ADU rules in Concord

Concord repealed its old attached-only ADU rule and re-enacted Section 28-5-52 on October 14, 2025 (Ord. No. 3186, Sec. III) to track the amended state statute. Subsection (b) provides that ADUs, 'which may be either attached or detached, shall be allowed as a matter of right in all zoning districts that permit single-family detached dwellings by right as set forth in Section 28-2-4(k) of this ordinance.' The Table of Accessory Uses carries a matching 'P' for Accessory Dwelling Unit in RO, RM, RS, RN, RD, RH, CN, CVP, IS and UT, exactly the ten districts where a single-family detached dwelling is itself permitted by right, so a detached backyard unit needs no hearing anywhere it is allowed. Two limits survive: the ADU must be accessory to a single-family detached dwelling and cannot go on a lot holding more than one principal dwelling, and manufactured housing may not be used as an ADU.

The same sentence in Section 28-5-52(b) allows attached and internal ADUs as of right in those ten districts. Subsection (g) requires only that an attached ADU have 'either an independent means of ingress and egress or ingress and egress through a common space shared with the principal dwelling,' which replaced the interior-door mandate the state repealed in 2025. Subsection (k) separately allows ADUs converted from existing structures even where the structure already violates setback, lot coverage or height rules, provided the conversion does not worsen the nonconformity, so basement and addition conversions run through the same by-right path as new construction. One labelling wrinkle: since August 31, 2026 a unit built entirely inside a preexisting detached garage or barn is a detached unit under RSA 674:71 as amended, while Concord's Glossary still files it under 'Attached accessory dwelling unit.' Nothing practical turns on which label applies, because subsection (g) is the only attached-only requirement in the section and Concord sets no detached-only standard.

Section 28-5-52(i) states there is 'no minimum floor area requirement for an ADU' and sets the maximum at 950 square feet, matching the state default in RSA 674:72, VII. The cap then scales up for bigger houses: it 'may be increased so that it is either up to fifty (50) percent of the floor area of the principal single-family detached dwelling or one thousand two hundred fifty (1,250) square feet (whichever is less).' A 2,500 square foot house supports the full 1,250 square foot ADU; a small house still gets at least the 950 square foot baseline. Both figures are measured under the Chapter 28 Glossary definition of Floor Area, 'the total gross area on all floors as measured to the outside surfaces of exterior walls, excluding crawl spaces, garages, carports, breezeways, attics without floors, open porches, balconies and terraces.' Concord sets no ADU-specific height or setback standard, and RSA 674:72, I bars it from adding lot size, setback, frontage or design review requirements beyond what the single-family dwelling alone would face.

Concord does not require anyone to live on site. Ordinance No. 3186, Sec. III repealed the former Section 28-5-52, which dated from the city's May 2017 response to the original state ADU act, and the twelve subsections of the replacement contain no owner-occupancy or principal-residence clause. Reading the rest of Chapter 28, including the Glossary, the Article 28-2 use tables, Article 28-7 parking and Article 28-9 administration, turns up no such condition either: the only owner-occupant requirement anywhere in the zoning chapter belongs to major home occupations under Sec. 28-5-30. This is Concord's own policy choice rather than state preemption, since RSA 674:72, VI still permits a New Hampshire municipality to require owner occupancy of one of the two units, so neighboring towns may differ.

Section 28-5-52(j) requires 'a minimum of one parking space ... for the principal single-family detached dwelling unit and one parking space ... for the ADU,' so the pair needs two spaces between them, one per dwelling unit. That is both the ceiling RSA 674:72, IV allows (at most one additional space per accessory unit) and the ceiling RSA 674:16, VII has imposed since September 13, 2025, under which a local legislative body 'shall not require more than one residential parking space per unit.' The general Table of Off-Street Parking Requirements at Section 28-7-2(e) still prints two spaces per dwelling unit for a single-family detached dwelling, but that number is preempted for residential units and does not reach ADUs in any event, because the table lists principal uses only and has no accessory dwelling unit row; on August 19, 2026 the Planning Board voted 8-0-0 to recommend the City Council cut every residential row of that table to one space. Nothing in Chapter 28 requires the space to be covered or garaged, which 2026 N.H. Laws ch. 329 bars municipalities from requiring as of September 13, 2026. The ADU space may be placed at a legally dedicated off-site location, though Concord routes off-site parking through a Planning Board conditional use permit under Section 28-7-11(a).

The Table of Accessory Uses marks Accessory Dwelling Unit 'P' in each of the ten districts where it is listed, and Section 28-2-4(a) defines 'P' as 'a use permitted by right in that district.' No special exception from the Zoning Board of Adjustment and no conditional use permit from the Planning Board is required, which is what RSA 674:72, I has demanded since July 1, 2025. Review is administrative: under Section 28-9-2(b) the Deputy City Manager for Development, or a designee, verifies zoning compliance in conjunction with issuing the building permit, and applications are filed through the city's Citizen Self Service permit portal. The one discretionary step that can surface is off-site ADU parking, which needs a Planning Board conditional use permit.

Nothing in Section 28-5-52 or elsewhere in Chapter 28 limits who may occupy an ADU or for how long, and because the October 2025 rewrite dropped owner occupancy a Concord owner may rent out both the house and the ADU. Ownership cannot be split: Section 28-5-52(f) prohibits condominium subdivision and states the principal dwelling, ADU and lot 'shall not be converted to a condominium or any other form of legal ownership distinct from the ownership of the principal single-family detached dwelling.' Section 28-5-52(l) requires the ADU to carry its own address and mail receptacle. We located no short-term rental licensing or registration scheme in Concord's code: a full-text scan of Chapter 15 (licensing of businesses, trades and occupations), Chapter 27 (housing maintenance and occupancy) and Chapter 28 at the current supplement returns no short-term, transient or vacation rental provision, and only rooming houses require a separate permit. Hotels and other lodging facilities remain a distinct use category that is not allowed in the residential districts where ADUs are permitted.