Do you need a site plan for a home addition permit? In most cities and counties, the answer is yes. A home addition changes the size, footprint, height or use of an existing building, so permit reviewers normally need to see exactly where the proposed work will be located on the property.

A home addition permit site plan, sometimes called a plot plan, is a scaled overhead drawing of the lot. It shows the proposed addition in relation to the existing house, property lines, setbacks, driveway, parking, easements, utilities, drainage and other structures.

The site plan is generally submitted with floor plans, elevations, building sections and structural drawings. Together, these documents help the building department review zoning, building-code, lot-coverage, stormwater and property-specific requirements. [1][2][3][4][5]

Does a Home Addition Require a Permit?

A building permit is normally required when a project enlarges the footprint, floor area, height or number of stories of an existing house.

Examples of projects that commonly require permits include:

• Bedroom addition
• Family-room or living-room addition
• Kitchen expansion
• Bathroom addition
• Home-office addition
• Laundry or mudroom addition
• Sunroom
• Screened porch
• Attached garage
• Second-story addition
• Dormer addition
• Rear or side-yard bump-out
• Enclosed porch or patio conversion

Portland states that a building permit is required for an addition to a one- or two-family dwelling. The city defines projects that expand the building footprint, add a dormer or add another floor as additions requiring permits. [1]

Fairfax County similarly lists new home additions, including sunrooms, screen porches, bump-outs, second-story additions, dormers, garages and carports, among projects that require permits. [3]

Seattle requires a construction permit to remodel or add onto a building, while Denver provides a separate residential permit pathway for new homes and additions. [4][5]

When Is a Site Plan Required?

A site plan is commonly required when the addition changes the exterior footprint or when the permitting authority must review how the project fits on the lot.

You are especially likely to need one when the addition:

• Extends toward a front, side or rear property line
• Changes the home’s ground-floor footprint
• Increases building or lot coverage
• Reduces usable yard or open space
• Affects an existing driveway or parking space
• Is near an easement or underground utility
• Requires excavation, grading or retaining walls
• Adds roof area and stormwater runoff
• Is near a septic system or private well
• Is located in a floodplain or environmentally sensitive area
• Affects protected trees
• Requires zoning, planning or residential-lot review

Minneapolis describes a construction site plan as a drawing showing the property lines, existing structures and the location of a proposed addition or other change. [2]

Portland requires the site plan for an addition to show the entire property, the footprints of all structures and the driveway. Existing conditions and proposed work must be clearly distinguished. [1]

Charlotte includes residential additions in its Individual Residential Lot Review process, which reviews zoning, drainage and urban-forestry requirements alongside the county building-permit process. [9]

What Is a Home Addition Site Plan?

A home addition site plan is a scaled drawing showing the property from above.

It allows the permit reviewer to answer questions such as:

• Where will the addition be built?
• How large will it be?
• How does it connect to the existing house?
• How close is it to each property line?
• Will it comply with the required setbacks?
• Will it affect the driveway or required parking?
• Does it increase lot coverage or impervious area?
• Is it located over an easement or utility?
• How will roof and surface water be managed?
• Will grading or retaining walls be required?

Austin defines a site plan as a detailed drawing showing proposed improvements on a lot, including buildings, landscaping, parking, driveways, drainage facilities and utilities. [7]

Site Plan vs Floor Plan

A site plan and a floor plan serve different purposes.

Site Plan

The site plan shows:

• The entire lot
• Property boundaries
• Existing house and structures
• Proposed addition location
• Boundary setbacks
• Driveways and parking
• Easements and utilities
• Drainage and site conditions

Floor Plan

The floor plan shows:

• Existing and proposed rooms
• Interior and exterior walls
• Doors and windows
• Room dimensions
• Plumbing fixtures
• Stairs
• Changes to the existing house

The site plan explains where the addition goes. The floor plan explains what is inside it.

Site Plan vs Structural Plans

A site plan does not replace structural or construction drawings.

Structural plans may show:

• Footings and foundations
• Slab construction
• Floor framing
• Wall framing
• Beams and headers
• Roof framing
• Connections to the existing house
• Bracing and load paths
• Structural calculations

Portland requires section drawings for new construction and additions to explain foundations, floor construction, walls, ceilings and roof conditions. [6]

What Should a Home Addition Permit Site Plan Show?

