Two quotes for a 1,000-square-foot ADU come back: one around $250,000, the other close to $450,000. Neither contractor is necessarily padding the number. Block Renovation, which manages ADU projects, puts it bluntly: "Two ADUs at the same square footage can land six figures apart in total cost, and the difference comes down to layout." At 1,000 square feet you're building a small house, usually with two bedrooms, and often with two bathrooms. It's also the size California guarantees for an ADU with more than one bedroom. This guide covers what a unit this size costs, where the money goes, what state law says about the 1,000-square-foot line, and the fees that grow with size and plumbing fixtures.
Quick answers
- Typical budget: Block Renovation puts a 1,000 sq ft ADU at $250,000 to $500,000 in 2026; one Southern California builder publishes $125,000 to $465,000.
- Per square foot: Block's range is $250 to $500 per square foot for a detached new build.
- State law: a California city can't set its maximum ADU size below 1,000 square feet for a unit with more than one bedroom.
- What moves the number: layout, the number of bathrooms, site work, finishes, and fees that scale with size and plumbing fixtures.
What a 1,000 sq ft ADU costs
Block Renovation's guide to 1,000 sq ft ADU floor plans and costs says the cost "generally runs between $250,000 and $500,000 depending on where you live, what finishes you choose, and how complicated your site is," or "$250 to $500 per square foot for a detached new build." DYM Builders, an ADU contractor based in Southern California, lists a 1,000 sq ft unit at "$125,000 – $465,000" in its size table. Treat both as published ranges from companies that build ADUs, not as independent surveys.
The two ranges overlap from about $250,000 to $465,000. By Block's own description, where a project lands depends on location, finishes and how complicated the site is, so a simple unit on a flat, open lot sits toward the bottom and premium finishes on a hard site push toward the top. For the general per-square-foot figures and how ADU type (conversion, attached, detached) changes the price, see our ADU construction cost guide, which this post builds on.
Where the money goes
Block breaks a 1,000 sq ft build into categories. It's one company's split, but it's a useful checklist for reading a bid:
| Category | What it covers | Block's range |
|---|---|---|
| Permits and design | Architectural drawings, structural engineering, energy calculations, permit applications | $8,000 to $25,000 |
| Site prep and foundation | From a flat lot with good soil to a slope needing grading or retaining walls | About $25,000 to $60,000 |
| Framing | Structural shell, sheathing and roofing | $40,000 to $70,000 |
| Mechanical, electrical, plumbing | HVAC, wiring, plumbing; utility connections can add more | $35,000 to $75,000 |
| Interior finishes | Insulation, drywall and trim at mid-spec | $30,000 to $55,000 |
| Cabinets and countertops | Kitchen and bathroom | $25,000 to $60,000 |
Two lines deserve attention. Site prep and foundation can more than double depending on the lot, which is why a sloped backyard changes the budget more than almost any design choice. And on top of the mechanical, electrical and plumbing line, Block notes that "the utility connection to the main house or the street can be a five-figure line by itself." In our experience, those two lines explain most of the gap between two honest quotes for the same floor plan.
Why the price per foot drops but the total doesn't
DYM's cost guide states the general rule: "Larger ADUs tend to cost less per square foot." That's true, and it's easy to misread. A 1,000 sq ft unit usually costs less per foot than a 400 sq ft studio because some of the most expensive pieces don't scale with size. In our experience, a unit needs one electrical panel, one water heater, one sewer connection and one kitchen whether it's 400 or 1,000 square feet, so those costs get spread over more floor area in the bigger unit.
But the total still climbs, and at 1,000 square feet it often climbs faster than the extra floor area alone would suggest, because the extra space usually buys the expensive rooms: a second bedroom and very often a second bathroom. A bathroom packs plumbing, tile, fixtures, ventilation and waterproofing into a small space. So the useful question at this size isn't the per-foot rate. It's what the 1,000 square feet contains.
The 1,000 sq ft line in California law
California limits how small a city can set its maximum ADU size. Government Code section 66321 bars local ordinances from setting "A maximum square footage requirement for either an attached or detached accessory dwelling unit that is less than either of the following: (A) Eight hundred fifty square feet of interior livable space. (B) One thousand square feet of interior livable space for an accessory dwelling unit that provides more than one bedroom." For layouts at the 800 sq ft size, see our 800 sq ft ADU floor plans.
In practice, that means a city's size cap can't stop you at less than 1,000 square feet if the unit has two or more bedrooms, or less than 850 square feet for a studio or one-bedroom. Many cities allow more under their own rules. Separately, Section 66314 says an attached ADU "shall not exceed 50 percent of the existing primary dwelling" and a detached ADU "shall not exceed 1,200 square feet," so a 1,000 sq ft detached unit sits comfortably inside the state's outer limit. Other rules (height, setbacks, lot coverage) still apply, and they're worth checking with your city early. For what makes a room count as a bedroom, see our guide to 2 bedroom ADU floor plans. For every size and height limit by ADU type, see how big an ADU can be.
