I am in the process of a garage build and have a question about footers. The garage will be 50′ x 30′ and will have a second floor apartment. The required depth for footers in my area is 32″. The contractor has dug the area for the footers and started laying rebar. However, I am not sure whether the area dug for the footers is sufficient. The garage will be on a slope. The area for the footer along the front (50′ side) of the garage is dug to approximately 36″ but the area that is dug out is close to level such that, because the area is on a slope, the back left corner of the footer is only around 18″ deep.
I assumed that all areas of the footer need to be at least 32″, but the way it is currently dug out there will be some areas where it will not be 32″ deep and will be as little as 18″ deep. Is it okay to have a portion of the foundation that does not extend below the frost line? Would that risk a crack in the foundation caused by the portion of the foundation that is not below the frost line heaving?
Assuming that all portions of the foundation have to extend below the frost line, the only reason I can think that the 18″ at the back of the garage might be sufficient is that after the foundation and walls are poured the contractor might be thinking about grading the back area of the garage so that the ground is higher than it currently is, (in other words adding 14″ of dirt to get to the 32″) but I don’t know whether that would count toward the required 32″ depth for footers to get below the frost line.
Any insight would be greatly appreciated. I plan on asking the contractor tomorrow, but would like to have an understanding of the issue before speaking with him.