Single-family and townhome subdivision site plans

What a subdivision site plan carries

For a single-family or townhome developer, the site plan is a concept lotting plan and yield study. It lays out the lots, local streets, cul-de-sacs, alleys, open space, the amenity and the land held for stormwater, and it counts the result. A yield study assesses zoning (setbacks, parking ratios, height, density) and site constraints (topography, drainage, flood, tree cover, access) to find the realistic buildable lot count ^{[6, 7]}, and it distinguishes the maximum yield from the most profitable one ^[7].

The site data table on the sheet carries: gross acreage; land in rights-of-way, open space and detention; net developable area; the zoning district with its minimum lot size and density cap; the lot count and units per acre against that cap; lot widths and areas by product; street sections; the mix of detached and attached units; and phasing.

The plan sits at the sketch or concept stage, before the preliminary plat and well before any recordable survey ^{[6, 8]}. It is a preliminary site plan: the boundary survey and the recorded subdivision plat are prepared, signed and sealed by a licensed land surveyor, and the engineered construction plans for grading, drainage, utilities and roads by a licensed engineer ^[9]. Those professionals build their sealed sheets on the layout.

Yield is what the land is worth. In NAHB's Cost of Constructing a Home survey, a builder sample, finished lots were 13.7% of the new-home sales price in 2024, down from 17.8% in 2022, while construction costs reached a record 64.4% ^[10]. One consultant guide puts land development at 50 to 60% or less of finished-lot value ^[11], and a credible lot count tied to zoning and site constraints drives residual land value, the absorption schedule and loan sizing ^[6]. The yield study is how a builder or lender tests whether the deal has legs before survey and engineering money is spent ^[12].

Density and yield by product

These are typical planning ranges drawn from architect and consultant sources, not code guarantees; zoning, open space and stormwater decide the actual yield ^[1].

Lot sizes and frontages

Minimum lot sizes come from the zoning district. Raleigh's UDO shows how detached and attached minimums step down by district ^[17]:

Raleigh's cottage court and conservation or compact development provisions grant smaller lots and higher density in exchange for preserving common open space ^[17]. Open space set-asides have no single national standard; the percentage comes from the local ordinance. Cul-de-sac lots often carry a reduced minimum width, such as 50 ft measured at the setback line in Walla Walla, Washington ^[18]. The curvilinear suburban layout typically uses lots of 6,000 to 10,000+ sq ft.

Streets, cul-de-sacs, blocks and access

National references (FHWA, AASHTO, ITE, NACTO) inform street design, but local subdivision ordinances and state DOT guides govern in practice; VDOT's Subdivision Street Design Guide (Appendix B) is one state example ^[24]. Trip generation sets the traffic case: the ITE Trip Generation Manual, 11th Edition, averages 9.43 vehicle trips a day per single-family detached unit (Land Use Code 210, 174 studies, range 4.45 to 22.61) ^[25]. As a rule of thumb, developments above approximately 12 DU/AC trigger traffic impact studies, turn lanes or signal warrants in many jurisdictions ^[1].

Five subdivision layouts

NAHB notes limited market uptake for cottage courts where the ordinance grants no density bonus ^[13]. The connected grid maximizes yield and disperses traffic; the cul-de-sac layout trades connectivity and land for privacy and easy phasing.

Townhomes: the IRC and IBC line

A townhouse is a single-family dwelling unit in a group of three or more attached units, each extending from foundation to roof, with open space on at least two sides ^[26]. Detached one- and two-family dwellings and townhouses of not more than three stories with separate means of egress fall under the International Residential Code; four or more stories, stacked units, or units that fail the townhouse definition push the building to the IBC, typically Group R-2 ^[3]. The number of attached units does not by itself force the IBC, as long as nothing is stacked and each unit keeps two open sides ^[26].

• Separation walls. Under IRC R302.2.2 (2021) the common wall must be 2-hour fire-resistance-rated if not sprinklered, reducible to 1-hour where both units are sprinklered per P2904 or NFPA 13D; sprinklered townhouse units also need not be structurally independent (R302.2.6) ^{[27, 28]}.
• Sprinklers. The IRC model code requires sprinklers in new one- and two-family dwellings and townhouses, but many jurisdictions delete the mandate on adoption ^[27].
• Accessibility. True townhouses are generally not subject to accessibility codes, but where four or more dwelling units sit in a single structure, IRC R320.1 triggers IBC Chapter 11 Group R-3 provisions, with potential Type A and Type B units ^[26].

