Renting a basement, ADU or in-law suite: a legal checklist

What each term means

• Basement apartment: a unit in a basement, with its own kitchen and bath, often with a separate entrance.
• ADU: a second, smaller dwelling on the same lot as a house. It may be attached, a garage conversion or a separate backyard cottage.
• In-law suite: a part of a home set up for relatives, often with a separate entrance. Whether it is a legal separate unit depends on the city.

The test cities usually apply is whether the space can be lived in on its own, with sleeping, cooking and bathing areas. If it can, it is likely a dwelling unit and must meet dwelling rules.

Step 1: zoning and permits

Zoning decides whether a second unit is allowed on your lot and under what limits, such as size, parking, owner occupancy or utility connections. Some states have pushed cities to allow ADUs; for example, California publishes state guidance at HCD's accessory dwelling unit page. Even there, the city sets many details.

Call your city or county building and planning office. Ask whether a second unit is allowed, whether a permit exists for yours, and whether the city requires a rental license or inspection. See rental license and city inspection programs. If the work was done without a permit, ask what it takes to legalize it before you advertise.

Step 2: safety under the building code

Local building codes are usually based on model codes such as the International Residential Code (ICC), which the city may adopt with changes. The items inspectors look at most often in basements and converted spaces are:

• Egress: every bedroom needs a way out, usually a window or door of a minimum size, and a basement needs a clear path to the outside.
• Ceiling height and natural light and ventilation in sleeping rooms.
• Smoke alarms and carbon monoxide alarms in the right places. Read smoke and CO alarm rules for rentals.
• Safe heating, working electrical and plumbing, and a water heater with a proper vent.
• Moisture control. A damp basement leads to mold; see landlord responsibilities for mold.
• Fire separation between the units where the code requires it.

A permit inspection is the simplest way to know the space meets the code that applies in your city.

Step 3: utilities, address and access

Decide who pays for what before the first tenant. If you share a meter with the main house, you need a fair way to split the bill or you pay it yourself and price it into rent. A separate meter or submeter keeps it clean. See who pays utilities and RUBS billing for the options your state may allow.

Think about the address and mail, a separate entrance, locks, and how emergency crews find the unit. If you live in the house, think about noise, parking and privacy, and put those rules in the lease.

Step 4: insurance and taxes

Tell your insurer you plan to rent the space. A standard homeowners policy may not cover a rented unit, and a claim on an unpermitted unit may be denied. Ask what policy fits. For taxes, if you rent part of the property, you divide expenses between personal and rental use; ask your tax preparer. The post on splitting expenses when you live in one unit of a duplex shows the idea.

Example a made-up owner rents a 600 square foot basement unit in a house of 2,400 square feet. Square footage gives a 25 percent share, so a $4,000 yearly property tax bill would put $1,000 to the rental. Your preparer may suggest a different method.

How DoorKeeping handles it

DoorKeeping keeps the permit, the inspection result, the lease and the smoke alarm records as documents under the unit, and works with one LLC per property if you set it up that way. Ask Claude or ChatGPT, for example, "Show everything filed for the basement unit." Work orders and vendor links work for the unit like any other.

DoorKeeping does not check zoning or permits and gives no legal advice. Your city does.

Sources

1. California HCD: Accessory dwelling units, read Oct 30, 2026
2. International Code Council: model building codes (International Residential Code), read Oct 30, 2026

Questions

Can I rent my basement without a permit?

It is risky. Unpermitted units can bring fines, problems with insurance and trouble enforcing the lease. Ask your city what it takes to make the unit legal.

What makes a basement bedroom legal?

Usually a proper exit window or door, enough ceiling height, light and ventilation, and working alarms. Your city's adopted building code sets the exact numbers.

Does my homeowners insurance cover a rented ADU?

Often not by itself. Tell your insurer, and ask what coverage the unit needs.