Where a Home Battery Can and Cannot Be Installed

A homeowner usually has a location in mind before anyone measures anything. A utility room off the hallway. The wall behind the bed, because the wiring is right there. A closet that is doing nothing useful.

Most of those are not available, and the reason is not aesthetic. Residential energy storage has its own section in the building code, separate from anything a PV solar array has to satisfy, and that section says where a battery may go, how much energy may sit in each of those places, and how far units have to be from each other and from the house. Getting this wrong is not a correction notice on a drawing. It is a battery on a wall that has to come off it.

This post covers where the unit can physically go and what determines that. It is a different question from who reviews the installation and what they fail it for, which covers the electrical inspector, the fire official and the utility verification. Location is settled in design; those reviewers arrive later and check that what was built matches what was allowed.

The four permitted locations, and nothing else

Jurisdictions on the 2021 International Residential Code apply Section R328 to residential energy storage. R328.4 is a closed list. Energy storage systems shall be installed only in the following locations:

1. Detached garages and detached accessory structures.
2. Attached garages separated from the dwelling unit living space in accordance with Section R302.6, the ordinary garage separation requirement.
3. Outdoors, or on the exterior side of exterior walls, located not less than 3 feet from doors and windows directly entering the dwelling unit.
4. Enclosed utility closets, basements, and storage or utility spaces within dwelling units with finished or noncombustible walls and ceilings. Where those walls and ceilings are unfinished wood-framed construction, they must be provided with not less than 5/8-inch Type X gypsum wallboard.

And a prohibition that has no exception in the section: energy storage shall not be installed in sleeping rooms, or closets or spaces opening directly into sleeping rooms.

The code's own commentary is unusually direct about why: people are most at risk where they sleep.

Location and size are one decision

The most common planning error is carrying a PV solar habit across to storage: treating the room and the system size as separate questions. R328.5 ties them together.

An individual unit is capped at 20 kWh. The aggregate rating then depends entirely on where the system is installed:

Location	Aggregate limit
Utility closets, basements, storage or utility spaces	40 kWh
Attached or detached garages, detached accessory structures	80 kWh
On exterior walls	80 kWh
Outdoors on the ground	80 kWh

Installations exceeding the permitted individual or aggregate ratings are not simply refused. R328.5 pushes them into Section 1207 of the International Fire Code, which is a different and heavier review. That is a meaningful scope change, not a footnote.

The practical effect is that an interior utility closet halves the energy a house can hold compared with the garage twelve feet away. A homeowner who wants whole-home backup and a closet installation is frequently asking for two things that cannot both happen, and somebody has to say so before the proposal is signed rather than after.

Two separate three-foot rules

Both appear in R328 and they are easy to conflate:

• R328.4 item 3 — an outdoor or exterior-wall installation must be at least 3 feet from doors and windows entering the dwelling directly.
• R328.3.1 — individual units must be separated from each other by at least 3 feet, except where smaller separations are documented as adequate on the basis of large-scale fire testing complying with IFC Section 1207.1.5.

A single unit on a blank exterior wall passes the first and never encounters the second. A two-unit or three-unit installation on the same wall has to satisfy both at once, and the available wall length is usually what decides whether the design works. Measuring the wall at survey, not at install, is the whole difference.

The listing decides how much of this applies

R328.2 requires energy storage to be listed and labeled in accordance with UL 9540.

Then R328.1 provides an exception that matters more than it looks: the requirements of R328 do not apply to an ESS listed and labeled to UL 9540 and marked "For use in residential dwelling units", where it is installed in accordance with the manufacturer's instructions and NFPA 70. The code commentary explains the basis — that exemption is aimed at products whose cell-level testing shows they will not go into thermal runaway or produce flammable gas.

Two consequences follow, and both are operational rather than theoretical.

First, two products are not interchangeable from a siting point of view. One may carry that marking and one may not, and the same house can therefore accommodate one and not the other. Equipment substitution late in a project is already a documented failure mode; what happens when equipment is substituted is a scope and cost question generally, and on storage it can also be a siting question that reopens the permit.

