feet away, part of an integrated steel skeleton which itself has been grounded. (We have construction photos to verify it.) The easiest thing would be to ground the antennas and cables to that steel beam. It is not practical to run a wire the long distance to the service grounding location.

It is possible to expose the beam by cutting away the roof but we want to minimize the amount of damage done to the roof. Cadweld does not seem practical. A grounding clamp would do the trick but would require exposing a lot of the roof in order to gain access to the side of the flange.

Question: can we drill a hole into the top flange of the steel I-beam and use a self-tapping screw to attach a 6 AWG ground wire to which we could ground the antennas and coax cables? Our thinking is to drill a 1.25" hole down to the flange to expose the steel and then drill, say a 3/8" hole directly into the flange to attach the wire. If so, what specs are appropriate for that screw. What type of conduit would be appropriate to bring the wire through the roof sheathing, insulation and membrane?