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A large brick colonial at the end of a long curving driveway on a wooded lot, with a white board fence and a wide lawn in late-day sun
Fairfax County

Fairfax County Lot CheckStream buffer, marine clay, easements, historic district, zoning, sewer or septic

Type an address. See what the county’s own maps say about the lot.

Two acres, a well and a septic field· Great Falls, Fairfax County

Answers: Fairfax County’s own maps, read live. Pictures: artist’s renderings of real places.

Lot Check

What do Fairfax County’s maps say about your lot?

Standing on the lot? Check it without typing. Your location is only used on this page and is not saved.

  • Stream buffer
  • Marine clay
  • Easements
  • Historic district
  • Zoning
  • Sewer or septic

Type an address. In a few seconds: a drawing of the lot and six plain answers.

Updated October 30, 2026Live answers from Fairfax County’s maps; rules read October 30, 2026A 10-second check, plus a 4-minute read

Quick answer

Type a Fairfax County address above. Lot Check asks the county’s own maps, live, about six things on that lot: the stream buffer (land within 100 feet of a stream), marine clay, easements, a historic district, zoning, and sewer or septic. You get a drawing of the lot and a plain answer for each.1,2,4,5,6,7 It is free and nothing you type is saved. It is not a survey or a legal determination: the county’s lines are approximate, and a plat, a title search and the county decide.

Ahmed Makkiyah Compiled byAhmed MakkiyahREALTOR®, Douglas Realty of Virginia · English and ArabicMobile 734.•••.•••• · Direct 703.•••.••••
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Lot Check, in six numbers

Fairfax County, October 30, 2026

6checks: stream buffer, marine clay, easements, historic district, zoning, sewer or septic8
100 fthow far the stream buffer reaches from a stream that flows all year1
19%of Fairfax County’s land is in a stream buffer8
28%of the sewer map is outside the public sewer area: septic land7,8
21,618septic tanks on the Health Department’s map8
15historic overlay districts in the county5

Countywide numbers asked of Fairfax County’s map services on October 30, 2026.

The six checks

What each check means, drawn.

Six pictures, one rule each, from the county’s own pages.

In shortEach check has a picture below: what it is, where it is, and the one thing it stops you from doing.

100 ftStream bufferStreamNew shed: a hearing
1Stream bufferLand within 100 feet of a stream that flows all year. What was there can stay; a new shed, patio or pool needs an exception with a public hearing.1
Marine clayWet: swells, pushesDry: shrinks, settlesDownspout away
2Marine clayA soil that swells when wet and shrinks when dry, mapped mainly east of I-95 and I-395. Keep water away from the house and big trees back from it.2,3
HouseMow itStorm drain easement
3EasementsA strip someone else may use, like a storm drain line. It stays with the land. You mow it; you don’t build on it.4
ARBHistoric district lineNew addition
4Historic districtInside one of the county’s 15 historic overlay districts, an addition also needs the Architectural Review Board.5
R-CR-ER-1R-4Smallest new lotR-C 5 acresR-E 75,000 sq ftR-1 36,000 sq ftR-2 15,000 sq ftR-3 10,500 sq ftR-4 8,400 sq ft
5ZoningThe district sets the smallest new lot, from 5 acres in R-C to 8,400 square feet in R-4. Squares drawn to scale.6
Public sewertankSeptic tank and field,pumped every 5 years
6Sewer or septicInside the county’s sewer service area most houses use public sewer. Outside it, a septic tank and drain field, pumped at least every 5 years.7

Fairfax County by the numbers

How common each one is.

Asked of the same county maps the tool reads, on October 30, 2026.

In shortAbout 1 acre in 5 of the county is stream buffer, and more than a quarter of the sewer map is septic land.

How much of Fairfax County’s land

Stream buffer19% · 73.5 sq mi
Marine clay soils4.9% · 18.9 sq mi

Shares of 384.7 square miles on the county’s zoning map, towns included. Asked of the county’s maps on October 30, 2026.8

Sewer or septic, by area

64%28%8%
Public sewer areaOutside it: septicTown or city sewer

Shares of the county’s approved sewer service area map.7,8

21,618septic tanks on the Health Department’s map8
15,636private wells on record8
77,771easements on the county’s maps (recorded and stormwater)8
383,581parcels: every lot Lot Check can read8

Buying or selling

What to do with the answers.

