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Building a detached ADU in Granada Hills

On a Granada Hills lot you can always build a detached backyard house of up to 800 square feet, 16 feet tall, set 4 feet from the side and rear lines 12. The typical lot in 91344 is 8,345 square feet, so many owners go further and use Los Angeles's own rules for a unit of up to 1,200 square feet and two stories 73. What decides the final size and spot is rarely the lot's size. It is the zone's floor-area limit, whether the lot is on a hillside or in the fire zone, and how far the unit sits from the street and the utilities.

Edited by Ryan Rambo, construction managerFacts checked 2026-10-11

How big a backyard house can I build on my Granada Hills lot?

Start with two numbers. State law guarantees one detached, newly built ADU of up to 800 square feet with 4-foot side and rear setbacks on any lot with a house 1, and it can be at least 16 feet tall 2. The city's own ADU ordinance allows a detached unit of up to 1,200 square feet and up to two stories 3.

The 800 square foot unit is the floor. Your zone's residential floor area (RFA) limit, lot coverage and front setbacks can trim a larger ordinance unit, but RFA may not be enforced on a state-law ADU or used to push a detached unit below 800 square feet 4.

You can usually stack options too. Los Angeles lets a detached state-law ADU be combined with an attached ordinance ADU, or an attached state-law ADU with a detached ordinance ADU, and a junior ADU of up to 500 square feet inside the house generally combines with the single-family options 56. For what fits on a smaller lot, see what size ADU fits on a 6,600 sq ft lot, and for height, how tall an ADU can be in LA.

What are my Granada Hills neighbors actually building?

Mostly bigger units than the state minimum. We pulled every new-building ADU permit issued in 91344 from January 2, 2025 to October 2, 2026: 104 permits, with a median size of 1,036 square feet, and 65 of them over 800 square feet 8.

A few other things stand out in those permits 8:

A handful (6) were SB 9 projects, so treat these as a picture of local practice, not a count of backyard houses. The per-ZIP permit trend is in how many ADUs are being built in the Valley, and what those sizes cost is in ADU cost in Granada Hills.

My lot is big. Why might the city still cap my ADU below 1,200 square feet?

Because a big lot usually carries a big house, and the floor-area limit counts both. In the R1, RE, RS and RA zones, the RFA limit can apply separately to an ordinance ADU and further limit its size 4. The median house in 91344 is 1,786 square feet 7, so a large house on an average lot can use up more of the allowance than you would expect.

The zone letters on your lot matter here, because RA, RE and RS lots do not share one formula. Look up your zone in ZIMAS before you pick a plan size.

One Granada Hills tract has its own layer. The Balboa Highlands Historic Preservation Overlay Zone (HPOZ), the Eichler neighborhood adopted in 2010, is the first post-World War II neighborhood in the Valley with historic district status 10. The city says an HPOZ standard that would hold an ADU to less than 800 square feet is superseded for a state-law ADU 9. If your lot is in that tract, ask City Planning's HPOZ staff what review your design needs before you pay for plans.

Check your own lot, free.

Put in your address and see your zoning, lot size, fire and hillside zones, sewer distance and what is already built, from the city's own records.

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My lot slopes. What changes for a detached ADU?

A slope by itself does not rule out a backyard house, but the city's Hillside Area label changes the review. Whether you are in a Hillside Area is set by the city's Hillside Area Map, not by how steep the yard looks 11; ZIMAS shows it per parcel.

If your lot is in a Hillside Area, expect the Baseline Hillside Ordinance to shape a larger ordinance ADU, and expect more soil and grading review. Both are covered in building an ADU in an LA Hillside Area and when an ADU needs a soils report.

If the lot is in both a Hillside Area and the fire zone, the city generally cannot require street improvements for an ADU, but an ordinance ADU there may face dedications and a 20-foot street frontage requirement 12. That is one reason some owners on those lots stay with an 800 square foot state-law unit.

Does the fire zone change how I build a detached ADU in Granada Hills?

It changes how you build more than whether you can. About one in six single-family parcels in 91344 touch the city's Very High Fire Hazard Severity Zone on a 2019 map layer 13, and the Fire Department expects more parcels to be added under CAL FIRE's 2025 maps 14.

For a detached unit the practical effects are fire-resistant materials, a possible Fire Department access review on a deep lot, and sprinklers in some cases. An ADU cannot be required to have sprinklers when the main house was not required to have them 16. The details are in building an ADU in a Granada Hills fire zone and when an ADU needs fire sprinklers in LA.

How far back can I put it before access and utilities get hard?

The deeper the unit sits, the more it pulls in. On new construction valued at $50,000 or more, if any part of the building is 150 feet from the edge of an improved street or approved fire lane, LADBS sends you to the Fire Department's Hydrants and Access Unit for clearance 15. Long Granada Hills lots with the unit at the very back are where this comes up. See LA's 150-foot fire access rule.

