IRC R313: Automatic Residential Fire Sprinklers

Section R313 of the International Residential Code (IRC) requires an automatic fire-sprinkler system in new one- and two-family homes. That is the model code. In Arizona, though, a state law overrides it almost everywhere, so most new homes here are built without sprinklers even though the IRC asks for them. This page explains what R313 says, why Arizona cities delete it, and the one local jurisdiction where you still need sprinklers.

What R313 requires

R313 says an automatic residential fire-sprinkler system must be installed in new one- and two-family dwellings and townhouses, designed to the residential standard NFPA 13D or the IRC's own Section P2904. The goal is to control a fire long enough for everyone to get out. Here is the core requirement:

An automatic residential fire sprinkler system shall be installed in one- and two-family dwellings.

This has been in the IRC since the 2009 edition. On paper, every new custom home in Arizona would need a sprinkler system. In reality, almost none do, because of state law.

The Arizona override (A.R.S. 9-807)

Arizona Revised Statute 9-807 bars cities and counties from enforcing a code that requires fire sprinklers in new single-family or two-family homes, unless the local mandate was already on the books before a 2009 cutoff. So when an Arizona city adopts the IRC, it amends out R313 (or makes it optional). That is why Phoenix, Scottsdale, Cave Creek, Carefree, and the counties do not force sprinklers on a standard new house. The state decided the cost should be the owner's choice, not a mandate.

There is a real exception: Fountain Hills adopted its residential sprinkler requirement in 2008, before the cutoff, so it is grandfathered and still enforced. A new home in Fountain Hills needs sprinklers reaching every level plus attached garages and carports. See the Fountain Hills fire sprinkler requirements page for the full local rule and what it costs.

What it means for an Arizona custom home

For most Valley builds, R313 is a code section you can read about but will not have to follow, because your city deleted it. You can still choose to install sprinklers, and some owners do for fire safety or insurance, but it is voluntary. Budget impact is the headline: a 13D system typically adds a few dollars per covered square foot, so a Fountain Hills home where it is mandatory carries a cost a comparable Scottsdale home skips.

For example, two identical floor plans, one in Fountain Hills and one in nearby Scottsdale, will price differently because only the Fountain Hills home must plumb and pressure-test a sprinkler system before its final inspection. This is one of the clearer cost gaps between neighboring jurisdictions, covered in what drives the cost of building a custom home in Arizona .

Edition note

The R313 requirement itself is consistent across the 2018, 2021, and 2024 IRC. What varies in Arizona is not the edition but the local amendment: nearly every AHJ here strikes R313 under A.R.S. 9-807, while Fountain Hills keeps it. Always check the local amendment, not just the base edition, on the Arizona building code editions by city page.

How it connects

R313 is the active-suppression side of fire safety. It backs up the warning systems in R314 smoke alarms and the fire-separation rules in R302 . On wildland-edge lots it pairs with defensible space planning. For the local sprinkler question most often asked, see do I need fire sprinklers in a new home in Fountain Hills, Arizona .

Source

Read the section on the official ICC site: 2021 IRC R313 on codes.iccsafe.org . The ICC I-Codes are copyrighted, so only the short clause is excerpted; the explanation, and the Arizona override, are ours.