Maricopa County Adopted Building Codes (Unincorporated Areas): The 2018 I-Codes That Apply

If your lot sits outside any city, in the unincorporated county near Rio Verde Foothills, the Cave Creek fringe, or open desert, then Maricopa County, not a city, is the authority that reviews your plans and inspects your build. The county runs an older code edition than the big cities next door, so the exact rules can differ. This page lists the codes unincorporated Maricopa County actually enforces, when the Board of Supervisors adopted them, and which pieces are mandatory versus voluntary.

Which codes the county enforces

Unincorporated Maricopa County adopted the 2018 family of International Codes (often called I-codes) for almost everything, plus the 2017 electrical code. The county bundles its adoptions and local edits into one document, the Maricopa County Local Additions and Addenda (MCLAA). Here is the current list:

• 2018 International Residential Code (IRC): one- and two-family homes and townhouses. This is the main code for a custom house.
• 2018 International Building Code (IBC): larger and commercial structures.
• 2018 International Plumbing Code (IPC): water supply, drains, and fixtures.
• 2018 International Mechanical Code (IMC): heating, cooling, and ventilation.
• 2018 International Fuel Gas Code (IFGC): gas piping and gas appliances.
• 2018 International Existing Building Code (IEBC): work on existing structures.
• 2017 National Electrical Code (NEC): all wiring and electrical work.
• 2018 International Energy Conservation Code (IECC): adopted as voluntary, not mandatory.
• 2018 International Green Construction Code (IgCC): adopted as voluntary, not mandatory.

The IRC is the one a single-family builder lives in day to day. The Maricopa County Planning and Development Department is the authority having jurisdiction (AHJ) that adopts, amends, and enforces these codes in the unincorporated area, so the county's building officials, not a city and not the state, have the final word on a rural build.

What the county says

The county records the adoption plainly in its Adopted Regulations index:

Text Amendment to the Maricopa County Local Additions & Addenda to adopt and amend the following construction safety codes: 2018 International Building Code, 2018 International Residential Code, 2018 International Plumbing Code, 2018 International Mechanical Code, 2018 International Fuel Gas Code, 2018 International Green Code (voluntary), 2018 International Energy Conservation Code (voluntary), 2018 International Existing Building Code, and 2017 National Electric Code.

The Board of Supervisors approved that amendment on August 17, 2022. It took effect 30 days later. A grace period let projects use the prior codes through December 30, 2022. The codes also carry AZBO and MAG regional amendments, the standardized edits used across the Phoenix area, on top of each model code. So the rule you build to is the published 2018 edition (2017 for electrical) as changed by the county's MCLAA.

When this comes into play

The edition controls real decisions from day one of design:

• Your framing, bracing, and foundation details follow the 2018 IRC as amended for the county. A plan copied from a newer 2021 or 2024 city project may carry details the county code does not require, or miss county-specific edits.
• Outlet spacing, arc-fault and ground-fault protection, and panel sizing follow the 2017 NEC. This is two cycles behind Phoenix's 2023 NEC, so an electrician must use the right code book for the jurisdiction.
• Energy compliance is voluntary at the county level, not mandatory. The 2018 IECC is adopted as a voluntary standard, so the county does not force the same energy paperwork a city like Scottsdale requires. Many builders still design to it for comfort and resale, but it is your choice, not a county mandate.

Here is a concrete example. Say you submit a custom home plan for a five-acre parcel near Rio Verde Foothills in 2026. The county plan reviewer checks your framing against the 2018 IRC. Your wiring is checked against the 2017 NEC. Your gas piping is checked against the 2018 IFGC. If your designer reused a set drawn to Scottsdale's 2021 codes, the editions will not line up. The plan can come back with corrections before a permit issues.

What this means for you

Hand your designer, structural engineer, and trades one clear instruction. Build to Maricopa County's 2018 I-codes and the 2017 NEC, with the county's Local Additions and Addenda applied. Treat the energy code as voluntary unless you choose to follow it. That instruction prevents the most common rural-build mistake, which is using a nearby city's newer code on a county lot. The cities around you (Scottsdale on 2021, Phoenix on 2024) are ahead of the county. A set drawn for a city build is not automatically right for the county.

This entry is the anchor for the rest of the Maricopa County building-codes module. From here, see Maricopa County Residential Building Permit Requirements for how these codes get checked during plan review, and Maricopa County Septic and Well Requirements for a New Home for the water and wastewater side a rural lot needs. For the bigger picture, see what you need to build on rural land in Rio Verde and how to buy land to build a house in Arizona .

Source

The adopted codes, the adopting action, and the effective date are published by Maricopa County: Adopted Regulations on maricopa.gov , with the broader code and ordinance picture at Ordinances, Regulations and Codes . Arizona's statewide adoption picture is tracked by the code authors at ICC Code Adoptions for Arizona .

This page is general information, not a code interpretation. Editions and amendments change, so confirm the current adopted code and any project-specific amendment with Maricopa County Planning and Development before you rely on a specific edition.