# Fairfax County, VA Site Plans — Professional Seals, RPAs, and the 2,500 Sq Ft Rule
Fairfax County operates one of the most rigorously structured permitting departments in Virginia. If you are planning to build, renovate, or add an accessory structure, you cannot simply sketch a box on a piece of graph paper and get approved.
The county's modernized Zoning Ordinance (zMOD) and environmental protection laws require precision. And most importantly, Fairfax County requires that your site plan be certified by a Virginia-licensed professional.
Before you log into the PLUS portal to submit your application, here is exactly what Land Development Services expects to see on your house location plat.
Do You Need a Site Plan for a Small Permit in Fairfax County?
Yes. In Fairfax County, almost all residential building permits require a site plan (referred to as a House Location Plat for small projects).
Crucially, your site plan must be certified by a professional engineer, land surveyor, architect, or landscape architect licensed in Virginia. While a homeowner can submit the application, the plan itself must bear a professional seal. In limited circumstances for small projects (like decks or porches), you may be allowed to hand-draw the proposed structure onto an existing, previously sealed plat from your closing documents, provided it remains legible and to-scale.
Fairfax County uses a tiered approach based on land disturbance:
- ≤ 2,500 sq ft: House Location Plat (may be drawn on an existing plat)
- 2,500–5,000 sq ft: Conservation Plan (includes erosion and sediment controls)
- > 2,500 sq ft (altering drainage/grade >18″): Infill Lot Grading Plan
Who Runs Into This in Fairfax County
- New homeowners who want to build a deck, only to discover they don't have their original house location plat and must pay a surveyor before applying.
- Homeowners adding a pool who assume they just need a simple layout, but trigger the 2,500 sq ft disturbance rule and must submit a full Conservation Plan.
- Waterfront property owners whose projects fall within a Resource Protection Area (RPA), requiring extensive environmental review just to build a shed.
- Contractors trying to navigate the new zMOD rules regarding accessory structure heights and setbacks.
What Needs a Site Plan in Fairfax County
- Fence permit site plan — Fences are subject to zoning regulations; accessory structure rules may apply.
- Shed permit site plan — Required. Under zMOD, sheds up to 12 feet tall may be placed 5 feet from side/rear lot lines.
- Deck permit site plan — Required. Any deck attached to a house requires a permit. (Wood patios applied directly on the ground do not; elevated patios do).
- Pool permit site plan — Required. A conservation plan is often triggered due to the 2,500–5,000 sq ft disturbance. Must show equipment, barriers, setbacks, and RPA notation.
- Garage permit site plan — Required. Conservation plan may be required based on disturbance area.
- Addition permit site plan — Required. Large additions usually require an Infill Lot Grading Plan.
- ADU ( (Accessory Living Unit) — Requires Zoning Administration registration separate from the building permit, plus a site plan showing footprint, setbacks, and parking.
Why This Trips People Up in Fairfax County
The Professional Seal Requirement. Many jurisdictions allow homeowners to draw their own site plans for basic residential projects. Fairfax County explicitly requires certification by a Virginia-licensed professional. Attempting to submit a completely self-drawn, unsealed plan to the PLUS portal will result in immediate rejection.
Resource Protection Areas (RPA). Because Fairfax County contains numerous streams and waterways feeding into the Chesapeake Bay watershed, RPAs are strictly enforced. If your property contains an RPA, your site plan must delineate it, and development within that area is heavily restricted and heavily scrutinized.
The zMOD Transition. The modernized Zoning Ordinance (zMOD) went into effect in July 2021. It changed the rules for accessory structures. For example, if you are building a shed or gazebo, if it is 12 feet in height or under, it can be 5 feet from the side and rear lot lines. If it is over 12 feet, it must meet stricter primary setbacks.
Infill Lot Grading. If you alter the grade of your property by more than 18 inches, or block existing drainage patterns, you graduate from a simple plat to an Infill Lot Grading Plan, which is significantly more complex and expensive to produce.
Zoning and Setbacks in Fairfax County
Setbacks are governed by zMOD and vary significantly by your specific zoning district (e.g., R-1, R-2, R-C).
Typical R-1 District (Single-Family Detached):
- Front setback: 30 feet minimum
- Side setback: 8 feet minimum
- Rear setback: 25 feet minimum
Accessory Structures (Sheds, Gazebos, Play Equipment):
- Up to 12 feet in height: May be located 5 feet from side and rear lot lines.
- Lots larger than 36,000 sq ft: May be located in the front yard (but not within the minimum front setback).
- Lots 36,000 sq ft or less: Cannot be located in the front yard.
Note: Corner lots have two front yards in Fairfax County, meaning street-side setbacks apply.
How the Tool Handles This — 5 Steps
SitePlans.ai loads Fairfax County parcel data so you can visualize your property and setbacks before hiring a professional:
- Enter your address — Lot lines load from county GIS records.
- Place your project — Add your shed, pool, or deck to the lot.
- Verify zMOD Setbacks — Use the tool's measuring features to ensure your 12-foot shed is at least 5 feet from the line, or your addition meets the 25-foot rear setback.
- Identify RPAs and Easements — Note any known easements or RPAs to ensure you are avoiding them.
