That might depend on the context in which you're asking, it sounds like it's probably new home construction. Also depends just how completely you're talking about demo. I don't think that keeping a detatched garage has any bearing on the question, although if it was an attached garage and it will be an attached garage it might mean it's a remodel...
For example, if this was to be done on an FHA 203k loan, you'd have to keep some portion of the original foundation or else its considered new construction and doesn't fit with the rehab/remodel program for which the loan is intended.
If you're asking in the context of whether the new work would have to meet current code, it most likely would need to meet current codes regardless of whether it was a new construction or remodel.
And I'm just a lay person so someone could know better than I, but more info would probably be needed.