To split utilities between a main house and an ADU, you pick one of three arrangements: the utility company installs a separate meter on the ADU and bills the tenant directly, you install a private sub-meter and bill the tenant yourself, or you keep shared service and divide the single bill using a formula or a flat fee. The right choice depends on your local rules, what you can spend on infrastructure, and how much billing transparency you and your tenant need.
The Three Setups
These arrangements are not variations on one theme. They differ in who owns the metering hardware, who reads it, and who sends the bill. Sort that out before you call a contractor.
A separate meter is installed by the utility company on its own service line to the ADU, with an independent account in the tenant’s name. The tenant pays the utility directly and you never touch the money. It’s the cleanest arrangement from a landlord’s perspective. It’s also the most expensive to set up, because it usually requires trenching a new service line, a dedicated meter base, and sometimes a panel or transformer upgrade.
A sub-meter is a device you own, installed downstream of the main utility meter, that tracks what the ADU consumes. The utility still sends one bill for the whole property to you. Each cycle you read the sub-meter, calculate the tenant’s share, and collect. Cheaper to install than separate service, but you become the billing department, and you need records that will survive a dispute.
Shared service with no additional hardware is the simplest. One bill arrives; you split it by a formula or charge a flat fee. The tradeoff is transparency: neither side knows what the ADU actually consumed, and that gap breeds arguments over time.
Three Billing Methods
The physical setup dictates which billing methods are open to you. Whichever you pick belongs in the lease before the tenant moves in.
Ratio Utility Billing (RUBS)
A Ratio Utility Billing System divides one master bill among units using a formula. Common variables are square footage, number of occupants, or number of bedrooms. If the ADU is 25 percent of the property’s total livable square footage, the tenant pays 25 percent of each bill.
RUBS makes sense when metering isn’t practical, but it’s an estimate, not a measurement. A tenant who conserves still pays a share driven partly by what happens in the main house. Some jurisdictions ban RUBS. Others regulate it, typically by prohibiting landlords from profiting on utility charges or by requiring specific disclosure about how the formula works. Check your local rules before committing.
Flat Fee Added to Rent
A flat fee adds a fixed monthly amount to the rent. The tenant gets predictability; you skip the monthly math. The risk is all yours: if actual costs exceed the fee, you absorb the difference. Set the amount using at least twelve months of historical utility data, build in a cushion, and review it annually.
Direct Billing Through a Separate Meter
When the ADU has its own utility meter, the utility bills the tenant for verified consumption. This is the most transparent option and the one tenants generally prefer, because they pay only for what they use. You stop being a billing intermediary, which removes a common source of friction. The tradeoff is the higher upfront installation cost.
If sub-meter reading and invoicing sound like more work than you want, third-party billing services will read meters, generate invoices, and collect payments for a monthly per-unit fee. Most cater to multi-unit properties, though some will take on a single rental.
Check Local Rules and Utility Policies First
Before choosing an approach, check two separate sets of rules: your local building or zoning code, and your utility provider’s service policies. They don’t always agree, and you need to satisfy both.
Some jurisdictions require ADUs to have their own utility connections, especially for water and sewer. Others allow shared service but impose conditions such as occupancy limits or mandatory tenant disclosure. Utility providers increasingly push new ADUs toward separate metering, and the provider’s service agreement will spell out whether it will authorize a second meter on a single-family lot and what documentation it wants.
Most utilities want to see a certificate of occupancy or an approved building permit before they’ll recognize the ADU as a legitimate service point. Without that paperwork, you won’t get a new account activated, and operating without proper authorization can trigger fines or disconnection. Talk to the building department and the utility early, and keep written records of every conversation and approval.
Many states also require landlords to disclose shared utility arrangements to tenants before the lease is signed. The specifics vary; the principle doesn’t. Tenants have a right to know upfront whether utilities are shared and how they’ll be billed.
What Installation Actually Involves
A shared-service arrangement with RUBS or a flat fee needs no new hardware. Sub-metering and separate metering both require permits, licensed contractors, and inspections.