Exact requirements vary, but the following information is commonly useful for a residential addition application.

Property Boundaries and Lot Dimensions

Show the complete legal outline of the property.

Include:

• Front property line
• Side property lines
• Rear property line
• Length of each boundary
• Lot width and depth
• Irregular or angled boundaries
• Property address

The property lines are the reference points used to measure the addition’s setbacks.

Do not automatically use a fence, hedge or landscaped edge as the legal boundary. A licensed boundary survey may be needed when the proposed addition is close to a property line.

Street, Alley and Right-of-Way

Show and label the street or streets adjoining the property.

Where applicable, include:

• Street name
• Public alley
• Sidewalk
• Curb or road edge
• Public right-of-way
• Secondary street on a corner lot

This information helps reviewers identify the front property line and determine which setback requirements apply.

Existing House

Show the complete footprint of the existing dwelling.

Include relevant:

• Exterior walls
• Existing roof outline
• Porches and decks
• Existing additions
• Attached garage or carport
• Doors and windows near the proposed work
• Existing floor level where available

The existing house should be clearly labelled:

Existing House

Other Existing Structures

Show structures and improvements that could affect the addition.

These may include:

• Detached garage
• Carport
• Shed
• Accessory dwelling unit
• Deck, patio or pergola
• Swimming pool
• Retaining walls
• Water tanks
• Fences and gates
• Mechanical equipment

Existing structures can affect setbacks, building separation, access, drainage and lot-coverage calculations.

Proposed Addition Footprint

Clearly identify the new construction using a label such as:

Proposed Home Addition

Use a bold outline, hatching or a different line type so the new work can be distinguished from the existing house.

The plan should clearly separate:

• Existing construction
• Construction proposed for removal
• New proposed construction

Portland specifically requires plans to distinguish existing conditions from proposed work. [1]

Addition Length, Width and Floor Area

Show the outside dimensions of the addition.

Include:

• Overall length
• Overall width
• Additional floor area
• Changes in building shape
• Bay windows or projections
• Covered entries
• Attached decks or patios

A useful site-plan note may read:

Proposed One-Story Addition: 18 ft × 24 ft — 432 sq. ft.

The site-plan dimensions should match the floor plans, elevations, foundation plan and roof plan.

Front, Side and Rear Setbacks

Show the shortest measured distance from the proposed addition to every nearby property line.

Include:

• Front setback
• Left-side setback
• Right-side setback
• Rear setback
• Corner-side setback on a corner lot
• Distance from projections where required

Setbacks are measured from the legal property line—not from the curb, sidewalk or fence unless the local code specifically says otherwise.

Portland explains that setback requirements vary by residential zone and may also be affected by overlay zones or plan districts. [10]

Roof Overhangs and Building Projections

Show the proposed roof outline where it extends beyond the exterior walls.

Projections that may affect setbacks include:

• Eaves
• Gutters
• Bay windows
• Chimneys
• Covered porches
• Exterior stairs
• Decks and balconies

A wall may meet the required setback while the eave or covered porch does not. Show both the wall footprint and roof outline when relevant.

Connection to the Existing House

Show where the addition joins the existing dwelling.

Identify:

• Existing wall proposed for removal
• New connecting wall
• New doorway or opening
• Existing and proposed roof junction
• Changes to exterior steps or paths
• Changes to an existing deck or patio

Detailed structural connections are usually shown on the framing plans and building sections.

Building Height and Number of Stories

Show or note the proposed building height.

Relevant information may include:

• One-story or two-story addition
• Wall height
• Maximum roof height
• Roof pitch
• Finished floor elevation
• Height above natural grade

Charlotte’s residential-review guide requires plans with building elevations for additions and asks applicants to show floor plans, dimensions and building height. [8]

Existing and Proposed Roof

Show the existing and proposed roof outlines where they affect the building footprint or drainage.

The roof plan may identify:

• Existing roof to remain
• Roof area to be removed
• Proposed roof
• Ridge and valley locations
• Roof-fall direction
• Gutters and downspouts

This helps reviewers understand the complete covered area and how rainwater will be handled.

