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R1 Zoning: What It Means and What You Can Build

R1 zoning is a single-family residential district, but the rules differ by city. Compare 10 real codes, state duplex and ADU laws, and how to check a lot.

Pillar team17 min read

R1 zoning (also written R-1) is a residential zoning district meant mainly for detached single-family homes. It usually allows one house per lot, plus accessory buildings and often an accessory dwelling unit, and sets a minimum lot size, setbacks and a height limit. Each city or county writes its own R1 rules, so the label alone tells you little.

This guide is written by Pillar, a land research platform. The figures come from each jurisdiction's code or planning department and from state statutes and agency pages, read on November 10, 2026. Codes change, so open the linked section before you rely on a number.

What does R1 zoning mean?

The "R" means residential. The number means whatever the local code says it means, and some codes split R1 into variants such as Phoenix's R1-6 and R1-10.

R1 is also not always the lowest-density residential district. Phoenix's RE-35 requires 150-foot-wide lots, Fairfax County's R-A district requires 5 acres, and Albuquerque's R-A requires 10,890 square feet against 3,500 in R-1.

What can you build on R1 zoning?

In most of the codes below, an R1 lot takes one detached house plus accessory structures. What changes is the lot size and the envelope the house has to fit inside. Here are ten codes, plus Houston, which has no zoning.

  • Phoenix, Arizona (R1-6, R1-10). The R1-6 standard option requires a 60-foot lot width and 94-foot depth, at up to 5.5 dwelling units per gross acre. Setbacks are 20 feet front, 25 rear, 10 on a street side, and 10 and 3 on the interior sides. Height is 2 stories and 30 feet. Lot coverage is 50%, plus 10% for an ADU or attached shade structures. R1-10 requires an 80-foot width at 3.5 units per acre. Section 608 allows one detached house per lot and two ADUs.
  • New York City (R1-1, R1-2, R1-2A). Section 23-11 requires 7,125 square feet and a 75-foot width in R1-1, and 4,750 square feet and 50 feet in R1-2 and R1-2A, for a detached residence. The standard floor area ratio is 0.75, though on a standard lot of 4,000 square feet or more the floor area of any one dwelling unit can't exceed a ratio of 0.60. The front yard is 20 feet, each of two side yards is 8 feet, and lot coverage on an interior lot is 40%. Section 22-122 limits R1 and R2 lots to single-family detached residences unless the lot is a "qualifying residential site," a term defined in Section 12-10. Its tests include lot area, location in the Greater Transit Zone and community facility space that existed on December 5, 2024, so check it for your lot.
  • Los Angeles, California (R1). Section 12.08 of the municipal code requires a 5,000-square-foot lot at least 50 feet wide. The front yard is 20% of lot depth, up to 20 feet, but where developed lots making up 40% or more of the frontage have front yards within 10 feet of each other, the minimum is their average. Side yards are 5 feet for a building of up to two stories (10% of lot width, and no less than 3 feet, on a lot narrower than 50 feet), plus 1 foot for each story above the second. A side wall more than 14 feet high and more than 45 feet long needs an offset at least 5 feet deep and 10 feet long. The rear yard is 15 feet. Outside a Hillside Area or Coastal Zone, residential floor area can't exceed 45% of lot area. The uses include one-family dwellings and, on a lot whose side lot line adjoins a commercial or industrial zone, two-family dwellings, if the lot extends no more than 65 feet from that zone and has 5,000 square feet of lot area for each two-family dwelling. The Department of City Planning's zoning summary, updated January 2026, lists the height as 28 or 33 feet depending on roof slope in Height District 1. The RS zone (7,500 square feet) and the RE zones (9,000 to 40,000) require larger lots.
  • Fairfax County, Virginia (R-1). Section 2102 says R-1 "provides for single-family detached dwellings on large lots" and limits a conventional subdivision to 1 dwelling unit per acre, with a 36,000-square-foot minimum lot, a 150-foot width on interior lots, setbacks of 40 feet front, 20 side and 25 rear, and a 35-foot height limit.
  • Raleigh, North Carolina (R-1). Section 2.1.1 limits R-1 to 1 unit per acre. A detached house needs a 40,000-square-foot lot 100 feet wide, with setbacks of 20 feet from the primary street, 10 from a side lot line and 30 from the rear, and a height limit of 40 feet and 3 stories.
  • Albuquerque, New Mexico (R-1). The Integrated Development Ordinance effective May 2026 calls R-1 the "Residential – Low-Density" district (section 2-3(B)). It sets a 3,500-square-foot minimum lot, a 25-foot width, setbacks of 10 feet front, 5 interior side and 10 rear, and a 26-foot height limit. Section 4-3(B)(1) allows only one single-family dwelling per lot unless the homes are part of a cottage development.
  • Spokane, Washington (R1). For a conventional subdivision, the dimensional table sets a 1,200-square-foot minimum lot, a 15-foot width and an 80-foot depth, with 65% building coverage, a 40-foot height limit, and setbacks of 10 feet front and 15 rear. Unit lot subdivisions follow separate standards, with no minimum area for the child lots. The use table permits single-unit buildings, middle housing and ADUs. The code's definition of middle housing includes duplexes through sixplexes, cottage housing and courtyard apartments.
  • Portland, Oregon (no R1). Chapter 33.110 allows houses, duplexes, triplexes and fourplexes in the R20 through R2.5 zones, each subject to its own housing-type standards (Table 110-2). Triplexes and fourplexes need frontage on a maintained street and a minimum lot area, which is 3,000 square feet in R5 (Table 110-7). In R5, height is 30 feet, setbacks are 10 feet front and 5 feet side and rear, and the maximum floor area ratio rises from 0.5 for one unit to 0.8 for four or more (Table 110-4).
  • San Diego, California (RS-1-1 to RS-1-14). The RS zones allow 1 dwelling unit per lot. Minimum lot size runs from 40,000 square feet in RS-1-1 to 5,000 in RS-1-7. RS-1-7 requires a 50-foot width and 50 feet of street frontage, with setbacks of 15 feet front, 4 side and 13 rear.
  • Milwaukee, Wisconsin (RS1 to RS6). Chapter 295, subchapter 5 sets the minimum lot for a detached house from 20,000 square feet in RS1 to 3,600 in RS6, widths from 100 to 30 feet, and a 45-foot height limit. A two-family dwelling is allowed only where the premises was legally established and occupied as one as of October 1, 2002; otherwise it is a prohibited use. One accessory dwelling unit per parcel is a limited use, whether internal, attached or detached. When it is added to an existing home, at least one owner must live in that home as a primary residence when the permit application is filed.
  • Houston, Texas (no zoning). The city says it "does not have zoning" and that its codes "do not address land use." Lot size is shaped by tools such as a neighborhood-initiated Special Minimum Lot Size, and by deed restrictions, some of which the city is authorized to enforce by suit.

