| Max size | 800 sq ft2021 text; not updated for 2025 law |
|---|---|
| Min size | 300 sq ft |
| Bedrooms | Not statedno bedroom cap found |
| Type | Attached or in a garagefree-standing ADU not recognized |
| Parking | 1 spacededicated off-street; off-site silent |
| Owner-occupancy | Requiredin either the ADU or the primary home |
| Short-term rental | Not stated |
| Utility connection | Tie into the existing electrical connection or choose a separate metersame statewide |
The July 2025 state law (RSA 674:71–73) overrides local ordinance language that conflicts with it — even language a town still has posted. Here's what that means in Dover:
State law since July 2025 entitles you to a detached ADU generally — not just a garage conversion. Dover's ordinance text only recognizes a detached ADU built inside an existing detached garage; a free-standing cottage-style ADU isn't defined as legal under that wording, but state law overrides the town's narrower definition. City staff have acknowledged the garage-only rule was slated to change, though no revised ordinance text confirming the fix has been located.
State law says the town can't deny you the choice of separate electrical service for your ADU. Dover's ordinance still requires the ADU and main house to share a single electric/water/sewer bill and treats separate metering as disqualifying — but state law overrides that.
State law says the choice of entrance location is yours. Dover's rule still steers your ADU entrance to the side or rear of the building unless you can prove it's physically impossible to do otherwise — treating a front entrance as a last resort — but state law overrides it.
Dover doesn't just permit your ADU once — you have to re-file and re-pay every single year to keep it legal, forever, which isn't something a regular house has to do. The new state law doesn't explicitly ban this kind of recurring paperwork, so whether it crosses a line is a question for a land-use attorney.
Dover's ADU rules (Zoning Ordinance §170-24, reproduced in full inside the City's own ADU application packet) allow one accessory dwelling unit by right — as a permitted use, not a special exception — in residential districts including R-12 and R-20 (and R-40, for a single ADU). The size window is 300 to 800 square feet, owner-occupancy of one of the two units is required (doesn't say which — compliant with state law), one off-street parking space is required, and a recorded restrictive covenant plus an annually-renewed Certificate of Use ($50 fee) are mandatory before a Certificate of Occupancy issues. Where Dover's ordinance — as written in the newest documents the city has published — falls short of the July 1, 2025 state law (RSA 674:71-73 as amended by HB 577), state law overrides it: (1) the ordinance only recognizes a detached ADU if it's built inside an existing detached garage, not a free-standing structure, but the state now guarantees a detached ADU generally; (2) it requires electric, water, and sewer to be metered on a single bill, but the state says you can't be denied separate electrical service; (3) it steers your ADU's entrance to the side or rear of the building unless relocating it there is 'physically impossible,' but the state says the entrance choice is yours. A fourth issue — the requirement to re-file and re-pay for a Certificate of Use every year, indefinitely — isn't clearly addressed by the state statute either way and would need an attorney's read. Notably, city zoning staff indicated in 2024 that Dover knew the garage-only detached rule and the 800 sq ft cap needed to change ('that would likely go to 950 sq ft'; 'detached ADU must have a garage is going away') — but the city's newest application, covenant, and certification forms still show the unrevised 2021 ordinance language, and no confirmation has been found that Dover has since updated its ADU ordinance to match state law. Until it does, the state-law floor controls wherever the two conflict. See conflicts[] for full citations.
Get a free personalized report for your address in Dover — including where the 2025 law works in your favor.
Get My Free Dover ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Dover's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — Dover allows one accessory dwelling unit by right in its residential zoning districts, and state law since July 2025 broadens that right beyond what the city's own paperwork describes. Under RSA 674:72 (as amended effective July 1, 2025), one accessory dwelling unit — attached or detached — is allowed by right on single-family lots statewide.
800 sq ft — 2021 text; not updated for 2025 law. State law doesn't let any town cap ADU size below 750 sq ft.
Attached or in a garage (free-standing ADU not recognized). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
1 space — dedicated off-street; off-site silent. State law caps what any town can require at one additional space, located on- or off-site at the owner's choice.
Required — in either the ADU or the primary home. Where owner-occupancy is required, state law lets the owner choose which unit to live in.