ADU rules in Lebanon

Section 610.A allows one ADU, attached or detached, on any lot holding a one-family or two-family dwelling, and the Article III use tables list "Accessory dwelling unit (ADU) per Section 610" as a permitted use in R-1, R-2, R-3, R-O, R-O-1, PB, RL-1 and RL-2, plus the Pattern Zones Overlay covering downtown Lebanon and downtown West Lebanon. Rural Lands Three (RL-3) is the one exception: an ADU there needs a special exception from the Zoning Board of Adjustment, exactly as a one-family dwelling does in that district. One design condition applies to detached units only: Section 610.B requires the building to maintain the principal building's architectural style, proportional mass, size and height so that it is not taller than the principal building, and only a special exception can allow a taller one. Section 610.F adds that any new or altered structure intended to be used as an ADU must sit behind the principal building's front building line, again waivable only by special exception. Since August 31, 2026 the detached category is wider than it was: 2026 NH Laws ch. 210 struck the clause that had classed a unit completely contained within a preexisting detached structure as attached, and Lebanon's Appendix A defines "ADU, Detached" by reference to RSA 674:71, III "as amended", so a unit inside an existing garage, barn or carriage house is now a detached ADU in Lebanon and Section 610.B reaches it. RSA 674:73, rewritten by 2025 NH Laws ch. 197 effective July 1, 2025, separately requires every New Hampshire municipality to permit one detached ADU.

The same Section 610.A grant covers an attached or internal unit: a basement or upper-floor conversion, an addition, or any other unit within or physically attached to the principal dwelling. Lebanon does not define "attached" itself; Appendix A adopts RSA 674:71, II "as amended", so the local meaning tracks the statute, and since August 31, 2026 that statute (amended by 2026 NH Laws ch. 210:1) reaches only a unit "within or attached to the principal dwelling unit". A unit completely contained within a preexisting detached garage or barn, which was an attached unit in Lebanon before that date, is now a detached ADU and picks up the Section 610.B design condition. Only one ADU is allowed per lot, and the underlying district's dwelling-unit density requirements do not apply to it. An ADU inside the principal building must have interconnected smoke and carbon monoxide alarms (Section 610.H), and RSA 674:72, III bars the city from dictating whether the unit's entrance is independent or through space shared with the principal dwelling.

Section 610.E scales the cap to the gross living area of the principal dwelling. If the principal unit is 1,500 sq ft or less, the ADU may be the greater of 750 sq ft or 65% of the principal unit. If the principal unit is over 1,500 but under 3,000 sq ft, the ADU is capped at 960 sq ft. If the principal unit exceeds 3,000 sq ft, the ADU may go above 960 sq ft so long as it stays within 33% of the principal unit; and on a parcel larger than 4 acres a detached ADU may reach 50% of the principal unit. On a two-family lot the same tiers are measured against the smaller of the two principal units. Gross living area is an Appendix A term: measured to exterior dimensions with a 7 ft minimum ceiling height, excluding garages, porches, decks, outside stairs and balconies, and including walk-out basement floor area with a 7 ft ceiling. Both Lebanon's 750 sq ft floor and its 960 sq ft standard sit at or above the RSA 674:72, VII limits (a 750 sq ft minimum the city may not go below, and a 950 sq ft state default).

Section 610.C requires the property owner to occupy one of the dwelling units as their permanent residence. The ordinance does not say which unit, matching RSA 674:72, VI, which lets a municipality require owner occupancy but not specify the unit. Enforcement runs through the deed: before the zoning permit issues, the owner must record an "Accessory Dwelling Unit Owner Occupancy Restriction" at the Grafton County Registry of Deeds in a form satisfactory to the Zoning Administrator, so prospective buyers are on notice of the prohibition against renting out both units, and the applicant pays the recording fees. A signed, recordable copy of the restriction and a check for the recording fees are part of the ADU Permit submission (Section 610.I.4 and I.5). A temporary leave of absence of up to one year is allowed, but during it the owner's unit may not be rented or occupied by anyone else. The 2025 statutory overhaul left this municipal option intact, so the requirement remains lawful.

Section 610.G requires one parking space for the ADU on top of the one space each principal dwelling unit already needs under the Section 607.1 Table of Minimum Off-Street Parking Requirements (1.0 space per one-family or two-family dwelling unit), and it lets the owner satisfy that space either on-site or at a legally dedicated off-site location. This mirrors RSA 674:72, IV, which caps a municipality at one additional space per ADU and guarantees the owner the on-site or off-site choice. Section 607.1.D separately allows the Planning Board to approve an "alternative parking solution" for residential uses under RSA 676:16-a. Inside the Pattern Zones Overlay, Section 411.5 states a minimum of one on-site parking space per dwelling unit, which reads more strictly than Section 610.G's off-site option. Two statewide ceilings sit above all of this: RSA 674:16, VII has barred any municipality from requiring more than one residential parking space per unit since September 13, 2025, and effective September 13, 2026 (2026 NH Laws ch. 329:1) it also bars requiring that the space be garaged. Lebanon's one space per dwelling unit plus one for the ADU sits inside both ceilings, and neither Section 607 nor Section 610 requires a garage anywhere.

In the eight districts where the Article III tables list it, an ADU is a permitted use approved administratively, with no public hearing. The owner files an ADU Permit application carrying the Section 610.I checklist (existing and proposed site conditions and parking plan, floor plans for all units and structures, a gross living area calculation for both the primary dwelling and the ADU, the signed recordable owner-occupancy restriction, a check for Registry recording fees, any NH DES Subsurface Systems Bureau septic approval, water and sewer connection applications, and an impact fee invoice acknowledgment). The Zoning Administrator must act within 30 days and issues the zoning permit if the application complies (Section 901.3); the building permit follows (Section 901.5). A Zoning Board of Adjustment special exception is needed only in three situations: an ADU in the RL-3 district, an ADU structure placed forward of the principal building's front building line (Section 610.F), or a detached ADU taller than the principal building (Section 610.B).

Section 610's purpose statement names rental income as an intended use, describing ADUs as a way "to offer small dwelling units as rentals to offset the expense of maintaining the dwelling", and nothing in Section 610 limits lease length or tenant relationship (RSA 674:72, VIII also forbids a familial-relationship requirement). What the ordinance does forbid, through the recorded owner-occupancy restriction, is renting out both units. Lebanon has no short-term rental ordinance, registration or licensing program: the city code on eCode360 contains no STR chapter, and its single mention of short-term rentals runs the other way (City Code Section 85-4.C bars the Health Officer from using the minimum housing standards chapter to "impose any additional restrictions on dwellings used as a vacation rental or short-term rental as defined in RSA 48-A:1, V"), and the zoning ordinance's only transient-lodging category is the "tourist home (or bed and breakfast facility)", which Appendix A defines as accommodations without kitchen facilities rented to ten or fewer transient guests for more than 12 days per year and which is allowed only by special exception in the residential districts. A self-contained ADU with a kitchen does not fit that definition, so short-term letting sits in unmapped territory; confirm with the Zoning Administrator before listing one. Selling the ADU off separately is not available: RSA 674:72, I prohibits subsequent condominium conveyance of an ADU apart from the principal dwelling unless the municipality allows it, and Section 610 does not.