Garage conversion ideas: layouts and plans for 1-car, 2-car and 20x20 garages

Garage sizes and what fits

Most garages fall into two sizes. This Old House's June 2026 conversion guide puts a single-car garage at about 200 to 240 square feet and a two-car garage at about 400 to 440. Yours may be bigger or smaller, especially in older San Diego neighborhoods, so measure the inside face of the walls before you sketch anything.

Sizes: This Old House. Legal limits are generous for conversions. San Diego's municipal code sets no maximum size for an ADU converted from existing space, and state law lets a conversion grow by up to 150 square feet beyond the existing footprint, limited to what's needed for getting in and out. The city can't make you replace the parking you lose. For the permit and code basics, read our main guide to the garage conversion ADU.

Minimums your layout has to meet

California's residential code sets a few numbers every plan has to hit:

• Habitable rooms need a ceiling of at least 7 feet. A new raised floor over the slab eats into that.
• At least one habitable room must be 70 square feet or more, and habitable rooms other than kitchens need to be at least 7 feet in every direction.
• Habitable rooms need glazing equal to at least 8% of the floor area and openable area of 4% for natural ventilation, unless the plan meets the code's artificial light and mechanical ventilation alternatives.

One-car garage conversion ideas

At 200 to 240 square feet, a single-car garage is a studio. The layouts that work keep everything along the long walls and leave the middle open:

• Galley studio. Kitchenette run on one long wall, bathroom at the back corner behind it, bed or sofa bed along the opposite wall. Shared plumbing, one open room.
• Bath across the back. Shower bath and a closet across the rear 5 or 6 feet, kitchen at the side, living zone at the front where the old door opening becomes the window wall. This gives the most light to the room you use most.
• Office or guest studio first. If you don't need a full kitchen now, a room conversion is a different permit. Our guide to converting a garage to living space covers the bedroom-or-office route.

Small garage conversion ideas live or die on storage. Build-ins under a window seat, a wall bed and a pocket door to the bath save floor space that swinging doors and freestanding furniture take. In a space this small, a stacked washer-dryer in the bathroom is usually easier than a separate laundry closet.

Two-car garage conversion floor plan ideas, including 20x20

A 20x20 garage is 400 square feet measured to the outside of the walls. Furring out the walls for insulation and adding drywall takes several inches off each side, so draw your plan from interior measurements. That's still enough for a real one-bedroom:

• Split plan. Bedroom and bath across the back half, kitchen and living across the front half facing the old door opening. The bath and kitchen share the center wall, so drains stay short.
• Side bedroom. Bedroom along one side with its escape window on the side wall, bath beside it, and an L-shaped kitchen opening to the living area. Works best on a detached garage with side-yard access.
• Open studio with a sleeping alcove. Fewer walls, more light, lower framing cost. Good if the unit is for a family member rather than a tenant.

Is it attached to your house? An attached two-car garage is just under the size limit for a junior ADU, which state law caps at 500 square feet inside the home (an attached garage counts as part of the home). A junior ADU needs only an efficiency kitchen and can share a bathroom with the house. Our guide to attached vs detached ADUs explains the trade-offs.

Want to compare with bigger layouts? Our ADU floor plans guide shows what fits at 400, 600 and 800 square feet in new construction.

Where the kitchen and bath go

Plumbing is the one part of a garage layout you can't move cheaply later. Every new drain under a garage slab means cutting and trenching concrete, and drains need slope to reach the sewer. A few rules of thumb keep that work small:

• One wet wall. Put the kitchen sink, toilet, shower and any laundry back to back or side by side on one wall, so they share a drain run and a vent.
• Closest to the sewer. Put that wall on the side of the garage nearest the house's sewer line or cleanout. A detached garage at the back of a deep lot may need a long trench, or a pump if the slab sits below the sewer.
• Use what's there. If the water heater or washer hookups are already in the garage, that corner has water, a drain or a vent nearby. Ask your designer whether you can build from it.
• Keep the bath off the front. The old door opening is your best light. Don't spend it on a bathroom.

For a conversion, the city can't require a separate utility connection, so you can usually tie into the house's water and power. Whether the house's electrical panel can carry a new kitchen is a separate question your electrician answers. For fixtures, appliance sizes and layouts, see our ADU kitchen and bathroom guide.

Windows and light

Garages are dark. Most have no windows at all, or one small one on a side wall. Two code rules shape the window plan:

• Every sleeping room needs an escape opening. Under the 2025 code it must have at least 5.7 square feet of net clear opening (5 at grade floor), be at least 24 inches high and 20 inches wide, with the sill no more than 44 inches above the floor.
• Glazing of at least 8% of floor area. In a 400 square foot unit that's 32 square feet of glass, a figure the old door opening alone can supply. The residential code sets the rule.

Ideas that add light without new openings in every wall: a glass entry door, a skylight or solar tube over the kitchen, and clerestory windows high on a wall that faces a neighbor. A side wall close to the property line may limit openings under the fire code (see our ADU building code guide), so ask your designer before you plan windows there. New windows also have to meet the state energy code.

The garage door wall: keep, replace or reframe

The big opening at the front is the defining choice in a garage conversion. You have three options:

Whichever you pick, the infill becomes an exterior wall of a home. It needs framing that ties into the structure, insulation and an energy-code compliant window package, and the edge of the slab where the door used to sit usually needs work to keep water out. Los Angeles County's standard notes and details for garage conversions show how one building department expects the work drawn; your city's plan checker will want something similar.

Moving the entry to the side of the garage gives a tenant more privacy from the main house and the street, and it frees the front wall for windows. If you need a new doorway in a detached garage, the 150 square foot expansion allowed under state law can cover a small entry.

Garage conversion plans: free and pre-approved options

Free and pre-approved plans are built for new detached ADUs. The state's pre-approved plan programs cover detached units, and the County of San Diego's free plans are new buildings of 600 to 1,200 square feet. A conversion is drawn around a garage that already exists, with its own slab, framing and setbacks, so most owners need a designer to measure it and draw a custom set.

A few cities do publish conversion plans. Piedmont offers a city-designed 484 sq ft garage conversion with a kitchen, full bath, combined living and sleeping area and laundry, and waives ADU permit fees for city-designed plans, but if you rent the unit it must be affordable to very low-income households. It's a useful reference for what fits in a two-car footprint even if you're not in Piedmont.

Garage ADU plans still go through review. In the City of San Diego, the steps are in the city's ADU bulletin and our guide to getting an ADU permit in San Diego. If tearing the garage down and building new makes more sense, see pre-approved ADU plans in San Diego, or consider a factory-built unit in its place with our guide to the prefab ADU in California. Short on space for any of these? Compare a tiny home ADU.

Before and after: what to check

The before-and-after photos online show finishes. The things that decide whether the project works are mostly invisible:

• Is the garage permitted? A conversion is cheapest when the existing building is legal. If it was enlarged or altered without permits, expect the city to look at that work too.
• Slab and moisture. Many garage slabs have no vapor barrier. Your plan will need one under the new floor.
• Ceiling height after the floor goes in. Measure from the top of the finished floor, not the slab.
• Where storage goes. The garage held bikes, tools and holiday boxes. Plan a shed or closet for them before you lose the space.
• Budget. Kitchens and baths drive the cost. Our breakdown of garage conversion cost covers San Diego prices and line items, and you can see what an ADU costs in San Diego for comparison.

When you're ready for bids, check a contractor's license and compare verified ADU builders in San Diego, or start with our shortlist of the best ADU builders in San Diego. Our guide on how to hire an ADU contractor covers deposits and contracts.

Common questions