Can a home battery go in the garage? The US code rules on rooms, kWh limits and bollards

The location and kWh table, edition by edition

The model code works as a whitelist. Section R328.4 of the 2021 IRC says an energy storage system (ESS) "shall be installed only in" four kinds of place, and R328.5 then caps the total energy in each. The table sets the model numbers beside California's version, the largest state departure in the records checked, and the 2024 edition kept every model figure while renumbering the section.

Two details in the table change real decisions. The 40 kWh indoor line is the tightest, so a battery bank that fits in a garage may not fit in the basement next to the panel. And California's figures above 80 kWh apply only to the outside of the house and to structures set apart from it; inside an attached garage California holds the same 80 kWh as the model code. The rationale in a March 2023 addendum argued for 100 kWh in attached garages, but the table the Commission approved on June 27, 2023 printed 80, and the 2025 express terms say the table remains unchanged.

The exception that can move the decision to the manual

Before the location list applies, check the first subsection. The 2021 text Washington's council circulated opens R328.1 with two exceptions: an ESS "listed and labeled in accordance with UL 9540 and marked 'For use in residential dwelling units'" and installed per the manufacturer's instructions and NFPA 70, the National Electrical Code; and any ESS under 1 kWh. California wrote the same residential-marking exception into its own code in 2020, when it rebuilt its battery section.

Read literally, a unit carrying that residential marking and installed to its manual sits outside the rest of the section, which leaves the manual and the electrical code as the governing placement documents. Whether a permit office reads it that broadly is a local decision, and the inspector who signs the final is the one whose reading counts. The practical move is to ask the plan reviewer which reading the office uses before a contractor drills the garage wall. If the office applies the full section anyway, the table above is the test; if it applies the exception, the installation manual's clearances and allowed locations become the test, and the manual should be in the permit packet either way.

The listing itself is not optional. R328.2 requires listing and labeling to UL 9540. Washington's adopted amendment (WAC 51-51-0328, effective March 15, 2024) keeps three narrow exceptions: repurposed unlisted electric-vehicle batteries, where approved, outdoors or in detached sheds at least 5 feet from exterior walls, property lines and public ways; batteries built into an electric vehicle, when the installation follows Section 625.48 of NFPA 70; and systems under 1 kWh. A secondhand module without a label is not a garage battery under any of these texts.

What makes an attached garage acceptable

The garage line in R328.4 is conditional: "attached garages separated from the dwelling unit living space in accordance with Section R302.6." R302.6 is the IRC's garage-to-dwelling separation section, the same wall-and-ceiling requirement that applies whether or not a battery is present. A garage converted from a carport, or one where a later remodel cut openings into the shared wall, may no longer meet it. A battery permit can bring that wall back into the inspector's view, so the cheapest time to find a gap is before the battery arrives.

Fire detection is the second condition. R328.7 requires smoke alarms under Section R314 in rooms, basements and attached garages that hold an ESS, and where a smoke alarm cannot be installed because of its listing, the 2021 text calls for a heat detector "listed and interconnected to the smoke alarms." If the smoke alarm you would use is not listed for a garage, expect the plan reviewer to ask for a heat detector tied into the house alarm circuit. Washington's 2023 correlation draft would have changed this to a listed heat alarm without the interconnection wording; the enacted Washington rule does not include that change, so the model language stands there.

Ventilation is the third, and it rarely bites for lithium-ion products. R328.9 requires mechanical ventilation, under Section M1307.4, for indoor installations of batteries that produce hydrogen or other flammable gases during charging. Lithium-ion home batteries are not usually in that group, but ask the installer to confirm in writing whether the chemistry quoted produces gas while charging, since the answer decides whether an exhaust fan belongs on the quote.

Bumper zones: when a garage battery needs bollards

The 2021 IRC's impact rule is one sentence: an ESS "installed in a location subject to vehicle damage shall be protected by approved barriers." California spelled out what that means in the 2022 California Residential Code, and the geometry it used is the most specific published answer to where a car is likely to hit. Under that text, the normal driving path is the space between the garage vehicle opening and the back wall, up to 48 inches above the finished floor, as wide as the garage door opening. Impact protection was required for an ESS in that path, on the back wall within 36 inches to either side of it, or on a side wall within 24 inches of the back wall and within 36 inches of the path.

One exception does a lot of work. Where the clear height of the garage door opening is 7 feet 6 inches or less, an ESS mounted at least 36 inches above the finished floor needed no impact protection under that text. If the manufacturer's manual allows a wall-hung unit at that height, the barrier line can drop off the quote entirely.

California replaced its own wording with the 2024 IRC's model language in the 2025 edition, and the 2024 IRC now carries a garage-specific subsection, R330.8.1, with an impact-protection figure. That subsection's wording is not reproduced here, so treat the geometry as California's adopted text through 2025 and the clearest worked reading of "subject to vehicle damage," and ask your permit office which version it enforces. Washington's council proposed the same geometry in 2023, but the enacted Washington rule does not contain it.

