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Family housing guide · 2026

In-law suites in New Hampshire: every option, priced honestly.

Keeping a parent close — without anyone giving up their independence — used to mean fighting your town for a variance. Since July 1, 2025, it doesn't: every single-family lot in NH can add one in-law unit by-right. Here's the full menu of ways to do it, and what each honestly costs.

The four ways to add an in-law suite

Detached backyard home (ADU)

$184,000+ · published all-in pricing

A complete private home in the yard — own entrance, kitchen, laundry, no shared walls. Maximum privacy and independence, strongest rental/resale value later. Single-level plans (no stairs) up to 950 sf by-right.

Best for: independent parents, long-term flexibility, future rental income.

Addition to the main house

Quoted per project

A new attached wing with its own kitchen and bath. Shortest walk to family, shared systems keep cost down, and NH's law can allow attached units beyond the detached cap in some towns.

Best for: daily-care situations and lots too tight for a detached unit.

Above-garage conversion

Quoted per project

Uses structure you already own — often the cheapest path to a legal second unit. The tradeoff is stairs, which matters for aging parents.

Best for: adult kids, caregivers, or rental income rather than elderly parents.

Basement in-law conversion

Quoted per project

Finishing existing space with egress, kitchen, and bath. Lowest construction scope, but light, ceiling height, and egress rules decide feasibility — we confirm all three before quoting.

Best for: tight budgets where the basement already has walk-out access.

All four are things we build — see services for the conversion paths and models for the detached homes.

The math families actually run

The comparison that decides this for most families isn't construction option A vs option B — it's an in-law home vs assisted living. The Genworth/CareScout Cost of Care survey put New Hampshire assisted living at a median of $89,175 per year (about $7,431/month) in its 2024 survey — a bill that recurs forever and builds nothing. Our 384 sf Barrington costs $184,000 once — roughly two years of assisted living — and at the end you own a second home on your land that can become a rental producing income later. See the rental math →

It's why our largest single-level plan — Ella's Retreat, 981 sf, 2 bed / 2 bath, $401,000 all-in — was designed the way it was: no stairs, two real bedrooms (one for a caregiver or grandkids), and a footprint that fits behind most NH homes.

What the 2025 law changed

Before: in-law apartments needed special exceptions, hearings, and a planner's goodwill — months of maybe. Now: NH RSA 674:71-73 makes one ADU per single-family lot a right, statewide. Detached units up to 950 sf, setbacks identical to your house's, no discretionary review for a compliant unit. The plain-English breakdown →

Common questions

Do I need a special permit for an in-law suite in NH?
Not for a compliant ADU. Since July 1, 2025, NH RSA 674:71-73 allows one accessory dwelling unit by-right on every single-family lot — no special permits, hearings, or discretionary review. You still pull a normal building permit; you just don't have to ask permission to have an ADU at all.
What's the difference between an in-law suite and an ADU?
"In-law suite" is the family name; "accessory dwelling unit" is the legal one. If it has its own kitchen, bath, and sleeping area, NH law treats it as an ADU — which is good news, because that's what the by-right law protects.
Detached or attached — which is right for aging parents?
Detached wins on privacy, quiet, and single-level living (no stairs); attached/conversions win on lowest cost and shortest walk to help. Most families choosing for a parent in good health pick detached single-level; families providing daily care often pick attached.
Do I need to live in the main house?
In most NH towns, no — but some towns still impose an owner-occupancy requirement, so we confirm your town's specific rule before you build.
What does a detached in-law home cost?
Our architect-designed detached models run $184,000 (384 sf, 1-bed) up to larger two-bedroom, two-bath single-level plans — every price published, all-in. Conversions and additions are quoted per project after a site look.
Does your lot qualify? Find out for free.

We check your parcel against the by-right law and your town's setbacks — no cost, no obligation.

Get a free zoning review