Residential Code Explained
The International Residential Code in plain language, section by section, as it applies to building a home in the Arizona desert.
IRC R303: Light, Ventilation & Heating
IRC R303 sets the minimum natural light, fresh air, and heat for habitable rooms. Each room needs window glass equal to at least 8 percent of its floor area and openable area equal to 4 percent, unless you swap those windows for mechanical ventilation and electric light.
Read the referenceIRC R305: Ceiling Height
IRC R305 sets the minimum ceiling height for the rooms you live in at 7 feet (84 inches). Bathrooms, laundry rooms, and basements can drop to 6 feet 8 inches, and beams or ducts may hang down to 6 feet 4 inches without failing the room.
Read the referenceIRC R308: Safety Glazing
IRC R308 requires safety glazing, usually tempered glass, in spots where someone could fall through and get cut. That means glass in and beside doors, around tubs and showers, near stairs, and large low panes. Tempered glass breaks into dull pebbles instead of sharp shards.
Read the referenceIRC R309 Garages and Carports: Floors, Slope, and the Carport Line
IRC Section R309 sets the basics for a home's garage and carport. The floor has to be noncombustible and sloped so liquids run to a drain or out the door, a carport has to be open on at least two sides or it counts as a garage, and any garage door opener has to meet the UL 325 safety standard.
Read the referenceIRC R311: Means of Egress
IRC R311 sets the safe path out of a house. Stairs allow a maximum 7.75-inch riser and require at least a 10-inch tread, hallways must be at least 36 inches wide, and every home needs one side-hinged egress door giving at least 32 inches of clear width.
Read the referenceIRC R311.7: Stairways
IRC R311.7 sets stair geometry so people climb safely. Risers cap at 7.75 inches, treads run at least 10 inches, headroom is at least 6 feet 8 inches, the stair is at least 36 inches wide, and a graspable handrail sits 34 to 38 inches above the nosings.
Read the referenceIRC R312: Guards & Window Fall Protection
IRC R312 requires a guard at any walking surface more than 30 inches above the ground, at least 36 inches tall, with openings too small to pass a 4-inch sphere. R312.2 adds window fall protection: an operable window sill lower than 24 inches needs a limiter or guard.
Read the referenceIRC R318 Subterranean Termite Protection: What an Arizona Home Needs
IRC Section R318 requires new homes in termite-prone areas, which cover Arizona's low desert, to be built with subterranean termite protection. Builders choose from set methods: a soil-applied termiticide, a bait system, pressure-treated or naturally durable wood, physical barriers, or steel framing. In very heavy zones, foam plastic below grade faces added limits.
Read the referenceIRC R322 Flood-Resistant Construction: Building in an Arizona Flood Zone
If your Arizona lot sits in a mapped flood hazard area, IRC Section R322 controls how you build. The lowest floor must sit at or above the design flood elevation, any enclosure below it needs flood openings and flood-resistant materials, and your utilities have to sit above the flood level.
Read the referenceIRC E3601 & E3602: Electrical Service & Panel
IRC E3601 and E3602 govern a home's electrical service: the power feed and main panel. A single-family home needs a service rated at least 100 amps, fed by conductors sized to the load, with a clear 36-inch-deep working space kept open in front of the panel.
Read the referenceIRC E3607 System Grounding: How Your Home Ties to Earth and Why the Main Bond Matters
IRC Section E3607 grounds your home's electrical system at one point: the main service. There, the main bonding jumper ties the neutral to the metal enclosure, and the grounding electrode conductor runs to earth. This single bond is what makes a breaker trip during a ground fault instead of leaving metal parts live.
Read the referenceIRC E3608 Grounding Electrode System: Ground Rods, the Ufer, and Arizona Desert Soil
IRC Section E3608 lists the electrodes that connect your home to the earth: a metal water pipe, a concrete-encased electrode in the foundation, a ground ring, a driven rod, or a plate. Every one present must be bonded together. In dry Arizona soil, the concrete-encased electrode does most of the work.
Read the referenceIRC E3703 Required Branch Circuits: The Kitchen, Laundry, and Bath Circuits Your Home Needs
IRC Section E3703 sets the minimum circuits every new home must have. The kitchen needs at least two 20-amp small-appliance circuits. The laundry area needs its own 20-amp circuit, and the bathrooms need one too. The garage gets a 20-amp circuit, and central heating equipment gets its own dedicated circuit.
