Room addition, ADU or in-law suite: which should you build?

Ranges are our planning figures (updated October 2026), not quotes. Every project is priced after a site visit.

Choose a room addition when the new space has to be part of daily life in the house: a larger family room, a primary suite with a real closet and bathroom, a home office or a playroom. It shares the existing kitchen, heating and cooling and the front door, so it adds space without adding a second household.

An addition is the most widely allowed of the three. Every jurisdiction we work in permits additions on residential lots that meet the zoning setbacks and lot-coverage limits; there is no special ADU review, no owner-occupancy rule and no rental question. That makes it the simplest path in places such as Casselberry, which has no ADU ordinance, or Winter Park and Lake Mary, which allow only limited guest houses.

The trade-off is privacy. An addition cannot be rented as a separate unit, and if someone needs their own kitchen and entrance, an in-law suite or an ADU fits better. For what drives the price of an addition — size, foundation, roof tie-in and finishes — see the room addition cost guide.

An in-law suite is an attached addition designed for one person or a couple: a bedroom, an accessible bathroom, a sitting area and usually a private exterior door. It suits a parent or an adult child who wants privacy but will still share meals and the main kitchen.

The kitchen is the line to watch. An attached suite without a full kitchen is usually permitted as a room addition. Add a full kitchen and many jurisdictions treat it as an accessory dwelling unit, with their own size, occupancy and parking rules. Winter Park, for example, allows guesthouses for guests, staff or family but not with a kitchen or as a rental, and Lake Mary allows guest houses only in two districts and not for rent.

Because it is built like an addition, an in-law suite follows the room-addition planning range and timeline: about 3–5 months from permit to finish, as for other room additions. Accessibility features such as a curbless shower, grab-bar blocking and wider doorways are easiest to include at the design stage. More on in-law suites.

An accessory dwelling unit is a complete second home on the lot, attached, detached or converted from a garage, with its own kitchen, bathroom and entrance. It is the only one of the three that can house a separate household, and the only one that can be rented where the rules allow.

Florida law lets cities and counties adopt ADU rules but does not require them to (F.S. 163.31771), so the answer depends on your address. Inside Orlando city limits an ADU is a permitted use and long-term leases are allowed; unincorporated Orange County allows ADUs only on homestead property and bars rentals of 180 days or less; unincorporated Seminole County requires leases of at least 30 days and owner occupancy; Oviedo allows one per lot with a zoning permit. The full table is on ADU rules by city.

Inside the City of Orlando, the ADU Incentive Program can rebate up to $10,000 toward construction plus impact and permit fees when the unit is rented to a household at or below 120% of area median income for 12 of the first 24 months. Read the program conditions before you plan around it.

Our planning ranges: a room addition or attached in-law suite $40,000 – $120,000; an ADU or garage conversion $50,000 – $180,000; a second-story addition $150,000 – $300,000+. Size, the foundation, the roof tie-in, utilities and the kitchen and bathroom count decide where a project lands within its range.

A full kitchen is one of the biggest single items, which is one reason an in-law suite without one usually costs less than an ADU of the same size. A detached ADU also needs its own foundation, roof and utility runs, while a garage conversion reuses the slab and walls. For the full cost breakdown, see the room addition cost guide.

All three add assessed value. Under Florida's Save Our Homes rules the yearly increase in a homestead's assessed value is capped, but changes, additions and improvements are assessed at just value when they are added (F.S. 193.155). The county property appraiser sets the figure, so ask them how your project will be assessed before you commit to the size.

• Designing a full kitchen into a suite where ADUs aren't allowed. In a city without an ADU path, a second full kitchen can stop the permit; keep the suite as living space or check the rules first.
• Counting on rental income before checking the lease rules. Minimum lease terms, owner occupancy and homestead requirements differ between Orlando, Orange County, Seminole County and the smaller cities.
• Forgetting the septic system. Adding a bedroom to a home on septic can require the system's capacity to be reviewed before the permit is issued; homes in areas such as Black Hammock, Chuluota and Geneva are commonly on septic.
• Leaving accessibility to the end. A curbless shower, grab-bar blocking and wider doorways are cheap to include in the design and expensive to add later.
• Skipping the HOA. Many communities review additions and detached structures for rooflines, materials and color before the permit is filed.

• Who will live in the space, for how long, and do they need their own kitchen?
• Does my city or county allow an ADU on my lot, and does it require owner occupancy, homestead status or a minimum lease?
• How much of the yard can I give up, and where are the setbacks?
• Is the lot on septic or in a mapped flood zone?
• Does my HOA or architectural review board need to approve it, and how long does that take?

1. Check whether your city or county allows an ADU at your address, and on what terms — ADU rules by city.
2. Decide whether the space must connect to the house (addition), needs privacy but shares the kitchen (in-law suite), or must work as a separate home (ADU).
3. If rental income matters, confirm the minimum lease, owner-occupancy and homestead rules before design.
4. Set a budget against the planning ranges above, then book a site visit for a written, itemised estimate.