It would be much appreciated if someone could elaborate using sketches. I am an architect from africa and working for a construction company. In all my years of experience in africa, i have never come across such thing as Subgrade or Below grade. The terminology gets very confusing when working in excavation as they call out everything in grades instead of top of footing or bottom of slab. So if someone has similar experience or relative knowledge, please help explain the difference in terminologies for Subgrades, below grades and any other grades to be dealt with in construction. Also, is it common to come across these terms in architecture in the states? 

Thanks and best regards