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I have an attached garage. There is an exterior-rated door between the garage and the living space.
Should the entire wall be built as an exterior wall, as far as sheathing, width, etc? Is there a code standard that defines this?
I'm in Oregon, USA, but am looking for a general answer.
No, the wall between the home and garage is designed and built as an interior wall. HOWEVER, it is a fire wall. Your code in Oregon requires 1) fire rated door between the spaces, and 2) fire rated wall "assembly", and 3) insulation.
1) The door needs to be fire rated door and frame, which can be a solid core door and a solid wood frame (not a frame with an applied stop). (See R302.5.)
2) The wall needs one layer of 1/2" gypsum board on the GARAGE side of the wall...other side of wall doesn't matter and 5/8" gypsum board on the ceiling of the garage if habitable rooms are located above the garage. (The building department is worried about a fire starting in the garage, not vise verses. They're protecting the house.) (See Table 302.6.)
3) Insulation is required for the building envelope.
No other Code items are required for this wall, including shear wall, structural wall, etc. HOWEVER, remember that the garage cannot open directly into a sleeping room (bedroom).
IRC R302.6 defines the applicable separation requirements prescriptively -- it calls out 1/2" drywall as the garage-side finish as acceptable for the application, while R302.5 requires a solid wood or metal door of not less than 1 3/8" or, equivalently, a 20min fire rating -- which is about the same as the finish rating of 1/2" drywall -- for a house-garage door.
So, as far as I can tell, no, you can use standard interior non-load-bearing wall construction for a house-garage separation provided the door and garage-side drywall meet Code and the house structure allows for it. However, if it was my house, I'd go significantly more conservative and use a 60-minute rated door and frame, as well as 1-hour fire-rated/smoke barrier construction -- the house/garage wall is intended to be a firebreak of sorts, and 1hr construction is not that much more costly than a standard wall.
Of course, since this the house/garage separation is typically part of the building envelope, this means that it needs to function as a thermal, air, and water/vapor barrier as well, which implies that it needs to be insulated and barrier sealed.
The garage to residence wall is a separation wall and a part of the envelope of the conditioned space. Because it separates two occupancy classifications, it requires a fire separation assembly according to a matrix you can find in the building code, or residential code. The fire rating necessitates a rated solid core door with weather seals and an automatic closer. It's not because it's considered the "exterior". There is no precise definition of an exterior wall. The building envelope generally refers to the exterior surfaces. However, you could in some cases have the envelope and the exterior wall as two different assemblies. For instance, a sun room, or an atrium would be the exterior face, but not the building envelope. Generally the envelope is synonymous with the assembly between the weather membrane (the felt paper) to the finished inside surface. This could include enclosed air as an assembly item, which is the case with an attic, subfloor, and of course a garage.
