Architectural Symbols

Architectural symbols let the people who build a structure share one graphic language. A team can read the same plan whether or not they share a spoken language, and turn the paper into a building. A single plan holds hundreds of these marks. They are grouped by function: electrical, piping and plumbing, materials, structure, and the floor plan itself. Accurate reading is a professional skill. The sheet types that hold them are described under blueprint symbols.

Switches

Switch with a pilot light. The pilot, or indicator, lights when the switch is on and goes dark when the switch is off. That matters when the lamp or appliance is somewhere the switch itself cannot see.

Time switch. A timer, electronic or mechanical, opens and closes a circuit at set times of day. It is used to save energy, and as a security measure when a house is empty, because lights that change make the building look occupied.

Two-pole switch. Used for receptacles or appliances on 240 volts. It switches two hot legs, not the single leg of a one-pole switch, and it has a ground terminal.

Dimmer. The light can be set between off and fully on, either by a knob or by a lever, instead of only those two states.

Doors, closets, and traps

A standard door on a floor plan is readable even to an untrained eye. Doors are distinguished by the direction they swing. A bifold door is easier to miss.

A water-closet symbol means a toilet. Newer plans draw it in more than one shape.

The P-trap is one of the wastewater traps used in a house to catch sewer gas and keep it from coming up through a kitchen sink or a shower drain.