In-law suites in Fairfax CountyToday’s rules, the November 17 vote, and Loudoun, Prince William and Arlington
Pick your home and where the suite would go. See today’s answer and the answer if the Board says yes.
Most suites go inside the house· Annandale, Fairfax County
Rules: Fairfax County’s own pages, October 30, 2026. Pictures: artist’s renderings of real places.
The checker
Can your house have an in-law suite?
Virginia’s July 1, 2027 law on these units is written not to apply to a county that already had its own rules before 2026, and Fairfax County did. So the county’s rules, and the November 17 vote, decide. What the law says5
Fairfax County zoning only. The towns of Herndon, Vienna and Clifton and the cities of Fairfax and Falls Church have their own rules. HOA rules are private and can be stricter. Nothing you type is saved or sent.
Pick the county, your home and where the suite would go. In Fairfax, see today’s answer next to the answer if the Board passes staff’s proposal.
Updated October 30, 2026Rules read on Fairfax County’s pages, October 30, 2026A 30-second checker, plus a 5-minute read
Quick answer
Yes, if it is a single-family house. Today Fairfax County allows one in-law suite inside the house with a $285 permit (one-time): up to 800 square feet or 40% of the house, or the whole basement, for up to 2 people, and the owner must live there. A backyard cottage needs 2 acres and a special permit.1 On Tuesday, November 17, 2026, the Board of Supervisors holds its hearing on staff’s proposal: 1,200 square feet, 3 people, no owner rule, and a backyard cottage by right on lots of 36,000 square feet or more.2,3 Use the checker above for your house; it also covers Loudoun, Prince William and Arlington, whose rules are below. Not the county’s below-market Affordable Dwelling Units, which share the letters ADU.
In-law suites in Fairfax County, in six numbers
Today and proposed, 2026
Proposed numbers are staff’s; the Board can change them on November 17.
Today against the proposal
What would change on November 17.
Every rule, side by side. Green marks a change.
In shortBigger (1,200 sq ft), one more person, no owner rule, and backyard cottages on lots of 36,000 sq ft or more.
| Rule | Today | Staff’s proposal |
|---|---|---|
| Which homes | Single-family detached houses, one suite per lot | The same; townhouses and duplexes only under an option, inside and by special permit |
| Size | 800 sq ft or 40% of the house, whichever is less, or the whole basement (as of July 1, 2021) | 1,200 sq ft or 40% of the house, whichever is less, or the whole basement; garage space does not count |
| Bedrooms | Up to 2 | 1 or 2 |
| People in the suite | Up to 2 | Up to 3 |
| Owner lives there | Yes: in the house or the suite | Not required: both can be rented |
| Backyard cottage | Only on 2 acres or more, by special permit, up to 1,200 sq ft | By right on 36,000 sq ft or more; smaller lots by special permit |
| Joined by a hall | Counts as inside only with finished, heated, enclosed access | A connection of 10 feet or less counts as inside |
| Zoning permit | Administrative permit: $285 (one-time), $75 per renewal, about 30 days, recorded in the land records | No separate zoning permit; building permits and inspections still |
| Parking | The house’s spaces plus 1 | No extra space |
| Airbnb and short stays | Not allowed in a suite | Not allowed on a property with a suite |
The proposal is staff’s recommendation, called Option 1 in the county’s text. The Planning Commission and the Board can pick an alternative printed beside it, or a number in between: for the backyard cottage, any lot size from no minimum up to 2 acres.3
Some rules stay either way: one suite per lot, 1 or 2 bedrooms, building permits and inspections, and no short-term rentals.1,3,4
The other counties
Loudoun, Prince William and Arlington.
Each county’s rule today, side by side with Fairfax.
In shortLoudoun and Arlington already allow a full unit. Prince William allows only a wet bar until Virginia’s law starts July 1, 2027.
