Buying a House That Works for Three Generations

Multi-generational households — parents, adult children, and often grandchildren under one roof — are a meaningful share of buyers in Greater Boston, driven by the cost of housing, the cost of eldercare, and cultural expectation. The housing stock accommodates it unevenly, and the right structure depends on which problem you are actually solving.

Four ways to do it

A house with a genuine in-law setup. A separate entrance, a bedroom and bathroom on the first floor, and ideally a kitchenette. The best of these are purpose-built or professionally converted with permits. The worst are a finished basement with a hotplate and no egress window, which is neither legal nor safe.

A two-family house. Two fully separate legal units. Maximum independence, and if the arrangement ends, the second unit rents. In much of Greater Boston — Medford, Malden, Quincy, Somerville, Waltham — two-families are a substantial part of the housing stock rather than an exotic option. More on multi-family here.

A single-family with an accessory dwelling unit added. Newly much more feasible: the Affordable Homes Act of 2024 allows ADUs of a defined size by right in single-family districts statewide, subject to the conditions in the statute. That removed the special-permit hurdle that had made this impractical in many towns. What the ADU law changed.

A large single-family with flexible space. No separate unit, but a first-floor bedroom and full bath, a second living area, and enough separation that people are not on top of each other. Often the simplest and the easiest to resell.

What to check before you buy

Is the existing in-law setup legal? This is the question. A second kitchen in a single-family district may or may not be permitted, and an unpermitted apartment is a liability that transfers to you — it can affect financing, insurance, and your ability to sell. Ask the building department for the permit history and ask directly whether the configuration is lawful. Do not accept a seller's assurance.

Egress. Every sleeping room needs a compliant means of escape. Basement bedrooms frequently do not have one. This is a life-safety issue before it is a code issue.

Ceiling height and headroom in basement conversions, which is often what makes an otherwise workable space non-compliant.

Heating zones. Separate zones and separate thermostats prevent the most common daily friction in shared houses.

Sound. Between floors especially. Insulation between levels is inexpensive during a renovation and impossible afterwards.

Parking. Count the cars honestly, then check what the town requires and what the driveway actually holds in winter with snowbanks.

Ageing in place

If the arrangement exists because a parent is joining the household, design for the next fifteen years:

A full bathroom and a bedroom on the entry level, so the stairs are not load-bearing for daily life.
At least one step-free entrance, or one that can be ramped.
Doorways wide enough for a walker or wheelchair — 32 inches clear is the working minimum.
A curbless or low-threshold shower, and blocking in the walls for grab bars even if you do not install them yet.
Lever handles rather than knobs, and good lighting on stairs and at every threshold.

None of this reads as institutional when it is done well, and all of it is far cheaper designed in than retrofitted.

The financing and ownership questions

Two-family and ADU purchases have real financing implications. Some loan programmes allow projected rental income from a second unit to help you qualify; a legally separate unit changes how the property is underwritten and appraised.

More importantly, decide the ownership structure before you buy, in writing. Who is on the deed? Who contributes what to the down payment, the mortgage, the tax and the maintenance? What happens if one party wants out, or dies, or needs care?

Families avoid these conversations and it is exactly why multi-generational arrangements go wrong. Have them with an attorney present, once, at the start. The estate planning considerations apply directly here, particularly around how title is held.

Which towns work

Two-family stock concentrates in the denser communities — Medford, Malden, Somerville, Quincy, Waltham. Larger single-family homes with the space for an ADU are more common in the outer MetroWest towns. Which fits depends on whether you want two legal units or one house with flexibility.