ADU Floor Plans

Plan books sort ADUs by square footage. That is the wrong place to start. The questions that shape a good plan are who lives there, how private they need to be from the main house, how they get in, and what the lot and city allow. Size follows from those answers, and your city's caps, covered in ADU size, set the ceiling. Here are the main plan types and what each one suits.

Studio plans

One main room holds living, sleeping and kitchen, with a separate bathroom. Studios suit one person, a guest suite or an office that can double as a rental later. They work best with a tall ceiling, a large window or two, and built-in storage so the bed area does not become the closet. The challenge is separation: a sleeping alcove, a half wall or a change in ceiling height makes a studio feel like more than one room.

One-bedroom plans

A separate bedroom with a door is what most long-term occupants want, whether a tenant, a grown child or a parent. The typical arrangement puts the kitchen and living area together at the entry and the bedroom and bath at the quieter end. A one-bedroom plan leaves room for a stacked washer and dryer and real closet space, which matter more to a long-term occupant than an extra few feet of living room.

Two-bedroom plans

Two bedrooms suit two unrelated adults, a parent with a caregiver, or a small family. Check your city first:

• South Salt Lake limits an external ADU to two bedrooms.
• Salt Lake City's ADU handbook says the number of bedrooms is not regulated.
• Millcreek caps occupancy of attached and detached ADUs at two adults and any number of children.
• Holladay limits ADU occupants to a single family, which it defines to include up to four unrelated people living as one housekeeping unit.

Two bedrooms also push against size caps and, in some cities, parking thresholds, so a second bedroom has to earn its place.

Single-level and accessible plans

For a parent or anyone planning to age in place, the plan should work without stairs: a step-free entry, wide doorways, a curbless shower with room for grab bars, and a bedroom close to the bath. These choices cost little at the drawing stage and a great deal later. See in-law ADUs and multigenerational ADUs.

Two-story and loft plans

Going up saves yard, but cities limit it:

• Murray: a detached ADU is limited to one story.
• South Salt Lake: an external ADU may not exceed two stories.
• Sandy: up to 1.5 stories and 18 feet, if the unit meets the house's setbacks and is no taller than the house.
• Millcreek: no story limit in the ADU chapter, but second-story balconies are prohibited.
• Salt Lake City: second-story windows facing side or rear property lines are restricted unless an exception applies, such as clerestory windows set high in the wall.

Stairs take floor area on both levels, so a small two-story plan can end up with less usable space than it appears. A loft over a vaulted living room is often the better compromise.

Plans shaped by an existing space

Conversions start with a fixed shell. A garage conversion is usually a long rectangle with one short side facing the driveway, so the plan often runs front to back with the bath in the middle. A basement ADU works around stairs, mechanical equipment and where egress windows can go, since bedrooms need a code-compliant escape opening. An above-garage ADU is shaped by the roof and the stair.

Pre-approved plans in Salt Lake City

Salt Lake City lists ADU plans pre-approved by its building code staff. On our review date the list had five designs from different firms: a 650 square foot one-bedroom, a 775 square foot two-bedroom, an 800 square foot two-bedroom, a detached garage conversion and a second-story garage conversion. You contact the firm to use a plan. The city is clear that a site review is still required and that all review and permit fees still apply. The list is updated regularly.

What makes a small plan work

• Plumbing grouped.Kitchen, bath and laundry back to back keep pipe runs short.
• Storage designed in.Closets, a pantry and a spot for bikes or tools, planned rather than found.
• Light and height.Tall windows and a vaulted ceiling make a small room feel larger.
• Privacy.Windows and doors placed so the two homes do not look into each other.
• Furniture tested.A bed, a sofa and a table drawn at real size before the plan is final.

Before you choose a plan

The plan has to fit the property, not the other way round. Work through Can I build an ADU? first, then read designing an ADU to match the house. Our ADU feasibility review tells you which plan types fit your lot before anyone draws one. To start, See What Your Property Can Support.

Questions about ADU floor plans