The wheel-barrier setback is the one people miss. A barrier has to sit at least 54 inches, four and a half feet, in front of the battery, which eats most of a parking bay's depth in front of the back wall. In a garage that is already tight for the car, bollards 6 inches off the battery's face are usually the only physical option that still lets the car in, and raising the battery above 36 inches may beat both.

Counting kWh: per unit, per space, and per property

The model wording says "the aggregate rating of the ESS shall not exceed" the four figures, without saying whether the limit is per location or for the whole house. California's State Fire Marshal settled that for California in 2023, in the rationale it filed with its March 2023 addendum to the initial express terms, that it "was not the intent to limit installations to one location on the property, or to limit to only 80 kWh for all ESS installed on the property." California rewrote the sentence so the ratings apply "in each location" and added a 600 kWh ceiling for the whole property. Outside California the model sentence is unchanged, so a split installation, say some units in the garage and some on an outside wall, is a question to put to the local plan reviewer before the design is drawn, not after.

The arithmetic is simple once the unit size is fixed. The U.S. Department of Energy's Q1 2025 cost benchmark models a residential battery of 13.5 kWh, which makes a convenient yardstick; any product's own nameplate kWh slots into the same steps. Off-grid banks reach these limits fastest: three 13.5 kWh units already total 40.5 kWh, and the off-grid solar cost guide shows which daily loads and storage days push a bank out of the basement. The table counts how many such units each line allows.

The basement line catches the most people: three 13.5 kWh units total 40.5 kWh, just half a kilowatt-hour over, and that third unit pushes the installation either into the garage or out of the residential section altogether. Where an installation exceeds the per-unit or aggregate caps, the code text sends it to Section 1207 of the fire code, the commercial-style ESS rules, which bring their own plan review. Few backup plans need anything close to the caps; the battery-or-not decision guide and EnergyBS's critical load sizing guide size a battery from the loads you actually want running.

The 20 kWh per-unit rule is about the listed unit, not the system. A system sold as a 40 kWh battery made of two listed 20 kWh units passes the per-unit test, while a single listed cabinet above 20 kWh does not fit the residential section at all. The spec sheet and the UL 9540 listing name the unit; that is the number to compare.

Reading one number as the whole rule

Treating the 80 kWh garage figure as permission for any battery anywhere in the garage. The cap is one of five conditions: a listed unit no larger than 20 kWh, a fire-separated attached garage, a smoke alarm or interconnected heat detector, 3-foot spacing unless testing documents less, and impact protection where a car can reach it. A garage install that meets the kWh cap but sits at bumper height on the back wall, with no barrier, fails on the last of them.

The 3-foot spacing rule and the wall it needs

R328.3.1 requires individual units to be at least 3 feet apart "except where smaller separation distances are documented to be adequate based on large-scale fire testing" under Section 1207.1.5 of the fire code. If a manufacturer's documentation supports closer spacing, the permit set should include it whenever the drawing shows units closer than 3 feet. Without it, the 3-foot gap is the rule, and it changes how much wall a battery bank takes.

Take units 2 feet wide, a round figure for illustration. Three of them in a row with 3-foot gaps need 2 + 3 + 2 + 3 + 2 = 12 feet of clear wall. With test documentation that allows them to touch, the same three need 6 feet. In a two-car garage the difference decides whether the bank fits on the side wall outside the bumper zones or has to go on the back wall, where it may need bollards. The bollards then multiply: at the 5-foot maximum spacing, protecting the 12-foot bank plus 6 inches each side, 13 feet in all, takes four bollards, while the 6-foot touching bank, 7 feet with its setbacks, needs three.

Three units in a two-car garage, placed by the numbers

A two-car attached garage, 20 feet wide inside, with a 16-foot door centered in the front wall and a clear opening height of 7 feet. The owner wants three 13.5 kWh units, 40.5 kWh, which is too much for the basement's 40 kWh line but well inside the garage's 80 kWh.

The driving path is 16 feet wide, centered, so it ends 2 feet from each side wall. On the back wall, the protected band runs 36 inches beyond each edge of the path, 22 feet in all, wider than the 20-foot wall, so every back-wall spot below 48 inches is in a bumper zone under California's 2022 text. On each side wall, the first 24 inches from the back wall are in a zone too, because the whole side wall sits within 36 inches of the path.

Two layouts pass without bollards. Mounting the units with their bottoms at least 36 inches above the floor uses the exception, because the door's clear height is under 7 feet 6 inches. Or the bank goes on a side wall more than 24 inches forward of the back wall, where the remaining question is whether the plan reviewer still treats that spot as "subject to vehicle damage." With 3-foot gaps the bank needs 12 feet of side wall; the side wall must also leave room for the car door to open, which the code does not measure but the owner will. Adding a heat detector interconnected with the house smoke alarms and confirming the garage separation wall completes the garage list.

An outside wall instead: the 3-foot door rule and California's noncombustible zone

The exterior-wall option comes with its own setback: the ESS must be at least 3 feet from doors and windows directly entering the dwelling unit. On a typical side elevation, with a back door, a laundry-room window and a hose bib, that rule often leaves only one stretch of wall. Measure from the edge of the battery cabinet to the edge of each opening, and ask whether the office treats a garage service door as an opening into the dwelling, since the text speaks only of doors and windows "directly entering the dwelling unit."

