A 1,000 square foot ADU runs $137,250–$375,000 all in, nationally, at a standard finish. Detached, which is realistically what a 1,000 square foot unit is, prices around $300,000. In California that is closer to $546,000.
This is the size where the interesting question stops being cost per square foot and starts being permission. 1,000 square feet is the largest ADU California requires your city to allow, and only if it has more than one bedroom.
So the cost table below is the easy half of this page. The statute section is the half that decides whether you get to use it.
1,000 sq ft ADU cost by type
The five types at 1,000 square feet, nationally, at a standard finish. Three of these rows are priced past what the type page itself calls a typical size, and the table flags which.
The real comparison here is detached at $300,000 against attached at $238,000. Sharing a wall saves you roughly $62,000 at this size, which is the largest that gap gets on any page in this silo.
| Build type | Base rate | Typical all-in | Range |
|---|---|---|---|
| Detached ADU | $300/sq ft | $300,000 | $225,000–$375,000 |
| Above-Garage ADUBeyond its typical size | $250/sq ft | $250,000 | $187,500–$312,500 |
| Attached ADUBeyond its typical size | $238/sq ft | $238,000 | $178,500–$297,500 |
| Garage Conversion ADUBeyond its typical size | $183/sq ft | $183,000 | $137,250–$228,750 |
| Junior ADU | Not available at this size. Capped at 500 sq ft of interior livable space by state law, so it cannot be built at this size. | ||
National, standard finish, before any city adjustment. Typical all-in is the point estimate; the range is the engine's residual spread for site conditions, utilities and contractor.
What Changes at 1,000 Square Feet
1,000 is the ceiling of the state guarantee, not the start of a new tier. Government Code section 66321(b)(2) stops a local ordinance from setting a maximum ADU size below 850 square feet of interior livable space, or below 1,000 square feet for an ADU that provides more than one bedroom. Read the condition carefully: the 1,000 square foot floor is tied to bedroom count. A 1,000 square foot studio does not get the same protection a 1,000 square foot two bedroom does.
The impact fee exemption is long gone. Section 66311.5 exempts ADUs of 750 square feet or less, and charges everything above that proportionately against the primary dwelling's square footage. At 1,000 square feet next to a 2,000 square foot house you are paying half the fee. That is not a reason to build smaller at this size, it is a reason to have the number before you budget.
A junior ADU is not in this conversation at all. The JADU category caps at 500 square feet of interior livable space under section 66313, so it has been irrelevant since the 600 square foot page. I keep the row on the table anyway, because "why is that one blank" is a question worth answering once.
Conversions stop being the cheap trick. A $183,000 garage conversion at 1,000 square feet assumes a three car garage you already own and are willing to lose entirely. Most people at this size are building new, which is why the detached and attached rows are the ones I would actually plan against.
If you want to see what this size actually looks like laid out, we have 3 original 1,000 sq ft floor plans drawn to scale with room dimensions, each with a walkthrough of what works and what to watch.
1,000 sq ft ADU cost by city
1,000 square feet priced through every city index we maintain. The spread from the cheapest market to the dearest on this table is the single clearest argument on the site that a national ADU cost number is close to useless.
| City | Cost index | Garage conversion | Detached | Full range |
|---|---|---|---|---|
| SaratogaCalifornia | 2.54 | $464,820 | $762,000 | $348,615–$952,500 |
| Los AltosCalifornia | 2.48 | $453,840 | $744,000 | $340,380–$930,000 |
| Los GatosCalifornia | 2.48 | $453,840 | $744,000 | $340,380–$930,000 |
| CupertinoCalifornia | 2.31 | $422,730 | $693,000 | $317,048–$866,250 |
| San FranciscoCalifornia | 2.31 | $422,730 | $693,000 | $317,048–$866,250 |
| Santa ClaraCalifornia | 2.31 | $422,730 | $693,000 | $317,048–$866,250 |
| SunnyvaleCalifornia | 2.31 | $422,730 | $693,000 | $317,048–$866,250 |
| San JoseCalifornia | 2.19 | $400,770 | $657,000 | $300,578–$821,250 |
| BellevueWashington | 2.08 | $380,640 | $624,000 | $285,480–$780,000 |
| SeattleWashington | 2.02 | $369,660 | $606,000 | $277,245–$757,500 |
| CampbellCalifornia | 1.99 | $364,170 | $597,000 | $273,128–$746,250 |
| BoulderColorado | 1.90 | $347,700 | $570,000 | $260,775–$712,500 |
| OaklandCalifornia | 1.85 | $338,550 | $555,000 | $253,913–$693,750 |
| DenverColorado | 1.79 | $327,570 | $537,000 | $245,678–$671,250 |
| San DiegoCalifornia | 1.73 | $316,590 | $519,000 | $237,443–$648,750 |