Can you build a duplex or an ADU on an R1 lot?

A duplex is often not allowed under the local code alone, though state laws now require many cities to allow one and some R1 zones, such as Spokane's, already do. An ADU is allowed more often. Read the local code first, then state law.

ADUs. Phoenix allows two per lot. Albuquerque allows one, up to 750 square feet (section 4-3(F)(6)). Raleigh allows one on a lot with a detached house. Fairfax County permits one "accessory living unit" by administrative permit, only with a single-family detached house and wholly inside it. The unit can't exceed 800 square feet or 40% of the principal dwelling's gross floor area, whichever is less, or it may fill the basement or cellar, up to that level's size as of May 10, 2023. Either the unit or the house must be owner-occupied, and the unit may have no more than two bedrooms and two occupants (subsection 4102.7.B).

Duplexes. Most R1 districts above do not allow one outright. Albuquerque shows why you read past the use table: the table marks a duplex as permitted in R-1, but section 4-3(B)(5) prohibits it there unless the lot is in or within 1,320 feet of a Main Street or Premium Transit area, or the building straddles a lot line with one unit on each lot. Spokane and Portland allow duplexes and larger buildings in the zones above.

State laws that override local rules. These are the ones we read:

  • California. SB 9 requires ministerial approval of qualifying two-unit projects and urban lot splits on eligible parcels in single-family zones. Eligibility turns on location, environmental, tenant-protection, historic-resource and other conditions in the statute. Litigation over SB 9 in charter cities was unresolved in the sources we read: a trial court held SB 9 unconstitutional as to five charter cities in 2024, and on November 12, 2025, the Court of Appeal reversed that judgment in an unpublished opinion and sent the case back to be reconsidered under the law as amended by SB 450. We found no later ruling in a primary source, so ask the city how it applies SB 9. Separately, HCD's March 2026 ADU Handbook says a single-family lot is entitled to ministerial approval of a converted ADU, a junior ADU, and a detached ADU of up to 800 square feet with 4-foot side and rear setbacks.
  • Oregon. ORS 197A.420, which began as HB 2001 in 2019 and has been amended since, requires each county, each city of 25,000 or more and each city of 1,000 or more within Metro to allow duplexes, triplexes, quadplexes, cottage clusters and townhouses on each lot zoned for residential use. Cities outside Metro with at least 2,500 but fewer than 25,000 people must allow a duplex. "Zoned for residential use" is a defined term: the land must be inside an urban growth boundary, allow a detached single-unit dwelling, and not be zoned primarily for commercial, industrial, agricultural or public uses. The statute also treats cities and several named communities in Tillamook County as cities of 25,000 or more, whatever their size. Cities have until January 1, 2027 to conform to the 2025 amendments, and until January 1, 2028 for the cottage cluster changes.
  • Washington. RCW 36.70A.635, enacted by HB 1110 in 2023, applies to cities that plan under the Growth Management Act. Cities of at least 25,000 but fewer than 75,000 people must allow at least two units per lot on lots zoned predominantly for residential use, and cities of 75,000 or more at least four. Those numbers rise to four and six within a quarter mile's walk of a major transit stop, or when at least one unit (two in the larger cities) is affordable housing. A city under 25,000 must allow two units per lot if it sits in a contiguous urban growth area with the largest city in a county of more than 275,000 people. The section does not apply to critical areas and their buffers, among other exclusions, and a city may instead apply it to at least 75% of its single-family lots. Each city's deadline is tied to its comprehensive plan schedule. RCW 36.70A.681 requires cities and counties that plan under the act to allow at least two ADUs per lot in urban growth area zones that allow single-family homes, except on lots with critical areas or their buffers and in certain impaired drinking-water watersheds. Under RCW 36.70A.680, the ADU rules take effect with each jurisdiction's next periodic comprehensive plan update.
