ADUs in New Hampshire: Why More Families Are Building Instead of Moving

A stat crossed my feed recently that stopped me: a record 25.2 million adults under 35 were living with their parents in 2025 — more than even the pandemic peak. And here's the part that surprised me most — roughly 70% of them had jobs. This isn't a story about people who can't find work. It's a story about affordability. The median home price hit $430,000 in 2025, up 34.4% from 2019, and median asking rent climbed to $1,673. People aren't failing to launch. They're doing the math and staying put.

I see a version of this constantly in Southern NH — grown kids who'd genuinely love their own space, aging parents who don't want to leave the community they raised their family in, families who need a caregiver close by but not underfoot. The old answer used to be: someone moves, or everyone crowds into one house and hopes for the best. There's a better option, and New Hampshire actually made it a lot easier to pursue a few years ago.

What NH's ADU Law Actually Says

Under RSA 674:72, New Hampshire municipalities are required to allow one accessory dwelling unit — attached or detached — as a matter of right on any lot zoned for a single-family home. That's a big deal: "as a matter of right" means a town can't put you through a discretionary approval process just because you want to build one.

Here's what the law actually locks in:

• Size: Living space is capped at 950 square feet, and towns can't restrict it below 750 square feet. That's real living space — a full one-bedroom, easily.

• Owner occupancy: Towns can require that the owner live in one of the two units, but they can't dictate which one. Verification has to be "reasonable" — not invasive.

• No family requirement: There's no rule saying the person living in the ADU has to be related to you. It can be a family member, or it can be a tenant.

• No bedroom limits. Municipalities can't cap the number of bedrooms in the unit.

• Parking: If a town requires parking for the main home, it can ask for up to one more space for the ADU — on-site or at a legally designated off-site spot, your choice.

• Conversions count. Turning an existing garage or other structure into an ADU is allowed, even if it doesn't meet standard setback rules.

In plain terms: if you own a single-family home in New Hampshire, you very likely have the legal right to add a second, fully separate living space on your property — no special hearing required.

Why This Matters Right Now

An ADU solves more than one problem at once, which is part of why it's gaining traction:

For multigenerational families, it means aging parents can live steps away instead of states away — with their own space, their own door, their own independence.

For grown kids, it's a genuinely different proposition than "moving back into your childhood bedroom." A real ADU has its own kitchen, bathroom, and entrance. It's their own place, on family land.

For homeowners looking for income, a legal, well-built ADU can be rented out — helping offset a mortgage in a market where affordability is stretched thin for everyone.

And because the state has already done the legwork of making this legal by right in most towns, the biggest remaining question isn't "can I?" — it's "who do I build it with?"

Who I'd Point You To

I've gotten to know Kinstruct, a Pembroke/Suncook-based builder that specializes specifically in ADUs and tiny homes here in New Hampshire — they're active in the aging-in-place and accessory dwelling space and know the design and permitting side well. If you're at the stage of "is this even realistic for my property," that's a great first conversation to have alongside one with me about the real estate and land side of it.

Is This Right for Your Property?

Not every lot is a perfect fit — septic capacity, lot size, and specific town requirements still matter even under the state law. But if you've got adult kids priced out of buying, parents you'd love to have closer, or just a mortgage you wouldn't mind help with, it's worth finding out what your property can actually support.

Reach out and I'll walk you through it — what your town allows, what a realistic budget looks like, and whether your lot has what it needs.