ADU Permits in Indiana: Accessory Dwelling Unit Rules by City

What Is an ADU?

An accessory dwelling unit (ADU) is a secondary, self-contained housing unit on the same lot as a primary single-family home. ADUs go by many names — in-law suite, granny flat, backyard cottage, carriage house, garage apartment, or basement apartment. Regardless of what you call it, an ADU has its own entrance, kitchen or kitchenette, bathroom, and sleeping area.

ADUs come in several forms:

• Detached ADU — A standalone structure in the backyard, often called a backyard cottage or carriage house
• Attached ADU — An addition built onto the existing home with a separate entrance
• Garage conversion — Converting an existing attached or detached garage into living space
• Basement apartment — Finishing a basement as a self-contained unit with its own entrance
• Above-garage unit — Living space built above an existing or new garage

In Indiana, building any of these requires navigating both zoning approval and the building permit process — and the rules vary dramatically from one jurisdiction to the next.

Indiana Has No Statewide ADU Law

Unlike states such as California, Oregon, and Washington that have passed laws requiring cities to allow ADUs, Indiana has no statewide ADU legislation. This means every city and county in Indiana sets its own rules about whether ADUs are allowed, where they can be built, and how large they can be.

Some Indiana jurisdictions welcome ADUs. Others don’t mention them in their zoning code at all, which effectively prohibits them. And many fall somewhere in between — allowing ADUs only through a variance, special exception, or conditional use process that adds time, cost, and uncertainty.

Before you spend money on plans or break ground, your first step is always to check your local zoning ordinance. Contact your city or county planning department and ask specifically whether ADUs are permitted in your zoning district.

Zoning Is the First Hurdle

The building permit process is straightforward once you have zoning approval. The harder part is determining whether your property’s zoning classification allows an ADU in the first place.

Here’s what to check:

1. Zoning district — ADUs are typically allowed (if at all) only in residential zones. Some jurisdictions restrict them to specific residential classifications (R-1, R-2, etc.).
2. Permitted vs. conditional use — If ADUs are a permitted use, you can build one by right as long as you meet the standards. If they require a conditional use permit or special exception, you’ll need to apply, possibly attend a hearing, and get approval from a board — a process that can take 2-4 months and may be denied.
3. Lot size minimums — Many ordinances require a minimum lot size before an ADU is allowed, often 6,000–10,000 square feet or more.
4. Number of units — Most jurisdictions that allow ADUs limit you to one ADU per lot.

If your zoning code doesn’t mention ADUs at all, you’ll likely need to apply for a variance — an expensive, time-consuming process with no guarantee of approval.

Where ADUs Are Allowed in Indiana

Indianapolis / Marion County

Indianapolis is the most ADU-friendly jurisdiction in Indiana. Through the IndyRezone initiative, the city updated its zoning ordinance to explicitly allow ADUs in most residential zoning districts. Key Indianapolis ADU rules include:

• ADUs are permitted in the D-A (dwelling, attached) and D-5 through D-12 zoning districts
• The property owner must occupy either the primary dwelling or the ADU (owner-occupancy requirement)
• Detached ADUs are limited to 750 square feet or 40% of the primary dwelling’s floor area, whichever is less
• Maximum height for a detached ADU is typically 22 feet (one and a half stories)
• ADUs must meet all setback requirements for accessory structures
• A building permit is required through the Department of Business and Neighborhood Services (DBNS)
• Separate entrance required; the entrance cannot face the primary street frontage for detached ADUs in some zones

Apply through the Accela Citizen Access portal or in person at DBNS.

Fort Wayne / Allen County

Allen County permits ADUs in certain residential zones, but with tighter restrictions than Indianapolis. Detached ADUs are generally capped at 700 square feet. Fort Wayne’s zoning ordinance requires ADUs to comply with accessory structure setback rules, and the city may require a development plan review depending on the location. Contact the Allen County Department of Planning Services or Fort Wayne’s Division of Community Development for your specific situation.

Bloomington / Monroe County

Bloomington has been relatively progressive on ADUs compared to most Indiana cities. The city allows ADUs in several residential zoning districts, and the Bloomington Plan Commission has discussed expanding ADU allowances. Current rules include size limits, owner-occupancy requirements, and design standards intended to maintain neighborhood character. Monroe County’s unincorporated areas have different (typically more restrictive) rules.

Hamilton County (Carmel, Fishers, Noblesville)

Hamilton County cities have historically been more restrictive on ADUs. Carmel’s zoning ordinance does not broadly permit ADUs by right in most residential zones — they may require a variance or planned unit development (PUD) approval. Fishers has similar restrictions. If you’re in Hamilton County and want to build an ADU, expect to work through a conditional use or variance process. Contact your city’s planning department early to understand what’s feasible.