Read the referenceIRC E3705 Conductor Sizing and Overcurrent Protection: Matching Wire to Breaker in Arizona Heat
IRC Section E3705 pairs each wire size with a maximum breaker: 14-gauge copper on a 15-amp breaker, 12-gauge on 20 amps, and 10-gauge on 30 amps. The breaker protects the wire from overheating. In hot Arizona attics, the code also makes you lower a wire's rated capacity, which can force a larger size.
Read the referenceIRC E3901 Receptacle Placement: The 6-Foot Rule and Kitchen Outlets
IRC Section E3901 decides where the outlets go in your home. The main rule is that no point along a wall is more than 6 feet from a receptacle, which spaces them about 12 feet apart. Kitchens, bathrooms, hallways, and outdoor areas each get their own required outlets on top of that.
Read the referenceIRC E3902 GFCI and AFCI Protection: Where Your Home Needs Each
IRC Section E3902 requires two kinds of electrical protection in a new home. GFCI outlets guard against shock in wet areas like bathrooms, kitchens, garages, and outdoors. AFCI protection guards against electrical fires on the circuits feeding living areas and bedrooms. Which code edition your Arizona city adopted changes exactly where each one is required.
Read the referenceIRC E4204 Pool Equipotential Bonding: The 8 AWG Copper Grid
IRC Section E4204 requires an equipotential bonding grid around every permanent pool and spa. Solid copper wire, no smaller than 8 AWG, ties the pool shell, the deck within 3 feet, metal fittings, pump equipment, and the water itself into one connected network so no dangerous voltage can build between them.
Read the referenceIRC N1101 Energy Code Scope: Arizona's Climate Zone 2B
IRC Section N1101 is the scope of the residential energy code, and it sets the climate zone that drives every insulation and window number in your build. The whole Phoenix metro, plus Casa Grande and Apache Junction, sits in climate zone 2B, the hot-dry zone that tells the code to design for cooling.
Read the referenceIRC N1102 / IECC: Building Thermal Envelope
IRC N1102 sets the insulation and window minimums for a home's thermal envelope. In Arizona climate zone 2B the prescriptive numbers are about R-38 ceilings, R-13 wood-frame walls, a 0.40 maximum window U-factor, and a 0.25 maximum solar heat gain coefficient to keep the sun out.
Read the referenceIRC N1103 Duct Sealing and Leakage Testing in an Arizona Attic
IRC Section N1103 makes a new home's ducts get sealed and then leak-tested. The postconstruction limit is 4 cubic feet per minute of leakage per 100 square feet of floor area. In Arizona, where ducts run through a scorching attic, meeting that limit is what keeps the cooling you paid for inside the house.
Read the referenceIRC Fireplace and Chimney Rules: Hearths, Clearances, and Chimney Height
The IRC's Chapter 10 sets how a fireplace and chimney are built so they do not set the house on fire. A hearth extension protects the floor from embers, a masonry chimney keeps a set clearance from framing and rises well above the roof, and most custom homes use a listed, factory-built unit installed to its own instructions.
Read the referenceIRC R302: Fire-Resistant Construction
IRC R302 sets the fire separation between your garage and the living space. A wall shared with the house needs at least 1/2-inch gypsum board on the garage side, and a ceiling under habitable rooms above the garage needs 5/8-inch Type X gypsum board, plus a self-closing rated door.
Read the referenceIRC R310: Emergency Escape & Rescue Openings
IRC R310 requires every bedroom and basement to have at least one window or door big enough to climb out of in a fire. The opening must give 5.7 square feet of clear space, at least 24 inches tall and 20 inches wide, with the sill no higher than 44 inches off the floor.
Read the referenceIRC R313: Automatic Residential Fire Sprinklers
IRC R313 calls for an automatic fire-sprinkler system in new one- and two-family homes. But Arizona law (A.R.S. 9-807) bars cities from enforcing that mandate on most new homes, so it is deleted by amendment almost everywhere. Fountain Hills is the local exception.
Read the referenceIRC R314: Smoke Alarms
IRC R314 says where smoke alarms go in a house: inside every bedroom, outside each sleeping area near the bedrooms, and on every story including the basement. In a new home the alarms must be hardwired with battery backup and interconnected so when one sounds, they all sound.
