ADU rules in Madbury, NH
Madbury is a Strafford County town between Dover and Durham.
Madbury is in our service area. This page covers what the town ordinance says about ADUs.
What’s allowed on your lot in Madbury.
Madbury’s ADU text, effective March 11, 2025, sends an ADU to the Planning Board for a conditional use permit, which the 2025 state law no longer allows for the first ADU.
- Size limit
- Max 50% of the principal dwelling's finished living area
- Where it can go
- Attached or detached
- Owner on site
- Owner must occupy the house or the ADU
- Parking
- Off-street parking for the combined needs of the house and ADU
- Approval
- Conditional Use Permit from the Planning Board, then building permit
- Water setback
- Shoreland overlay with no new structures: 300 ft Bellamy Reservoir, 100 ft Bellamy and Oyster Rivers, 75 ft other streams and ponds, 150 ft Little Bay
Allowed
- Attached or detachedADU is a subordinate unit within or attached to a single-family dwelling, or in a detached structure. Attached or detached allowed.Art. V §4.A, §4.C.1
- DesignADU must be secondary to a principal single-family dwelling, and its exterior should be consistent with the character or appearance of the house.Art. V §4.C.2-3
- LotThe ADU does not count as an extra dwelling unit for minimum lot size. It must meet all pertinent zoning and building requirements.Art. V §4.C.4, C.6
- How manyOne ADU per lot.Art. V §4.C.5
- SizeGross living area may not exceed 50% of the principal dwelling's finished living square feet. No fixed sq ft cap or minimum.Art. V §4.C.7
- ApprovalConditional Use Permit from the Planning Board (Article IV, Section 9). Application must show how the ADU meets §4.C with a photo of the house exterior and a sketch of dwelling locations, setbacks and parking. No building permit until all requirements are met.Art. V §4.C.8, C.12, §4.D
- ParkingOff-street parking to serve the combined needs of the house and ADU. No number given.Art. V §4.C.9
- SepticExisting, replacement or proposed septic must be certified by a licensed septic designer as adequate for the ADU under RSA 485-A:38.Art. V §4.C.10
- Owner on siteEither the principal dwelling or the ADU must be owner-occupied.Art. V §4.C.11
- ShorelandShoreland Protection Overlay District covers land within 300 ft of the seasonal high water level of the Bellamy Reservoir; 100 ft of the Bellamy and Oyster Rivers; 75 ft of other brooks, streams, ponds and public water supplies on USGS maps; 150 ft of the Little Bay Estuary shoreline and of tidal wetlands next to it. Prohibited inside: any structure (except fences, footbridges, catwalks, wharves as limited) and any on-site septic system. Separately, the Wet Area Conservation Overlay requires a 25 ft undisturbed buffer and a 75 ft building and septic setback from most wet areas (50 ft from poorly drained soils), and septic must be 100 ft from public water or permanent streams.Art. X §2, §4.B; Art. IX §5.A-B; Art. IV §4
- State lawThe town text requires a conditional use permit. Since July 1, 2025 the first ADU is allowed as a matter of right, and the town’s 50% cap cannot hold an ADU below 750 sq ft.RSA 674:72, I and VII
Not allowed
- Not allowedMore than one ADU per lot.Art. V §4.C.5
- Not allowedADU larger than 50% of the principal dwelling's finished living area.Art. V §4.C.7
- Not allowedAny structure or on-site septic system in the Shoreland Protection Overlay District.Art. X §4.B
- Not allowedSingle-family homes (and so ADUs) in the Commercial and Light Industrial zone.Art. VII §2.C (Change 6)
Read 2026-11-15 from Madbury Zoning Ordinances (Land Use Ordinances and Regulations, March 2017) with Changes 1-6 (Base book dated March 2017 (https://www.madbury.gov/media/451). ADU text = Change 5 to Article V, Section 4, effective March 11, 2025 (https://www.madbury.gov/media/2216). Change 6 (Article VII multi-family) listed with no effective date shown). Anything not listed here, we check with the Madbury land-use office for your lot.
Front, side and rear in Madbury.
NH RSA 674:71-73 (HB 577) - one attached or detached ADU by right on a single-family lot
Madbury's dimensional table, as printed in the ordinance.
| District | Front | Side | Rear | Lot / cover / height |
|---|---|---|---|---|
| GRAprimaryGeneral Residential and Agricultural DistrictArt. V §2.B, §3.A-F. GRA frontage 200 feet contiguous road frontage (Planning Board may reduce on curves, with a 200 ft wide setback line). | 50 feet | 15 feet | 15 feet | Single-family 80,000 square feet (two-family 120,000) · 25% of lot area (impervious improvements) · Height No general building height limit found in the zoning ordinance |
Verified 2026-11-15 against Madbury Zoning Ordinances (Land Use Ordinances and Regulations, March 2017) with Changes 1-6. Towns amend ordinances, so confirm with the land-use office before you build. Official source
ADUs in Madbury.
- How big can an ADU be in Madbury?
- Max 50% of the principal dwelling's finished living area, per Art. V §4.C.7 as read 2026-11-15.
- Does the owner have to live on the lot in Madbury?
- Owner must occupy the house or the ADU (Art. V §4.C.11).
- Can an ADU in Madbury be detached?
- Attached or detached, under Art. V §4.A, §4.C.1.