In California the reward for a fireproofed wall is large: 200 kWh instead of 100 kWh on or within 3 feet of the wall. Footnote a to Table R330.5 sets the size of that noncombustible surface: at least 5 feet horizontally from each edge of the ESS, at least 1 foot below its bottom edge, and at least 8 feet above it or up to a noncombustible eave, whichever is less. For a 2-foot-wide cabinet whose bottom sits 1 foot above grade and whose top sits at 5 feet, that zone runs 12 feet wide, from grade to 13 feet up or to a lower noncombustible eave. On a one-story house with the eave at 10 feet, the job is a 12-by-10-foot panel of fiber-cement or masonry plus a noncombustible soffit above it. The code official may approve reductions based on large-scale fire testing, so ask before pricing the full panel.

Outdoors on the ground, the same California table gives 200 kWh at 3 feet from property lines and dwellings and 600 kWh at 10 feet. The model code holds ground-mounted systems to 80 kWh and applies the same 3-foot distance from doors and windows that open into the dwelling, since its location item covers "outdoors or on the exterior side of exterior walls" in one sentence.

Basements and utility rooms: what the 40 kWh space must look like

Indoors, R328.4 allows "enclosed utility closets, basements, storage or utility spaces within dwelling units with finished or noncombustible walls and ceilings." An unfinished basement with open joists does not qualify as it stands: walls and ceilings of unfinished wood-framed construction need at least 5/8-inch Type X gypsum wallboard. That board is the fire-rated version, and the code names the thickness, so a quote that says "drywall around the battery" should say 5/8-inch Type X.

The prohibitions sit at the end of the location list. No ESS in sleeping rooms, or in closets or spaces opening directly into sleeping rooms. California's earlier wording also banned habitable spaces generally; the 2025 express terms delete that phrase because, in the State Fire Marshal's words, it "conflicts with the allowance of energy storage systems to be in a utility closet that opens to the dwelling unit." A hall utility closet next to a living room is therefore inside the rule, and a closet off a bedroom is not.

Indoor placement also carries the 3-foot spacing rule, the smoke-alarm requirement, and the manual's own clearances to doors, vents and gas appliances. A cramped mechanical room that holds the water heater and furnace often runs out of space before it runs out of kWh.

Which edition your state enforces, from the official pages

None of the location rules applies until a jurisdiction adopts the edition that contains them. The location list and kWh caps entered the model residential code with the 2021 IRC. California's 2019 code carried only a short "stationary storage battery systems" section until the State Fire Marshal added the locations and caps through an amendment approved on August 13, 2020, effective with the July 1, 2021 supplement.

Washington shows how a state adds requirements on top of the model text. Its R328.12 requires commissioning: verifying the installation against the approved plans and manufacturer's instructions, handing over the manufacturer's installation, operation, maintenance and decommissioning instructions, and labeling the system with the contact details of qualified service providers. When a builder installs the system before sale, R328.12.1 makes the builder pass that information to the buyer at closing. A buyer of a new Washington house with a battery already in the garage should ask for that packet.

Where a state has not adopted the 2021 or a later IRC, a city or county may have, and a fire marshal may enforce fire code rules even where the residential code is older. The permit office can tell you in one phone call which edition governs your address, and that answer should come before any layout decision.

Agreeing the spot with installer and inspector

A battery location is cheapest to change while it is a line on a drawing. The permit set is where the code questions above get answered, and an installer's site plan should show the battery's position, its distance to doors and windows, the spacing between units, the alarm locations and any impact protection. Our guide to adding a battery to existing solar covers the interconnection and panel paperwork that travels with that drawing, and the home battery cost guide lists the quote lines where barriers, drywall and alarm work belong.

Insurance is the other paper trail. The standard HO-3 form covers the dwelling "including structures attached to the dwelling," so a battery in an attached garage is part of that insured structure, and adding it can change the replacement cost the policy needs to carry. The solar and homeowners insurance guide works through the 80 percent coinsurance test and the questions to put to the insurer in writing; the same questions apply when the addition is a battery. If an incentive program is paying part of the cost, its rules may require a reservation before installation; see the battery incentives guide before the permit is filed.

What the permit drawing must show

• The code edition and section the permit office enforces at your address: R328 (2021), R330 (2024), or a state version.
• Whether the office applies the R328.1 exception for units marked for residential dwelling units, or the full location list.
• The UL 9540 listing and the kWh rating of each listed unit, compared with the 20 kWh per-unit cap.
• The aggregate kWh in each location, and whether the office counts the limit per location or for the whole property.
• The spacing between units, and the large-scale fire test documentation if the drawing shows less than 3 feet.
• The impact-protection decision for a garage location: mounting height, zone, and the barrier type if one is required.
• The smoke alarm or interconnected heat detector location, and for indoor spaces, the wall and ceiling finish.