Read the referenceIRC R315: Carbon Monoxide Alarms
IRC R315 requires carbon monoxide alarms in a home that has a fuel-fired appliance or fireplace, or an attached garage that opens into the house. The alarms go outside each sleeping area near the bedrooms, and inside any bedroom that contains a fuel-burning appliance.
Read the referenceIRC R316 Foam Plastic: Thermal Barriers and Ignition Barriers
IRC Section R316 controls foam plastic insulation, which burns fast and gives off heavy smoke. The code caps its flame spread and smoke rating, and it requires a thermal barrier, usually half-inch gypsum board, between the foam and the living space. Attics and crawl spaces with limited access can use a lighter ignition barrier instead.
Read the referenceIRC R328 Energy Storage Systems: Home Battery Rules
IRC Section R328 governs home battery systems, like a solar backup battery. Each unit is capped at 20 kWh, and the total in an indoor utility space is capped at 40 kWh. Batteries must be listed to UL 9540, kept out of bedrooms, and spaced about 3 feet apart.
Read the referenceIRC R401-R405: Foundations, Soils & Drainage
IRC R401 through R405 cover the foundation chapter: how the soil is classified, how the ground must drain, and when a foundation has to be engineered. The headline rule is that the lot must slope away from the house at least 6 inches over the first 10 feet.
Read the referenceIRC R403: Footings
IRC R403 sets the minimum size and depth for the footings under your house. A standard footing must be at least 12 inches wide and 6 inches thick, placed at least 12 inches below undisturbed grade, and footings on expansive soil must be engineered to handle the soil movement.
Read the referenceIRC R404 Foundation and Retaining Walls: The Arizona Engineering Line
IRC Section R404 sets how foundation walls and retaining walls are built and reinforced. Foundation walls are sized from tables by wall height and soil pressure. Any retaining wall not braced at the top that holds back more than 48 inches of unbalanced soil has to be engineered, which is common on Arizona hillside and expansive-soil lots.
Read the referenceIRC R506: Concrete Slab-on-Ground Floors
IRC R506 sets the rules for a concrete slab poured directly on the ground. The slab must be at least 3.5 inches thick, and in the 2021 IRC a 10-mil vapor retarder goes under any heated slab to keep ground moisture from wicking up into the finished floor.
Read the referenceIRC R507 Deck Requirements: Ledger Attachment and Lateral Load in Arizona
IRC Section R507 governs how an exterior deck is built and, most of all, how it attaches to the house. The ledger has to be bolted rather than nailed, a separate lateral-load connection ties the deck back to the floor framing, footings carry the loads to the ground, and guards are required more than 30 inches above grade.
Read the referenceIRC R602: Wood Wall Framing & Bracing
IRC R602 sets the rules for wood-framed walls: what size studs to use, how far apart to space them, and how much braced wall panel a house needs to resist wind and earthquakes. A standard braced wall panel must be at least 48 inches long.
Read the referenceIRC R802: Roof-Ceiling Framing
IRC R802 sizes the wood that holds up your roof: rafters and trusses. It sets the maximum span a given rafter can cover based on its size, the lumber, and the roof load, and it requires rafter or ceiling ties so the roof does not push the walls outward.
Read the referenceIRC Fuel Gas Piping: Appliance Shutoff Valves and Sediment Traps
The IRC gives every gas appliance in your home its own shutoff valve, set in the same room, within 6 feet, and upstream of the flexible connector. Most appliances also get a sediment trap, a capped stub of pipe that catches rust and scale before the debris can foul the appliance's gas valve.
Read the referenceIRC G2411 CSST Bonding: Protecting Gas Lines from Lightning
Section G2411 requires the gas piping in your home to be electrically bonded. Flexible CSST tubing gets an extra rule: it must connect to the home's grounding electrode system through a bonding jumper no smaller than 6 AWG copper, so a nearby lightning strike drains to ground instead of arcing through the thin tubing wall.
Read the referenceIRC G2417 Gas Pressure Test: Proving a New Gas Line Holds
Section G2417 requires every new gas line to pass a pressure test before it goes into service. The installer caps the piping and pressurizes it to at least 3 psig, or 1.5 times the working pressure, then holds it for 10 minutes minimum while a gauge confirms it does not drop. An inspector witnesses the result.