  • Arizona. A.R.S. 9-462.13 requires municipalities of 75,000 or more to allow duplexes, triplexes, fourplexes and townhomes as a permitted use on all lots zoned for single-family residential use within one mile of the central business district, and on at least 20% of any new development of more than 10 contiguous acres. The deadline to adopt was January 1, 2026; where a municipality missed it, the statute allows middle housing on all of its single-family lots without limitation. The statute excludes areas without water and sewer service or sufficient urban services, and land in the vicinity of public and military airports, among others. A.R.S. 9-461.18 requires municipalities of more than 75,000 to allow at least one attached and one detached ADU on any lot where a single-family dwelling is allowed, except on tribal land and near military and certain other airports.
  • Maine and Massachusetts. Maine requires municipalities to allow an ADU on the same lot as a single-family home, or a two- or three-unit building, in any area where residential uses are permitted, including as a conditional use. The statute has exceptions, including one for a protected drinking-water watershed in Lewiston and Auburn, and the unit must still meet shoreland zoning rules. Massachusetts has allowed one ADU by right in single-family zoning districts since February 2, 2025. The unit can be no larger than half the principal dwelling's gross floor area or 900 square feet, whichever is smaller, and a city or town may still apply site plan review, septic (Title V) requirements, and setback, bulk and height regulations.

What is the difference between R1 and R2 zoning?

It depends on the code. In each of these, R2 allows more homes on the same land than R1, but in different ways:

  • Fairfax County: R-2 still provides for single-family detached dwellings, at 2 units per acre. A conventional subdivision needs a 15,000-square-foot minimum lot and an 18,000-square-foot average, against a 36,000-square-foot minimum in R-1.
  • Raleigh: R-2 halves the minimum lot to 20,000 square feet and adds two-unit living in an attached house.
  • Los Angeles: R2 is the "Two-Family Dwellings" zone, with the same 5,000-square-foot minimum lot as R1.
  • Phoenix: R-2 is the Multi-Family Residence District. Its standard option allows 10 primary dwelling units per gross acre, against 5.5 in R1-6.
  • Spokane: R2 allows the same housing types "at a slightly larger development intensity than the R1 zone."

What else limits an R1 lot?

The base district is one layer. Others can be stricter.

  • Overlays and historic districts. Raleigh's overlay districts include historic, neighborhood conservation, watershed protection and airport overlays.
  • Private covenants and HOA rules. Zoning does not cancel a deed restriction. Arizona's ADU statute says it "does not prohibit restrictive covenants concerning accessory dwelling units entered into between private parties," and Maine's statute has a similar clause. California goes the other way for ADUs: HCD's handbook says Civil Code sections 714.3 and 4751 nullify covenants that effectively prohibit or unreasonably restrict an ADU on a lot zoned for single-family use.
  • Lot width and frontage. A lot can meet the area minimum and fail the width or frontage minimum, such as San Diego's 50 feet of street frontage in RS-1-7 or Fairfax County's 150-foot width. Frontage is also a different question from legal access; see road frontage vs. legal access.
  • Parking. Albuquerque requires 1 space per single-family dwelling with two or fewer bedrooms and 2 spaces with three or more (Table 5-5-1). Washington bars the cities covered by its middle housing law from requiring off-street parking for middle housing within a half mile's walk of a major transit stop, with exceptions for a state-certified safety study and for areas within a mile of a large commercial airport.
  • Water and sewer. Maine requires written verification that an ADU is connected to adequate water and wastewater services before it can be occupied. Arizona's middle housing statute does not apply to areas that are not served by water and sewer or that lack sufficient urban services. Where there is no sewer, septic feasibility depends on soil, lot area and setbacks; our septic vs sewer guide gives state and county lot-size examples.