Every service also has to reach the back of the lot. Before you settle on a spot, check these:

  1. Sewer. Where the main is, whether the backyard house can tie into your existing line, and whether that line is sound. See sewer main more than 200 feet away.
  2. Water. Whether your meter is big enough. See do I need a new water meter for an ADU.
  3. Power. Whether your panel and service can carry the new load. See ADU electrical panel upgrades in LA.
  4. What is in the way. Easements and protected trees can block a trench or a footprint. See ADU easements and LADWP and protected oak trees in Granada Hills.

A longer run means more trenching, so the spot you pick changes the all in number.

What should I look up before I pay for plans?

Five lines from the city's parcel report tell you most of what you need. Search your address in ZIMAS and write down:

  1. Zone (RS, RA, RE, R1 and so on), which sets the floor-area limit for a larger unit 4.
  2. Hillside Area, yes or no 11.
  3. Very High Fire Hazard Severity Zone, yes or no, and check CAL FIRE's 2025 map too 14.
  4. HPOZ, which in Granada Hills means Balboa Highlands 10.
  5. Lot size and depth, so you can tell whether the back of the lot is more than 150 feet from the street 15.

Then measure your house's floor area against the zone's limit, and find your sewer line and electrical panel. Putting those answers together for one specific lot is the kind of thing a lot check settles.

Quick answers

Can I build a 1,200 square foot detached ADU in Granada Hills?

Often, under the city's ordinance, which allows up to 1,200 square feet and two stories 3. Your zone's floor-area limit and lot coverage can lower that, but not below 800 square feet 4.

Can I build a two-story backyard house in Granada Hills?

Yes, the city's ordinance allows up to two stories for a detached ADU 3. In 91344, 26 of 104 new-building ADU permits issued since January 2025 describe a two-story building 8.

Can I have a detached ADU and a junior ADU on the same lot?

Generally yes. A junior ADU of up to 500 square feet inside the house generally combines with the single-family ADU options 56.

Does the Balboa Highlands HPOZ stop an ADU?

No. The city says an HPOZ standard that would hold an ADU under 800 square feet is superseded for a state-law ADU 9. Design review for anything larger is a question for City Planning's HPOZ staff.

Sources

  1. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1), issued Aug. 1, 2025, section II.A (State ADUs, GC § 66323(a)(2)), Los Angeles City Planning / LADBS. Facts checked 2026-10-11
  2. California Government Code § 66321 (mirror of the official text), California Legislature, via Public.Law. Facts checked 2026-10-11
  3. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1), issued Aug. 1, 2025, Table 1 (detached ADUs), Ordinance ADU column, Los Angeles City Planning / LADBS. Facts checked 2026-10-11
  4. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1), issued Aug. 1, 2025, Q.3 (how ADU size is measured and limited), Los Angeles City Planning / LADBS. Facts checked 2026-10-11
  5. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1), issued Aug. 1, 2025, section I.A (Combinations of ADUs and JADUs), Los Angeles City Planning / LADBS. Facts checked 2026-10-11
  6. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1), issued Aug. 1, 2025, section B (JADUs), Los Angeles City Planning / LADBS. Facts checked 2026-10-11
  7. Lot and house sizes of single-family parcels in ZIP 91344 (Greenlight analysis of the County Assessor parcel layer), Los Angeles County Office of the Assessor (data); Greenlight (method). Facts checked 2026-10-11
  8. New-building ADU permits issued in ZIP 91344, Jan. 2025 to Oct. 2026 (Greenlight analysis of LADBS permit data), LADBS via City of Los Angeles Open Data (data); Greenlight (method). Facts checked 2026-10-11
  9. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1), issued Aug. 1, 2025, section II.A (State ADUs override local limits), Los Angeles City Planning / LADBS. Facts checked 2026-10-11
  10. Balboa Highlands Historic Preservation Overlay Zone, Los Angeles City Planning. Facts checked 2026-10-11
  11. Zoning Code glossary: Hillside Area, Los Angeles City Planning. Facts checked 2026-10-11
  12. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1), issued Aug. 1, 2025, Q.32 (offsite improvements), Los Angeles City Planning / LADBS. Facts checked 2026-10-11
  13. Greenlight parcel count: LA County Assessor parcels (City of LA single-family, ZIP 91344) intersected with the City of LA Very High Fire Hazard Severity Zones layer, LA County Assessor parcel layer / City of Los Angeles GeoHub (Greenlight analysis). Facts checked 2026-10-11
  14. 2025 CAL FIRE Fire Hazard Severity Zones Map Recommendation (Apr. 4, 2025), Los Angeles Fire Department. Facts checked 2026-10-11
  15. Accessory Dwelling Unit Plan Check Correction Sheet (PC/STR/Corr.Lst.20A1, Rev. 8/03/2021), item B.7, Los Angeles Department of Building and Safety (LADBS). Facts checked 2026-10-11
  16. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1), issued Aug. 1, 2025, Q.31 (fire sprinklers), Los Angeles City Planning / LADBS. Facts checked 2026-10-11

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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.