| Rule | Fairfax today | Loudoun | Prince William | Arlington |
|---|---|---|---|---|
| Which homes | Single-family detached houses | Houses; ask Zoning about a townhouse | Single-family detached houses | Single-family detached houses in the R districts |
| Own kitchen | Yes | Yes | No: a wet bar or warming kitchen only | Yes |
| Size | 800 sq ft or 40% of the house, or the whole basement | Suburban: half the house or 1,200 sq ft; rural: 70% or 2,500 sq ft | Part of the house, not a separate unit | 35% of the house, up to 750 sq ft, or the whole basement |
| Backyard cottage | 2 acres or more, by special permit | Yes, in a building out back | Not allowed | Yes: a footprint up to 560 or 650 sq ft |
| Owner lives there | Yes | Not required; same ownership as the house | It stays part of the house: no separate rental | Yes |
| People | Up to 2 | No number in the rule | Open to everyone in the house | Up to 3 |
| Permit | $285 (one-time), about 30 days | Zoning permit in LandMARC | Zoning approval, then a building permit | Zoning permit, about 30 days |
| From July 1, 2027 | Its own rules keep deciding | Its own rules keep deciding | State law: a unit allowed, fee $500 or less (one-time) | Its own rules keep deciding |
Loudoun’s rule is the most open: a unit inside the house or in a building out back on most lots, and the rule does not say the owner must live there. It must stay under the same ownership as the house, and on septic the Health Department approves it first.8
Arlington allows one in a single-family house or a building out back, if the owner lives in one of the two and no more than 3 people live in the unit. The permit takes about 30 days, then building permits and a certificate of occupancy.7
Prince William allows only a wet bar or a warming kitchen in a single-family house today: no oven, stove or range hood, no locked door to the house, no separate meter or mailbox. From Thursday, July 1, 2027, Virginia’s new law opens the door to a full unit there, unless the county adopts its own rules first, which must follow the state law closely.5,9
The towns and cities have their own rules, and so does any HOA. The checker covers county zoning only.
The dates
Where the vote stands.
Two hearings, then a state law on top.
In shortThe Board holds its hearing on Tuesday, November 17, 2026, at 4:30 PM. Until it votes, today’s rules apply.
- Fri, Oct 2, 2026
The county posts its questions and answers
Staff’s FAQ on the proposal, with the options the Board can pick.3
- Thu, Oct 29, 2026
Planning Commission hearing
The Planning Commission heard the proposal at 7:30 PM; its recommendation goes to the Board.2
- Tue, Nov 17, 2026, 4:30 PM
Board of Supervisors hearing and vote
In the Government Center auditorium, 12000 Government Center Parkway, Fairfax. Anyone can speak or send written comments; the Clerk to the Board lists how.2
- Thu, Jul 1, 2027
Virginia’s new law starts
SB 531: a county that had no rules of its own before 2026 must allow these units in single-family zones, with a permit fee of $500 or less (one-time). Fairfax, Loudoun and Arlington had rules; Prince William did not.5
This page shows the rules as written for the hearing. The Board can adopt them, change them or put them off. I will update this page after November 17 with what passed.2
Three kinds
Inside, joined by a hall, or out back.
Where the suite sits decides which rule you follow.
In shortInside the house is allowed today. A short hall and a backyard cottage are where the proposal opens new doors.
Before you build
What it takes, besides zoning.
The checks that stop more projects than the zoning rule does.
In shortZoning is the first test. The HOA, the septic system and the building permits come next.
Check your HOA first
County zoning is one test; your HOA’s covenants are another, and the county does not enforce them. Many HOAs limit second kitchens, rentals or new buildings.
Septic or a well?
Any added bedroom is reviewed by the Health Department first, suite or not. Pump and haul is not allowed for a suite.1,3
Building permits, still
A stove or cooking appliance, wiring, plumbing, an egress window for a bedroom: each needs a permit, under today’s rules and the proposal.1,6
Digging a cottage?
Disturb more than 2,500 square feet and you need a grading plan. Near a stream, the 100-foot buffer limits new buildings.3,6 See your lot’s buffer, easements and septic
Safety inside
Today’s rules: a working fire extinguisher, and smoke and carbon monoxide alarms tied in with the house’s.1
Record it
Today the owner records the permit in the county land records before anyone moves in, which is how a future buyer can find it.1
Buying or selling
A house with a suite, at sale time.
What to ask for, and what to fix before you list.
In shortA suite is worth most when its permits are on record. Buyers ask; lenders and appraisers too.
Buying a house with a suite?
Ask for the recorded permit and the building permits for the kitchen and bath. The suite’s people limit and the no-short-stays rule come with the house.
A basement kitchen with no permit
It may not count as a legal suite, and a buyer’s lender or appraiser may ask. Find the permits before you list: pull your permit history.
Your tax bill can rise
The county says a property’s value for tax purposes may rise with any improvement, a suite included.3
Questions
What people ask about in-law suites.
Can I have an in-law suite in Fairfax County?