Driveway and Vehicle Access

An addition can narrow, remove or relocate an existing driveway.

Show:

• Existing driveway
• Garage or carport access
• Proposed driveway changes
• Vehicle crossover or curb cut
• Gates
• Turning or manoeuvring space where relevant

Where the addition changes access, see our guide on site plans for driveway permits.

Parking Areas

Show existing and proposed parking spaces where required.

The addition should not unintentionally remove required parking or block access to an existing garage.

The plan may include:

• Garage parking
• Carport parking
• Driveway parking
• Uncovered parking spaces
• Parking-space dimensions

Local zoning codes determine whether additional or replacement parking is required.

Walkways, Steps and Entrances

Show pedestrian access to the addition.

This may include:

• Front walkway
• Side-yard path
• New exterior door
• Steps and landings
• Ramp
• Connection to a deck or patio

The addition should not block necessary access to the rear yard, utility meters, pool equipment or other parts of the property.

Lot Coverage and Building Coverage

A home addition increases the area of the lot covered by buildings.

Where required, the site plan may show:

• Total lot area
• Existing house footprint
• Existing garages and accessory buildings
• Covered porches and patios
• Proposed addition footprint
• Total building coverage
• Maximum permitted coverage

Definitions vary. Some jurisdictions measure only building footprints, while others include covered decks, porches, eaves or other structures.

Impervious Area

The addition may also increase the property’s impervious area.

Impervious surfaces can include:

• Building roofs
• Driveways
• Concrete patios
• Walkways
• Parking pads
• Other hard surfaces

Charlotte’s residential-lot process includes stormwater review to protect drainage infrastructure and address flooding or runoff impacts. [9]

An impervious-area calculation may be required when the project exceeds local thresholds or when the lot is subject to stormwater restrictions.

Easements

Show every known easement affecting the property.

Common examples include:

• Utility easement
• Drainage easement
• Sewer easement
• Stormwater easement
• Access easement
• Shared-driveway easement

Label the easement width and purpose.

Do not place the addition, foundation, roof projection or retaining wall inside an easement without checking whether construction is allowed and obtaining any required approval.

Utilities and Underground Services

Show known utilities close to the addition.

These may include:

• Sewer line
• Water service
• Gas line
• Electrical service
• Stormwater pipe
• Utility pole
• Overhead power lines
• Water, gas and electrical meters

The addition should not block service access or place foundations over infrastructure without approval.

Before excavation begins, underground services should be located through the appropriate utility-location service.

Plumbing, Electrical and Mechanical Work

Separate trade permits may be required when the addition includes:

• Electrical wiring and lighting
• New electrical panel or circuits
• Plumbing fixtures
• Bathroom or kitchen
• Heating and cooling equipment
• Gas piping
• Water heater

Portland states that addition projects may also require electrical, mechanical and plumbing permits. Denver similarly requires an issued residential construction permit before trade permits for new residential additions can proceed. [1][11]

Roof Drainage and Downspouts

An addition creates more roof runoff.

The site plan or drainage plan may show:

• Roof-fall direction
• Gutters
• Downspouts
• Rainwater connection
• Stormwater pipe
• Drywell or infiltration area where permitted
• Lawful discharge point

Roof water should not be directed toward the existing foundation, neighbouring property or an area where it can cause ponding or erosion.

Surface Drainage and Grading

Show how surface water moves around the proposed addition.

The plan may include:

• Existing and proposed spot elevations
• Direction-of-flow arrows
• Contours
• Swales
• Drainage channels
• Stormwater inlets
• Areas of ponding

Charlotte reviews whether proposed work modifies drainage features such as catch basins, pipes, ditches or swales and whether it could cause flooding on adjoining property. [9]

Existing and Proposed Ground Levels

Site levels are important when the property slopes or the addition requires excavation.

Show where relevant:

• Natural ground levels
• Existing finished floor level
• Proposed finished floor level
• Proposed finished grade
• High and low points
• Direction of site fall

Elevations and building sections usually provide more detailed vertical information.

Cut, Fill and Excavation

Show major earthwork needed for the project.

This may include:

• Excavation area
• Depth of cut
• Imported fill
• Proposed building pad
• Slopes or batters
• Temporary excavation near property lines

Additional engineering or site-development approval may be needed when the project disturbs a large area or affects slope stability and drainage.

