Should you price an attached garage at the same cost per square foot as the house?

Published September 28, 2026

What the $162 figure already covers

NAHB's 2024 survey put the average construction cost of a single-family home at $428,215 for 2,647 square feet of finished floor space, or about $162 a square foot. Garage space isn't in that denominator. The cost side is another story. One line in NAHB's breakdown reads "Windows and Doors (including garage door)," averaging $15,990, or 3.7% of construction cost.

So if you multiply $162 by living area plus garage area, you count costs like that door twice.

The wall between the garage and the house

Minnesota uses the International Residential Code with its own amendments, and its version of the garage rules, in state rule 1309.0302, requires at least 1/2-inch gypsum board on the garage side of the walls and attic separating it from the house, and at least 5/8-inch Type X gypsum board under any habitable room above the garage. Structural members that hold up that ceiling get 1/2-inch board too. Even a detached garage within 3 feet of the house needs 1/2-inch board on the inside of the walls facing it.

The door into the house has to be solid wood or solid or honeycomb-core steel at least 1-3/8 inches thick, or a 20-minute fire-rated door. No opening may lead from the garage directly into a bedroom. Ducts are covered as well: the 2021 IRC text excerpted by Larimer County, Colorado, calls for at least No. 26 gage sheet steel for ducts in the garage or passing through the separation, with no openings into the garage. The edition and local amendments vary, and the permits guide covers where to find the rules that apply to your lot.

EV charging: conduit, circuit or charger

Most residential Level 2 chargers run at up to 30 amps and deliver 7.2 kW, according to the Department of Energy's Alternative Fuels Data Center, and they need a dedicated 40-amp circuit under the National Electrical Code. For new construction, AFDC describes three levels:

• EV-capable: panel capacity and conduit for a future 208/240-volt, 40-amp circuit
• EV-ready: the full circuit, including wiring and receptacle, much like a dryer circuit
• EV-installed: the charger itself goes in during construction

AFDC puts the cost of adding EV-ready elements after construction at four to six times what they cost during it. Installations must meet local and state codes, and a permit may be required. The IRC itself doesn't yet mention EV charging.