The IRC, IBC and IFC sections on this page are model code text; the edition and the amendments a jurisdiction has adopted govern the project.

For attached product that tips into multifamily, the exterior and amenity views are covered in apartment rendering.

Fire access and hydrants

• Access roads. IFC Section 503 sets a 150 ft maximum dead end and a 20 ft minimum width. Dead-end roads over 150 ft require turnarounds (Table D103.4); where a hydrant sits on the access road the minimum width is 26 ft; roads must support 75,000 lb apparatus at a maximum 10% grade ^[29].
• Two entrances. Separate entrances must be at least 150 ft apart, or one-half the diagonal dimension (IFC D104.3) ^[29].
• Hydrants. In IRC single-family and R-3 areas, hydrants are spaced 500 ft or less (600 ft if all homes are sprinklered), with a maximum of 300 ft from a one- or two-family dwelling to a hydrant under the Las Vegas and Henderson amendment; commercial, R-1 and R-2 areas use 300 ft or less (400 ft if sprinklered) ^[4]. The 2024 IFC Appendix C retains Table C102.1 with sprinkler-based spacing increases of 50% for NFPA 13 and 25% for 13R, 13D and P2904 systems ^[30].

These rules fix the street network: the dead-end limit decides how long a cul-de-sac can run before a turnaround, and the two-entrance rule decides when the plan needs a second connection to the outside road.

Stormwater, open space and infrastructure

• Detention land take. Detention typically consumes 3 to 15% of residential site area ^[5].
• Design storms. Detention and retention typically must control the 2-, 10-, 25- and 100-year storms; Knox County, Tennessee is one example ^[31]. Pond sizing is the engineer of record's work.
• Construction permit. The federal NPDES Construction General Permit is triggered at 1 acre of disturbance, or less if the site is part of a larger common plan of development ^[32].
• Infrastructure cost. Consultant estimates put infrastructure at about $25,000 to $50,000+ per lot, and overall land development commonly at $25,000 to $100,000 per finished lot (consultant ranges, not survey data) ^{[33, 34]}.
• Septic. Where public sewer is unavailable, private septic systems are required and soil and percolation suitability drive the minimum lot size ^[33].

The blog covers the detention question in stormwater as a site plan variable and detention basins and site area.

Approval path: sketch plan to recorded plat

The typical subdivision approval chain has five steps ^{[8, 35, 36]}:

Washington confirms that final plat approval is ministerial and non-discretionary once the preliminary terms are met ^[36]. The studio's plan carries the first step and is the base for the preliminary plat; the recorded plat is signed and sealed by a licensed land surveyor, and the construction plans by a licensed engineer ^[9].

Rezoning adds time where the base zoning does not match the product, and PUD rezonings are common for master-planned subdivisions; upzonings from single-family to multifamily or commercial can raise land value 20% to over 100% ^[37]. A simple rezoning in a favorable jurisdiction takes 3 to 12 months ^[38]. In Los Angeles, projects that required an EIR added about 504 days on average, while SB 35 streamlining cut some timelines from 7 months to under 3 ^[39]; New York City's ULURP runs about 200 days minimum ^[40]. Opposition typically centers on school capacity, traffic and density ^[1].

State preemption is changing what zoning allows, and it moves fast, so the plan is drawn to the code in force. Middle-housing status as the sources stood on July 30, 2026:

• Oregon. 2019 HB 2001 required middle housing in residential zones ^[41].
• Washington. 2023 HB 1110 requires duplexes in cities of 25,000 to 75,000 and up to 6-plex near transit in cities over 75,000 ^[42].
• Vermont. The 2023 HOME Act allows duplexes everywhere single-family is allowed and up to 4 units where served by sewer and water ^[43].
• Maine. LD 2003 middle-housing reform took effect in 2023 ^[41].
• California. Long-running preemption through ADU laws, SB 9 lot splits and SB 35 streamlining ^[43].

State ADU mandates and lot-split laws, including Montana's, are set out with their current statute numbers in the ADU section below.

Background on the reform wave is on the blog in zoning reform and residential blocks.

Plat rules by state

In every state the sources cover, the recorded subdivision plat must be signed and sealed by a licensed land surveyor (or in some states a licensed engineer), and it is approved by the local governing body or the planning commission ^[44]. The rows below are states with a primary statute on file; elsewhere the plat statute and the local subdivision ordinance set the rule.

