What does S3 mean on an electrical blueprint?

S3 denotes a 3-way light switch. A pair of 3-way switches allows controlling the exact same ceiling light or fan from two distinct locations, such as the top and bottom of a stairway or opposite ends of a hallway.

What does HB mean on an architectural floor plan?

HB stands for Hose Bibb (also called an outdoor hose spigot or sillcock). It indicates the physical location of an exterior water faucet for connecting a garden hose.

How can you tell if a wall is load-bearing on a blueprint?

Load-bearing structural walls are typically shown with solid black fill or diagonal cross-hatching, whereas interior partition walls appear as thin hollow parallel lines. Load-bearing walls also run perpendicular to the ceiling joists above.

Architectural & Drafting Decoder

Blueprint & Floor Plan Symbols Meaning

Reviewing house plans, kitchen remodeling blueprints, or commercial floor drawings? Decode electrical outlet symbols (GFI, S₃, 240V), plumbing codes (HB, CO, WH), and door swings.

Discipline:

Showing 15 blueprint symbols

⦵ (2 lines)

Standard Duplex 120V Wall Outlet

Code: ⦵ (2 lines)

Electrical & Lighting

A circle with two parallel lines extending through it. Represents a standard 2-plug 120V household receptacle (15A or 20A).

Where found: Spaced every 12 feet along living room, bedroom, and hallway walls.

Builder & Remodeler Tip:

Building code requires an outlet within 6 feet of any door opening and no point along a wall more than 6 feet from an outlet.

Standard Architectural Drafting (AIA)Plan Legend

GFI / GFCI

Ground Fault Circuit Interrupter (GFCI) Outlet

Code: GFI / GFCI

Electrical & Lighting

A duplex receptacle circle marked with the letters "GFI" or "GFCI". Trips power within milliseconds if it detects water contact or current leakage to ground.

Where found: Mandatory in bathrooms, kitchen countertops within 6 feet of sinks, garages, outdoors, and basements.

Builder & Remodeler Tip:

A single GFCI outlet can protect all standard outlets wired downstream from it on the same circuit.

Standard Architectural Drafting (AIA)Plan Legend

⦵ (3 lines)

240V Heavy Duty Appliance Outlet

Code: ⦵ (3 lines)

Electrical & Lighting

A circle with three lines through it. Designates a heavy-duty 30A to 50A 240V dedicated circuit receptacle.

Where found: Behind the kitchen electric stove/range, electric clothes dryer, EV car charger, or central air handler.

Builder & Remodeler Tip:

Uses thicker 10 AWG or 6 AWG copper wire and a double-pole circuit breaker.

Standard Architectural Drafting (AIA)Plan Legend

Single-Pole Light Switch

Code: S

Electrical & Lighting

The letter "S". Controls a light fixture from a single physical location (turning ON or OFF).

Where found: Mounted 48 inches above finished floor on the latch side of entry doors.

Builder & Remodeler Tip:

Switches only break the black hot wire; the neutral white wire typically passes through the box.

Standard Architectural Drafting (AIA)Plan Legend

S₃

3-Way Light Switch

Code: S₃

Electrical & Lighting

The letter "S" with a subscript "3". Controls the same ceiling light fixture from two different locations.

Where found: Top and bottom of staircases, or at opposite ends of a long hallway or open-concept living room.

Builder & Remodeler Tip:

Requires 3-wire Romex cable (black, white, red traveler wire) running between both switch boxes.

Standard Architectural Drafting (AIA)Plan Legend

Hardwired Smoke Detector

Code: SD

Electrical & Lighting

A circle containing "SD". Indicates an interconnected hardwired smoke alarm with battery backup.

Where found: Inside every bedroom, outside bedroom sleeping areas, and on every story of the house.

Builder & Remodeler Tip:

Modern building code requires all smoke alarms to interconnect: if one detects smoke, all alarms throughout the home sound together.

Standard Architectural Drafting (AIA)Plan Legend

◯ with R

Recessed Can Light (Pot Light)

Code: ◯ with R

Electrical & Lighting

A circle with an "R" or crosshatch pattern inside. Represents an LED downlight recessed flush into the ceiling.

