Designing a Home for Multiple Generations

The first decision in a multigenerational home is not how many bedrooms you need; it is whether the second household needs a private suite inside the house, a private wing with its own entrance, or a fully separate dwelling. Those three arrangements produce completely different plans, different budgets, and different approval paths, and almost every problem we see in a multigenerational project traces back to picking a floor plan before answering that question. The honest way to work it out is to describe an ordinary Tuesday evening. Is everyone eating together, or is one household making their own dinner? Does a grandparent want to watch television at ten at night without being in the family room? Is anyone expecting to have friends over independently? The answers point at an arrangement quickly, and once you have that, the plan follows. This article is part of our custom home design guide.

A suite inside the house is the cheapest and least private, a private wing is the usual compromise, and a separate dwelling is the most expensive and the only one that gives everyone a genuinely separate life. The suite is a bedroom, a full bathroom, and often a sitting area, opening off the main house. It works well when the second household wants company more than independence, and it is by far the least expensive because it shares everything. The private wing adds an exterior door, a small kitchenette or wet bar, and a deliberate sound barrier between zones, so the two households can go days without crossing paths inside the house if they choose. That is what most of our clients end up building. The separate dwelling gives everyone a real front door and complete independence, and it prices like the small house it is, in the custom home band of $250 to $400 per finished square foot excluding land. There is detail on that path in ADU cost in Boise.

A separate exterior entrance changes the psychology of the arrangement more than any other single element, and it is cheap to include at design. Without one, every arrival and departure is an announcement, every visitor passes through someone else's living room, and the second household ends up feeling like long-term guests. With one, they come and go on their own terms. The details matter. The door should have its own sheltered approach, ideally with a covered landing so someone is not fumbling for keys in January weather, and it should be reachable from parking without crossing the main entry sequence. A path with no steps, or a gently graded walk rather than a ramp, is worth planning at the grading stage when it costs nothing to arrange. If the wing sits at the back of the plan, think about how a delivery driver or a visiting friend finds it, because an entrance nobody can locate does not function as an entrance.

Get the sound separation right before drywall and it costs very little; try to fix it afterwards and it is a demolition project. This is the part of multigenerational design that gets skipped most often and generates the most regret. The wall between the two zones should be a double or staggered stud assembly, so the drywall on one side is not physically connected through the same framing to the drywall on the other, with the cavity filled with insulation. Then seal it properly, because sound follows air, and a wall with a beautifully insulated cavity and an unsealed gap at the top plate performs like a much cheaper wall. Use solid-core doors with real seals rather than the hollow doors that come standard. Avoid stacking a bathroom, a laundry, or a stairway directly above a bedroom, and if the plan forces it, insulate the floor cavity and isolate the plumbing from the framing. Waste pipes running through a shared wall are a specific offender and easy to route elsewhere on paper. None of this is exotic construction. It is ordinary work done deliberately at the right moment.

Put the second household's sleeping and bathing on the ground floor, even if the rest of the plan is two storeys. The reason a family builds this kind of house is usually that stairs are already a concern or are about to become one, and a beautiful suite on the second floor is a suite with a countdown on it. A main-floor suite with a full bathroom, a genuine closet, and an egress window is also the most flexible room in any plan. Before anyone moves in it is a guest room and an office; afterwards it is a bedroom; later it is whatever the household needs. Size it so a queen bed, a chair, and a dresser fit without the room feeling like a hotel, and give it a window on more than one wall if the elevation allows, because a room with light from two directions feels twice its size. Where the suite lands in the plan matters too, and the general principles are in floor plan ideas that work in Treasure Valley homes.