Size Restrictions by Jurisdiction

ADU size limits vary significantly across Indiana:

Jurisdiction	Max ADU Size	Notes
Indianapolis	750 sq ft or 40% of primary dwelling	Whichever is less
Allen County	700 sq ft	Detached ADUs
Bloomington	Varies by zone	Check current ordinance
Carmel	Case by case	Typically requires variance
Fishers	Case by case	Typically requires variance

Most jurisdictions also impose minimum size requirements — typically at least 220–400 square feet of habitable space, consistent with the International Residential Code’s minimum room size standards that Indiana adopts.

Permit Requirements for an ADU

Once you’ve confirmed your zoning allows an ADU, you’ll need permits. An ADU project typically requires:

Building Permit

The primary permit covering the structure itself — foundation, framing, roofing, insulation, drywall. You’ll need to submit:

• Site plan showing the ADU location on the lot, distances to property lines, and relationship to the primary dwelling
• Floor plans with room dimensions, door and window locations, and egress details
• Elevation drawings showing exterior appearance and height
• Foundation details (for new construction)
• Structural details including wall sections and connection details (for attached ADUs or garage conversions)

Trade Permits

Separate permits are typically required for:

• Electrical — New circuits, panel, outlets, and lighting
• Plumbing — Kitchen, bathroom, water heater, sewer/septic connection
• Mechanical (HVAC) — Heating and cooling system for the ADU
• Gas — If the ADU will have gas appliances

Zoning Approval

Some jurisdictions require a separate zoning approval or certificate before issuing a building permit. In Indianapolis, zoning compliance is checked as part of the building permit review. In cities where ADUs require a conditional use permit, that approval must come first.

Setback and Lot Coverage Requirements

ADUs must comply with your jurisdiction’s setback rules, which dictate how far the structure must be from property lines:

• Rear setback — Typically 3–5 feet for accessory structures, sometimes more for ADUs
• Side setback — Usually 3–5 feet, matching accessory structure rules
• Primary structure setback — Attached ADUs must meet the same setbacks as the primary house

Lot coverage is another constraint. Most zoning codes limit how much of your lot can be covered by buildings and impervious surfaces — typically 30%–50%. The ADU footprint counts toward this limit along with your house, garage, driveway, and patio.

Parking Requirements

Many Indiana jurisdictions require one additional off-street parking space for an ADU. In Indianapolis, one dedicated parking space is required for the ADU in addition to the parking required for the primary dwelling. The space can be in a driveway, garage, or designated parking area on the lot.

Some jurisdictions waive the parking requirement if the property is within a certain distance of public transit. Check your local ordinance for specifics.

Owner-Occupancy Requirements

Most Indiana cities that allow ADUs require the property owner to live on-site — either in the primary dwelling or the ADU. This requirement exists to maintain neighborhood character and prevent investors from turning single-family lots into duplexes without residing there.

In Indianapolis, owner-occupancy is a condition of ADU approval. Violation can result in enforcement action.

Practical impact: If you build an ADU and later move away, you may not be able to rent both the primary house and the ADU simultaneously. Some jurisdictions require you to remove the ADU’s kitchen facilities if you no longer occupy the property. Verify the specific rules in your area before investing in an ADU as a rental income strategy.

Utility Connections

How utilities are handled depends on your jurisdiction and the ADU type:

Shared Utilities

Many attached ADUs and conversions share the primary home’s utility connections — same electric meter, same water meter, same sewer lateral. This is the simplest and cheapest approach but means you can’t bill an ADU tenant separately for utilities.

Separate Meters

Some jurisdictions require or allow separate utility meters for detached ADUs. Separate metering adds cost:

• Electric meter — $500–$2,000+ for the meter base, panel, and utility connection fee
• Water meter — $1,000–$5,000+ depending on the utility provider’s tap fee
• Gas meter — $500–$1,500+ for a separate gas service

Contact your local utility providers (Indianapolis: Citizens Energy Group for water/gas, AES Indiana for electric) early in the planning process. Utility work often requires its own permits and inspections.

Sewer and Septic

ADUs in areas with municipal sewer typically connect to the existing sewer lateral, though a separate connection may be required. Properties on septic systems face additional scrutiny — the existing septic system must be sized to handle the additional wastewater load, and an upgraded or second system may be required. The local health department reviews septic capacity.