Where found: Kitchen ceilings, living room accent grids, and hallways.

Builder & Remodeler Tip:

Modern remodelers use ultra-thin wafer LED recessed discs that don’t require bulky metal attic cans.

Standard Architectural Drafting (AIA)Plan Legend

Hose Bibb (Outdoor Spigot)

Code: HB

Plumbing & HVAC

The letters "HB" on exterior walls. Designates an outdoor threaded water valve for connecting garden hoses.

Where found: Front and rear exterior foundation walls.

Builder & Remodeler Tip:

In cold freeze zones, ensure the blueprint specifies a "frost-free hose bibb" with a shutoff valve placed inside the heated envelope.

Standard Architectural Drafting (AIA)Plan Legend

Water Heater

Code: WH

Plumbing & HVAC

A circle labeled "WH". Indicates the location of the domestic hot water tank or tankless unit.

Where found: Basement utility room, garage closet, or dedicated attic platform.

Builder & Remodeler Tip:

Look for an adjacent floor drain (FD) or pan drain piped outside to prevent water leaks.

Standard Architectural Drafting (AIA)Plan Legend

Sewer Cleanout

Code: CO

Plumbing & HVAC

The letters "CO". A threaded pipe plug that provides plumbers direct access to clear main drain pipe clogs with a sewer snake.

Where found: Base of main plumbing drain stacks and where the building sewer exits the foundation.

Builder & Remodeler Tip:

Never drywall or tile over a cleanout cap! Plumbers need direct access during emergency sewer backups.

Standard Architectural Drafting (AIA)Plan Legend

⌒ (Quarter Arc)

Single Swing Hinged Door

Code: ⌒ (Quarter Arc)

Doors & Windows

A straight line at an angle with a dotted or solid quarter-circle arc. The arc visualizes the swing clearance needed for the door to open.

Where found: Standard interior bedroom, bathroom, and exterior entry doors.

Builder & Remodeler Tip:

The arc reveals whether a door is "left-hand" or "right-hand" swing and prevents doors from hitting vanity mirrors or toilets.

Standard Architectural Drafting (AIA)Plan Legend

∧∧ (Zig-zag)

Bifold Closet Door

Code: ∧∧ (Zig-zag)

Doors & Windows

Two connected panels forming a triangular chevron or accordion shape.

Where found: Bedroom closets, laundry utility alcoves, and pantry openings.

Builder & Remodeler Tip:

Bifolds save floor space in tight rooms where a full 36-inch swing door would collide with furniture.

Standard Architectural Drafting (AIA)Plan Legend

▭ in wall

Pocket Door

Code: ▭ in wall

Doors & Windows

A door panel that slides directly into a hidden split-stud hollow cavity inside the wall frame.

Where found: Small half-baths, en-suite master bathroom entries, and walk-in pantries.

Builder & Remodeler Tip:

Cannot run electrical outlet boxes or heavy plumbing pipes through the pocket wall cavity where the door slides.

Standard Architectural Drafting (AIA)Plan Legend

Solid / Hatched

Load-Bearing Structural Wall

Code: Solid / Hatched

Walls & Structural

A wall rendered with dark solid black fill or diagonal cross-hatch shading.

Where found: Center spine of the house, exterior perimeter walls, and beneath roof trusses.

Builder & Remodeler Tip:

NEVER remove or cut studs in a load-bearing wall during an open-concept remodel without installing a calculated steel or LVL beam!

Standard Architectural Drafting (AIA)Plan Legend

Parallel Clear

Non-Load Bearing Partition Wall

Code: Parallel Clear

Walls & Structural

Two parallel hollow lines with white or empty space inside. Serves only as a room divider.

Where found: Closet walls, bathroom privacy partitions, and hallway dividers.

Builder & Remodeler Tip:

Safe to modify or remove for open-concept floor plans with standard drywall and framing demolition.

Standard Architectural Drafting (AIA)Plan Legend