I am constructing my house on a rocky plot. Some of the columns will be placed over rocks and we were not able to dig deep in the rock. So, these column footings will be on the surface. Is it safe?
The sound rock (if determined by an engineer) should be able to support the building weight and the gravity load induced by the occupant without the significant settlement that typically identified as the bearing failure or the differential settlement that may cause/trigger the structural failure due to the bearing failure. In general, serviceability concern outweighs the safety concern in this regard (bearing failure).
However, due to the shallowness in footing placement, the building lateral stability is the most critical concern. As the building may lift and rotate during a wind storm or shift laterally and rotate during an earthquake event; if the foundation is not properly designed (keyed into the ground) to provide adequate resistances against the lateral and uplift movements.
Thus, consulting with an engineer is absolutely essential in ensuring lateral stability for safety in this case.