| Long BeachCalifornia | 1.67 | $305,610 | $501,000 | $229,208–$626,250 |
| AnaheimCalifornia | 1.56 | $285,480 | $468,000 | $214,110–$585,000 |
| Los AngelesCalifornia | 1.56 | $285,480 | $468,000 | $214,110–$585,000 |
| PortlandOregon | 1.56 | $285,480 | $468,000 | $214,110–$585,000 |
| EugeneOregon | 1.44 | $263,520 | $432,000 | $197,640–$540,000 |
| RiversideCalifornia | 1.44 | $263,520 | $432,000 | $197,640–$540,000 |
| SacramentoCalifornia | 1.44 | $263,520 | $432,000 | $197,640–$540,000 |
| BendOregon | 1.36 | $248,880 | $408,000 | $186,660–$510,000 |
| FresnoCalifornia | 1.27 | $232,410 | $381,000 | $174,308–$476,250 |
| TacomaWashington | 1.27 | $232,410 | $381,000 | $174,308–$476,250 |
| RenoNevada | 1.24 | $226,920 | $372,000 | $170,190–$465,000 |
| SalemOregon | 1.24 | $226,920 | $372,000 | $170,190–$465,000 |
| Colorado SpringsColorado | 1.18 | $215,940 | $354,000 | $161,955–$442,500 |
| HendersonNevada | 0.92 | $168,360 | $276,000 | $126,270–$345,000 |
| SpokaneWashington | 0.92 | $168,360 | $276,000 | $126,270–$345,000 |
| Las VegasNevada | 0.89 | $162,870 | $267,000 | $122,153–$333,750 |
Standard finish. The cost index is that city's published average against our national reference, so these columns move whenever a city cost page does. Full range spans every eligible build type at this size.
What finish level does to it
At 1,000 square feet the finish decision is worth $126,000 on a detached build. That is more than the entire cost of a 400 square foot junior ADU, which is a strange sentence to type and a true one.
| Finish level | Multiplier | Detached ADU | Above-Garage ADU | Attached ADU | Garage Conversion ADU |
|---|---|---|---|---|---|
| Budget | 0.86x | $258,000 | $215,000 | $204,680 | $157,380 |
| Standard | 1.00x | $300,000 | $250,000 | $238,000 | $183,000 |
| High-end | 1.28x | $384,000 | $320,000 | $304,640 | $234,240 |
National point estimates at 1,000 sq ft. The junior ADU column, where it appears, is priced at its 500 sq ft statutory cap rather than at this page's size.
A worked budget
Where $300,000 goes on a 1,000 square foot detached build at a standard finish, nationally.
| Line item | Share | Amount |
|---|---|---|
| Site work and excavation | 8% | $24,000 |
| Foundation | 9% | $27,000 |
| Framing and structural shell | 15% | $45,000 |
| Roofing, siding, and windows | 11% | $33,000 |
| Mechanical, electrical, and plumbing | 13% | $39,000 |
| Utility connections | 7% | $21,000 |
| Interior finishes | 14% | $42,000 |
| Kitchen and bath | 9% | $27,000 |
| Design and engineering | 6% | $18,000 |
| Permits and fees | 5% | $15,000 |
| Contingency | 3% | $9,000 |
| Total | 100% | $300,000 |
Detached ADU, 1,000 sq ft, standard finish, national. $300 per sq ft all in, with a planning range of $225,000–$375,000.
Frequently asked questions
How Much Does a 1,000 Sq Ft ADU Cost?
Nationally, $137,250–$375,000 all in at a standard finish depending on build type, with a detached unit around $300,000. California prices the same detached build near $546,000. Our ADU cost pillar explains what all in includes and what it does not.
Can My City Cap My ADU Below 1,000 Sq Ft?
In California, not if the unit has more than one bedroom. Government Code section 66321(b)(2) prohibits a local maximum size requirement below 850 square feet of interior livable space, or below 1,000 square feet for an ADU providing more than one bedroom. A studio or one bedroom unit only gets the 850 square foot protection, so bedroom count is doing real legal work here.
Does a 1,000 Sq Ft ADU Pay Impact Fees?
Yes. The exemption in Government Code section 66311.5(c)(1) only reaches 750 square feet of interior livable space. Above that, subdivision (c)(2) requires impact fees to be charged proportionately in relation to the primary dwelling's square footage, so a 1,000 square foot ADU beside a 2,000 square foot house pays roughly half the fee.
Is 1,000 Sq Ft Too Big for an ADU?
Not legally, and rarely practically, but it is the size where lot coverage and setbacks usually bite before the budget does. On a standard suburban lot a 1,000 square foot footprint plus required setbacks and any parking leaves very little yard. I would check the coverage math on your specific lot before falling for a plan at this size.
If I were building 1,000 square feet, I would make sure the plan shows more than one bedroom before I filed anything, purely so the state's 1,000 square foot floor is on my side if the city pushes back on size.
Then I would price it against 800 square feet honestly. The extra 200 square feet costs $60,000 of construction and buys you a second real bedroom, and that is usually the best 200 square feet in the whole project.
Price a different size
The same five build types and the same engine, priced at every size we cover.