Bedford NH ADU Guide: What HB 577 Lets You Build

If you own a single-family home in Bedford, you have a right today that you didn't have two years ago: you can add a second, self-contained home to your property — including a detached backyard cottage — by right. No special exception, no discretionary board approval. That's New Hampshire's HB 577, effective July 1, 2025, and it quietly changed the math on nearly every single-family lot in town. Here's the practical Bedford NH ADU picture as it stands in mid-2026.

What the state law now guarantees

HB 577 rewrote RSA 674:72. Anywhere single-family homes are allowed, towns must permit at least one accessory dwelling unit — attached or detached — as a matter of right, subject only to the same building-permit and zoning standards that would apply to the house itself. Towns can no longer pile on extra lot-size minimums, setbacks, frontage, or design-review hurdles just because an ADU is involved. They can't cap an ADU below 750 square feet, and the default cap is 950 square feet unless the town allows more. They also can't require the ADU be connected to the house by an interior door, and they can't require that whoever lives in it be related to you.

The provision most Bedford homeowners miss: existing structures are protected for conversion. If a detached garage, barn, or carriage house stood on your lot on or before July 1, 2025, the town must allow you to convert it to an ADU even if it sits inside today's setbacks or exceeds lot coverage. For older Bedford properties with a garage tucked near the lot line, that's a grandfathered opportunity that new construction can't replicate.

Bedford's local rules on top of that

Bedford updated its ADU fact sheet in July 2025 to align with the new law. The local highlights: one ADU per single-family parcel; attached or detached both allowed; Bedford permits up to 1,000 square feet or 50% of the main home's floor area, whichever is less (state law means the 50% rule can't push you below 750). One of the two units must be owner-occupied — the town can't tell you which one. One parking space for the ADU using your existing driveway, no new curb cut. If you're on septic, NHDES must sign off on capacity for both units. No short-term rentals — nothing under 30 consecutive days, so no Airbnb. The ADU can never be condo-ed off separately, impact fees (roughly $1,100–$1,200) are due before occupancy, and a building permit is required. Note that some older Bedford requirements — like the 1.5-acre minimum for detached units — predate HB 577, which no longer allows lot-size requirements beyond what your zoning district demands of the house itself; confirm current application with the Planning Department at (603) 472-5243.

The 2026 numbers

Converting existing space (garage, walk-out basement, space over the garage) generally runs $80K–$150K in today's market. A new detached unit runs $150K–$300K+ depending on size, site work, and septic. On the income side, Bedford rents are among the strongest in southern NH: one-bedrooms average roughly $2,000–$2,300 a month and two-bedrooms around $2,500. A $200K detached ADU renting at $2,100 grosses about $25K a year — before you count what a legal second dwelling adds to resale value, or what it's worth to house aging parents or a boomerang kid in Bedford instead of paying for care or a second mortgage elsewhere.

Quick answers

Q: Can I build a detached ADU in Bedford NH?
A: Yes. Since July 1, 2025, state law (HB 577) requires Bedford to allow one attached or detached ADU by right on single-family lots, subject to standard building and dimensional rules. Bedford allows up to 1,000 sq ft or 50% of the main home, whichever is less.

Q: Can I convert my old garage even though it's close to the property line?
A: If it existed on or before July 1, 2025, yes — HB 577 protects conversions of existing structures even where they violate current setbacks or lot coverage. Confirm specifics with Bedford Planning.

Q: Can I rent my Bedford ADU on Airbnb?
A: No. Bedford prohibits rentals under 30 consecutive days. Month-to-month and longer leases are fine, and one unit must be owner-occupied.

Is your lot ADU-ready?

Every lot is different — septic capacity, driveway layout, and what's already standing on the property change the answer. Grab our ADU Feasibility Checklist, or just send me your address and The Phinney Team will run a free feasibility read on your property: what you could build, what it would rent for, and what it would do to your home's value. Call (603) 568-3399 or reach us through teamphinney.com.

This guide is general information, not legal advice. ADU rules change — Concord is rewriting its zoning code and towns across NH are still aligning ordinances with HB 577 — so confirm current requirements with the Bedford Planning Department before you design or build.

Sources

• Town of Bedford ADU Fact Sheet (rev. July 30, 2025)
• NH Municipal Association: The Revised Law on Accessory Dwelling Units 2025 (HB 577)
• McLane Middleton: How Do NH's ADU Law Changes Affect Property Owners? (April 2026)
• HB 577 bill text (RSA 674:71-72)
• Zumper: Average Rent in Bedford, NH and Apartments.com Bedford rent trends