How do you find the R1 rules for a specific property?

  1. Find the parcel on the official zoning map. Record the full label, including any suffix (R1-6 is not R1-10) and any overlay, and confirm which city or county has jurisdiction. Zoning is not the future land use designation; our guide to zoning vs. future land use explains the difference.
  2. Open the district chapter in the current code. Read the purpose statement and note the date of the edition.
  3. Read the use table, then the use-specific standards. The table shows permitted, conditional and accessory uses. The standards can reverse it, as Albuquerque's duplex rule does.
  4. Read the dimensional standards: minimum lot area, width, frontage, setbacks, height, lot coverage and floor area ratio.
  5. Check overlays and any site-specific conditions attached to the parcel.
  6. Check state law on ADUs, duplexes and lot splits, and whether this city and this lot fall inside it.
  7. Check covenants and easements. Read the recorded plat, the deed restrictions and any HOA documents. A recorded easement or right-of-way can also take ground out of the buildable area.

Then answer four questions before you make an offer:

  • Can the lot be split? Compare its area and width with twice the minimums, then read the subdivision rules. In California, check SB 9's lot split. On a deep lot, a rear lot behind the house may be possible where the code allows flag lots.
  • Can a second unit be added? Read the ADU section, then state law.
  • What is the buildable envelope? Subtract the setbacks, then apply coverage, floor area ratio and height. Take a rectangular interior lot at the minimums of Phoenix R1-6's standard option: 60 by 94 feet is 5,640 square feet. Setbacks of 20 feet front, 25 rear, and 10 and 3 at the sides leave a rectangle 47 feet by 49 feet, or 2,303 square feet. That is under the 50% coverage limit of 2,820 square feet, so the setbacks bind first. This is a first pass, before easements, overlays and any other standard that applies to the lot. Use surveyed dimensions for this, not a map estimate; see deeded vs. GIS acres.
  • Which approval would the project need? Raleigh's code shows four, and they do different jobs. A rezoning changes the official zoning map and is a legislative decision. The applicant must schedule a pre-application conference, which the Planning Director may waive, and hold a neighborhood meeting before filing unless the city is the applicant. A variance comes from the Board of Adjustment, requires unnecessary hardship from conditions peculiar to the property, and cannot change a use standard. A special use permit requires Board of Adjustment review at a quasi-judicial hearing. A planned development is "a customized zoning district" approved with a master plan through the rezoning process. Names and decision-makers differ elsewhere. Our land feasibility guide covers what to do with the answer.

How do you compare R1 lots across cities?

Don't filter on the district name. An "R1" filter across the cities above puts Spokane lots zoned for middle housing, with a 1,200-square-foot minimum, next to Fairfax County lots that need 36,000 square feet for one house, and it misses every single-family lot in Portland, San Diego and Milwaukee.

Compare districts on the same fields instead: principal dwelling units allowed per lot by right, ADUs per lot, minimum lot area and width, and any state law that changes those numbers. Los Angeles R1 and San Diego RS-1-7 have different names, but both list a 5,000-square-foot minimum lot 50 feet wide for one house, so they belong in the same bucket. Two districts both called R1 may not. The desktop site screening checklist covers the rest of a first pass.

Where Pillar fits

Pillar's map layers show zoning alongside floodplain, wetlands, utilities and future land use over parcel boundaries on one map. That makes a quick first screen before you read the code. Coverage varies by dataset. A zoning map label, in Pillar or on a county GIS site, is not the code. It does not give you the dimensional standards, the overlay rules, state law or covenants, so confirm anything decisive with the jurisdiction.

Quick answers

What is the minimum lot size in R1? There is no standard. Among the conventional R1 standards above, the minimum lot runs from 1,200 square feet in Spokane to 40,000 in Raleigh. Alternative development and subdivision rules can differ.

What is R1 zoning in California? Each city defines its own; there is no statewide R1 standard. Los Angeles's code sets a 5,000-square-foot minimum lot in R1. The state ADU law and SB 9 sit on top of the local rules, subject to the limits above.