Retaining Walls

Show existing and proposed retaining walls near the addition.

Include:

• Wall location
• Wall length
• Maximum wall height
• Distance to the addition
• Distance to property lines
• Drainage behind the wall

The addition should not place an unassessed load on an existing retaining wall.

Trees and Landscaping

Show significant trees where excavation, construction access or the building footprint may affect them.

The plan may identify:

• Tree-trunk locations
• Trees to remain
• Trees proposed for removal
• Tree-protection areas
• Street trees
• Required replacement planting

Charlotte’s residential-lot review may include protection of right-of-way trees, heritage trees and required tree-save areas. [9]

Swimming Pool and Pool Barrier

If the property contains a swimming pool, show:

• Pool location
• Pool fence
• Pool gate
• Doors or windows from the addition toward the pool
• Decks, stairs or raised surfaces near the barrier

The addition should not create an unapproved opening into the pool area or make the pool barrier climbable.

Septic System and Private Well

Properties without public sewer or water may need to show:

• Septic tank
• Drain field
• Reserve disposal area
• Private well
• Required separation distances

Adding bedrooms can affect the required septic-system capacity. Health-department review may be required before the building permit is approved.

Floodplain and Environmental Constraints

Additional review may apply when the property is located in a:

• Floodplain
• Wetland area
• Steep-slope area
• Coastal zone
• Landslide-prone area
• Environmentally critical area
• Historic district

Seattle advises applicants to research the property and applicable land-use requirements before submitting an addition permit. Major additions can require full plan review where the scope is too large or complex for a simplified inspection process. [5][12]

North Arrow and Drawing Scale

The site plan should include a north arrow and be prepared at a consistent, readable scale.

Common residential scales include:

• 1 inch = 10 feet
• 1 inch = 20 feet
• 1/8 inch = 1 foot for a compact lot

Portland requires addition site plans to be drawn to scale, show the entire lot and clearly state the scale used. The city does not accept Google Maps images as permit site plans. [1]

Minneapolis also requires a north arrow, drawing scale and dimensions locating the proposed improvement. [2]

Drawing Title and Revision Information

A simple title block should identify:

• Property address
• Drawing title
• Drawing number
• Scale
• Date prepared
• Revision number
• Description of revisions

This helps reviewers confirm they are examining the current version of the plan.

Ground-Floor Addition vs Second-Story Addition

Ground-Floor Addition

A ground-floor addition changes the physical footprint of the house.

The site plan will normally need to show:

• New footprint
• Boundary setbacks
• Lot coverage
• Reduced yard area
• Drainage changes
• Excavation and foundations
• Effects on parking and access

Second-Story Addition

A second-story addition may not enlarge the ground-floor footprint, but it can still require extensive review.

Important considerations can include:

• Overall building height
• Sidewall height
• Structural capacity of the existing house
• New stairs
• Upper-floor windows
• Privacy and overlooking
• Roof modifications
• Temporary construction access

The site plan still shows the property layout, while elevations and sections explain the vertical addition.

Sunrooms, Screened Porches and Enclosed Patios

A sunroom or screened porch may be treated as a home addition when it:

• Is attached to the house
• Has a permanent roof
• Creates enclosed floor area
• Uses permanent foundations
• Includes heating or cooling
• Changes an existing deck or patio

The plans may need to address:

• Foundation and framing
• Glazing and windows
• Energy-code compliance
• Emergency egress
• Roof drainage
• Setbacks and lot coverage

What Other Drawings May Be Required?

A site plan is normally only one part of the application.

The building department may also request:

• Existing floor plan
• Demolition plan
• Proposed floor plan
• Foundation plan
• Roof plan
• Front, side and rear elevations
• Building sections
• Structural framing plans
• Structural calculations
• Window and door schedule
• Energy-code documents
• Electrical plan
• Plumbing plan
• Mechanical plan
• Stormwater or grading plan

Fairfax County requires submitted building plans to clearly illustrate the nature and full scope of the proposed work. [13]

Do You Need a Survey for a Home Addition?

Not every addition permit requires a new boundary survey. An existing survey, mortgage-location plan or recorded plat may provide a usable base.

