Check Height Limit Restrictions
ADU height limits determine whether you can build a two-story unit, how much headroom you'll have, and even roof design options. Most jurisdictions limit ADUs to 16-25 feet, but rules vary significantly.
Quick Summary
Typical one-story
16-18 feet
Two-story allowed
20-25 feet
Measured to
Roof peak or midpoint
Why Height Limits Matter
Height restrictions affect more than just whether you can have two floors:
- Ceiling height: Code requires minimum 7.5-8 feet ceilings. Combined with roof structure, a 16-foot limit means single-story only.
- Roof design: Higher limits allow pitched roofs with attic storage or vaulted ceilings. Lower limits may require flat roofs.
- Two-story option: A 20+ foot limit opens up two-story designs, maximizing floor space on a small footprint.
- Construction cost: Two-story ADUs can cost less per square foot than single-story (shared foundation and roof).
How Height Is Measured
Different jurisdictions measure height differently. Know which method yours uses:
To Roof Peak
Height measured from grade to the highest point of the roof. This is the most restrictive method and limits roof pitch options. A 16-foot limit to peak allows about 8-foot ceilings with a standard roof.
To Roof Midpoint
Height measured to the midpoint between eave and peak. This allows steeper roof pitches within the same height limit. A 16-foot limit to midpoint might allow a peak of 18-20 feet.
From Average Grade
On sloped lots, height is often measured from the average grade around the building (not the lowest or highest point). This can work for or against you depending on where you place the ADU.
From Natural vs. Finished Grade
Some codes measure from natural (original) grade, others from finished (after grading) grade. If you're adding fill, natural grade measurement is more restrictive.
Typical ADU Height Limits by Type
| ADU Type | Typical Limit | Notes |
|---|---|---|
| Detached (one-story) | 16-18 ft | Most common |
| Detached (two-story) | 20-25 ft | May require more setback |
| Garage conversion | Existing height | Usually can't increase |
| Attached to main house | Match main house | Often same as primary |
| Above garage | 18-25 ft | Varies by jurisdiction |
Height and Setback Interactions
Many jurisdictions tie height limits to setbacks. Common rules include:
Daylight Plane
Building must stay within an imaginary plane starting at a set height at the property line and angling up at 45 degrees. This limits how tall you can build near property lines.
Stepped Height
Maximum height increases with distance from property line. For example: 16 feet within 5 feet of property line, 20 feet if 10+ feet away.
Two-Story Setback Increase
Two-story ADUs may require greater setbacks than one-story (e.g., 5 feet for one story, 10 feet for two stories).
Frequently Asked Questions
Can I add a loft within my ADU?
Yes, if ceiling height allows. Lofts typically need 5-7 feet of headroom. A 16-foot ADU with a flat ceiling can include a sleeping loft. Vaulted ceilings create loft opportunities in the peak area.
Do cupolas or roof structures count toward height?
Usually yes, except small exceptions for chimneys, vents, and solar panels. Decorative cupolas typically count. Check your specific code for allowed exemptions.
What if my lot is sloped?
Sloped lots can work to your advantage or disadvantage. A two-story ADU built into a hillside might appear as one story from the street. Or a downslope lot might limit height severely. Consult an architect familiar with your jurisdiction.
Ready for the Next Step?
The final feasibility item is parking requirements—some cities require additional parking for ADUs while others have waived this entirely.