A simple, non-technical reference for novices, builders, and project managers.
Construction drawing symbols are the standardized marks used to depict walls, doors, windows, electrical components, plumbing fixtures, and mechanical equipment on construction drawings. To read them, begin by reading the legend, followed by the basic line types, and then follow the references from one sheet to another. Symbols used by different companies and different areas may differ, so the project legend should always be followed.

The first time you open a set of construction drawings, you can feel like you're reading a foreign language. Numbers, dashed lines, little triangles, abbreviations everywhere, and circles with numbers. But each mark contains meaningful data on what is actually being constructed, how, and of what.
The good news is most symbols obey certain conventions. After mastering the essentials, a messy flowchart is an easy-to-follow map.

Why Symbols Matter
Architects, engineers, contractors, and estimators communicate through drawings. Symbols enable a designer to convey a lot of information in a small amount of space.

One is no small mistake when it comes to misreading. The framing can change if the wrong wall type is identified. When the electrical symbol is not recorded, it may represent a fixture that was not budgeted. Without a clear identification, it is not possible to show a price, which is why symbol reading is the basis of any good price estimation.

Step 1 is to look for the Legend.
Take a look at the legend (also known as the symbol key) before viewing any single floor plan. Describes the symbols as used in that particular project.

Symbols aren't perfectly universal. There is a minor variance in standards like the National CAD Standard (NCS) and conventions of particular companies. If there is any discrepancy between the legend and the general chart, trust the legend.

Step 2 Line Types
Lines are the simplest of symbols and the easiest to learn:
• The outlines of walls and cut elements are typically indicated by thick solid lines.
• Fine detail and dimensions are indicated on thin solid lines.
• Dashed (hidden) lines show something that exists but isn't visible in that view, like a footing below the floor.
• Center lines (long dashes and short dashes) indicate the center of a column, opening, or symmetrical object.
• Lines that are broken are shortened to fit into the space of the page.

Step 3 Understand the Architectural Symbols
Architectural sheets provide information about the building layout. The most common symbols:

• Walls parallel lines, hatching or filling to indicate material.
• The curved line that is used to indicate the direction of the swing. Double doors have two arcs, and sliding doors have overlapping rectangles.
• A small opening in the wall, marked by thin parallel lines, in a window.
• Stairs with parallel lines and an arrow indicating the direction of the stairs (up or down).
• A circle, hexagon, or diamond with a number referencing a door, window, or finish schedule.

Once you have used the section, elevation, and detail markers, follow the steps as outlined below:

These symbols function as signposts and take you to another sheet:
• Section markers indicate the location of the building "cutting." The arrow indicates your direction of view.
• Elevation markers indicate in a separate view which wall or face is shown.
• A “detail callout” is typically a half-circle. The number at the top indicates a detail, and the bottom number indicates a sheet where the detail is found.

Material Hatching Patterns

Hatching is used to fill a cut surface so that materials can be identified at a glance. Typical conventions include:
• Concrete: random dots and small triangles
• Earth: diagonal lines with stippling.
• Brick: parallel lines at a diagonal angle
• Insulation: Wavy, cloud-shaped loop
• Wood: a cross through a rectangle or lines across the grain.

Each pattern varies among firms, so consult the legend for each pattern.

Electrical, Plumbing, and HVLAC Symbols

Compact symbols are used on electrical plans:
• A circle that has two parallel lines is typically a duplex receptacle (standard outlet).
• An "S" represents a light switch, and "S2" or "S3" indicates multi-way switching.
• It is often a ceiling light and will have a circle with a cross or X in it.
• A linear or fluorescent light fixture is typically a rectangle.
• A curved line between the switch and the fixture indicates which fixture(s) are activated by which switch.

Plumbing plans use pipe line types and fixture symbols. The standard rule is that the line for cold water is solid, hot water is dashed, and waste and vent lines are single. Toilets, sinks, and tubs are simplified shapes. Line styles are different for different firms—see the legend.

Ductwork, diffusers, and equipment are represented in HVAC plans as rectangles and arrows. Airflow direction is indicated with arrows, and sizes and airflow values are indicated with labels.

Structural Symbols
Structural drawings have their own "shortcut." Search for grid lines with lettered or numbered bubbles, steel section callouts (W12x26), and rebar size and spacing notes. They both demonstrate the way loads flow within the building.

Avoid abbreviations, scale, and notes.

Drawings contain a lot of abbreviations: TYP. Typical, N.T.S., not to scale, EQ., equal and A.F.F., above finished floor, GWB, and gypsum wallboard. Look in the abbreviation list and general notes; often requirements are found here but not in the general notes.
Look also at the scale (e.g., 1/4" = 1'-0") and the north arrow. Otherwise, it is impossible to read the dimensions and orientation of the photos correctly.

Practical tips for reading drawings.

• Begin with the cover sheet and sheet index.
• Before the floor plans, read the legend and general notes.
• Cross-reference sheets. The plan, section, and schedule may all be used to describe the same element.
• Never assume. If the symbol is not understood, seek its meaning from the designer.
• Mark up as you go—highlight that which you have counted.

A Quick Example: How One Missed Symbol Makes the Budget!

Let's say there is a floor plan that has 24 recessed light symbols and a note in the general notes that says, “Make all the recessed light symbols dimmable.” If the estimator does not count the symbols and forgets the note, all of the fixtures and dimmers are incorrect. That is why it is important to read together the symbols, notes, and schedules.

Understand why this is important for cost estimation.

All symbols on a drawing are something that needs to be purchased, installed, and paid for. Every outlet, door, beam, and duct run has a quantity take-off, and the budget is based on the quantities from the quantity take-off. Incomplete or incorrect symbols result in misestimations, change orders, delays, and disagreements.

This is where expert support comes into play. At every design estimation, we read drawings every day and convert them into detailed and accurate cost estimates. Being a contractor preparing a bid, a developer reviewing a budget, or an owner who needs to understand what the drawings contain and what it will cost them to construct will benefit from the understanding we can provide.

Frequently Asked Questions

What is the meaning of a cross in a floor plan in a circle?
Typically it is a ceiling-mounted fixture, although some companies use it for other products. Check the legend.

What is the difference between a section and an elevation?
An elevation is a view of the exterior surface of a building. A slice is provided, which reveals layers inside.

Is the construction drawing symbol the same throughout the world?
There are many that are similar, but some differ from firm to firm, discipline to discipline, and region to region. Standards, like the National CAD Standard, assist, and the project legend supersedes general charts.

What is the quickest way to learn how to read blueprints?
Always draw from the legend on actual drawing sets; use the cross-reference between the sheets.

Please have someone else read the drawings and give me an estimate of the costs.
Yes. Professional takeoff estimators take off quantities from your plans and provide you with a comprehensive estimate of your costs.
To find out more, visit designestimation.com.