Free tool
Home Battery Siting Checker
The room a homeowner has in mind is often the one the code rules out. Test prohibited locations first, then the four permitted ones, the energy limits, and the readiness items inspection actually turns on.
Location first, then kilowatt-hours
IRC Section R328 decides where a home battery may go before it decides how large the system may be. A sleeping room — or a closet that opens into one — is never available. The four permitted locations each carry their own aggregate energy allowance, and individual units are capped at 20 kWh.
This tool enforces that order: prohibited rooms first, then location, then listing and energy limits, then readiness. An unanswered item is reported as unanswered rather than treated as a pass.
1. Prohibited locations
Section R328.4. Either of these ends the analysis — no energy rating repairs them.
Is the proposed location a sleeping room?
Bedrooms are never available under R328.4, regardless of finished walls or detection.
Is it a closet or space that opens directly into a sleeping room?
A hallway closet that opens into a bedroom is prohibited even when the closet itself is not a sleeping room.
2. Which permitted location?
R328.4 names four. The aggregate energy limit depends on which one you pick.
3. Listing and energy limits
R328.2 and R328.5. Individual units are capped at 20 kWh; aggregate depends on location.
Is each unit listed and labeled to UL 9540?
R328.2. Manufacturer instructions and the listing become binding under R328.3.
Is every individual unit 20 kWh or less?
Is the aggregate within the allowance for this location?
40 kWh in interior utility spaces; 80 kWh in attached or detached garages, on exterior walls, or outdoors. Above that, the project leaves R328 for the fire code.
4. Readiness items
These do not create a permitted location, but they fail inspections when skipped.
Are multiple units separated by not less than 3 feet (unless a smaller distance is documented from large-scale fire testing)?
R328.3.1 — a different 3-foot rule from the outdoor opening clearance.
Is smoke-alarm (or listed heat-detector) protection in place for the room per R328.7 / R314?
Answer the location questions first
A prohibited room ends the analysis before any kilowatt-hour arithmetic is worth reading. Start with sleeping rooms, then pick a permitted location.
Informational use only, please verify before you rely on it
This reproduces the structure of IRC Section R328 as commonly adopted in the 2021 edition. It is not a determination. Jurisdictions adopt different editions and amend freely, manufacturer instructions are binding under R328.3, and the authority having jurisdiction decides. Confirm with the building department that will issue the permit.
This tool is provided for general informational and educational purposes only. Its output is an illustrative estimate generated from the values you enter and from general assumptions that will not match every deal, market, lender, or homeowner. It is not tax, legal, accounting, financial, or professional advice, and it is not a quote, an offer, a credit decision, or a guarantee of pricing, approval, timing, savings, or eligibility.
You are solely responsible for independently confirming all information presented here including any figures, rates, fees, margins, timelines, tax treatment, and federal, state, local, or utility incentives, with the applicable lender, authority having jurisdiction, and your own qualified tax, legal, and financial advisors before acting on it, relying on it, or presenting it to a homeowner or any third party. Incentive programs, lender terms, and permitting requirements change frequently and vary by jurisdiction.
Seamless Home is not a tax advisor, law firm, lender, or licensed installing contractor, and makes no representation or warranty as to the accuracy, completeness, or currency of the information produced by this tool. To the fullest extent permitted by law, Seamless Home accepts no liability for any decision made or action taken in reliance on it.
Why the order matters
The common error is sizing the battery first and hunting for a wall that fits it. Where a home battery can and cannot be installed sets out why the room and the kilowatt-hours are one decision: the aggregate limit depends on the location, and a prohibited room has no limit that saves it.
Storage also changes the reviewers. Who inspects a solar battery covers the electrical inspector, the fire official and the utility's separate verification. And what a critical load panel is decides which circuits the battery will actually keep alive — a design question that sits beside siting rather than inside it.
For the operations path that follows a lawful location, see solar battery storage operations.
Frequently Asked Questions
Where can a home battery be installed?+
Under IRC Section R328.4 as commonly adopted in the 2021 edition, four places are permitted: detached garages and detached accessory structures; attached garages separated from living space per R302.6; outdoors or on an exterior wall at least 3 feet from doors and windows that open directly into the dwelling; and enclosed utility closets, basements or storage or utility spaces with finished or noncombustible walls and ceilings. Sleeping rooms, and closets or spaces that open directly into sleeping rooms, are prohibited.
Why does this tool ask about bedrooms first?+
Because a prohibited location ends the analysis. No UL 9540 listing, no energy rating and no smoke alarm makes a bedroom or a closet opening into one lawful under R328.4. Testing energy limits before the location question is how people arrive at a confident wrong answer.
How many kilowatt-hours can a house have?+
Under R328.5 an individual unit is capped at 20 kWh. Aggregate depends on location: 40 kWh within utility closets, basements and storage or utility spaces, and 80 kWh in attached or detached garages, on exterior walls, or outdoors. Above those ratings the installation leaves the residential section for Section 1207 of the International Fire Code.
What are the two different 3-foot rules?+
Outdoors or on an exterior wall, R328.4 requires not less than 3 feet from doors and windows that enter the dwelling directly. Separately, R328.3.1 requires individual units to be separated from each other by not less than 3 feet unless a smaller distance is documented from large-scale fire testing. Satisfying one does not satisfy the other.
Does UL 9540 listing settle the location?+
No. R328.2 requires listing and labeling to UL 9540, and R328.3 makes the manufacturer's instructions binding, but neither overrides the location list in R328.4. A listed product in a sleeping room is still prohibited.
Does a home battery need its own smoke alarm?+
Effectively yes. R328.7 requires rooms and areas within dwelling units, basements and attached garages containing energy storage to be protected by smoke alarms in accordance with R314, and where a smoke alarm cannot be installed based on its listing, a listed heat detector interconnected to the smoke alarms is required instead.
Is this a determination?+
No. It reproduces the structure of IRC Section R328 as commonly adopted in the 2021 edition. Jurisdictions adopt different editions, amend freely, and some apply the International Fire Code more broadly. Confirm against the edition your building department has adopted and against the product listing.
Related resources
Where a Home Battery Can and Cannot Be Installed
The four locations R328 permits, the 20 kWh unit cap, and the two separate 3-foot rules.
Learn more →Who Inspects a Solar Battery
The reviewers storage adds, and why they do not arrive on the same visit.
Learn more →What a Critical Load Panel Is
Which circuits a battery actually backs up.
Learn more →Battery Backup for Homeowners
What a home battery runs, what it does not, and who is accountable.
Learn more →Confirm the room before you quote the runtime
Seamless Home treats battery location as a design gate, not a field preference. Tell us what you want the battery to keep alive, and we will confirm whether the house can put it somewhere the code allows.
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