Second, the manufacturer's instructions become binding. R328.3 requires installation in accordance with the manufacturer's instructions and the listing. Where a product sheet specifies a clearance, an ambient temperature range or a mounting substrate more restrictive than the code, the product sheet governs. An inspector who finds an installation that meets R328 and contradicts the installation manual is looking at a failure.

There is also a narrow exception in R328.2 for repurposed unlisted battery systems from electric vehicles, where approved, installed outdoors or in detached sheds not less than 5 feet from exterior walls, property lines and public ways. It is worth knowing it exists, mostly so it is not mistaken for a general allowance.

What else the section requires once the location is settled

Choosing a compliant location does not finish the scope. Four more requirements attach to it, and each is a line item somebody has to own.

Fire detection (R328.7). Rooms and areas within dwelling units, basements and attached garages containing an ESS must be protected by smoke alarms in accordance with Section R314. Where a smoke alarm cannot be installed based on its listing, a listed heat detector interconnected to the smoke alarms is required instead. On an older house this frequently means adding interconnected detection that does not currently exist.

Impact protection (R328.8). An ESS installed where it is subject to vehicle damage must be protected by approved barriers. In a garage that means bollards or an equivalent approved barrier, on a slab, in a location that still leaves the vehicle able to park.

Ventilation (R328.9). Indoor installations of technologies that produce hydrogen or other flammable gases during charging require mechanical ventilation in accordance with Section M1307.4. This is aimed at lead-acid chemistries rather than the lithium products in most residential proposals, but it is the reason the chemistry belongs on the permit application rather than being assumed.

Documentation and labeling (R328.11). The manufacturer's installation, operation, maintenance and decommissioning instructions must be provided to the owner or placed conspicuously near the equipment, and the installed system must carry a label with contact information for qualified maintenance and service providers. That second item has a long tail: it is the label a homeowner reads years later when something stops working, and it is part of why who stands behind the installation should be a settled question at handover rather than a discovered one.

Why this belongs in design, not on site

Every requirement above is knowable before a crew is scheduled. None of them is knowable from a satellite image or a phone call.

The sequence that works is unglamorous. Confirm the code edition the jurisdiction has actually adopted, because R328 changes between editions and local amendments are common. Establish at survey which of the four permitted locations physically exist at the property, with the wall lengths and clearances measured rather than estimated. Set the system size against the aggregate limit for the location that survives. Check the chosen product's listing and marking, and read its installation manual for clearances the code does not impose. Then draw it, and put the detection, barrier and labeling scope on the plan set where a reviewer and an installer can both see it.

Done in that order, storage siting is an afternoon of design work. Done in the other order, it is a crew standing in a garage with a unit that cannot go where the contract says it goes, and a homeowner who was told something that was never true. What storage adds at each stage of fulfillment sets out where this sits in the wider sequence, and for a homeowner reading this from the other side, battery backup explained without the trade vocabulary covers what the system will actually do once it is legally on the wall.

Seamless Home owns that middle. Design, permits, interconnection and inspections sit with us as the licensed contractor, and installers work as our subcontractors, so the siting question is answered on a drawing before it becomes an argument on a driveway. Coverage is confirmed per service area rather than promised as blanket availability. If a project has a storage scope and nobody has yet said which of the four locations it uses, get in touch.

The bottom line

Under IRC Section R328 a home battery may only go in a detached garage or accessory structure, an attached garage separated per R302.6, outdoors or on an exterior wall at least 3 feet from doors and windows entering the dwelling, or an enclosed utility, basement or storage space with finished or noncombustible walls and ceilings. Never a sleeping room or a space opening into one. Individual units are capped at 20 kWh; the aggregate is 40 kWh inside and 80 kWh in a garage, on an exterior wall or on the ground. Units need 3 feet between them absent large-scale fire test data, and the product's own listing can be stricter than any of it.

The code edition the jurisdiction has adopted decides which version of those rules applies, so the last step is always local confirmation — and it belongs in design, where changing your mind costs an hour.