| Max size | 950 sq ftup to 1,250 sq ft in some cases |
|---|---|
| Min size | No town minimum'no minimum floor area requirement' |
| Bedrooms | Not statedold 2-bedroom cap appears dropped |
| Type | Attached or detachedincl. nonconforming conversions |
| Parking | 1 space for the ADUmay be at an off-site location |
| Owner-occupancy | Not requireddropped in the 2025 rewrite |
| 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 Concord:
State law bars any ADU size cap below 750 sq ft, and Concord's old, pre-amendment ordinance capped ADUs at 750 sq ft with a 600 sq ft minimum. That old rule is now superseded — Concord's own October 2025 amendment raises the cap to 950 sq ft (up to 1,250 in some cases) and drops the minimum entirely. If you see the 750/600 numbers anywhere (an old Municode cache, an old city handout), they're outdated.
State law caps what a town can require at one additional parking space for the ADU, with the owner choosing on-site or off-site. The old ordinance's "2 spaces plus 1 per bedroom" rule directly violated that cap. Concord's own October 2025 amendment already fixes this — it now requires just 1 space for the house and 1 for the ADU, with the ADU's space allowed off-site.
State law gives the homeowner the choice of an independent entrance or shared access. The old ordinance effectively forced a shared interior doorway — that's gone in the October 2025 amendment, which now explicitly leaves the choice to you.
State law says an ADU can't be held to stricter design review than an ordinary single-family home. Concord used to require a special Planning Board design review specifically triggered by having an ADU; the October 2025 amendment strikes that trigger (Section IV) — ADUs are no longer singled out for extra design review.
Concord used to require proof you lived in one of the two units. That requirement doesn't appear in the October 2025 amendment's rewritten section — it looks like the city voluntarily dropped it. This isn't a state-law conflict (state law allows, but doesn't require, an owner-occupancy rule), just a town-level change worth double-checking directly with the Code Administrator before relying on it.
This isn't a conflict with state law — it's a documentation gap. The text of the October 2025 amendment is available, but formal City Council adoption could not be confirmed. If it HASN'T been adopted yet, the pre-2025 ordinance (with the 750 sq ft cap, 2-space-plus-per-bedroom parking, common-wall rule, etc.) is technically still on the books, though RSA 674:71-73 as amended by HB 577 is self-executing statewide law regardless — meaning Concord homeowners get the state-law floor (950 sq ft, 1 extra parking space, choice of entrance) even if the city's own code text hasn't caught up. Confirm adoption status with David Hall (Code Administrator) before relying on the amendment's exact numbers.
Concord's Code of Ordinances, §28-5-52, was substantially rewritten in an October 2025 city amendment. The rewritten section closely tracks the new state law (RSA 674:71-73 as amended by HB 577, effective July 1, 2025): ADUs — attached or detached — are allowed by right in any district that allows single-family homes; the floor-area cap is 950 sq ft (extendable up to 1,250 sq ft or 50% of the main house, whichever is less) with no stated minimum; parking is capped at 1 space for the house plus 1 for the ADU, and the ADU's space can be off-site; attached ADUs can have either a shared or independent entrance; existing nonconforming structures (like a detached garage that doesn't meet setbacks) can still be converted to an ADU as long as the conversion doesn't make the nonconformity worse; and the old mandatory owner-occupancy documentation and mandatory Architectural Design Review trigger both appear to have been dropped. Two important caveats for a homeowner: (1) the PRE-amendment ordinance text (the 2017-era rules: 750 sq ft cap, 2-parking-spaces-plus-one-per-bedroom, mandatory shared interior door, mandatory owner-occupancy proof) still appears in older captures of the city code and may survive in old city handouts — if you find that language anywhere, it's superseded, both by Concord's own amendment and by state law; (2) the amendment document itself doesn't show a filled-in adoption date, so it's worth confirming with the city that it's actually in force before relying on the exact numbers — though the state-law floor applies either way. Permitting runs through Concord's EnerGov self-service portal; a Certificate of Occupancy for a new ADU requires passing building/mechanical/electrical/plumbing inspections, a water/sewer connection (or private test results), a blower-door test (≤3.0 ACH), a fire life-safety inspection, and payment of all invoiced impact fees before occupancy. Key city contacts: Rose Fife, Inspector (RFife@concordnh.gov, 603-225-8580) and David Hall, Code Administrator (DHall@concordnh.gov, 603-230-3647); Planning 603-225-8515; Engineering 603-225-8520; Fire 603-225-8650.
Get a free personalized report for your address in Concord — including where the 2025 law works in your favor.
Get My Free Concord ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Concord's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — Concord allows one accessory dwelling unit (attached or detached) by right in every district that permits single-family homes. 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.
950 sq ft — up to 1,250 sq ft in some cases. State law doesn't let any town cap ADU size below 750 sq ft.
Attached or detached (incl. nonconforming conversions). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
1 space for the ADU — may be at an off-site location. State law caps what any town can require at one additional space, located on- or off-site at the owner's choice.
Not required — dropped in the 2025 rewrite. Where owner-occupancy is required, state law lets the owner choose which unit to live in.