Read the referenceIRC M1401 & Manual J: HVAC Sizing
IRC M1401.3 requires heating and cooling equipment to be sized from a real load calculation, not a square-foot guess. The load is figured with ACCA Manual J, and the equipment is then picked with Manual S, so the system matches the actual house.
Read the referenceIRC M1403 Heat Pump Equipment: Install Rules for an Arizona Home
Section M1403 governs how a heat pump gets installed. The unit must be listed and set up the way its manufacturer directs, and the outdoor condenser has to sit on a support raised at least 3 inches above the ground so defrost water drains away instead of pooling under the equipment.
Read the referenceIRC M1411 Condensate Disposal: Keeping AC Water Out of an Arizona Ceiling
IRC Section M1411 controls how your air conditioner gets rid of the water it makes. When the air handler sits where an overflow could damage the home, the code requires a backup: a secondary drain, an auxiliary pan, or a float switch that shuts the unit off before the pan overflows. In Arizona that backup is what saves a ceiling.
Read the referenceIRC M1413 Evaporative Cooling: Installing a Swamp Cooler in Arizona
Section M1413 sets how an evaporative cooler, the swamp cooler common on Arizona roofs, gets installed. The unit has to be listed, set on a level platform you can reach for service, flashed where it meets the wall or roof, and fitted with backflow protection so its water line cannot foul the home's drinking water.
Read the referenceIRC M1502 Dryer Exhaust Duct: Length, Metal, and the Clearance Rules
IRC Section M1502 keeps a clothes dryer from starting a lint fire. The exhaust duct has to be 4-inch smooth metal, run no more than 35 feet with deductions for every bend, and vent outdoors through a damper at least 3 feet from any opening and 10 feet from an air conditioning condenser.
Read the referenceIRC M1505 Whole-House Ventilation: Fresh Air for a Tight Arizona Home
A modern Arizona home is built tight to keep the heat out, which also traps stale air in. IRC Section M1505 answers that with mechanical ventilation: a whole-house fan sized to the home's floor area and bedroom count, plus local exhaust fans that pull moisture and odor out of every bathroom and the kitchen.
Read the referenceIRC M1601: Duct Construction & Insulation
IRC M1601 sets how ducts are built, sealed, and insulated. Joints and seams must be sealed against air leaks, and supply ducts run through an unconditioned attic must be insulated to at least R-8, which in Arizona heat is one of the biggest factors in a comfortable, efficient home.
Read the referenceIRC P2503: Plumbing Inspection & Tests
IRC P2503 requires plumbing to be tested before it is covered. The drain, waste, and vent piping gets a rough-in test, usually a 10-foot water column held for 15 minutes with no leaks, and the water supply gets its own pressure test, so leaks are found before walls close.
Read the referenceIRC P2708 Shower Requirements: The 900-Square-Inch Rule and Anti-Scald Valves
IRC Section P2708 requires a shower compartment to hold at least 900 square inches of interior space and measure at least 30 inches across, kept clear to 70 inches above the drain. It also requires an anti-scald valve, balanced-pressure or thermostatic, that limits water to 120 degrees Fahrenheit at the head.
Read the referenceIRC P2804 Water Heater Relief Valves: Settings and Discharge Piping
IRC Section P2804 requires every storage water heater to have a temperature-and-pressure relief valve, or a separate pressure valve and temperature valve. The pressure setting cannot exceed 150 psi and the temperature valve opens by 210 degrees. A discharge pipe then carries any release safely down near the floor.
Read the referenceIRC P2902 Backflow Prevention: Protecting Drinking Water from Cross-Connections
IRC Section P2902 protects your drinking water from backflow, water flowing the wrong way through a pipe. It requires backflow preventers wherever clean water could meet dirty water, such as outdoor hose bibbs, lawn irrigation, and pool fills. In Arizona, where most homes water desert plants, these devices sit on every build.
Read the referenceIRC P2903 Water Pressure: The 80 PSI Limit and Thermal Expansion
IRC Section P2903 caps the water pressure inside your home at 80 psi. Where the city main runs higher, and parts of the Phoenix area do, a pressure-reducing valve is required. That valve creates a closed system, so a water heater then needs an expansion tank to absorb the pressure that heating water builds up.
