We had a great discussion about this about a year ago, in this picture see while the foundation will continue under the gararge door but it dosn't continue to full height. So the floor can move up and down with moisture and frost.
Since that time we did just what you are doing. The city wanted the floor removed for crawl space to be dug out and foundation brought up to height. Or we could have an engineer design it.
He had us scribe treated 2x6 so they sat level and set them on treated 1x4 blocks every 16" this was to allow air flow under the structure. The 2x6 across the door opening was also held 3/4" off the concrete.
instead of building the front wall on top of the deck like normal he had us
nail studs to the side of the floor joists and keep them away from the concrete 1 1/2". That way if the floor moved those nails would let go before it lifted the front of the garage.
Last edited by nealtw; 07-24-2012 at 06:27 PM.