Before anybody draws a line
Does Indiana allow ADUs? It depends on your town.
There's no statewide rule that lets you add a second home to your lot. Your town or county decides, and the answers around here run from "yes, by right" to "not at all." Here's what the ordinances say today.
Indiana doesn't require towns to allow accessory dwelling units. A 2026 housing law, House Enrolled Act 1001, gave the state a definition of an ADU and told every town and county to review its zoning with ADUs in mind by January 1, 2027. It did not make them legal everywhere. Early versions of the bill would have, and some news coverage still describes those versions, but that language didn't survive to the final act. Whether you can build one is still up to your local zoning.
Rules below checked against each ordinance on September 28, 2026. Every town and county has to finish its zoning review by January 1, 2027, so some of these may change. We re-check your parcel's rules before any design work starts.
What the state now calls an ADU
Since July 1, 2026, Indiana law defines an accessory dwelling unit as a self-contained living unit inside or on the same lot as a single-family house. It has its own cooking, sleeping and bathroom facilities, meets the building and fire codes, and is no bigger than 75 percent of the main house's living area or 1,000 square feet, whichever is smaller. A manufactured home doesn't count; the law treats those separately.
That definition matters because of the kitchen. A space with a bedroom and a bathroom is often just an addition. Add cooking facilities and most ordinances treat it as a second dwelling, with a different set of rules.
What each place allows, as of September 2026
Hendricks County, outside the towns
- Allowed by right in the Agriculture Residential (AGR) district, and by special exception in the RA, RB, RC and RD residential districts.
- One ADU per lot, in or as an accessory building. The owner has to live in one of the two homes.
- No bigger than 75 percent of the main house's footprint, and no bigger than 720 square feet or 7 percent lot coverage, whichever is greater.
- It has to meet the setbacks for a main house, and it doesn't get its own address. Special-exception units need two off-street parking spaces.
Avon
- Allowed by right in the E-1 and AG districts, and by special exception in R-1, R-2 and R-3.
- Either a detached "garden cottage" or an attached "accessory suite," one per lot.
- No more than 800 square feet or the size of the main house, whichever is less. A detached cottage tops out at 20 feet tall or the height of the house.
- No extra parking required, and no owner-occupancy rule.
Plainfield
- Allowed only in the Residential Flex (RF) district, a master-planned district. Not in the standard R-1 through R-6 districts.
- Where allowed: one per lot, no more than 75 percent of the main house or 800 square feet, and not until the main house has its certificate of occupancy.
- Separately, Plainfield has paused permits for large accessory buildings on single-family lots under two acres until February 28, 2027.
Danville
- Allowed by special exception in the R1, R2, R3 and RU districts.
- Attached or detached, one per parcel, one bedroom, between 400 and 800 square feet (and no more than half the main house's ground floor).
- The owner has to live in the main house, and the ADU can't have its own driveway.
- An accessory building with a bathroom, a kitchen or living space is treated as an ADU unless the owner records an affidavit saying it won't be lived in.
Brownsburg
- Not in residential neighborhoods. The Unified Development Ordinance allows accessory dwelling units only in the Motor Sports district; in every residential district they aren't permitted.
- Inside town limits, the realistic option today is an attached in-law suite built as an addition, without a second kitchen. Brownsburg held its state-required zoning review in July 2026, so watch for changes.
Zionsville
- No ADU ordinance. A proposal to allow detached units of 250 to 850 square feet in several residential districts was tabled in August 2025 and hasn't come back.
Putnam County and Greencastle
- Unincorporated Putnam County allows ADUs in its agricultural and residential districts: one per lot, up to half the main house's size, owner living on the property, sharing the main house's water and septic or sewer, with a deed restriction keeping both under one owner.
- Inside Greencastle, only by special exception in the A/R district, attached to the house, and no more than 600 square feet.
Parke County
- The county zoning ordinance dates from 1976 and has no ADU provision. Its 2025 comprehensive plan lists ADUs as a future goal. Farm properties have their own narrow exception for family members or employees.
Can I put a tiny house or an RV in my backyard?
On a residential lot, not as a place to live. Brownsburg, Avon, Plainfield, Zionsville's urban residential districts, unincorporated Hendricks County, Putnam County's residential districts and Greencastle all say a parked recreational vehicle can't be used for living or sleeping, and Danville says an RV or travel trailer can't be an ADU. If it's on wheels, expect it to be treated that way. The one narrow exception we found is Parke County's rule for a family member or employee on a working farm.
A small house on a real foundation is a different thing. It's a dwelling, it has to meet the building code, and it falls under the ADU rules for your parcel. That's the kind we build.
The septic question on a rural lot
If you're not on sewer, the ground often decides before the zoning does. Indiana sizes a home septic system at 150 gallons a day for every bedroom, and adding a bedroom needs a permit from the county health department before work starts. Two single-family homes can share one residential system only while their combined bedrooms stay at five or fewer; past that, the stricter commercial rules apply. Hendricks County also requires at least an acre and a half for new septic lots created since 2024.
That's why a soil evaluation is one of the first things we ask for on a rural ADU. It's cheap, and it tells you what the property can actually carry.
How we check a parcel
Three answers before any drawings.
Is it allowed?
Your zoning district, whether that's by right or a special exception hearing, and any covenants on top.
How big can it be?
The size cap, setbacks and height limit, worked out against your house and your lot.
Can the ground carry it?
Septic and well on a rural lot, or the water and sewer tap in town.
ADU rule questions
Asked on almost every call.
If it has its own kitchen, bedroom and bathroom, almost certainly, and it gets the ADU rules above. Danville goes further and treats any accessory building with a bathroom, kitchen or living area as one unless the owner records otherwise.
A bonus room over the garage without a kitchen is usually just part of the house, which is often the simpler route.
An attached in-law suite without a separate kitchen is often allowed where an ADU isn't, because it's an addition, not a second dwelling. Sometimes that's the right answer anyway: the family stays under one roof and the mechanicals are shared.
Where a zoning variance or special exception is the only way, it's a public hearing with no guaranteed outcome. We'll tell you plainly whether we'd bet on it.
Some might. Every town and county has to hold a public hearing reviewing its zoning, ADUs included, and report to the state by January 1, 2027. The law doesn't force any particular change, so what comes out of it is up to each place.
If your town is on the edge, it can be worth waiting a few months. We'll tell you if we think that's the case for your parcel.
Sources: Indiana House Enrolled Act 1001 (2026); 410 IAC 6-8.3 (residential septic); the zoning ordinances of Hendricks County (with Ord. 2025-31), Avon, Plainfield, Danville, Brownsburg, Zionsville, Greencastle and Parke County. This page is a plain-language summary, not legal advice; the ordinance and your planning office have the final word.
Check a parcel
Send us the address.
We'll look up the zoning, the size cap and the septic situation, and tell you whether an ADU is worth designing. We reply within three hours on a weekday.