Read the referenceIRC P3005 Drain Slope and Cleanouts: Getting the Waste Line Right Before the Pour
IRC Section P3005 sets how steeply drain pipes must slope and where cleanouts go. A 3-inch or larger house drain needs 1/8 inch of fall per foot, and smaller lines need 1/4 inch. Cleanouts are required every 100 feet, at the sewer junction, and at each turn over 45 degrees.
Read the referenceIRC P3009 Graywater Systems: Arizona's Type 1 Reuse Permit
IRC Section P3009 covers graywater soil absorption systems, the reuse of lightly used drain water for underground irrigation. The code hands the technical rules to your state. In Arizona that is the Department of Environmental Quality, whose Type 1 permit lets a home reuse under 400 gallons a day with no application.
Read the referenceIRC P3103 Plumbing Vent Terminals: Roof Height and Clearances
IRC Section P3103 sets where your plumbing vents can exit the roof. Every open vent pipe has to rise at least 6 inches above the roof, and its terminal has to sit at least 10 feet from any window, door, or air intake, or 2 feet above it. The rules keep sewer gas out of the house.
Read the referenceIRC P3201 Fixture Traps: The Water Seal That Keeps Sewer Gas Out
IRC Section P3201 governs the traps under every fixture, the U-shaped bends that hold a water seal against sewer gas. Each trap needs a seal 2 to 4 inches deep, and each fixture needs its own. S-traps, bell traps, and drum traps are banned. In dry Arizona air, unused traps evaporate and must be refilled.
Read the referenceIRC Water Heater Installation: Drain Pan, Drain Line, and Seismic Strapping
Where a water heater leak could reach finished space, the residential code sets the tank in a pan at least 1.5 inches deep, drained by a three-quarter-inch line to a safe outlet. Seismic strapping applies only in the higher design categories, which most of Arizona sits below. A garage tank on a slab often needs neither one.
Read the referenceIRC R324: Rooftop Solar Photovoltaic Systems
IRC R324 governs how rooftop solar panels are installed. Panels must meet the same wind and fire ratings as the roof, and R324.6 keeps clear access pathways for firefighters: two 36-inch paths to the ridge and an 18-inch clear setback below the ridge on most homes.
Read the referenceIRC R806: Roof/Attic Ventilation
IRC R806 requires a vented attic to have ventilation equal to at least 1/150 of the attic floor area. That ratio can drop to 1/300 when the vents are split evenly high and low and a vapor retarder is used, which keeps hot air moving out of the attic.
Read the referenceIRC R807: Attic Access
IRC R807 requires an attic access opening of at least 22 by 30 inches whenever the attic is big enough to enter, meaning 30 inches of height over at least 30 square feet. The opening also needs 30 inches of headroom above it so the space can be reached and serviced.
Read the referenceIRC R903 Roof Weather Protection: Flashing, Coping, and Monsoon Drainage
IRC Section R903 keeps a roof watertight through flashing, coping, and drainage. Flashing goes wherever the roof meets a wall or penetration, a cricket is required behind any chimney wider than 30 inches, and a low-slope roof that traps water needs a secondary overflow drain or scupper. On Arizona parapet roofs, these details carry the monsoon.
Read the referenceIRC R905: Roof Covering
IRC R905 sets the rules for roof coverings by type and slope. Asphalt shingles need a slope of at least 2:12, with doubled underlayment below 4:12, while clay and concrete tile need at least 2.5:12, which shapes how a low-slope Arizona roof gets covered.
Read the referenceIRC R908 Reroofing: When an Arizona Roof Must Strip to the Deck
IRC Section R908 controls reroofing. You can lay a new covering over an old one only if the deck is sound, but the code forces a full tear-off when the roof is water-damaged, already carries two layers, or is tile, slate, or wood shake. In Arizona, that means most tile reroofs strip to the deck.
Read the referenceIRC R609 Exterior Windows and Doors: Wind Rating and Flashing in Arizona
IRC Section R609 makes every exterior window and glass door strong enough for the local wind. Each unit carries a design pressure rating and an AAMA label proving it was tested, and it must be installed and flashed to the maker's instructions. In Arizona that is what holds up to monsoon wind, dust, and rain.
Read the referenceIRC R703: Exterior Wall Covering
IRC R703 sets the rules for siding and stucco on an exterior wall. For traditional stucco it requires three coats over lath, a water-resistive barrier behind it, and a weep screed at the base that drains trapped water out, kept at least 4 inches above the soil.
Read the reference
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