Electrical
For sub-metering, you’ll need a sub-panel in or near the ADU that isolates its circuits from the main house. The sub-panel connects downstream of the main panel, with a sub-meter between them. Your existing main panel needs enough capacity to carry the added load. Many older homes have 100-amp or 150-amp panels that can’t handle a second dwelling without an upgrade, and even a 200-amp panel may need evaluation depending on what the ADU draws.
For a fully separate meter, the utility installs its own meter base, typically fed by a dedicated service line from the transformer to the ADU. Costs can escalate quickly here. Adding a second service sometimes forces a transformer upgrade, which can run several thousand dollars, and the utility decides whether you pay or it absorbs the cost. Get a written estimate from the utility before committing.
Water and Gas
A separate water meter needs its own supply line from the main, plus a shutoff valve and meter pit. That means trenching, and trenching costs vary with distance and soil. A water sub-meter is simpler: it taps the existing supply line after the main meter and measures flow to the ADU.
Gas separation works the same way, with a sub-meter or separate meter on the line serving the ADU and a pressure regulator for safe delivery. Gas work requires a licensed plumber or gas fitter, and inspectors tend to look harder at gas permits.
Permits and Inspections
Plumbing and electrical permits are required for essentially any metering installation. Fees vary by jurisdiction and scope, from modest sums for sub-panel work to significantly more for a full separate service. Apply early; processing can add weeks.
After installation, an inspector must sign off before the system goes live. Only then can you have the utility activate a new account, which usually carries its own connection fee. Keep permits, inspection sign-offs, and utility correspondence together. Those documents matter during future sales, refinances, or disputes.
What Your Lease Should Cover
A handshake on utilities is a dispute waiting to happen. The lease should name which utilities the tenant is responsible for, the exact billing method, how the calculation works if you’re using RUBS or a sub-meter, when bills are due, and how payment is collected. For a flat fee, state the amount and how often it’s reviewed. For RUBS, include the formula variables and a sample calculation so the tenant can check their bill against the math.
Spell out what happens when utility charges go unpaid. Can you add them to next month’s rent? Is non-payment grounds for eviction? The answers depend on your state’s landlord-tenant law, but whatever the law allows, put it in writing.
When the Tenant Doesn’t Pay
This is where landlords get into the most trouble. Virtually every state prohibits landlords from shutting off a tenant’s utilities to collect unpaid bills or force an eviction. Cutting power, water, or gas to a rental unit is treated as an illegal lockout in most jurisdictions, even when the tenant owes you money. Penalties can include statutory damages, attorney’s fees, and in some states the tenant’s right to break the lease.
If the ADU has a separate meter and the tenant pays the utility directly, non-payment is between the tenant and the utility. The utility follows its own disconnection procedures, with notice requirements and often protections during extreme weather. You stay out of it.
If you’re the billing intermediary through sub-metering or RUBS, unpaid charges are a debt the tenant owes you. Your remedies are the ones you’d use for unpaid rent: written notice, any late fees the lease allows, and eviction if it comes to that. Flipping a breaker will cost you far more than the unpaid bill.
Tax Treatment of Utility Costs
If you rent the ADU, the utilities attributable to the rental unit are deductible as ordinary rental expenses. The IRS lists utilities alongside mortgage interest, insurance, repairs, and depreciation.1Internal Revenue Service. Topic No. 415, Renting Residential and Vacation Property Report them on Schedule E.
When the ADU has its own meter, the deduction is straightforward: the whole bill for that meter is a rental expense. When you share a meter, you have to allocate the total bill between personal use in the main house and rental use in the ADU. The IRS expects a reasonable method, such as square footage or the same RUBS formula you use to bill the tenant. Keep the underlying bills and documentation showing how you allocated. The base cost of a first telephone line into your residence is never deductible, even if you use that phone for calls about the rental.2Internal Revenue Service. 2025 Instructions for Schedule E (Form 1040)