Excavate Garage Floor My Only Option?

EDHC

I've got a garage conversion contract coming up in the spring (mountains of Northern California) and the designer is telling me that in order to raise the floor level of the garage up 14 inches to the level of the raised floor of the residence is for me to remove the garage slab and excavate the soil beneath so that there will be 18 inches of vertical space between the soil and the bottom of the new joists. I'm concerned that this will endanger the existing footings. The building department wasn't much help and said "go look on the web for an alternate solution." I'm prohibited from using active ventilation (fans). Using 2x10 joists and leaving the slab in place, I will be left with only 3-1/2 inches clearance between the bottom of the joists and the slab. Any ideas on how I can avoid hammering out the slab floor while ensuring good ventilation to keep it nice and dry?

tgeb

Put in the new floor with wood framing and use Icynene (foam) insulation, no ventilation necessary.

www.icynene.com

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Tom

www.gebcon.com