I want to add a room in the garage to make our house wheelchair accessible. This would be a front vestibule big enough for closet and a wheelchair; this would become part of the house through the existing door from garage to house. Would the concrete floor be strong enough for this or would I need to add any foundation for strength. Any additional comments welcomed.

John

If you have a concrete garage floorit is strong enough to add interior non-load bearing walls.

John, considering a car has been parked there the load bearing is probably OK. Some concrete floors have embedded grade beams if the local code requires. The floor minimum is most likely 3-4 " with a turned down edge footing. Interior wall plates can be nailed to the floor or held down with lead anchors or redheads. Use pressure treated 2/4 against the concrete. If the floor level of the house is the same as the garage you are lucky. They are usually lower and need a ramp. Maximum slope of the ramp is 1" per foot. Hope it works out for you.