Straight answers
Which US states let you build a granny pod as of right?
There is no national list worth trusting, but several states have passed accessory dwelling unit statutes that oblige municipalities to permit a backyard home, and four of them are unusually clear. Washington requires jurisdictions planning under the Growth Management Act to allow up to two units per single-family lot inside urban growth areas and prohibits owner-occupancy requirements. New Hampshire allows one unit, attached or detached, as a matter of right, and bars municipalities from restricting it below 750 square feet. Montana requires at least one unit on single-family lots. California requires local agencies to permit them ministerially, which means without discretionary review. Everywhere else the decision sits with your city or county.
Figures verified against the sources below · September 9, 2026
01 — The longer answer
The four state statutes with the clearest mandates
Washington: up to two units, and no owner-occupancy condition
HB 1337, codified at RCW 36.70A.680 to .696, took effect in July 2024 with local compliance due by 30 June 2025. Inside urban growth areas it requires two accessory dwelling units per single-family lot, prohibits owner-occupancy requirements, and limits the conditions a city can attach. Washington also runs a factory-built insignia program through Labour and Industries, so a factory-built unit has a defined approval path to go with the zoning one.
New Hampshire: detached units, with protected floor area
HB 577 amended RSA 674:71 through 674:73 with effect from 1 July 2025. One accessory dwelling unit, attached or detached, is allowed as a matter of right in districts that permit single-family dwellings, and RSA 674:73 requires municipalities to permit one detached unit specifically. Municipalities cannot restrict the unit below 750 square feet of living space, with 950 square feet as the cap. Guidance published before mid-2025 understates this, so check the date on anything you read.
Montana: one unit required, but read the vehicle caveat
SB 528, at MCA 76-2-345, has required municipalities to allow at least one accessory dwelling unit on single-family lots since 1 January 2024. The caveat matters more here than the mandate: the statute does not legalize permanent occupancy of a tiny house on wheels or an RV. It obliges the city to permit a dwelling, and a unit titled as a travel trailer through the county treasurer is not one.
California: ministerial approval, and combined units from 2026
California requires local agencies to approve accessory dwelling units ministerially rather than through discretionary review, which is what removes the neighbourhood hearing from the process. Since 1 January 2026, when SB 543 amended Government Code section 66323, that obligation covers any combination of the listed units, so a single-family lot can take a converted accessory dwelling unit, a junior accessory dwelling unit and a detached new-construction unit of up to 800 square feet with four-foot side and rear setbacks. For permanent placement the reliable routes are a foundation-built unit under the California Residential Code, or a factory-built unit carrying the state insignia affixed before shipment.
The pattern across all four is the same: the state sets a floor your city cannot go below, and everything above that floor stays local. A state statute tells you the answer is probably yes; your municipality tells you what you can actually build. Our state guides publish the building code in force with the sources each figure was checked against, and say so where something is unresolved instead of guessing.
03 — Sources
Each figure above links to the authority it came from.
Washington HB 1337, RCW 36.70A.680 to .696: two accessory dwelling units per single-family lot inside urban growth areas, owner-occupancy requirements prohibited, effective July 2024 with local compliance due 30 June 2025
app.leg.wa.govWashington Department of Commerce accessory dwelling unit framework and HB 1337 compliance guidance
commerce.wa.govNew Hampshire RSA 674:71 to 674:73 as amended by HB 577, effective 1 July 2025: one unit attached or detached as of right, 750 square feet protected and 950 square feet as the cap, with RSA 674:73 requiring one detached unit
nhmunicipal.orgMontana SB 528, MCA 76-2-345, effective 1 January 2024: municipalities must allow at least one accessory dwelling unit on single-family lots
archive.legmt.govCalifornia HCD Accessory Dwelling Unit Handbook: ministerial permitting of accessory dwelling units by local agencies
hcd.ca.govCalifornia Government Code 66323(a), as amended by Stats. 2025, Ch. 520 (SB 543), effective 1 January 2026: a local agency shall ministerially approve a building permit to create any of the listed units or any combination of them, including one accessory dwelling unit and one junior accessory dwelling unit within a single-family dwelling and one detached new-construction unit of up to 800 square feet with four-foot side and rear yard setbacks
leginfo.legislature.ca.govSB 543 (2025), Chapter 520, approved 10 October 2025: the Legislative Counsel's Digest states the bill requires a local agency to ministerially approve a building permit application for a combination of the specified accessory dwelling units or junior accessory dwelling units
leginfo.legislature.ca.govCalifornia HCD Factory-Built Housing Insignia of Approval, affixed before shipment under Health and Safety Code 19980
hcd.ca.gov
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