Converting Existing Structures vs. New Construction

Garage Conversions

Converting an existing garage into an ADU is often the most cost-effective approach. Key considerations:

• Foundation — Most garage slabs are not insulated and may not meet residential foundation requirements. You may need to pour a new slab or add insulation.
• Ceiling height — Garages often have ceiling heights below the 7-foot minimum required for habitable space. This can be a deal-breaker.
• Insulation and weatherization — Garage walls and roofs are typically uninsulated. Full insulation, vapor barrier, and finished walls are required.
• Egress — At least one bedroom egress window is required. The garage door opening is usually converted to a wall with windows.
• Parking replacement — If you convert your garage, you may need to provide replacement parking elsewhere on the lot.

Basement Apartments

Basement ADUs require careful attention to:

• Egress — Every sleeping room needs an egress window or door meeting IRC size requirements (5.7 sq ft minimum opening, sill no more than 44 inches above floor)
• Ceiling height — Minimum 7 feet for habitable rooms; beams can reduce to 6 feet 4 inches for limited areas
• Moisture control — Waterproofing, drainage, and ventilation are critical
• Separate entrance — Most ADU ordinances require an entrance that doesn’t pass through the primary dwelling

New Detached Construction

Building a new detached ADU gives you the most design flexibility but costs the most. Expect to hire an architect or designer, engineer the foundation, and manage a full construction project with all associated permits and inspections.

Short-Term Rental Considerations

If you’re considering using your ADU as a short-term rental (Airbnb, VRBO), research your local short-term rental regulations separately from ADU rules. These are typically two distinct regulatory frameworks:

• Indianapolis regulates short-term rentals through a registration and permitting process. Owner-occupied properties have different rules than non-owner-occupied. Since ADUs already require owner-occupancy, you may be able to rent the ADU short-term while living in the primary dwelling — but verify with DBNS.
• Carmel and some other Hamilton County cities have restrictive short-term rental ordinances that may prohibit or heavily regulate ADU rentals.
• Bloomington has its own short-term rental regulations influenced by the Indiana University rental market.

Zoning approval for an ADU does not automatically grant permission to operate it as a short-term rental. These are separate approvals in most jurisdictions.

Cost to Build an ADU in Indiana

ADU costs in Indiana are significantly lower than coastal markets but still represent a substantial investment:

ADU Type	Typical Cost Range
Basement conversion	$40,000–$80,000
Garage conversion	$50,000–$100,000
Above-garage unit (new construction)	$120,000–$200,000
Detached new construction	$100,000–$250,000+

These ranges assume mid-grade finishes and standard systems. Costs vary based on:

• Size — Cost per square foot typically runs $150–$300 for new construction
• Site conditions — Grading, utility distances, access for equipment
• Finishes — Basic vs. upgraded kitchen and bathroom fixtures
• Foundation type — Slab, crawl space, or full basement
• Utility connections — Shared vs. separate meters

Additional costs beyond construction:

• Permit fees: $200–$2,000+
• Architectural/design plans: $2,000–$10,000
• Survey: $300–$800
• Utility connection fees: $1,000–$5,000+
• Variance or special exception filing (if required): $200–$1,500

Steps to Get an ADU Permitted in Indiana

1. Check your zoning — Contact your local planning department to confirm ADUs are allowed on your property. Ask whether it’s a permitted use or requires a variance/conditional use permit.
2. Review the requirements — Get the specific size limits, setbacks, parking, and owner-occupancy rules for your jurisdiction.
3. Hire a designer — Work with an architect or residential designer to create plans that comply with local requirements and the Indiana Residential Code.
4. Apply for zoning approval (if required) — Submit your application for a conditional use permit, variance, or zoning certificate.
5. Submit for building permit — File your permit application with construction drawings, site plan, and any required documentation.
6. Obtain trade permits — Apply for electrical, plumbing, mechanical, and gas permits as needed.
7. Build and schedule inspections — Construction proceeds with inspections at each required stage (foundation, framing, rough-in, insulation, final).
8. Get your certificate of occupancy — After passing final inspection, you’ll receive a certificate of occupancy allowing the ADU to be occupied.

The entire process from initial zoning inquiry to certificate of occupancy typically takes 6–12 months in jurisdictions where ADUs are allowed by right, and 9–18 months where variance or conditional use approval is needed.

When to Hire a Permit Expediter

ADU permits are among the more complex residential permit projects because they involve both zoning and building code review. A permit expediter can help you navigate the process, especially if:

• Your jurisdiction requires a variance or conditional use permit
• You’re unsure whether your property’s zoning allows an ADU
• You want to avoid costly plan review rejections and resubmittals
• You’re converting an existing structure and need help identifying code compliance issues

An experienced expediter familiar with your local building department can save weeks of back-and-forth and help you avoid common pitfalls that delay ADU projects.