What two county lists require
Two county documents set out item by item what the site plan for an addition shows, and both are quoted here from the county's own host. Gwinnett County, Georgia sets out its requirements for a building addition to a home in a document revised August 2012 [1]. Its location plan:
"must be drawn to scale (i.e. 1"=10', 1"=20') and must show the lot boundaries, location of the existing home and driveway, easements, streams, buffers... and the proposed location of the addition." [1]
Los Angeles County Public Works reviews additions with its One- and Two-Family Dwelling Plan Review List, version 2.0, effective 1-1-2023 [2]. Item 22, under Code 106.4.3, asks for:
"Lot dimensions / yard setbacks / street name(s) / north arrow / existing building(s) to remain / distance between buildings / location of private sewage disposal system... / utilities / easements." [2]
The two lists overlap on the lot lines, the existing buildings and the easements, and each names items the other's quoted list does not [1, 2]:
| On the addition plan | Gwinnett County | Los Angeles County |
|---|---|---|
| The lot | Lot boundaries [1] | Lot dimensions [2] |
| What stands on it now | The existing home and driveway [1] | Existing buildings to remain, and the distance between buildings [2] |
| The new work | The proposed location of the addition [1] | The list covers dwellings and additions alike [2] |
| Limits on placement | Easements, streams and buffers [1] | Yard setbacks and easements [2] |
| Services on the lot | Not in the quoted item list [1] | The private sewage disposal system and utilities [2] |
| Orientation and scale | Drawn to scale, at 1 inch to 10 feet or 1 inch to 20 feet [1] | Street names and a north arrow [2] |
What an addition plan has to resolve
The yard setbacks on the Los Angeles County list are the lines the new wall is measured against [2]. The distance between buildings matters when the addition closes the gap to a detached garage or another structure on the lot, and Los Angeles County asks for it as a separate item [2]. On a lot with a septic system, the location of the private sewage disposal system goes on the plan, so the reviewer can see where the addition stands in relation to it [2]. Gwinnett asks for streams and buffers as well as easements, so where either crosses the lot it is drawn beside the addition [1].
Impervious square footage is the most common extra item on residential checklists, especially in North Carolina, Washington and Georgia [5]. Apex, North Carolina puts additions on one checklist with alterations and accessory structures [5], so the plan for an Apex addition carries the impervious area [5].
Washington's residential checklists set the strictest bar [4]. Bellevue, Washington sets a minimum sheet size of 18 x 24 inches for a residential site plan, with contour lines for existing and proposed grades at 2-foot intervals on the NAVD 88 vertical datum [4]. King County's Department of Local Services publishes its residential site plan requirements for new construction in an August 2025 edition [6], and Seattle publishes its own as Tip 103 [7]. Where proposed grades are required, they come from your engineer of record; the studio draws the plan on the existing contours of the survey.
The survey under the addition plan
Metro Nashville's residential building permit procedures cover additions along with decks, pools, sheds, garages and carports [8], and the department notes that a homeowner's mortgage loan survey works extremely well for a site plan [8]. Houston takes either a survey by a Texas registered surveyor or a complete site plan with dimensions for its residential permits [3]. Cobb County, Georgia asks for more: a current plan and survey sealed by a registered land surveyor before a building permit (Development Standards s.103.19.1) [9]. The full set of written rules on unsealed plans is in where unsealed site plans are accepted, and the survey itself is explained in site plan vs plot plan vs survey.
Who draws the rest of the addition set
The site plan is one sheet of an addition permit; the floor plans, framing and structure are drawn separately, and California cities publish who may draw them. In Los Angeles, the Department of Building and Safety lets an unlicensed person prepare the architectural plans for a two-story single-family dwelling, and "only the structural drawings need" a licensed signature where engineering details appear [10]. Dublin, California's Policy BDP 17 wants structural plans from a licensed professional when the building is one story with a basement or more than one story [11], so a second-story addition falls under that rule [11]. Milpitas applies its exemptions to plans designed to the conventional framing provisions of Chapter 23 of the 2025 California Building Code [12].
The studio draws the addition site plan, not the structure. Plans are preliminary, and engineering is by your engineer of record. Who prepares each part of a set is covered in who prepares a site plan and do I need an architect for a site plan. A second unit built onto the house is an ADU, with its own rules in ADU site plan requirements.
Order a home addition site plan
A detached building on the same lot is covered in detached garage and carport site plans, and every residential permit type in permit site plans. The general guide is site plan for a permit.
To order, open start a project, choose "Residential: home addition" as the project type, give the city or county, and attach one file: your survey, or a sketch of the addition's footprint. If the county publishes a checklist, name it under program and stage. The studio reads the jurisdiction's rules and replies by email to scope the plan.
Frequently asked questions
What does a site plan for a home addition need to show?
Gwinnett County, Georgia asks for the lot boundaries, the existing home and driveway, easements, streams and buffers, and the proposed location of the addition [1]. Los Angeles County adds the yard setbacks, street names, the north arrow, the distance between buildings, the private sewage disposal system and utilities (item 22, Code 106.4.3) [2].
What scale should an addition plot plan be drawn at?
Do I need a survey for a home addition permit?
Do I need an architect or engineer for a home addition?
For the building plans, it depends on the city and the structure. In Los Angeles, an unlicensed person may prepare the architectural plans for a two-story single-family dwelling, and only the structural drawings need a licensed signature where engineering details appear [10]. Dublin, California wants a licensed professional's structural plans when the building is one story with a basement or more than one story (Policy BDP 17) [11].
Must an addition site plan show impervious area?
In several states it is a standard item. Impervious square footage is the most common extra item on residential checklists, especially in North Carolina, Washington and Georgia, and Apex, North Carolina covers additions on one checklist with alterations and accessory structures [5].
Sources
- 1)Building Addition to a Home: building permit requirements (revised August 2012), Gwinnett County, Georgia, Planning and Development. Accessed 2026-10-10.
- 2)One- and Two-Family Dwelling Plan Review List, v2.0 (1-1-2023), Los Angeles County Public Works, Building and Safety. Accessed 2026-10-10.
- 3)Residential Permitting 101, Houston Permitting Center, Houston Public Works. Accessed 2026-10-10.
- 4)Residential Site Plan, City of Bellevue, Washington, Development Services. Accessed 2026-10-10.
- 5)Addition / Alteration / Accessory Structure Checklist, Town of Apex, North Carolina. Accessed 2026-10-10.
- 6)Residential Site Plan Requirements (August 2025), King County Department of Local Services, Washington. Accessed 2026-10-10.
- 7)Tip 103, residential site plan requirements, Seattle Department of Construction and Inspections, Washington. Accessed 2026-10-10.
- 8)Residential Building Permit Procedures, Metro Nashville Codes, Tennessee. Accessed 2026-10-10.
- 9)2026 Variance Application and Schedule, quoting Development Standards s.103.19.1, Cobb County, Georgia. Accessed 2026-10-10.
- 10)Information Bulletin P/BC 2023-073, Policy 4, Stamped Plans, Los Angeles Department of Building and Safety. Accessed 2026-10-10.
- 11)Policy No. BDP 17 (original effective date August 16, 2001), City of Dublin, California, Building and Safety. Accessed 2026-10-10.
- 12)Plans Required to be Designed by Architect or Engineer, City of Milpitas, California, Office of Building Safety. Accessed 2026-10-10.