International Residential Code (IRC)

The International Residential Code (IRC) is the model code for one- and two-family homes and townhouses up to three stories. It covers structure, fire safety, stairs and guards, emergency escape openings, smoke and carbon monoxide alarms, energy efficiency and the mechanical, plumbing and electrical systems. It is published by the International Code Council in a new edition every three years, but it has legal force only where a state or local government adopts it.

Chapter 1 of the IRC (administration) is where permits come from: it lists the work exempt from a permit (R105.2), when a permit expires (R105.5), the inspections (R109) and the certificate of occupancy (R110). Many states and cities replace or amend that chapter, which is why the same project needs a permit in one city and not in the next.

What the IRC says, section by section

The International Residential Code (IRC) is a model code. It is law only where a state or city adopts it, usually with changes, so the wording below shows how the model reads in published government copies, not the rule where you live. Each section below is quoted from a copy a government publishes, labelled with that copy’s jurisdiction and edition.

R105.2: Work exempt from permit

Other than storm shelters, one-story detached accessory structures, provided that the floor area does not exceed 200 square feet (18.58m2)…¹ As published by Federal Way, WA (2021 IRC wording, with Washington and local amendments).

More on this: Deck code requirements.

R105.5: Expiration of permit

R105.5 EXPIRATION, Every permit issued shall become invalid unless the work authorized by such permit is commenced within 180 days after its issuance, or if the work authorized by such permit is suspended or abandoned for a period of 180 days after the time the work is commenced.² As published by Arenac County, MI (Michigan Residential Code 2015).

R109 (R109.1, R109.3): Inspections

R109.1.1 Footing inspection. A footing inspection shall be made prior to placing concrete to verify depth, width, soil bearing capacity, reinforcement and location on a lot for all structures and buildings.³ As published by St. Mary’s County, MD (International Residential Code 2018, locally renumbered).

R110: Certificate of occupancy

…no building or structure erected or altered in any municipality after October 1, 1970, shall be occupied or used, in whole or in part, until a certificate of occupancy has been issued by the building official…⁴ As published by Connecticut (statewide) (2022 CSBC amendments to the 2021 IRC).

R310 (R310.1, R310.2.1-R310.2.3, R310.4.1): Emergency escape and rescue openings

R310.2.1 Minimum size. Emergency escape and rescue openings shall have a net clear opening of not less than 5.7 square feet (0.530 m2).⁵ As published by Galveston, TX (2021 IRC).

More on this: Egress window requirements.

R311.7.5: Stairways: risers and treads

The greatest riser height within any flight of stairs shall not exceed the smallest by more than 3/8 inches (9.5 mm).⁶ As published by Boise, ID (handout dated February 2022).

More on this: Stair code requirements.

R312.1.1-R312.1.3: Guards

R312.1.1 Where required. Guards shall be located along open-sided walking surfaces, including stairs, ramps and landings, that are located more than 30 inches (762 mm) measured vertically to the floor or grade below at any point within 36 inches (914 mm) horizontally to the edge of the open side.⁷ As published by Bonney Lake, WA (2012 IRC).

More on this: Railing and guard height requirements.

R314.3 (and R314.2.2/R314.4): Smoke alarms

Smoke alarms shall not be closer than 3 feet from a bathroom door containing bathtub or shower, unless this would prevent the placement of a smoke alarm required by Section R314.3.⁸ As published by Anne Arundel County, MD (IRC 2021).

More on this: Smoke alarm requirements.

R315: Carbon monoxide alarms

Carbon monoxide alarms shall be installed in the following locations: 1. Outside of each separate sleeping area in the immediate vicinity of the bedrooms. 2. On every occupiable level of a dwelling unit, including basements.⁹ As published by Los Angeles County, CA (Los Angeles County Residential Code).

More on this: Carbon monoxide alarm requirements.

IRC editions in use

The edition of the IRC that each state’s residential code is based on, from the state’s adoption record. A state code “based on” an edition usually changes parts of it. For 15 of the 50 states and DC in our guides, the state record states no statewide residential code based on an IRC edition; see each state’s page for what applies there. The full state-by-state table, with each state’s own code title and effective date, is on building codes by state.

How states adopt and amend the IRC

A state or city adopts the IRC by statute, regulation or ordinance, and usually amends it in the same act: it deletes some sections, rewrites others (often the permit exemptions in R105.2) and adds local rules for wind, snow, flood or wildfire. Adoption takes one of three forms:

• One code everywhere. The state code applies in every city and county, and local governments may not change it, or may change it only through the state.
• A statewide minimum. The state code applies everywhere, but cities may adopt stricter rules.
• Local choice. There is no statewide code for houses, or the state code applies only where a city or county adopts it.

How the residential code applies in the states whose code is based on a stated IRC edition, as each state’s record describes it:

• Statewide; applies everywhere (15): Connecticut, District of Columbia, Hawaii, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Jersey, North Carolina, Ohio, Rhode Island, South Carolina, Virginia
• Statewide minimum; local governments may go further (11): Alabama, Arkansas, California, Florida, Idaho, New Mexico, New York, Oklahoma, Pennsylvania, Tennessee, Washington
• Adopted locally (6): Delaware, Kansas, Nebraska, North Dakota, South Dakota, West Virginia
• Statewide; local amendments not allowed (3): Indiana, Kentucky, Utah
• Set by state statute for cities (1): Texas

Because of these amendments, the wording a city enforces can differ from the model code. Always check the edition and amendments your building department lists; our city pages show the edition each city enforces and quote its own exemption list where it publishes one.