Most multigenerational homes work best with one full kitchen and one good kitchenette rather than two full kitchens. A kitchenette with a sink, an under-counter refrigerator, a microwave or a small oven, and enough counter to make a meal covers the actual need, which is not cooking Thanksgiving twice. It is being able to make breakfast, make coffee at whatever hour you wake up, and heat lunch without being in someone else's kitchen. It costs a fraction of a second full kitchen and takes far less floor area. There is also a regulatory dimension. A second full cooking facility, combined with a separate entrance and a bathroom, is what many jurisdictions use to define an accessory dwelling unit, which brings size caps, setbacks, parking, and sometimes owner-occupancy requirements into scope. That may be perfectly fine, and in some cases it is exactly what you want, but it needs to be a decision rather than an accident discovered during plan review. We confirm the definition for the specific zone before the plan is finalised.

Duplicate the things people use daily and share the things they use monthly. Laundry is the honest test case. Sharing a laundry sounds reasonable until two households are negotiating over a washer at nine at night, and a second stacked washer and dryer inside the private zone costs a small amount of floor area and a plumbing and electrical rough-in. It is one of the cheapest sources of goodwill in the whole project. The same logic applies to storage. Give the second household somewhere to put suitcases, holiday boxes, and the furniture they could not part with, because otherwise those things end up in the shared garage and become a source of friction. Conversely, a second garage bay is usually unnecessary if parking is available, and a second dishwasher in a kitchenette rarely earns its space. The rule we use is simple: if the item gets used every day, duplicate it; if it gets used a few times a year, share it.

Accessibility looks institutional when it is added to a house that was not planned for it, and invisible when it is built into the geometry. Wider doors and hallways do not read as accessible; they read as generous, and they make moving furniture easier for everyone. A curbless shower with a linear drain and a frameless glass panel is a contemporary detail that happens to be rollable. Lever handles look better than knobs. A comfort-height toilet is standard now. Blocking in the walls around the toilet and shower for future grab bars costs a sheet of plywood and thirty minutes at framing and is completely invisible until the day it is needed, at which point it saves opening a tiled wall. Lighting is the underrated one: older eyes need considerably more light than younger ones, and layered lighting with good task levels and no glare does more for daily function than most of the hardware. The full list is in building a home you can age in.

The line between a large house with a private wing and a house with an attached accessory dwelling unit is drawn by local zoning, and it usually turns on the kitchen, the entrance, and the bathroom. If your plan has all three inside the private zone, expect the jurisdiction to look at it as an accessory dwelling. Boise, Meridian, Eagle, Kuna, and Star permit through Ada County; Nampa, Caldwell, and Middleton through Canyon County; and unincorporated land follows its own rules. Size caps, parking, and occupancy conditions differ across all of them. On a rural parcel there is an additional constraint: the septic system is permitted for a specific number of bedrooms, and adding sleeping space adds load, which is a Central District Health question and can require an expanded drainfield. None of these are reasons to abandon the plan. They are reasons to ask early, because the answer sometimes shifts the design from a detached unit to an attached wing, or the reverse, and that is a much easier change to make on paper.

Design the arrangement between the households before you design the house. We are builders, not counsellors, but we have seen enough of these projects to know that the ones that go well have talked through the awkward questions first. Who is contributing what to the build, and what happens to that contribution if the house is sold. Who pays which utilities. Are meals shared by default or by invitation. What happens if care needs increase beyond what the household can provide. What is the exit plan if it simply is not working after two years. Getting those answers on paper, ideally with a lawyer involved where money changes hands, is worth more than any design detail. It also feeds directly back into the plan, because a household that expects to eat separately most nights needs a different kitchen arrangement from one that eats together every night, and that is a design decision with a cost attached.

Multigenerational plans are the ones where the cheap decisions and the expensive decisions are furthest apart. Sound separation, blocking, door widths, and a stubbed kitchenette rough-in cost almost nothing at framing and a great deal afterwards. We work through the arrangement, the zoning position, and the plan together, then put a line-item budget against it before we break ground. Look at how we handle drawings in home plans and design, price a size and finish level with the estimator, or tell us who is moving in and we will help you work out which arrangement fits.