Accessory Dwelling Units — also called granny flats or in-law suites — let homeowners add a second living space to their property for aging parents, adult children, guests, or rental income. Florida law around them is shifting fast: a statewide bill that would require nearly every city and county to allow ADUs by right passed the Senate unanimously in February 2026, and it could take effect as soon as this summer. If you're considering an ADU on the Treasure Coast, the rules you check today may already be changing.

What Is an ADU, and What Can It Be Used For?

An ADU is a secondary, self-contained living space on a single-family property — with its own entrance, kitchen, and bathroom — that's smaller and separate from the main house. On the Treasure Coast, homeowners typically create one by:

  • Converting a detached or attached garage into living space
  • Building an apartment above an attached garage
  • Finishing a basement with a separate walk-out entrance
  • Constructing a new detached structure, if the lot allows it
  • Adding a smaller attached "junior ADU," such as a converted sun porch that shares some utilities with the main home

Where they're allowed, ADUs can house elderly parents, adult children moving back home, live-in caregivers, or renters — and many owners use rental income from an ADU to help offset their mortgage.A 1977 Stuart, FL residence shown with an original attached ADU

Florida's "Granny Flat Bill" Could Change the Rules Statewide

In February 2026, the Florida Senate unanimously passed SB 48 — nicknamed the "Granny Flat Bill" — which would require cities and counties statewide to allow ADUs on single-family-zoned lots without a public hearing, variance, or special exception, so long as the plans meet basic site requirements. The bill still needs House approval, but if it clears, local governments would have until December 1, 2026, to update their rules, with the law potentially taking effect July 1, 2026. Local governments could still restrict short-term (under 30-day) rentals of the ADU itself. 

This matters a lot locally because ADU rules vary sharply within Martin County. Always confirm current rules with the relevant planning department before you budget or design: City of Stuart Community Development at (772) 288-5315, or Martin County Growth Management for unincorporated areas.

Do ADUs Actually Increase Home Value?

Yes — the National Association of Realtors has found that a permanent ADU can add roughly 20% to 35% to a property's value, depending on the market and how the space is finished. Beyond resale value, the more immediate benefit for most owners is rental income or reduced housing costs for family, so it's worth running the numbers on your specific property rather than relying on averages alone.

Before You Build: A Quick Cost and Lifestyle Check

Do the math first. Add up permit fees, construction costs, and the resulting increase in your annual property tax bill, then compare that total to the rent you'd realistically expect. That tells you how long the ADU takes to pay for itself before it starts generating net income.

Think through how it fits your life, not just your finances:

  • Privacy vs. company — a renter on your property is a very different experience than an empty guest room. Be honest about which one you actually want.
  • Aging in place — some owners rent out a main house that's become too large or hard to maintain, and move into a smaller, more manageable ADU on the same lot, in the neighborhood they already know.
  • Adult children returning home — an ADU can keep family close while still giving everyone real privacy, which spare bedrooms rarely provide.
  • Caregiving arrangements — some owners trade reduced or free rent for help with maintenance or personal care, which can be more economical than paying for services separately.

Frequently Asked Questions

Can I build an ADU in Stuart, FL right now?
Yes. The City of Stuart currently allows ADUs on residential lots, with a maximum height of 30 feet, typical setbacks of 6 feet on the side and 10 feet at the rear, and one required parking space. Waterfront lots need additional South Florida Water Management District review.

Can I build an ADU in unincorporated Martin County?
Under current rules, unincorporated Martin County restricts ADUs mostly to nonresidential developments, capped at three per lot — more limited than Stuart's rules. This is likely to change if Florida's pending statewide ADU law takes effect, which would require the county to allow ADUs on single-family lots by right.

How much does it cost to permit an ADU in Stuart?
Estimated permit fees run $6,500–$14,700, not including construction, with a typical review and permitting timeline of 7 to 12 weeks.

How much value does an ADU add to a home?
According to the National Association of Realtors, a permanent ADU can add approximately 20% to 35% to a property's value, in addition to any rental income it generates.

Do I have to live in the main house to rent out an ADU in Stuart?
No. Stuart does not currently require owner-occupancy, meaning both the main home and the ADU can be rented to separate tenants.

Talk to a Local Specialist Before You Build or Buy

ADUs aren't the right fit for every property or every homeowner, but with Florida's rules potentially loosening statewide this year, now's a good time to find out what's actually possible on your lot. As an SRES® serving the Treasure Coast, I can help you evaluate a property's ADU potential — whether you're adding one to your current home or shopping for a property that already has the flexibility built in.

This post is by Eric Slifkin, REALTOR® at Keller Williams Realty serving South Florida's Treasure Coast. Reach Eric at 772-288-1765, or contact us today to schedule a no-obligation consultation. 

Sources: