Quick answer
A height limit is the maximum vertical height a zoning code allows for a building, measured from a reference point on the ground to a reference point on the roof that the local code defines.
For an ADU it decides whether a loft or second story is possible. Two codes with the same number can allow different buildings, because they measure differently.
Quick facts
- Unit
- Feet (sometimes also stories)
- Who sets it
- The local zoning code
- Measured from
- Grade: natural, finished or average (varies by code)
- Measured to
- Highest point, or the midpoint of a pitched roof (varies by code)
- California floor, detached ADU
- 16 ft; 18 ft near transit or on multistory multifamily lots 1
- California floor, attached ADU
- 25 ft or the local limit for the house, whichever is lower 1
Key takeaways
- A height limit is the tallest a building may be, measured the way your code says.
- Codes differ on where to measure from (the ground) and to (the roof).
- Height decides if a loft or second story can fit.
- California sets minimum heights cities must allow for ADUs: 16, 18 or 25 feet, by situation 1.
- Those are floors. A city may allow more.
- Outside California, height is mostly local, and rules vary.
Why the height limit matters to you
Height is what turns a small lot into more space. If you can go up, you need less ground.
It also sets roof shape, ceiling height and whether a loft is usable. A few feet can decide between a cramped attic and a real bedroom.
Neighbors care about height too. A clear rule tells everyone what to expect before you build.
How to check height for your design
- Find your zoning district’s height limit in the city code.
- Read the code’s definition of height: the low point and the high point.
- In California, check which state floor applies: detached, near transit, multistory lot, or attached 1.
- Use the higher of the local limit and the state floor.
- Stack your design’s dimensions from grade to the measured roof point.
- Check any daylight plane or story limit on top of the foot limit.
Why the measuring method matters
Every height limit has two hidden choices: where you measure from and where you measure to.
The bottom point may be natural grade before construction, finished grade after it, or an average of the grade at the corners.
The top point may be the ridge, the highest point of any part of the roof, or the midpoint between eave and ridge on a pitched roof.
On a flat lot with a flat roof these choices barely matter. On a sloped lot with a gabled roof they can move the answer by several feet. That is why a designer reads the definition of “height” in the local code before drawing a second story. The cards below set out the two choices.
Height works with the other envelope limits: setbacks set where a building stands, coverage and floor area ratio set how big it is. Some codes add a daylight plane or step-back near property lines, which slices the corner off the allowed envelope.
Measured from (bottom point)
- Natural grade before construction
- Finished grade after construction
- Average grade at the building corners
Measured to (top point)
- The ridge of the roof
- The highest point of any part of the roof
- The midpoint between eave and ridge on a pitched roof
Your local code’s definition of “height” picks one from each card. On a sloped lot the pair can change the answer by several feet.
California’s minimum ADU heights
| Situation | Height a city must allow at least |
|---|---|
| Detached ADU on a lot with an existing or proposed single-family or multifamily dwelling | 16 feet |
| Detached ADU within one-half mile walking distance of a major transit stop or high-quality transit corridor | 18 feet, plus up to 2 more feet for a roof pitch aligned with the main house |
| Detached ADU on a lot with an existing or proposed multifamily, multistory dwelling | 18 feet |
| ADU attached to the primary dwelling | 25 feet, or the local height limit for the house if lower; a city need not allow more than two stories |
Sources: [1]
Reading the California floors correctly
These are floors, not caps. Section 66321(b)(4) bars a local height limit that “does not allow at least” these heights; a city may set a higher limit for ADUs.
Within that floor, section 66314(b)(1) lets a city apply objective height standards 2, and Chapter 13’s definitions are in section 66313 3.
The section was formerly part of Gov. Code 65852.2(c), before SB 477 (Stats. 2024, ch. 7) moved the ADU law into Chapter 13.
The transit terms come from Public Resources Code section 21155, which the statute cross-references. Whether a lot qualifies is a fact the city confirms; it is not a distance you can assume from a map.
This is California’s rule. Other states either leave ADU height to local codes or set their own floors; see ADU laws by state.
Sources: [1]
Worked example: does a loft fit under 16 feet?
Hypothetical design, for arithmetic only: a detached ADU in California on a single-family lot not near transit, with the 16-foot state floor as the local limit, measured to the highest point of the roof.
| Element | Dimension | Running height |
|---|---|---|
| Slab above grade | 0.5 ft | 0.5 ft |
| Main-floor ceiling height | 8 ft | 8.5 ft |
| Floor framing for a loft | 1 ft | 9.5 ft |
| Roof framing at ridge, including headroom | 6.5 ft | 16 ft |
This stack fits exactly at 16 feet, but leaves only a low loft under the ridge, not a full second story.
If the same lot qualified for 18 feet plus 2 for a matching roof pitch, the design would gain up to 4 feet.
If the local code measured to the roof midpoint instead, the ridge could rise higher again.
What to confirm with the planning department
- The definition of height: from which grade, to which point of the roof.
- Whether the lot qualifies for the transit or multifamily height in state law.
- Any daylight plane, step-back or story limit in addition to the foot limit.
- Overlay zones such as historic districts or the coastal zone, which can add review.
Common ways codes measure height
| Method | Measured from | Measured to | Effect |
|---|---|---|---|
| Highest point | Grade | The top of the roof | Strictest for pitched roofs |
| Roof midpoint | Grade | Halfway between eave and ridge | Allows a taller ridge |
| Average grade | The average of grade at the corners | The roof point the code names | Helps on sloped lots |
| Story limit | — | A count of floors | Applies on top of the foot limit |
Second example: an attached ADU on a two-story house
Hypothetical inputs only. A California lot has a two-story house. The local limit for the house is 30 feet. The owner wants an attached two-story ADU.
| Step | Rule | Result |
|---|---|---|
| State floor for attached ADU | 25 feet, or the house limit if lower 1 | 25 feet (lower than 30) |
| Stories | A city need not allow more than two | Two stories at most |
| Can the city allow more? | Yes, the floor is a minimum | Up to the local rule if the city chooses |
| Design check | Two floors plus roof framing | Must fit under the limit that applies |
If the local limit for the house had been 22 feet, the ADU floor would be 22 feet, because the statute uses the lower of 25 and the local house limit.
Where you will see height
- Elevation drawings in the permit set, with a dimension from grade to the roof.
- The zoning code table for your district.
- Plan check comments if grade points are missing.
- A survey with spot elevations on a sloped lot.
- Pre-approved plan sets, which list the height they assume.
Height on California’s “must approve” ADU
Section 66323 says a city must approve a new detached ADU with 4-foot side and rear setbacks on a single-family lot. The city may limit its height only to the state floors in section 66321 4.
In plain terms, the height floor follows the unit into the fast lane. The city cannot set a lower height for it.
Sources: [4]
Height rules in other states
Most states leave ADU height to cities and counties. Some state ADU laws set minimum heights or limit local rules. Many do not.
Rules vary. Check the ADU law tracker by state and then your city code.
How height affects cost
Taller buildings need more framing, longer stairs and often more engineering. A second story also needs a stair that meets the building code.
A tight height limit can push you to a one-story plan, which uses more ground. See the ADU cost guide and the cost calculator for drivers.
Benefits and limits of height limits
What it does well
- Protect neighbors’ light and privacy.
- Keep the scale of a street consistent.
- Give a clear number to design to.
Where it falls short
- Can rule out a second story.
- Different measuring methods cause confusion.
- Sloped lots can lose height to grade rules.
Height compared with other envelope limits
| Limit | Controls | Changes with a second story? |
|---|---|---|
| Height limit | How tall | Yes, it decides if one fits |
| Setback rules | Where it stands | No |
| Lot coverage cap | Ground footprint | No |
| FAR | Total floor area | Yes |
Checklist for your project
- Copy your district’s height limit and definition.
- Confirm which California floor applies, if any.
- Get grade points from a survey if the lot slopes.
- Draw elevations with the measured height marked.
- Check daylight planes and story counts.
- Submit. In California a complete application must be decided within 60 days 5.
Check your design
- ADU size envelope calculatorHeight, setbacks and footprint together
- ADU configuratorTry one- and two-story layouts
Related guides and research
Questions about height limit
How tall can an ADU be in California?
Cities must allow at least 16 feet for a detached ADU, 18 feet near major transit (plus 2 feet for a matching roof pitch) or on a multistory multifamily lot, and 25 feet or the house’s limit, whichever is lower, for an attached ADU (Gov. Code 66321(b)(4)). Cities may allow more.
Can I build a two-story ADU?
Only if the height limit that applies to your lot allows it. Under California’s 16-foot floor a full second story rarely fits; an attached ADU under the 25-foot floor, or a city that allows more, can make it possible.
How is building height measured?
From a defined grade to a defined point on the roof. Codes differ: some use natural grade and the highest point, others average grade and the midpoint of a pitched roof. The local zoning code’s definition controls.
Does a chimney or solar panel count toward the height limit?
Often not, within limits. Many codes exempt chimneys, vents and rooftop equipment up to a set projection, but the exemption and its size vary by city.
How tall can a detached ADU be?
In California, a city must allow at least 16 feet for a detached ADU, or 18 feet in some cases near transit or on multistory multifamily lots. A city can allow more. Outside California, the local zoning code sets the limit.
Can a California city limit an ADU to one story?
For an attached ADU, the state floor is 25 feet or the house limit if lower, and a city need not allow more than two stories. For a detached ADU, the 16-foot floor may not fit two full floors, so a one-story or loft design is common.
Is ADU height measured to the ridge?
It depends on the local code. Some measure to the highest point of the roof. Others measure to the midpoint of a pitched roof. Read the definition of height in your zoning code or ask the planning department.
Does the extra 2 feet near transit apply to every ADU?
No. California adds up to 2 feet for a roof pitch that matches the main house, for a detached ADU within half a mile walking distance of a major transit stop or high-quality transit corridor. The city confirms if your lot qualifies.
What is a daylight plane?
A daylight plane is an angled line starting at a set height on the property line and rising inward. A building may not cross it. It trims the top corners of a building near a neighbor. Not every city uses one.
Sources
- California Legislature, Government Code §66321 (as amended by SB 543, Stats. 2025, ch. 520), retrieved .
- California Legislature, Government Code §66314, objective standards including height (as amended by AB 1170, Stats. 2025, ch. 67), retrieved .
- California Legislature, Government Code §66313, definitions (as amended by SB 543, Stats. 2025, ch. 520), retrieved .
- California Legislature, Government Code §66323, ADUs a local agency must approve ministerially (as amended by SB 543, Stats. 2025, ch. 520), retrieved .
- California Legislature, Government Code §66317, ministerial review and timelines (as amended by SB 543, Stats. 2025, ch. 520), retrieved .
Expert review
Written by the HyreADU Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Heights were copied from Government Code §66321(b)(4) as read on leginfo.legislature.ca.gov on 7 October 2026. Section 66314 lets a city impose objective height standards [g66314]; Chapter 13 terms are defined in §66313 [g66313].
The worked example uses stated hypothetical dimensions only. Government Code §§66317 and 66323 were also read on 7 October 2026. The second worked example uses stated hypothetical inputs only.
Suggest a correction. We fix errors and say what changed.