September 14, 2026
Before a luxury home in Los Angeles has an architect, a budget, or a floor plan, it has a number: the maximum Residential Floor Area the lot is allowed to hold. That number comes from the City's Baseline Mansionization Ordinance and its hillside counterpart, and it decides more about a project than almost any design choice that follows. It also rewards the owners who understand how it is counted — because the rules treat a double-height living room, a front-loaded garage, and a basement very differently. This report covers the limits by zone, what counts toward them and what does not, how hillside lots are calculated, and the massing rules that shape the house inside the number. Figures are from Chapter 1 of the Los Angeles Municipal Code as currently published, which the Department of City Planning's January 2026 zoning summary identifies as the governing text.
First, Confirm Which Rules Apply to Your Lot
These limits apply only to property in the City of Los Angeles. West Hollywood, Beverly Hills, Santa Monica, Malibu, and Culver City are separate cities with their own codes, and unincorporated areas fall under Los Angeles County. A Los Angeles mailing address does not settle the question.
For a City parcel, three facts drive everything below, and all three are shown on the City's ZIMAS parcel lookup:
- The zone — RA, RE9 through RE40, RS, R1, or one of the R1 Variation Zones such as R1V2 or R1R3.
- Whether the lot is in a designated Hillside Area, which switches the calculation to a slope-based formula.
- Whether the lot is in the Coastal Zone. Coastal Zone lots outside the Hillside Area are not subject to Residential Floor Area limits at all; they are governed by a separate floor area calculation tied to their height district.
Los Angeles is also phasing in a new zoning code, Chapter 1A, through community plan updates. ZIMAS shows which chapter governs a parcel, and it is worth confirming before any of the numbers here are relied on.
The Limits by Zone
The current ratios were set by Ordinance No. 184,802, effective March 17, 2017, which the Planning Department summarized in Zoning Information File 2462. For lots outside the Hillside Area and Coastal Zone, the maximum Residential Floor Area of all buildings on the lot, including accessory buildings, is:
| Zone | Maximum Residential Floor Area | 20% bonus available? |
|---|---|---|
| R1 | 45% of lot area, regardless of lot size | No |
| RS | 45% for lots under 9,000 sq ft; otherwise 40% or 4,050 sq ft, whichever is greater | Yes |
| RE9, RE11 | 40% for lots under 15,000 sq ft; otherwise 35% or 6,000 sq ft, whichever is greater | Yes |
| RE15, RE20, RE40 | 35% or 6,000 sq ft, whichever is greater | Yes |
| RA | 25% for lots under 20,000 sq ft; otherwise 20% or 5,000 sq ft, whichever is greater | Yes |
In practice: a flat 7,500-square-foot R1 lot allows 3,375 square feet. A 12,000-square-foot RE11 lot allows 4,800, and a 30,000-square-foot RE15 lot allows 10,500.
The bonus in the RA, RE, and RS zones adds 20% to the maximum, and only one bonus is allowed per property. On a flat lot it is earned in one of two ways: keeping every story above the base floor to no more than 75% of the base floor's area, or stepping back at least 25% of the front-facing building width by at least 20% of the building depth. Both are massing decisions, so the bonus has to be designed for from the start — it cannot be claimed after the plans are drawn. The 2017 ordinance eliminated every bonus option in the R1 zone, and eliminated the green-building bonus everywhere.
The R1 Variation Zones Change the Number
Many R1 neighborhoods carry a variation zone suffix, and it changes the ratio substantially. The variable-mass (R1V), front-mass (R1F), and rear-mass (R1R) zones each come in four intensities, with ratios that step down as lot size increases, and each carries its own maximum lot coverage.
| Lot size | V1 / F1 / R1 | V2 / F2 / R2 | V3 / F3 / R3 | V4 / F4 / R4 | Max lot coverage |
|---|---|---|---|---|---|
| Up to 6,000 sq ft | 0.65 | 0.55 | 0.45 | 0.40 | 50% |
| 6,001–7,000 sq ft | 0.63 | 0.53 | 0.43 | 0.38 | 48% |
| 7,001–8,000 sq ft | 0.61 | 0.51 | 0.41 | 0.36 | 46% |
| 8,001–9,000 sq ft | 0.59 | 0.49 | 0.39 | 0.34 | 44% |
| 9,001–10,000 sq ft | 0.57 | 0.47 | 0.37 | 0.32 | 42% |
| Over 10,000 sq ft | 0.55 | 0.45 | 0.35 | 0.30 | 40% |
The spread is wider than most buyers expect. On the same 7,500-square-foot lot, an R1V1 designation allows 4,575 square feet and an R1V4 designation allows 2,700 — a difference of 1,875 square feet, determined entirely by a suffix on the zoning map. The front-mass and rear-mass zones add a second constraint, dividing the buildable envelope into a taller mass and a lower one at opposite ends of the lot.
