Accessory Dwelling Units (ADUs) and Homestead Exemptions: Tax Rules for In-Law Suites and Granny Flats

Accessory dwelling units (ADUs)—also known as in-law suites, granny flats, casitas, or carriage houses—have surged in popularity nationwide. Whether built as a detached backyard cottage, a converted garage, or an attached basement suite, ADUs offer flexible living arrangements for multigenerational families and supplemental rental income.

However, homeowners adding an ADU face complex property tax questions: Does having a secondary dwelling on your parcel jeopardize your primary residence homestead exemption? And what happens when an ADU is rented out to a tenant versus occupied rent-free by an aging parent?

Does an ADU Disqualify Your Homestead Exemption?

In general, building an ADU does not disqualify your entire parcel from receiving a homestead exemption, provided you continue to occupy the primary main house as your permanent domicile.

However, how the county appraiser treats the ADU portion of your property depends entirely on how the secondary unit is used: for family residential use or for commercial tenant leasing.

Commercial Proration: What Happens When You Rent Out an ADU?

When an ADU is leased to a third-party tenant for rental income, state appraisal rules require the assessor to prorate the parcel into residential exempt and commercial non-exempt portions.

For example, in Florida, if you rent your detached backyard cottage to a long-term tenant, the county appraiser will maintain your full homestead exemption and Save Our Homes assessment cap on the primary house, but remove homestead benefits from the square footage and land allocated to the rental ADU. That rental portion is assessed at full market value and taxed at non-homestead rates.

Multigenerational Family Use: The Caregiver Exemption

If an ADU is occupied by family members—such as aging parents or adult children—without commercial rent, the entire property typically retains its full residential status.

Furthermore, some states offer dedicated tax breaks for constructing living quarters for elderly relatives:

Under Florida Statutes § 196.075, counties are authorized to provide a dedicated exemption for the reduction in assessed value resulting from the construction or reconstruction of property to provide living quarters for a parent or grandparent who is 62 years of age or older. The exemption covers the entire value of the addition, up to 20% of the home's total assessed value.

How Building an ADU Affects Assessment Caps

Building an ADU is classified as new construction under state tax law. The capital cost of building the ADU pierces existing assessment caps on that new square footage.

When the ADU receives its Certificate of Occupancy, the appraiser determines the market value of the new accessory structure and adds it to your assessment baseline outside the cap. In subsequent years, the ADU becomes capped along with the rest of the property.

Short-Term Rentals (Airbnb) vs. Long-Term Tenants

Renting an ADU as a short-term vacation rental carries acute property tax risks. In states like Florida, renting an accessory unit or rooms on Airbnb for more than 30 days per year for two consecutive years can cause the county appraiser to deem the exemption abandoned on that portion of the property, triggering severe audit clawbacks.

ADUs provide extraordinary utility and housing flexibility, but planning for their property tax implications is vital. Consult your county property appraiser before finalizing rental arrangements to ensure your primary homestead exemption remains secure.