The attached garage where I live is not considered living space. Our square footage in realtors listings doesn't even include the finished basement I think? I can't remember. I know in the state I used to live in that basements weren't included, but that was a decade ago so it might have changed since then.
The square footage is not considered in the total living space. Though, where I live, many use it as additional living space such as a gym and man caves it seems.