One bathroom or two
At 1,000 square feet, the second-bathroom decision is the biggest single layout choice. Block's guide lays out three ways to use the space:
- Two bedrooms, one bathroom: a conventional layout with a walk-in closet; Block notes that "a 2-bedroom ADU with only one full bath will rent for less than a 2-bedroom with two baths in most markets."
- Two bedrooms, two bathrooms: bedrooms side by side with bathrooms between them, opening to a shared living area; Block calls it efficient for unrelated roommates.
- One bedroom with a home office: trades the second bedroom for a workspace, which Block suggests for remote workers or aging parents.
How much does a 2-bedroom, 2-bath 1,000 sq ft ADU cost? Block's $250,000 to $500,000 range covers its 1,000 sq ft layouts, including the two-bath version. Block doesn't price the layouts separately, but the second bathroom shows up in two of its categories: plumbing (part of the mechanical, electrical and plumbing line) and cabinets and countertops, which includes bathroom fixtures. In our experience, a second full bathroom is one of the most expensive things you can add within the same footprint, so get it priced as its own line when comparing bids.
Fixtures can also affect fees. For an ADU that gets a new utility connection, state law allows a connection fee or capacity charge that, according to the state housing department's ADU handbook, "shall be proportionate to the burden of the proposed ADU, based on its square footage or drainage fixture unit as compared to the primary dwelling" (Gov. Code section 66311.5, subd. (e)). Drainage fixture units are a plumbing measure of how much each fixture contributes to the drain load, so where an agency uses them, a second bathroom can raise the charge. Ask your water and sewer providers which method they use. Whether a second bath pays off as a rental is a separate question; our guide to how much value an ADU adds covers that side.
Size-driven costs to price separately
A 1,000 sq ft unit crosses both of the state's fee thresholds, so budget for these as their own lines:
- Impact fees. An ADU over 750 square feet can be charged impact fees in proportion to the size of the main house. Our ADU construction cost guide explains the 750 sq ft rule.
- School fees. Added space over 500 square feet can trigger school district fees; the same guide covers that line.
- Utility connection or capacity charges. Based on square footage or fixture units, as above.
- Service upgrades. A second kitchen, two bathrooms, a heat pump and a water heater can outgrow an older home's electrical service. Our electrical panel upgrade cost guide covers that range.
In our experience, none of these are large compared with construction, but together they can add up, and they're the lines most often missing from an early estimate.
Getting a 1,000 sq ft bid you can compare
Ask each builder to price the job in the same categories Block uses: design and permits, site prep and foundation, framing, mechanical, electrical and plumbing, finishes, and cabinets and counters, with fees and utility connections listed separately. Ask them to price the second bathroom as its own line if you're undecided. Two bids broken out that way can be compared line by line, and the reason one is six figures higher usually becomes obvious. Medici Construction Group is one licensed option for designing and building ADUs, holding California A, B and C-10 licenses under CSLB #1114433.
Frequently asked questions
How much does a 1,000 sq ft ADU cost?
Block Renovation puts it at $250,000 to $500,000 in 2026, depending on location, finishes and site. One Southern California builder publishes $125,000 to $465,000. Fees and utility connections can add to either figure.
What is the cost per square foot for a 1,000 sq ft ADU?
Block Renovation's range is $250 to $500 per square foot for a detached new build. Larger ADUs generally cost less per square foot than small ones, but the total is higher.
Can I build a 1,000 sq ft ADU in California?
Usually, if it has more than one bedroom. State law bars cities from setting a maximum ADU size below 1,000 square feet for units with more than one bedroom. Height, setback and other local rules still apply.
Is a 1,000 sq ft ADU cheaper per square foot than a small one?
Generally yes, because costs like the kitchen, electrical panel and utility connections are spread over more floor area. The total cost is still higher, especially with a second bathroom.
How many bedrooms fit in 1,000 sq ft?
Usually two. Block Renovation's 1,000 sq ft layouts include two bedrooms with one or two bathrooms, or one bedroom with a home office.
Do I pay impact fees on a 1,000 sq ft ADU?
You can. In California, ADUs over 750 square feet can be charged impact fees in proportion to the size of the main house. Units of 750 square feet or less are exempt.
Does a second bathroom cost more in fees?
It can. For a new utility connection, state law lets the connection fee or capacity charge be based on square footage or drainage fixture units, so an agency using fixture units may charge more for a second bath.
How much does a 2-bedroom, 2-bath 1,000 sq ft ADU cost?
Block Renovation's $250,000 to $500,000 range covers its 1,000 sq ft layouts, including a two-bedroom, two-bath plan. The second bathroom adds mainly to plumbing and to cabinets and fixtures, so price it as a separate line.