What Counts Toward the Limit
The Municipal Code's definition of Residential Floor Area is the area inside the exterior walls of every building on the lot. Three provisions in that definition matter more to luxury design than any other.
Tall ceilings count twice
Any floor area with a ceiling height greater than 14 feet counts as twice its square footage. Stairways and elevator shafts are counted once regardless of height. A 600-square-foot living room with an 18-foot ceiling therefore uses 1,200 square feet of allowance — on a 3,375-square-foot R1 envelope, the extra 600 square feet is nearly a fifth of the house. The double-height entry, the vaulted great room, and the two-story glass volume are all still possible; they are simply paid for in floor area that could otherwise be a bedroom.
Attics can count
Any portion of an attic with a ceiling height over 7 feet is included in the calculation.
Covered porches count
The 2017 ordinance eliminated the former 250-square-foot exemption for covered porches, patios, and breezeways. A solid-roofed outdoor room now counts as floor area. Porches, patios, and breezeways with a lattice roof do not.
What Does Not Count
The definition exempts four categories, and each one is a design lever.
- Required covered parking. Up to 400 square feet is exempt if all of it is located on the rear half of the lot or at least 55 feet from the front lot line. If it is not — the typical front-loaded attached garage — only 200 square feet is exempt. Moving the garage back is worth 200 square feet of house.
- Basements. On lots outside the Hillside Area and Coastal Zone, a basement is exempt when the floor or roof above it sits no more than 2 feet above the lower of natural or finished grade at any point. On Hillside Area lots, the threshold is 3 feet for at least 60% of the basement's perimeter. One depressed driveway up to 20 feet wide and up to two light wells — not visible from the street, projecting no more than 3 feet and no wider than 6 feet — do not disqualify the exemption.
- Small detached accessory buildings. Detached structures of 200 square feet or less are exempt, up to 400 square feet combined per lot.
- Lattice-roof porches, patios, and breezeways.
The basement exemption is the reason so many recent luxury homes in Los Angeles have gone down rather than up. A qualifying basement can hold a gym, a screening room, a wine room, and staff quarters without consuming any of the lot's above-grade allowance. The engineering, shoring, and waterproofing that make that possible are covered in our 2026 Los Angeles Subterranean & Basement Build Report.
Hillside Lots Use a Slope Formula
In a designated Hillside Area, the maximum is not a single percentage. The lot is divided into slope bands, each band's area is multiplied by its own ratio, and the results are added together. Steeper ground contributes less, and ground steeper than 100% contributes nothing.
| Slope band | R1 | RS | RE9 / RE11 | RE15 / RE20 / RE40 | RA |
|---|---|---|---|---|---|
| 0–14.99% | 0.45 | 0.45 | 0.40 | 0.35 | 0.25 |
| 15–29.99% | 0.45 | 0.40 | 0.35 | 0.30 | 0.20 |
| 30–44.99% | 0.40 | 0.35 | 0.30 | 0.25 | 0.15 |
| 45–59.99% | 0.35 | 0.30 | 0.25 | 0.20 | 0.10 |
| 60–99.99% | 0.30 | 0.25 | 0.20 | 0.15 | 0.05 |
| 100% and over | 0 | 0 | 0 | 0 | 0 |
Consider a 10,000-square-foot R1 hillside lot with 2,000 square feet in the flattest band, 3,000 in the 30–45% band, 3,000 in the 60–100% band, and 2,000 steeper than 100%. Its maximum is 900 + 1,200 + 900 + 0 = 3,000 square feet — against 4,500 had the same lot been flat. The calculation requires a slope analysis map prepared by a registered civil engineer or licensed land surveyor, and the Planning Department must approve the resulting maximum before a building permit application goes to the Department of Building and Safety.
