What Size ADU to Build in 2026 and 2027: 750, 1,000 or 1,200 Sq Ft After SB 1117

For years the answer to "what size ADU should I build?" in Sacramento had a hidden rule: stay at 750 sq ft or under, because the next square foot brings thousands of dollars in impact fees. SB 1117 changes that from January 1, 2027. This guide puts build prices, impact fees and school fees side by side for a 750, 1,000 and 1,200 sq ft ADU, so you can decide on the layout you actually need rather than on a fee threshold.

The short answer

• Until the end of 2026, 750 sq ft is a hard line in the City of Sacramento: at or under it, no impact fees; over it, impact fees on the whole ADU (about $5,600 at 800 sq ft).
• From 2027, for the first two ADUs on a lot, impact fees apply only to the area above 750 sq ft. In the City, park and flood-control fees on a 1,000 sq ft ADU drop from $5,590 to about $1,400.
• The build price is still the main cost. Fees are a few percent of the project; going from 750 to 1,000 sq ft on our published pricing adds $69,000 of construction and a third bedroom.
• Under 500 sq ft is the other threshold: no school fees. SB 1117 does not change that.

Three sizes, side by side

The build prices below are the starting prices published on our ADU floor plans: rate per square foot times size. Fees use the City of Sacramento's own rates (form CDD-0419, July 2026) and the Sacramento City Unified school fee ($5.38 per sq ft on City form CDD-0226). Your lot, district and site work move every number, so treat this as a comparison, not a quote.

	Model 105	Model 104	Model 106
Size	750 sq ft	1,000 sq ft	1,200 sq ft
Layout	2 bed / 2 bath	3 bed / 2 bath	2 bed / 2 bath
Published starting price	$243,000 ($324/sq ft)	$312,000 ($312/sq ft)	$345,600 ($288/sq ft)
City impact fees, 2026	$0 under state law*	about $7,006	about $8,124
City impact fees from 2027**	$0	about $2,813	about $3,931
School fee (SCUSD)	about $4,035	about $5,380	about $6,456

* The City's 2026 form still lists about $5,347 at exactly 750 sq ft, a leftover of older wording; state law has exempted 750 sq ft and under since January 1, 2026. Raise it at plan review. ** Park and SAFCA fees charged on the area above 750 sq ft at the City's current rates, STA transportation fee unchanged. The City has not yet published its 2027 method; the full calculation is in SB 1117 in Sacramento: ADU impact fees before and after.

What the new rule changes in the decision

The 751 to 850 sq ft range stops being a trap

Today, an ADU of 800 sq ft pays about $5,600 in City impact fees that a 750 sq ft ADU does not. That is why so many plans, including the City's own largest Shelf Ready plan at 747 habitable sq ft, stop just under the line. From 2027 the same 800 sq ft ADU pays park and SAFCA fees on 50 sq ft, about $280. A slightly larger kitchen, a wider hallway for accessibility or a laundry closet no longer costs thousands in fees.

A third bedroom gets cheaper to justify

For a family member or a rental, the jump from 2 to 3 bedrooms usually means going from about 750 to about 1,000 sq ft. On our published pricing that adds $69,000 of construction. Today it also adds about $7,000 in City impact fees; from 2027 about $2,800. The fee is no longer the deciding factor; the construction budget and how the space will be used are.

Per square foot, larger units cost less to build

Kitchens, bathrooms and utility connections are needed at any size, so the price per square foot falls as the unit grows: $324 at 750 sq ft, $312 at 1,000, $288 at 1,200 on our published rates. With the fee cliff gone, the per-foot advantage of a larger unit is no longer offset by a fee jump at 751 sq ft.

The 500 sq ft threshold stays

An ADU or junior ADU under 500 sq ft pays no school fees, and SB 1117 does not touch school fees. If a studio or a small one-bedroom fits your plan, staying under 500 sq ft still saves the school fee entirely.

Things that have not changed

• Your lot sets the ceiling. SB 1117 changes fees, not size limits, setbacks or lot coverage. What fits your lot is a site question.
• Third ADU on a lot. The new rule covers up to two ADUs. A third or later ADU over 750 sq ft is charged on its whole size.
• Utility connections. Water and sewer connection charges are not impact fees; a detached ADU can be charged in proportion to its size or plumbing fixtures.
• Outside the City. Sacramento County, Elk Grove and Roseville calculate ADU fees differently; several County fees already exempt ADUs up to 850 sq ft, or up to 1,000 sq ft with more than one bedroom. See ADU impact fees in Sacramento County, Elk Grove and Roseville.

Timing a 2026 project

If you are planning an ADU over 750 sq ft and your permit would be issued in late 2026, ask the City or County at which point fees are fixed on your application. For a 1,000 sq ft ADU in the City, the difference is about $4,200. Design and plan review usually take longer than the gap to January, so for many projects the question answers itself; if your permit is close, it is worth asking.

FAQ

Is 750 sq ft still the best ADU size in Sacramento?

It is still the largest size with no impact fees at all, and in 2026 it is the clear fee choice. From 2027 the extra cost of going larger is a fraction of what it is today, so the right size depends on the layout you need and your construction budget.

How much more does a 1,000 sq ft ADU cost than a 750 sq ft one?

On our published starting prices, $312,000 against $243,000, a difference of $69,000. In the City of Sacramento, impact fees add about $7,000 more today and about $2,800 more from 2027, plus a school fee on the extra 250 sq ft.

Does SB 1117 apply to junior ADUs?

Junior ADUs of 500 sq ft or less were already exempt from impact fees and still are. The new marginal rule is written for ADUs over 750 sq ft.

Sources: SB 1117 (Chapter 809, Statutes of 2026), Government Code 66311.5 as amended, effective January 1, 2027; City of Sacramento ADU Fee Estimate CDD-0419 (rev. 07-12-2026) and School District Impact Fees CDD-0226; Sacramento County park and fire development fee schedules (2026); Result Construction published starting prices by model (October 2026). Build prices are starting prices for a standard build; site work, finishes and utility runs change the final figure. Checked October 2026.