Backyard ADU: Five Plans, Sized to What Most Cities Allow
A backyard ADU is a small house on your lot: 300 to 400 square feet for a studio, 500 to 700 for one bedroom, 800 to 1,000 for two.
Free: draw, save in your browser, download a watermarked image. Paid: clean to-scale PDF and materials list.
| Type | Typical size | Rooms | Footprint |
|---|---|---|---|
| Studio | 300–400 sq ft | One room, bath, kitchen along a wall | 20 × 16 to 24 × 16 ft |
| One-bedroom | 500–700 sq ft | Living, kitchen, bedroom, bath | 28 × 20 to 32 × 22 ft |
| Two-bedroom | 800–1,000 sq ft | Living, kitchen, two bedrooms, one or two baths | 30 × 28 to 36 × 28 ft |
| Garage conversion | 400–480 sq ft | Studio or one-bedroom in a 20 × 22 ft garage | existing slab |
| Tiny house | 160–320 sq ft | One room, galley, wet bath | 20 to 30 ft × 8.5 ft |
Many states cap a detached ADU at 800–1,200 sq ft or a share of the main house; California allows at least 800 sq ft by right. Setbacks are commonly 4 ft at the side and rear; height limits 16–18 ft for one storey. Check your city.
Layouts
Pick a layout
Each one opens in the canvas below with its sizes already drawn; change anything.
One-bedroom ADU, 30 × 20 ft
About 600 sq ft: living room and kitchen in front, bedroom and bath behind a single wall. The size most state ADU laws allow by right.
Two-bedroom ADU, 30 × 28 ft
About 840 sq ft: open kitchen and living on the west, two bedrooms stacked on the east, one bath. Check the lot coverage; this is near most 800 to 1,000 sq ft caps.
In-law suite, 27 × 18 ft
A single-level suite with a walk-in shower, a sitting room and a small kitchen, planned for a parent: no steps, wide doors, bed reachable from both sides.
Tiny house, 24 × 8 ft
Under 200 sq ft on a trailer footprint: galley kitchen, sofa, bath at the end. Many cities treat a movable tiny house differently from a built ADU.
Studio ADU, 22 × 16 ft
About 350 sq ft in one room plus a bath: the cheapest ADU to build and the easiest to fit behind a house on a 40 foot lot.
A 30 × 20 ft one-bedroom ADU with every wall length on the plan. Click it to change the size, move the kitchen and bath, and add the lawn and path around it with the Ground tool.
About
The five plans below cover that range, from a 24 by 8 foot tiny house to a 30 by 28 foot two-bedroom, each with a full kitchen and bath drawn at real sizes. Pick one, type the dimensions your zoning allows, and move the walls. The canvas checks the kitchen aisle, the bed and toilet clearances and the door swings as you go, and every wall shows its length so the plan can be set out on the lot with a tape. A planning tool, not an AI and not a permit set; the setbacks and the maximum size come from your city.
01
How big your backyard ADU can be
Three numbers set the size: the maximum floor area in the ADU ordinance, the lot coverage you have left after the house and garage, and the setbacks. Since the state laws of 2017 to 2024 most California, Oregon and Washington cities must allow a detached unit of at least 800 square feet with 4 foot side and rear setbacks and a 16 foot height; many other states and cities use 800 to 1,200 square feet or half the size of the main house. Measure the backyard, subtract the setbacks from each side, and that rectangle is the largest footprint. Draw it on the canvas as the outline and fit the plan inside it.
Then decide the shape. A long thin lot wants the tiny-house or studio proportions; a square lot behind a garage takes the one-bedroom or two-bedroom plans. One storey is cheaper and avoids the height fight; a loft over the bath and kitchen adds sleeping space inside a 16 foot ridge on some plans.
02
Detached, attached or a garage conversion
A detached ADU is the plans on this page: its own foundation, walls and roof, its own front door, usually its own water and sewer taps from the house line. An attached unit shares a wall with the house and often the utilities, which is cheaper but limited by the house itself. A garage conversion uses the existing slab and roof, so it is the cheapest route to a studio or a one-bedroom, with the plumbing and the garage door as the two big costs; the garage conversion page has four layouts for that.
- Detached: most privacy and rent, most cost; needs a full permit set and a new sewer connection.
- Attached: shares structure and utilities; sound and privacy need a plan.
- Garage conversion: existing slab and roof; the slab is often below the house floor and uninsulated.
- Prefab or modular: a factory box craned in; still needs a foundation, utilities and a permit.
03
Where the kitchen and bath go
Put the wet rooms on the wall nearest the house sewer and water lines, and put them back to back so one wall carries the plumbing. In the one-bedroom plan the kitchen run and the bath share the wall between the living room and the bedroom; in the two-bedroom plan the bath sits in the corner nearest the house. A full kitchen means a range with a vented hood, a fridge and at least 42 inches of aisle in front of the counters, which the canvas checks, and most codes count a kitchen as what makes the building a dwelling unit. The bath wants a 30 by 30 inch shower, a toilet with 15 inches to each side and 21 inches in front, and a 36 inch door if anyone will ever use a walker.
04
What it costs, honestly
In 2025 a detached, stick-built backyard ADU in the United States runs from about $150,000 for a small studio to $400,000 or more for a two-bedroom in a high-cost city, which is $300 to $500 per square foot once the sewer connection, the utilities, the permit fees and the site work are in. A garage conversion is often $80,000 to $150,000. Prefab units are quoted at $100,000 to $250,000 before the foundation and the utility runs, which add $30,000 to $80,000. Impact fees vary from zero to tens of thousands; several states waive them under 750 square feet, which is one reason the one-bedroom plans sit at 600.
05
Schematic, then the architect
The plan you draw here is a schematic: a footprint, rooms, doors, fixtures and the wall lengths to set it out on the lot. It is not a permit set, a stamped drawing or an engineered foundation, and it is not an AI rendering. Take it to the planning counter to confirm the size and the setbacks, then to a designer for the permit drawings. The PDF export and the materials list are paid; drawing, saving in your browser and the clearance checks are free.
06
Frequently asked questions
- How big can a backyard ADU be?
- Usually 800 to 1,200 sq ft or half the main house, with California cities required to allow at least 800 sq ft detached. Setbacks of 4 ft at the side and rear and a 16 to 18 ft height limit are common. Your city sets the number.
- How much does a backyard ADU cost?
- About $150,000 to $400,000 built in 2025 for a detached stick-built unit, depending on size and city; garage conversions $80,000 to $150,000; prefab $100,000 to $250,000 plus foundation and utilities.
- Does an ADU need its own entrance?
- Yes. A dwelling unit needs its own exterior door, and most ordinances require it to be separate from the main house entrance. Each bedroom also needs an egress window or door.
- Can I rent out a backyard ADU?
- In most cities that allow ADUs, yes, for long-term rental; short-term rental is often restricted and some cities require the owner to live on the property. Check the ordinance before you build for rent.
- Does a backyard ADU need a kitchen?
- To count as a dwelling unit, yes: permanent cooking, a sink and a fridge. A building without a kitchen is a guest house or studio under most codes and cannot be rented as a home.
Sources
Where the numbers come from
Local amendments apply; check your own jurisdiction.