Yes, inside a single-family detached house, with an administrative permit: $285 (one-time), about 30 days. Today the suite can be up to 800 square feet or 40% of the house, whichever is less, or the whole basement, with up to 2 bedrooms and 2 people, and the owner must live in the house or the suite.
What is the Board of Supervisors voting on November 17, 2026?
A change to the county's accessory living unit rules. Staff's proposal raises the size cap to 1,200 square feet (or 40% of the house), allows 3 people, drops the rule that the owner live there, drops the separate zoning permit, and allows a detached backyard cottage by right on lots of 36,000 square feet or more. The hearing is Tuesday, November 17, 2026 at 4:30 PM, and the Board can change the numbers.
Can I build a backyard cottage in Fairfax County?
Today only on a lot of at least 2 acres, by special permit from the Board of Zoning Appeals, up to 1,200 square feet. Under staff's proposal, lots of 36,000 square feet or more could build one by right, and smaller lots could ask for a special permit.
Can a townhouse have an in-law suite in Fairfax County?
Not today: the rule is for single-family detached houses. Staff's main proposal keeps it that way; an alternative option the Board can pick would allow a suite inside a townhouse or duplex by special permit.
Can I rent out an in-law suite in Fairfax County?
Yes, to a long-term tenant, within the people limit. Today the owner must live in the house or the suite; staff's proposal drops that rule. Short-term rentals such as Airbnb are not allowed in an accessory living unit.
Is an in-law suite the same as an ADU?
In everyday talk, yes: an accessory dwelling unit. Fairfax County calls it an accessory living unit (ALU). It is not the county's Affordable Dwelling Unit program, the below-market homes sold to buyers under an income limit, which uses the same letters.
Can I have an in-law suite in Loudoun County?
Yes, inside the house or in a separate building, with a building and zoning permit. In suburban neighborhoods it can be up to half the house's floor area or 1,200 square feet, whichever is less; in rural areas, 70% or 2,500 square feet. One per lot under 20 acres. The ordinance has no rule that the owner live there, but the suite and the house must have the same owner. The towns, such as Leesburg, have their own rules.
Can I have an in-law suite in Prince William County?
Not a separate one with its own kitchen, not today. A home can have only one kitchen; a single-family detached house can add a wet bar or a warming kitchen with zoning approval, with no stove or oven, no locked door, no separate meter, and it can't be rented out. Townhouses can't add one. From July 1, 2027, a new Virginia law makes the county allow an accessory dwelling unit on single-family lots, unless it adopts its own rules first.
Can I have an in-law suite in Arlington?
Yes, on a lot with a single-family detached house in most single-family zones, with an accessory dwelling permit (about 30 days) and a building permit. Up to 3 people. The owner must live in the house or the unit. In the basement there is no size limit beyond its walls; elsewhere up to 35% of the house and unit together, at most 750 square feet. A backyard building can have a footprint of 560 or 650 square feet, depending on the zone.
Does Virginia's 2027 law change the rules in Fairfax County?
Probably not. The law that starts July 1, 2027 says it does not apply to a locality that adopted rules for these units before January 1, 2026, and Fairfax County had them for years (it calls them accessory living units). Loudoun and Arlington had theirs too. Prince William had none, so that is where the law changes most.
Does an in-law suite raise my property tax?
It can. The county says a property's value for tax purposes may rise with any improvement, an accessory living unit included.
Your next step
Want a house with room for family, or to sell one?
Tell me what you are after: a basement suite for a parent, a lot big enough for a cottage, or selling a house with a suite. I will find the houses that fit and check the permits with you. 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.
Fairfax Lot Check
Your lot size, stream buffer, easements, zoning and sewer or septic, by Fairfax address.
GuideNew Virginia laws
The July 1, 2027 law on backyard cottages, and 21 more.
MapWhat’s changing
The November 17 vote and other projects, on one map.
GuideFairfax County property tax
What a bigger house does to the bill.
GuideSingle-family homes
What houses cost, county by county.
Keep reading
- ToolFairfax Lot CheckType a Fairfax County address: the stream buffer, marine clay, easements, historic district, zoning and sewer or septic for that lot, from the county's own maps.
- Living hereNew Virginia laws for homeowners22 new laws from the 2026 session in plain words: deed fraud alerts, roof insurance, backyard cottages, the 14-day rent notice, each with its start date.
- Living hereWhat's changing in NoVAThis month's new homes, roads, airports, stores and laws on one map, each with its stage, next date and official source.
- TaxesFairfax County property taxThe 2026 rate, the average bill, due dates, appeals and relief.