Six moves, for buyers, sellers and anyone adding on.

In shortThe answers matter most before you write an offer and before you list.

Buying

Read the plat before you fall for the yard

The house location plat shows the lot line, the buffer and the easements where the house sits. Ask for it with the listing, or download it free from the county.4

Buying

On septic? Inspect it apart

Get a septic inspection besides the home inspection, and ask for the pump-out records: the county requires one at least every 5 years. From July 1, 2026, the inspector’s written report is due within 10 business days: the new law.7

Buying

Plans for a pool, shed or addition?

Check the buffer, easements and historic district first. Each can turn a weekend project into a hearing. Ask before you write the offer, not after: making an offer.1,4,5

Selling

Know your lot before a buyer does

Run the check, pull your plat and your permit history, and have answers ready for the buffer, the easements and the septic system. What to fix before selling.

Selling

Cracks on marine clay

Fairfax County warns that patching marine clay cracks is cosmetic, and a seller who patches and does not disclose may be sued. Have a geotechnical engineer find the cause first.2

Adding on

Room for an in-law suite?

On a single-family lot of 36,000 square feet or more, staff’s proposal for the Tuesday, November 17, 2026 Board vote would allow a backyard cottage by right. Check your house.

Questions

What people ask about their lot.

How do I know if my property is in a Resource Protection Area in Fairfax County?

Type the address in Lot Check, or in the county's Watershed and Resource Protection Area viewer. A Resource Protection Area is the stream buffer: land within 100 feet of a stream that flows all year, a connected wetland, or a shore. The county's map is a guide; before major work a site study sets the exact line.

Can I build a shed or a deck in a Resource Protection Area?

A shed, patio, pool or detached garage in the buffer needs an exception with a public hearing. A new uncovered deck on a house built before the buffer was mapped is often allowed with an administrative waiver and no fee. Fences are allowed if water can flow under them.

How do I find out if my house is on marine clay?

Lot Check reads Fairfax County's soils map for the lot: marine clay shows as Marumsco soils (units 71, 74 and 91) or as marine clay on the older 1990 map. The county maps it mainly east of I-95 and I-395. Not every house on it has problems; a geotechnical engineer can tell.

How do I find easements on my property in Fairfax County?

Lot Check shows the easements on the county's map: storm drainage, sewer, access and conservation. Utility easements for power, gas or cable are often only on your plat and in the land records, so check your house location plat and the title report too.

Does my Fairfax County house have septic or public sewer?

Lot Check looks for the Health Department's septic records on the lot and checks the county's approved sewer service area. Outside that area, houses use septic. The county requires a septic tank to be pumped at least every 5 years.

What is my zoning in Fairfax County?

Type the address in Lot Check to see the district, such as R-1 or PDH-3, in plain words, with the smallest lot the district allows for a new lot. The towns of Herndon, Vienna and Clifton set their own zoning.

Is Lot Check a survey?

No. It reads Fairfax County's public maps, whose lines are approximate. It is not a survey or a legal determination. A surveyor's plat, a title search and the county decide what your lot allows.

Your next step

Found something on the lot you want to talk through?

A stream buffer behind the yard, an easement across it, a septic system, marine clay: none of these has to stop a purchase or a sale, but each changes the questions to ask. Tell me the address. I answer in English or Arabic, with real numbers, not a pitch.

اقرأ دليل شمال فرجينيا بالعربية ←

وكيلك العقاري الموثوق في شمال فرجينيا.

Keep exploring

Your next pages.

Map

Is my house in a flood zone?

FEMA’s flood map for any Northern Virginia address.

 Tool

In-law suites in Fairfax County

What your lot allows today, and after November 17.

 Guide

What to fix before selling

Marine clay cracks, permits, and what buyers ask.

 Hub

Seller hub

Your home’s value, the costs, and the timeline.

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