The International Residential Code specifies how garages must be separated from dwelling units in residential construction. There are rules for openings (doors), for penetrations and for gypsum board in the wall assemblies.
First, you cannot have a door directly from a garage into a room used for sleeping. Where you are allowed to have doors leading from the garage into the dwelling unit the doors need to be solid wood a minimum of 1-3/8″ thick, solid or honeycomb steel a minimum of 1-3/8″ thick, or have a 20 minute rating.
Where you have ductwork running from the house through the garage it needs to be a minimum of 25 gage steel and there can’t be any openings into the garage. All penetrations through a rating need to be properly fire rated.
The garage needs to be separated from the unit by a minimum of 1/2″ gypsum board applied to the inside of the garage and that goes to 5/8″ gypsum board where the garage is below the rooms. You also need to protect any structure in the garage that is supporting the dwelling with 1/2″ gypsum board. Generally speaking we specify 5/8″ everywhere to avoid confusion on the distinction between different conditions.
On a detached garage, the garage wall needs to be protected where the structure is within 3′ of the dwelling unit.
