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Accessory Structures

ADU rules, shed permits, and garage conversion regulations.

The 120-square-foot shed is a fixture of American backyards because that is the classic permit-exemption threshold, though plenty of codes draw the line elsewhere. The exemption misleads in both directions. A small shed still has to obey setbacks, and a structure that skipped its required permit surfaces years later, at sale or after a storm claim.

Accessory dwelling units broke the old pattern. Several states, tired of local refusal, passed statutes that force approval of code-compliant ADUs, so the municipal ordinance now mostly implements what the legislature already decided.

All 50 States: Accessory Structures at the State Level

Each tile shows the strongest state-level rule for that state. Click a state to see its full statewide rules and how local cities are constrained.

Severity: Few Restrictions · Light Restrictions · Some Restrictions · Significant Restrictions · Heavy Restrictions

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What's Covered

ADU Rules

Rules for building accessory dwelling units (granny flats, in-law suites) including size limits, parking requirements, and owner-occupancy rules.

ADU Impact Fees

Impact fees, school fees, utility hookup charges, and waivers for ADUs. Many jurisdictions exempt ADUs under 750 sq ft from impact fees per state law.

ADU Owner Occupancy

Whether the property owner must live on-site to operate an ADU, deed-restriction requirements, and recent state-law changes lifting owner-occupancy rules.

ADU Rental Restrictions

Whether an ADU can be rented short-term (Airbnb), 30-day minimums, separate rental licenses, and long-term lease requirements.

Shed & Carport Rules

When a storage shed or carport needs a permit, the square-footage exemption thresholds, and the setback and height limits that apply either way.

Garage Conversions

Rules for converting a garage into living space, including whether you need to replace the lost parking and what building codes apply.

Tiny Homes

Zoning rules for tiny houses on wheels and foundations, including minimum square footage requirements and where they can be placed.

Frequently Asked Questions

Common questions about accessory structures in the United States.

What is an ADU?
An ADU, or accessory dwelling unit, is a secondary housing unit on a single-family lot, such as a backyard cottage, converted garage, or basement apartment. Many states have passed laws encouraging ADU construction to address housing shortages. Look up your city's rules →
Do I need a permit for a shed?
Most cities require a building permit for sheds over a certain size, commonly 120 square feet. Even smaller sheds must typically comply with setback and height rules, and some HOAs have additional restrictions. Look up your city's rules →
How big can a detached garage be?
Maximum detached garage size depends on your zoning district and lot size, but common limits range from 600 to 1,200 square feet. Height restrictions, setbacks, and lot coverage maximums also apply. Look up your city's rules →
Can I convert my garage into a living space?
Many cities now allow garage conversions, especially in states like California where ADU-friendly laws have streamlined the process. You will typically need building permits and must meet habitability standards for ventilation, egress, and insulation. Look up your city's rules →
Are tiny homes allowed as accessory structures?
Tiny home regulations vary widely. Some cities classify tiny homes on foundations as ADUs and allow them, while tiny homes on wheels may be treated as RVs and face stricter rules. Zoning, building codes, and minimum size requirements all factor in. Look up your city's rules →