A new or updated survey may be needed when:

• The addition is close to a property line
• Property corners cannot be located
• The fence may not follow the legal boundary
• The lot is irregularly shaped
• An easement location is uncertain
• Certified elevations are required
• The property is in a floodplain
• The permitting authority specifically requests one

A drafted permit site plan is not a legal boundary survey and should not be represented as one.

Can You Use Google Maps for an Addition Site Plan?

An online aerial image can help identify the general property layout, but it is usually not sufficient as the final permit site plan.

Aerial imagery may be:

• Outdated
• Distorted
• Missing legal property boundaries
• Missing accurate dimensions
• Missing easements and utilities
• Missing site levels
• Unable to show the proposed addition properly

Portland specifically states that it will not accept Google Maps or PortlandMaps images as permit plans for residential additions. [1]

Common Home Addition Site Plan Mistakes

Addition permits are often delayed because the site plan is incomplete or does not match the other drawings.

Common mistakes include:

• Property lines are missing
• The proposed addition is not clearly labelled
• Addition dimensions are missing
• Boundary setbacks are omitted
• Roof overhangs are ignored
• Existing and proposed construction look identical
• Demolition work is not identified
• The existing house footprint is inaccurate
• Driveway or parking changes are not shown
• Lot coverage is missing
• Impervious area is not addressed
• Easements or utilities are omitted
• Roof drainage is unclear
• Site grading is not shown
• Retaining walls are omitted
• Trees or septic systems are ignored
• The drawing is not to scale
• There is no north arrow
• The site plan conflicts with the floor plan or elevations

What Information Is Needed to Prepare the Site Plan?

Collect as much of the following information as possible:

• Property address
• Addition length and width
• Additional floor area
• One-story or two-story design
• Preferred addition location
• Distance to nearby property lines
• Existing and proposed floor plans
• Architect, designer or contractor drawings
• Photos of the property
• Rough sketch with measurements
• Existing survey or plot plan
• Recorded plat if available
• Known easements
• Utility information
• Driveway and parking layout
• Site levels or contours
• Drainage information
• Retaining-wall information
• Permit reviewer comments

Home Addition Permit Site Plan Checklist

Does a Site Plan Guarantee Permit Approval?

No. A clear site plan gives reviewers the information needed to understand the proposed location, but approval also depends on the structural design, zoning code, building code and property conditions.

The project may also require:

• Architectural and structural plans
• Licensed boundary survey
• Zoning or planning approval
• Setback variance or administrative adjustment
• Electrical, plumbing and mechanical permits
• Stormwater or grading approval
• Floodplain review
• Historic-district approval
• Tree-removal approval
• Septic or health-department approval
• HOA or architectural-review approval

Need a Site Plan for a Home Addition Permit?

Site Plan Pros prepares clear residential site plans for homeowners, contractors, designers and permit applications.

Your home addition site plan can show:

• Property boundaries
• Existing house and structures
• Proposed addition location
• Addition dimensions
• Boundary setbacks
• Lot coverage and impervious area
• Driveway and parking
• Drainage and grading
• Easements and utilities
• Other relevant property details

You may also find our guides on deck permit site plans, garage permit site plans, carport permit site plans and driveway permit site plans helpful.

Confirm the local setback, lot-coverage, drainage and building-permit requirements before finalising the addition design or beginning construction.

Sources

1. City of Portland — Residential Addition Permits and Plan Requirements
2. City of Minneapolis — Construction Site Plans
3. Fairfax County — Projects Requiring Permits
4. City and County of Denver — Permits for New Homes and Additions
5. Seattle Department of Construction and Inspections — Addition or Alteration Permits
6. City of Portland — Building Permit Plans for Residential Projects
7. City of Austin — Site Plans, Exemptions and Corrections
8. City of Charlotte — Individual Residential Lot Review Applicant Guide
9. City of Charlotte — Individual Residential Lot Reviews
10. City of Portland — Zoning, Setbacks and Property Requirements
11. City and County of Denver — Residential Trade Permits for Additions
12. Seattle Department of Construction and Inspections — Residential Dwelling Permit Guide
13. Fairfax County — Building Plan Minimum Submission Requirements