Rockingham County · New Hampshire
ADU rules in Stratham, NH
Stratham is a Rockingham County town on the Squamscott River and Great Bay.
This is a reference guide. Stratham is not on our service-area list, so call to ask whether we can take on a build there.
Town ADU rules
What’s allowed on your lot in Stratham.
Stratham permits an ADU of 400 to 1,000 sq ft with a building and occupancy permit. Several of its town rules are stricter than the 2025 state law allows.
- Size limit
- 400 to 1,000 sq ft, max two bedrooms; a detached ADU is also capped at 50% of the house's gross interior area and a 1,000 sq ft building footprint
- Where it can go
- Inside the house or in an accessory structure (detached)
- Owner on site
- Owner must live in either unit
- Parking
- 2 off-street spaces per unit (house and ADU); no new curb cut
- Approval
- Permitted use (P) with building permit and occupancy permit; Planning Board hearing if compliance is uncertain
- Rentals
- No transient occupancy
- Water setback
- Shoreland district: 150 ft from Squamscott River / Great Bay (structures need a special exception); wetlands: 25 ft no-disturbance + 50 ft CUP setback
Allowed
- How manyNo more than one ADU on a legal lot approved for or developed with a detached single-family dwelling.§5.4.3
- Attached or detachedAn ADU may be inside the single-family dwelling or in an accessory structure (detached). The definitions section says ADUs may be built at the same time as the house.§5.4.3; §2.1.3
- ApprovalADU is a permitted use (P) in R/A, MAH, PRE, TC and Route 33 LHHD. A building permit and occupancy permit are required. If it is unclear whether an ADU meets the rules, the Code Enforcement Officer may send it to the Planning Board for a public-hearing decision.§3.6 Table of Uses A.10; §5.4.3; §5.4.5.b
- Owner on siteThe property must be owner-occupied, with the owner living in either unit.§5.4.3.a
- SizeADU must be 400 to 1,000 sq ft, with no more than two bedrooms.§5.4.3.d (Rev. 3/25)
- SizeA detached ADU cannot exceed 50% of the house's gross interior square footage or 1,000 sq ft. The footprint of the building housing it, including attached garages, porches and decks, cannot exceed 1,000 sq ft.§5.4.4.a
- DesignThe building and property must keep the look of a one-family dwelling. Any new entrance goes on the side or rear. Parking must look like a single-family layout.§5.4.3.c, f
- ParkingAt least 2 off-street paved or gravel spaces per unit (house and ADU), shown on the sketch plan. No new curb cut for the ADU.§5.4.3.f, h
- HeightA detached ADU may not exceed 1.5 stories or the height of the house.§5.4.4.e (Adopted 3/25)
- LotA new accessory structure with an ADU (built after March 8, 2022) may not be in the front yard. Structures existing before March 8, 2022 may be converted and are exempt from the front-yard and height rules if height is unchanged and footprint grows no more than 15%. No new garage or pool attached or adjacent to the ADU if one already exists.§5.4.4.b-c
- SepticBefore the certificate of occupancy, the owner must show septic is adequate for both units under Stratham and NH standards (septic designer certification if the inspector asks), and that potable water is adequate.§5.4.3.i.i
- OtherOnly one family may live in the ADU, at the occupancy set by the Building Ordinance. The house cannot be a mobile home or condominium.§5.4.3.e, j
- RentalsNo transient occupancy of an ADU.§5.4.5.d
- ShorelandShoreland Protection District overlay: land within 150 ft of the Squamscott River and Great Bay shoreline (and the upland edge of adjacent tidal marsh), and within 100 ft of the seasonal high water of USGS-mapped brooks and streams. Permitted uses there do not include erecting structures; a 75 ft natural vegetation strip along the river/bay/tidal marsh (50 ft elsewhere) applies. Structures need a ZBA special exception for pre-existing lots of record. Wetlands Conservation District: 25 ft no-disturbance buffer plus a 50 ft setback where all construction needs a Planning Board CUP. State RSA 483-B also applies.§12.5; §12.6.1.a; §12.6.4; §11.2.3-11.2.4
- State lawThe town text asks for 2 parking spaces per unit. State law allows a town to require at most one extra space for the ADU, and no more than one space per unit.RSA 674:72, IV; RSA 674:16, VII
Not allowed
- Not allowedConverting the ADU/lot to a condominium or separate ownership.§5.4.3.g
- Not allowedA new curb cut to serve the ADU.§5.4.3.h
- Not allowedADU where the house is a mobile home or condominium.§5.4.3.j
- Not allowedDetached ADUs in Residential Open Space Cluster Developments.§5.4.4.d
- Not allowedNew accessory structure with an ADU in the front yard (post-March 8, 2022 structures).§5.4.4.c
- Not allowedA new garage or pool attached or adjacent to the ADU if the parcel already has one.§5.4.4.b
- Not allowedTransient occupancy of an ADU.§5.4.5.d
Read 2026-11-15 from Town of Stratham Zoning Ordinance ('Adopted March, 1987 Last Amended March, 2026'; technical corrections May 20, 2026 (incl. §5.4.3 wording)). Anything not listed here, we check with the Stratham land-use office for your lot.
