What size ADU fits on a 6,600 square foot lot in Los Angeles?

What does state law guarantee me on a lot this size?

State law guarantees one new detached ADU of up to 800 square feet with 4-foot side and rear setbacks on any lot with a house on it, and Los Angeles has to approve it ministerially, as a routine permit ⁴. A city cannot use lot coverage, floor area ratio, open space, front setbacks or minimum lot size to block an ADU of at least 800 square feet of interior livable space with those 4-foot setbacks ³.

Los Angeles applies this directly. Its Residential Floor Area (RFA) limit, the rule that caps how much building fits on an R1 lot, cannot be enforced against these state-path ADUs, and it cannot shrink a detached ADU below 800 square feet or an attached one below 850 or 1,000 square feet ⁶. So even if your house already uses most of the lot's floor area, the 800 square foot backyard house is still on the table.

As of January 2026, state law states these sizes as interior livable space; the ADU sections of the Government Code were last amended effective January 1, 2026 ³⁴.

How big can a detached backyard house be in Los Angeles?

A detached ADU in Los Angeles can be up to 1,200 square feet, which is the state's ceiling for detached units ². Anything over 800 square feet is built under the City's own ADU ordinance (LAMC 12.22 A.33), and the City can still apply its floor-area and lot-coverage limits to that larger unit ⁶.

The state also sets a floor on how small a city can make its maximum: no city may cap an ADU below 850 square feet, or below 1,000 square feet for a unit with more than one bedroom ³. In practice that means:

• Up to 800 sq ft: guaranteed with 4-foot setbacks, no RFA fight ⁴⁶.
• 800 to 1,200 sq ft: allowed under the City ordinance if your lot's remaining floor area and coverage allow it ²⁶.
• A two-story backyard house: the City ordinance allows up to two stories for a detached ADU, within the zone's height limit ⁸.

On a 6,600 square foot lot the gap between 800 and 1,200 square feet depends on how big the existing house is. That is a number you work out from the lot's zoning and the house's recorded size before you pay for plans.

How tall can my ADU be?

A detached ADU can be at least 16 feet tall on any single-family lot ³. If your lot is within a half mile walking distance of a major transit stop or a high-quality transit corridor, the minimum rises to 18 feet, plus 2 more feet if the ADU's roof pitch matches the house, for 20 feet total ³⁸.

An ADU attached to the house can be up to 25 feet or the zone's height limit for the house, whichever is lower ³. A detached ADU built under the City ordinance rather than the state's 800 square foot path can go to two stories within the zoning height limit ⁸. For most one-story backyard houses in the Valley, 16 feet is plenty for a sloped roof.

Can I convert my garage instead, and keep it where it is?

Yes. If you convert an existing garage or rebuild it in the same place and to the same dimensions, no setback is required, so a garage sitting right on the rear or side lot line can stay there ². You do not have to replace the parking you lose when a garage is converted or torn down for an ADU ².

Under the state's conversion path, the converted space can grow by up to 150 square feet beyond the existing structure, but only to make room for getting in and out, such as an entry ⁴. A typical two-car garage becomes a studio or one-bedroom. If you want more room than that, you build new under the 800 square foot rule or the City ordinance instead, and the new walls follow the 4-foot setbacks ²⁴.

Before you count on that, confirm the garage was permitted and that its slab and walls can be brought up to building code for a dwelling. A permit search on LADBS records answers the first part.

Can I also add a junior ADU inside the house?

Usually, yes. A junior ADU (JADU) is a unit of no more than 500 square feet built entirely inside the house, and an attached garage counts as part of the house for this purpose ¹⁵. State law requires a city to approve one ADU plus one JADU on a single-family lot ⁴.

Los Angeles goes further than the state minimum. Under the City's combination rules, a detached ADU on one path can be paired with an attached ADU on the other path, and a JADU can generally be added to either ⁷. A JADU needs its own entrance and at least an efficiency kitchen, and if it shares a bathroom with the house, the owner has to live in the house or the JADU ⁵.

What actually fits in the backyard of a 6,600 sq ft Reseda or Pacoima lot?

This is an example, not your lot. Take a lot 50 feet wide and 132 feet deep, which is 6,600 square feet, close to the medians in 91335 Reseda (6,639) and 91331 Pacoima (6,968) ¹⁰.

1. Subtract 4 feet from each side line for a new detached ADU. That leaves a buildable strip 42 feet wide ⁴.
2. Suppose the house, driveway and front yard use the front 70 feet. That leaves a backyard about 62 feet deep, or 58 feet after the 4-foot rear setback ⁴.
3. An 800 square foot one-story ADU at 20 by 40 feet fits inside that 42-by-58-foot area with room to spare, and it can be 16 feet tall ³⁴.
4. A 1,000 square foot two-bedroom at 25 by 40 feet also fits on paper, but because it is over 800 square feet it has to clear the City's floor-area and coverage limits ⁶.
5. If you also turn part of the house into a 500 square foot JADU, that does not take any yard space at all ¹⁵.

What shrinks that rectangle on a real lot is rarely the zoning. It is the sewer line running through the yard, a power line overhead, a protected tree, an easement, or a detached garage sitting where the ADU wants to go. New detached ADUs also have to sit behind the house on a normal lot ⁹.

What should I check before I pay for plans?

Check four things first: the lot's zoning and recorded size, the house's permitted square footage, whether the garage was permitted, and anything in the backyard that a building cannot sit on. The first three come from City and County records; the last one needs a look at the lot.

Two things Reseda and Pacoima owners can mostly skip: none of the single-family lots in 91335 or 91331 touch the City's Very High Fire Hazard Severity Zone map in our count, so the City's extra limits for ADUs in fire and hillside areas rarely come up ¹⁰. Whether you get the 18-foot height depends on your walking distance to frequent transit, which the City lets you show with a printout from ZIMAS ⁸.

This is the kind of question a lot check settles before an architect starts drawing.

Quick answers

Sources

1. Government Code § 66313 (ADU definitions), California Legislative Information. Facts checked 2026-10-08
2. Government Code § 66314 (ADU ordinance standards), California Legislative Information. Facts checked 2026-10-08
3. Government Code § 66321 (size, height and setback limits), California Legislative Information. Facts checked 2026-10-08
4. Government Code § 66323 (ADUs that must be approved ministerially), California Legislative Information. Facts checked 2026-10-08
5. Government Code § 66333 (junior ADUs), California Legislative Information. Facts checked 2026-10-08
6. ZA Memo 143, Revision 1: Implementation of the ADU Ordinance and State ADU Law (Q.3), Los Angeles City Planning and LADBS. Facts checked 2026-10-08
7. ZA Memo 143, Revision 1: Combinations of ADUs and JADUs, Los Angeles City Planning and LADBS. Facts checked 2026-10-08
8. ZA Memo 143, Revision 1: Table 1 (detached ADU options) and Q.34 (transit proximity), Los Angeles City Planning and LADBS. Facts checked 2026-10-08
9. ZA Memo 143, Revision 1 (Q.37, detached ADU location), Los Angeles City Planning and LADBS. Facts checked 2026-10-08
10. LA County Assessor parcel layer (Greenlight analysis of single-family lots by ZIP), Los Angeles County Office of the Assessor, via LA County GIS. Facts checked 2026-10-08

Greenlight is not a contractor, architect or engineer, and this is not legal advice. Rules change; every fact here shows the date we last checked it.