International Residential Code (IRC)

The International Code Council (ICC) writes and updates a model code on a three-year cycle, called the International Residential Code, or IRC, that sets the minimum safety and construction standards for detached houses, townhouses, and duplexes up to three stories. The IRC is not law by itself. It becomes law only when a city, county, or state formally adopts it, often with local changes called amendments.

The IRC covers nearly every part of a house: footings and foundations, framing, roofing, energy use, plumbing, mechanical systems, and electrical work. When a builder pulls a permit, the AHJ (the building department) checks the plans and the finished work against the adopted IRC. Pass, and the build moves forward. Fail, and it gets corrected before the next stage.

In the Phoenix metro, most jurisdictions build on the 2018 IRC. Maricopa County, the City of Phoenix, and the City of Scottsdale each adopt the IRC and add local amendments for issues like expansive soil, monsoon drainage, and energy performance in extreme heat. That is why the same code section can be applied a little differently in Cave Creek than in Apache Junction.

For example, the IRC sets the minimum size and depth of a footing, but a Casa Grande lot with clay soil may trigger a stricter, engineer-stamped foundation under the local amendment. The base rule is national; the local layer makes it fit Arizona ground.

The IRC differs from the International Building Code (IBC), which governs commercial and larger multifamily buildings. For a single-family custom home, the IRC is the rulebook, and knowing which edition your city adopted tells you which version of that rulebook your project answers to.