In-law suites, wings and lower-level apartments

The difference is the kitchen and the door. An ADU is a self-contained unit with its own sleeping, cooking and sanitary facilities and its own entrance, directly outside or through a shared hall that meets building-code egress. A bedroom suite with its own bath and sitting room but no kitchen is part of the house: no second unit, no separation assemblies, just an addition.

If you want the real thing, the 2025 law protects it. A town can't require owner occupancy, can't limit who lives there by family relationship or age, and can't require a special permit for one ADU. Older family-only bylaws, like Peabody's Family Accessory Living Area and Danvers' Extended Family Living Area rules, can't be applied where they conflict.

On a New England house the natural form is an ell: a lower wing off the back or side, with its own roof and its own door, the way farmhouses grew. It keeps the front of the house intact and gives the in-law unit a garden of its own. Some bylaws write that in: Wenham wants an attached ADU to keep the look of a single dwelling, Hamilton matches roof pitch and materials with any new entrance on the side or rear, and Lynnfield puts new entrances on the side or rear.

An attached unit makes the building a two-family under the Residential Code. The units are separated by 1-hour fire-rated wall and floor assemblies, or 1/2-hour if the building is fully sprinklered. Walls run from the foundation to the underside of the roof sheathing, tight to the exterior walls, and whatever supports a rated floor carries an equal rating. That's why the tie-in between the old house and the new wing gets drawn in detail.

Heat, hot water, electric service and the sewer or septic can be shared or separate. A town can't require separate water, sewer or electric connections for a protected ADU, though the utility or a state board still can, and Swampscott and Nahant actually require shared service. Separate systems give each household its own thermostat and its own bill; shared systems cost less to install.

Alarms follow the two-family rules. In an unsprinklered building, each unit needs interconnected detectors on the stair side of any door to a shared stairway, and a shared basement needs its own interconnected detection.

A basement can be a very good in-law unit, if it can meet three things. Ceilings: habitable basement space needs at least 6 ft 8 in. Escape: every room that becomes a bedroom needs an emergency escape opening, which below grade usually means a window well. Water: no finish survives a wet foundation, so drainage and moisture come before drywall.

Two rules work in your favor. A basement with code ceiling height already counts toward the main house's gross floor area, which can raise your ADU size cap. And under the Stretch code, bringing existing basement space into conditioned area without changing the footprint or roofline doesn't trigger a HERS rating. If the house is already a two-family, though, adding a third unit is a change of occupancy under the Commercial and Existing Building Codes, a much bigger job.

Single-level living is the brief more often than not: a step-free entry, wide doors, a curbless shower, a bedroom close to the bath, light from two sides. None of it costs much when it's drawn in from the start, and all of it is expensive to add later. On septic, each new bedroom counts at 110 gallons per day and the house and unit are counted separately, so we check the system before we size the plan.

We walk the house, find where a wing or a lower level fits, model it in 3D against the existing rooflines, and price it line by line with allowances called out. Our current work includes a basement converted to an apartment in Gloucester. Permits are pulled by us; the schedule, daily photos and selections live in your private portal.