- Export a conceptual plan — Use this PDF to communicate clearly with your required licensed surveyor or architect, saving them time (and you money).
Where This Tool Fits — and Where It Doesn't
| Situation | Best path |
|---|---|
| Brainstorming a deck or addition | SitePlans.ai for visualizing layout and zMOD setbacks |
| Submitting a House Location Plat | Licensed VA Surveyor required (You can sometimes draw a small deck onto an existing sealed plat) |
| Disturbance over 2,500 sq ft | Licensed Civil Engineer required (Conservation Plan) |
| Altering drainage or grade > 18" | Licensed Civil Engineer required (Infill Lot Grading Plan) |
| Property in an RPA or Floodplain | Licensed Surveyor/Engineer required |
What This Doesn't Replace
SitePlans.ai helps create preliminary, conceptual site plans. It does not provide the professional seal required by Fairfax County Land Development Services. Our tool is excellent for verifying whether your proposed project will physically fit within the county's zMOD setbacks before you spend thousands of dollars on a licensed surveyor or engineer. You must use a licensed professional for your actual PLUS portal submission.
Comparison: Your Options for a Fairfax County Site Plan
| Method | Cost | Time | Stamp | Notes |
|---|---|---|---|---|
| SitePlans.ai | Free first plan | Minutes | ✗ | Best for conceptual layout and checking setbacks before hiring a surveyor |
| Existing house plat + hand draw | Free | 1 hr | ✅ (pre-existing) | Accepted for small decks/porches if original plat is sealed and legible |
| Licensed VA Surveyor | $600–$1,500+ | 2–4 weeks | ✅ | Mandatory if you don't have an existing plat or for larger footprints |
| Civil Engineer | $2,000–$5,000+ | 3–6 weeks | ✅ | Mandatory for Conservation and Infill Lot Grading Plans (>2,500 sq ft) |
Common Mistakes That Delay Fairfax County Permits
- Submitting an unsealed plan — Using a homeowner-drawn sketch from scratch instead of a sealed House Location Plat.
- Ignoring the 2,500 sq ft rule — Applying for a simple plat when the total land disturbance (including staging areas and trenches) exceeds 2,500 sq ft, triggering a Conservation Plan.
- Violating zMOD accessory heights — Placing a 14-foot-tall shed in the 5-foot setback zone (structures over 12 feet require larger setbacks).
- Forgetting the RPA — Failing to denote a Resource Protection Area on the plan, resulting in an automatic kickback from environmental review.
- Applying in the wrong jurisdiction — Submitting to the county PLUS portal when you actually live inside the independent City of Fairfax.
Support and Local Resources
- Fairfax County Land Development Services — fairfaxcounty.gov/landdevelopment/
- PLUS Online Portal — fairfaxcounty.gov/plan2build/plus
- Fairfax County GIS/Property MapServer — fairfaxcounty.gov/maps/interactive-map-galleries
- Zoning Permit Branch — (703) 222-1082 (call to verify specific zMOD setbacks)
- FEMA Flood Maps — msc.fema.gov
Nearby Counties
- Prince William County site plan guide
- Virginia permit site plan requirements — State Site Plan Requirements
Frequently Asked Questions
1. Does Fairfax County accept homeowner-drawn site plans?
No, not from scratch. Your site plan (House Location Plat) must bear the seal of a Virginia-licensed professional. The only exception is if you are building a small project (like a deck) and you hand-draw it accurately onto a copy of an existing, previously sealed plat you received when you bought the house.
2. What is the difference between a House Location Plat and a Conservation Plan?
A House Location Plat is for projects disturbing 2,500 square feet or less. If your project disturbs between 2,500 and 5,000 square feet, you graduate to a Conservation Plan, which must include specific erosion and sediment controls.
3. What is an Infill Lot Grading Plan?
Required for projects disturbing more than 2,500 square feet that also alter the grade by more than 18 inches or alter existing drainage patterns (like building a new home or a massive addition). This requires extensive civil engineering.
4. How close to the property line can I build a shed in Fairfax County?
Under zMOD rules, if the shed is 12 feet in height or under, it can be placed 5 feet from the side and rear property lines. If it is taller than 12 feet, it must meet the primary building setbacks for your zoning district.
5. How do I submit my site plan to Fairfax County?
All building permits and site plans must be submitted digitally through the county's PLUS (Planning and Land Use System) online portal.
6. Can I build a shed in my front yard?
Only if your lot is larger than 36,000 square feet, and even then, it cannot be located within the minimum required front setback. If your lot is 36,000 square feet or smaller, accessory structures cannot be placed in the front yard.
7. What is an RPA and how does it affect my site plan?
A Resource Protection Area (RPA) is a vegetative buffer around sensitive waterways. If your property contains an RPA, your site plan must clearly delineate it. You generally cannot build inside an RPA without severe environmental mitigation and special exceptions.
8. Can I use SitePlans.ai for a Fairfax County permit?
SitePlans.ai is best used as a conceptual tool in Fairfax County. Because the county requires a professional seal, you cannot submit our output directly to the PLUS portal. However, you can use our tool to verify your layout, check zMOD setbacks, and create a clear visual guide to give to your licensed surveyor, ensuring they know exactly what you want before they start billing you.
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