Two provisions soften the formula. Every hillside lot is guaranteed a minimum — 25% of lot area in R1, stepping down to 13% in RA, and never less than 800 square feet. And lots in the RA, RE, and RS zones remain eligible for a bonus of 20%, or 30% where the guaranteed minimum is used, by meeting one of the design options the code lists. Hillside lots also carry grading limits; the foundation, grading, and haul implications are covered in our 2026 Los Angeles Hillside Construction Report.
The Rules That Shape the House Inside the Number
Floor area sets how much house there is. In the R1 zone, a second set of rules in Section 12.08 sets its shape.
- Height depends on the roof. In the standard R1 zone in Height District 1, a roof pitched at 25% or more may reach 33 feet; a flatter roof is capped at 28 feet. A flat-roofed modern house gives up five feet of height to a pitched-roof neighbor.
- The encroachment plane. An imaginary plane rises at 45 degrees from a point 20 feet above grade along the required front and side setbacks, and the building may not extend through it. It is what pushes upper floors inward from the property lines.
- Side wall articulation. Any side wall more than 14 feet high and more than 45 feet long must include an offset or plane break at least 5 feet deep and 10 feet long.
- Roof decks and driveways. Roof decks must sit at least 3 feet back from the minimum side yard, and outside the Hillside Area a driveway may be no wider than 25% of the lot width, or the existing driveway, and never required to be narrower than 9 feet.
The R1 Variation Zones substitute their own heights and encroachment plane origins, ranging from 30-foot masses with 22-foot plane origins in the most permissive zones down to 20-foot maximums with 14-foot origins in R1V4.
The Bottom Line
In Los Angeles, the size of a single-family home is decided by a formula before it is decided by a design. The formula is not complicated, but its details carry real consequences: a zoning suffix can move the allowance by nearly two thousand square feet, a tall ceiling can quietly consume a bedroom's worth of area, a garage location is worth 200 square feet, and a qualifying basement sits outside the calculation entirely.
The owners who get the most house from a lot are the ones who run the numbers before they buy, and who design to the formula rather than discovering it at plan check. The ones who get the least are the ones who fall in love with a double-height volume and a front garage on a lot whose ratio was never going to hold both.
How Blackbriar Plans a House to the Code
Blackbriar Development runs the floor area calculation at the very start, often before a lot is purchased. Our pre-construction process confirms the parcel's jurisdiction, zone, variation suffix, and hillside status, calculates the maximum including any available bonus, and tests the design moves that consume or preserve allowance — ceiling heights, garage placement, and what belongs below grade — while they are still sketches rather than redesigns. Our full-service approach carries that analysis through permitting and construction, so the house that is built is the one the numbers allowed.
If you are evaluating a lot or planning a new home in Los Angeles, see our recent work or start a conversation about what your site can hold.
FAQ
How big a house can I build on an R1 lot in Los Angeles?
Outside a Hillside Area or the Coastal Zone, the maximum Residential Floor Area in the standard R1 zone is 45% of lot area, including accessory buildings, with no bonus available. A 7,500-square-foot lot allows 3,375 square feet. The R1V, R1F, and R1R Variation Zones use their own ratios, from 0.30 to 0.65 depending on the zone and lot size, and hillside R1H lots use a slope-based formula.
Does a basement count toward the floor area limit?
Not if it qualifies. On a flat lot outside the Coastal Zone, a basement is exempt when the floor or roof above it is no more than 2 feet above grade at any point. On a Hillside Area lot, the threshold is 3 feet for at least 60% of the basement's perimeter. One depressed driveway and up to two concealed light wells are allowed without losing the exemption.
Do high ceilings count against my allowance?
Yes. Any area with a ceiling height greater than 14 feet counts twice, although stairways and elevator shafts are counted once regardless of height. Attic space with more than 7 feet of ceiling height also counts.
Does the garage count as floor area?
Partly. Up to 400 square feet of required covered parking is exempt if all of it sits on the rear half of the lot or at least 55 feet from the front lot line. Otherwise only 200 square feet is exempt, and the rest counts.
How do I find out which rules apply to my property?
Look the parcel up on the City's ZIMAS system, which shows the zone, any R1 Variation Zone suffix, Hillside Area and Coastal Zone status, and which chapter of the zoning code governs it. First confirm the property is in the City of Los Angeles at all — neighboring cities such as West Hollywood and Beverly Hills set their own limits.