ADUs and lot splits on single-family lots

State law now decides part of what a single-family lot must be able to hold. Where a statute guarantees an accessory dwelling unit (ADU) by right, the lot carries a second footprint with its own setbacks and access, and the lotting plan can test lot widths and depths against the statutory numbers before the plat is drawn. The mandates below are stated with their statute numbers as of October 10, 2026; the full state comparison is in ADU laws by state.

California, Washington, Montana and Arizona put the size and setback numbers in the statute, so a lotting plan can show compliance against a fixed figure; Oregon and Colorado set rules of process (no added parking, no owner occupancy, administrative approval) and leave the dimensions to each city ^{[45, 47, 48, 49, 51, 52]}.

Montana also caps the one-time ADU application fee at $250 per unit (76-2-345(4)) and bars impact fees on ADUs ^[51]. The Montana Supreme Court reversed the preliminary injunction against the 2023 housing laws on September 3, 2024 (2024 MT 200), and on March 17, 2026 upheld those laws, including MCA 76-2-345 (2026 MT 53) ^[53]; the City of Great Falls notes the decision and is enforcing the law ^[54]. Arizona bars fire sprinkler and commercial-code requirements for ADUs (9-461.18(D)) and bars building on a public utility easement without the utility's consent (9-461.18(E)), which puts the easement lines on the site plan ^[52].

Texas has no statewide ADU law: SB 673 passed the Senate on April 10, 2025, and died in the House ^{[55, 56]}. City codes decide instead, and Dallas has no by-right path: an ADU there needs an ADU Overlay rezoning or a Board of Adjustment special exception ^[57].

Pre-approved ADU plans still need a site plan

In Los Angeles and Phoenix, a pre-approved ADU plan still needs a lot-specific site plan. Los Angeles lists 9 mandatory plot plan items even when an approved standard plan is used, all to scale: property lines with dimensions, front, side and rear setbacks, separation from the primary dwelling, site drainage, north arrow, ADU dimensions and area, adjacent streets, the primary dwelling footprint, and driveways and parking ^[58]. Phoenix states: "A plot/site plan will still be required for permitting" ^[59]. California's Gov. Code 65852.27 (AB 1332, 2023) required local agencies to accept ADU plans for preapproval, with programs due Jan 1, 2025, and a detached ADU application that uses a preapproved plan is decided within 30 days ^[60]. Arizona's ARS 9-461.19 (SB 1529, Laws 2025 ch. 259) has municipalities post pre-approved ADU plans of 200, 600 and 1,000 sq ft from July 1, 2026, and duplex and triplex plans of 400 to 1,000 sq ft per unit from Jan 1, 2027; a municipality may not restrict who submits a plan ^[61]. The lot fit is covered in site plans for pre-approved ADUs.

Lot splits

California's SB 9 (2021, effective Jan 1, 2022; Gov. Code 66411.7, amended by SB 450 effective Jan 1, 2025) allows a one-time ministerial split of a single-family lot into two, with up to two units on each resulting lot, or up to four units on an unsplit lot ^[62]. Local rules fix the geometry. San Carlos allows no flag lots and requires each new parcel to be at least 1,200 sq ft and at least 40% of the original lot, with an owner affidavit to live in one unit for 3 years ^[63]; San Francisco requires a parcel of at least 2,400 sq ft ^[64]. Uptake has been small: through November 2022, Los Angeles received 211 SB 9 unit applications and approved 38, and received 28 lot split applications and approved none, while Santa Maria received no SB 9 applications despite permitting 401 ADUs in 2021 ^[65].

Oregon's SB 458 (2021), codified at ORS 92.031, allows a middle housing land division so that each middle housing unit can sit on its own lot: exactly one dwelling per resulting lot, a notation on the plat, no further division, an expedited procedure on request (now ORS 197A.140), and a tentative approval that is void if no final plat follows within 3 years ^{[66, 67]}. See Oregon middle housing land division.

For the single lot a homeowner brings to the permit counter, the drawing is a permit site plan; for a developer, the same statutes set what every lot in the subdivision must be able to hold.

Renderings for buyers and sales teams

Single-family renderings answer buyers and homebuilder sales teams. The usual set is 4 to 8 stills covering elevation options, the streetscape, the entry monument, model interiors and the amenity or clubhouse, with elevation options and streetscape carrying buyer decisions. The renderings are built on the lotting plan; see 3D rendering services.

Related site plans and guides

Obsolete office campuses are being re-planned into residential lots and pads: see office site plans. The neighborhood center that follows new rooftops is covered in retail center site plans, and a mixed master plan with a hotel pad in hotel site plans. For the basics, read what a site plan is and preliminary versus final site plans.