What plans does Fairfax County require to finish a basement or build an addition?

Fairfax County publishes Typical Finished Basement Details, based on the 2021 Virginia Residential Code. ^S1 A basement with a kitchen, wet bar or bedroom still needs a plan submission and county approval. ^S1 An addition needs full plans: foundation, framing, wind bracing, room uses, window and door sizes, and a site-related plan. ^S2

Section numbers below are from the 2021 Virginia Residential Code (VRC). Virginia has enforced the 2021 codes since January 18, 2024, and all Fairfax applications have had to meet the 2021 USBC since January 18, 2025. ^S3S4 For the next edition, DHCD's schedule, which is tentative, lists October 2027. ^S5

When does a finished basement need plans?

A finished basement that includes a kitchen, wet bar or bedroom requires a plan submission and county approval. ^S1 Cutting openings in exterior basement walls is outside the typical details, so a plan submission is required for that too. ^S1 A new window well also needs a plan submission. ^S1

The county's typical details can be used in place of an architectural plan submission when a basement qualifies. ^S6 Deviations require county approval before construction. ^S1 A copy of the handout must be on the job site at each inspection. ^S1

Finished basements also appear among project types eligible for Fast Track priority plan review. ^S6

What are the egress rules for a basement bedroom?

A basement needs an emergency escape and rescue opening (EERO) if the house was built after October 1, 2003, and every basement bedroom needs one regardless of the house's age. ^S1 One opening in a bedroom may serve the whole basement. ^S1 The 2021 VRC requires an operable opening in basements, habitable attics, and every sleeping room. ^S7

Check one thing: the county handout lists the below-grade exception as 5.0 square feet for windows opening directly outside at or below grade. ^S1 That matches the 5 square feet in R310.2.1. ^S7

Sprinklered dwellings are an exception to R310.1 in the 2021 VRC. ^S7 Ask LDS how it applies this exception to your basement before relying on it.

What are the smoke and carbon monoxide alarm rules?

The county handout requires a smoke alarm in the basement and in each basement bedroom. New smoke alarms must be interconnected, hardwired with battery backup, and at least 3 feet from doorways to bathrooms with tubs or showers. ^S1 The 2021 VRC requires smoke alarms in each sleeping room, outside each sleeping area, and on each additional story including basements (R314.3). ^S7 It requires interconnection (R314.4) unless listed wireless alarms are used, and primary power from building wiring with battery backup (R314.6). ^S7

A carbon monoxide alarm outside sleeping areas is required by the handout if you add a bedroom and the house has a gas-fired appliance or an attached garage. ^S1 The ICC text of the 2021 VRC shows R315.2.2, the section on alterations and additions, as "(Section deleted)." ^S7 The two sources differ, so confirm with Fairfax County LDS before finalizing your drawings.

What are the ceiling height and room size rules?

The county's basement handout sets these minimums: ^S1

• Habitable rooms (not closets, hallways, laundry, storage or bathrooms) at least 70 square feet and at least 7 feet in any direction. ^S1
• Hallways at least 36 inches wide. ^S1
• Ceiling height at least 7 feet. Beams, girders and ducts can project to within 6 feet 4 inches of the finished floor. ^S1
• Bathrooms vented to the outside by a fan, unless a window opens at least 1.5 square feet. ^S1
• Space under stairs protected with 1/2-inch drywall. ^S1 The VRC says the same for enclosed space under stairs (R302.7). ^S7
• All basement stairs lit, with switches at the top and bottom. ^S1

The VRC sets the baseline at 7 feet for habitable space, hallways and the parts of basements containing them, and 6 feet 8 inches for bathrooms, toilet rooms and laundry rooms (R305.1). ^S7

What does the county want for walls, fireblocking and electrical?

For a finished basement built to the typical details: ^S1

• Studs may be utility grade or better, with a single pressure-treated bottom plate, at 16 inches on center (24 inches with drywall finish). ^S1
• Fireblocking is required in concealed spaces of stud walls, soffits and drop ceilings, and around penetrations. ^S1
• Gypsum board is at least 1/2 inch. ^S1
• All basement receptacles need GFCI protection and must be tamper resistant. ^S1
• Arc-fault protection is required in dining rooms, libraries, bedrooms, recreation rooms, closets, hallways, laundry areas and similar rooms. ^S1
• At least one switched light is required in each room and hallway. ^S1

What energy values go on addition and basement plans?

The county asks you to show insulation R-values and U-factors on the plans. ^S2 Its Energy Conservation page gives these values for a new home or addition: ^S8

The county page's basement wall row says "R-13 or R-10 continuous," while the footnote to that row says "Use R-15 when applied continuously against the wall; use R-13 when applied between studs." ^S8 Confirm the basement wall value with Fairfax County LDS before finalizing your drawings.

A basement wall is one that is more than 50 percent below grade and encloses conditioned space. ^S8 The finished basement handout calls for at least R-13 batt insulation with a vapor barrier on the warm side, full height and length of the basement wall. ^S1 Mark the compliance values on the drawings, or attach a RESCheck certificate. ^S8

What does an addition need on its plans?

The county's checklist for additions lists: ^S2

• PDF plans, 11 by 17 inch sheets, scale 1/4 inch = 1 foot. ^S2
• A digital protected seal and signature, if applicable. ^S2
• A site-related plan. ^S2
• Foundation plan. ^S2
• Framing plans for floor and roof. ^S2
• Wind bracing plan. ^S2
• Each room labeled as to proposed use. ^S2
• Window and door sizes. ^S2
• Columns, beams and header sizes. ^S2

Plans also need the code year, designer name, address and occupation, a Building Plan Review Cover Sheet, a wall bracing method and worksheet, R-values and U-factors, and truss shop drawings. ^S9 Additions up to 500 square feet appear on the county's Fast Track list. ^S6

For the site, the county says small additions can use a conservation plan, and large additions or any work over 2,500 square feet of disturbance use an infill lot grading plan. ^S10 Excavation for a below-ground basement needs a stockpile location and erosion controls on the plan. ^S11 The grading plan must show where the foundation drain or sump pump discharges. ^S11 The county memo places these items in its infill lot grading section. This may apply to your project; confirm with LDS.

FAQ

PlanScan is an invite-only pilot that reads a residential plan set PDF and flags likely code issues, each with a citation, for Fairfax County only. Its rules are drafts, and it does not replace county review.