Setbacks
Front, side and rear in Stratham.
NH RSA 674:71-73 (HB 577) - one attached or detached ADU by right on a single-family lot
Stratham's dimensional table, as printed in the ordinance.
| District | Front | Side | Rear | Lot / cover / height |
|---|---|---|---|---|
| R/AprimaryResidential/AgriculturalTable 4.2; §4.3 notes (b),(c); §5.14. R/A frontage 200 ft continuous. R/A accessory buildings: Sheds ≤120 sf (no slab, ≤12 ft high, one per parcel): 5 ft side/rear, 15 ft from wetland, no permit (§5.14). | 30 ft (Route 33/108 lots: 10 ft from ROW or 20 ft from pavement, whichever greater) | 20 ft | 20 ft | 2 acres (duplex: 3 acres) · 20% (building cover); min 60% open space · Height 35 ft |
| MAHManufactured Housing/Mobile HomeTable 4.2; §4.3. MAH frontage 100 ft continuous. MAH accessory buildings: Same §5.14 shed rule. | 30 ft (note c) | 20 ft | 20 ft | 1 acre · 25% (building cover); min 50% open space · Height 35 ft |
| PREProfessional/ResidentialTable 4.2; §4.3 note (a); §3.11. PRE frontage 150 ft continuous. PRE accessory buildings: Same §5.14 shed rule; new accessory structures >100 sf need Planning Board review (§3.11.4). | 30 ft | 20 ft (30 ft where abutting residential uses/district) | 20 ft (30 ft where abutting residential) | 1 acre (duplex: 1.5 acres) · 30% (building cover); min 50% open space · Height 35 ft |
| TCTown Center§3.9 Town Center Tables 1-3. TC frontage Not given as frontage; frontage buildout 70% max. TC accessory buildings: Not specified. | Frontage setback 8 ft min / 25 ft max (residential) | 10 ft min | 10 ft min | 15,000 sf minimum (soil-based lot sizing unless public water/sewer) · Not given (8,000 sf max building footprint for single/two-family) · Height 2.0 stories max (single- and two-family) |
| LHHDRoute 33 Legacy Highway Heritage DistrictTable 4.2; §4.3 notes (i),(j) (Adopted 3/26). LHHD frontage 150 ft continuous. LHHD accessory buildings: Same §5.14 shed rule. | Within 10 ft of the average of abutting front setbacks, never required beyond 35 ft (note i) | 20 ft | 20 ft | 2 acres · 10% (building cover); single-family footprint incl. accessory structures max 3,000 sf (note j) · Height 35 ft |
Verified 2026-11-15 against Town of Stratham Zoning Ordinance. Towns amend ordinances, so confirm with the land-use office before you build. Official source
FAQ
ADUs in Stratham.
- How big can an ADU be in Stratham?
- 400 to 1,000 sq ft, max two bedrooms; a detached ADU is also capped at 50% of the house's gross interior area and a 1,000 sq ft building footprint, per §5.4.3.d (Rev. 3/25) as read 2026-11-15.
- Does the owner have to live on the lot in Stratham?
- Owner must live in either unit (§5.4.3.a).
- Can an ADU in Stratham be detached?
- Inside the house or in an accessory structure (detached), under §5.4.3; §2.1.3.
Planning an ADU in Stratham?
Call (978) 987-0089 and we will say whether we can build there. See the ADU models