How to Read Construction Blueprints

If you’re going to build anything bigger than a breadbox, you’ll almost certainly need construction blueprints. It’s a sure thing you’ll need these technical drawings if you’re planning to build a new home. In fact, you can use blueprints to plan out everything from a house to an underground bunker

The construction industry is built on blueprints, so to speak. Nearly every general contractor and construction professional sees them at some point during the building process. They’re even useful if you’re tearing something down: Demolition experts use blueprints to figure out which areas need to be blasted to bring a building down.

What Are Blueprints?

Blueprints are a type of construction drawings that show how a building is to be designed, what materials are to be used, and where features like doors, windows, sinks, and appliances will go. 

Put simply: If you’re going to construct a building, you’ll need a set of blueprints. And whether you’re an architect, an engineer, or a construction worker, you’ll need to know how to read them. 

These construction plans are also useful to keep on hand in case you need to want to make modifications later, or need to do maintenance/repair work. They’re also necessary to make sure the project has secured the correct building permits and complies with building codes. 

Blueprint reading is an essential skill that workers in the architecture design and construction industry need every step of the way.

Blueprint Basics

Blueprints are typically drawn on a 1/4 inch scale, which means that every quarter-inch on the plan equals 1 foot of actual length on the completed structure.

5 Key Features of a Blueprint

Anatomy of a Blueprint

Just as the general building industry uses a glossary of construction terms you need to know before embarking on a project, reading a blueprint also requires you to become familiar with numerous terms and symbols.

Blueprints can be larger or smaller depending on the scope and complexity of a project. The most common sizes of blueprints for the construction of a new home are 18×24 inches or 24×36 inches. In addition to the central drawing, each sheet of a blueprint usually includes the following features.

1. Title block

Title Block

The title block usually contains:

  • Company logo and contact information
  • Client name
  • Architect name
  • Project name
  • Site address 
  • Site location
  • Drawing title
  • Date drawn
  • Number of sheets
  • Approvals
  • Scale

The title block may be a rectangle that occupies a corner of the drawing or a narrow band that spans the length or width of the sheet. In either format, the title block contains useful baseline information about the project.

Title blocks are often found at the bottom right corner of the drawing frame. Also in the lower right is the drawing or print number, which is important for filing the blueprint and finding the right drawing when it’s mentioned on another blueprint. 

2. Revision block

Revision Block

A revision block lists any changes made to the drawing with the date, description of the change, and name or initials of the person making or authorizing the change. Revision blocks are included for various parts of the plan. 

When blueprints are first drawn, the revision block is empty, awaiting revisions to component parts. These are entered as changes are made and “as-built” drawings accumulate accordingly.

Interesting fact: Letters and numbers are both used in revision blocks, but the letters I, O, Q, S, X, and Z are avoided because they can be mistaken for numerals.

3. Grid system

Grid System

Like a map, blueprint sheets often include a grid system along the horizontal and vertical edges, with numbers on one axis and letters on the other. This makes it easy to reference a particular spot on the drawing.

4. Notes and legends

Legend

Symbols, abbreviations, notes, and other practical information relevant to each particular drawing often appear at the bottom or on the side of a floorplan. This is the key to decoding the shorthand of symbols in drawings. 

An architect’s plan may provide various notes in a project, including general notes that cover the entire project; notes applying to a particular design discipline; or notes that only apply to the sheet where they appear.

A legend is critical because it’s easy to get confused reading blueprints, especially if different architects or engineers produce them. Symbols that look similar don’t always mean the same thing to construction workers in different fields or specialties.

Besides, although there are standard symbols for specific types of projects, some architects and construction firms use custom symbols that you won’t find anywhere else. The legend makes these easy to understand.

A few examples of typical plan symbols include:

  • A compass symbol to indicate the building’s orientation
  • A straight line to indicate a door, with an arc showing how it will open
  • Thick lines to denote exterior walls
  • A triple line to show where a window will be
  • Appliances such as a tub, stove, toilet, etc., drawn in simple outline form as they would appear from overhead

5. Drawing or plan

The main area filling the center of each blueprint sheet is devoted to the drawing or plan, illustrating a particular view, feature, or system of the project.

Types of Sheets in a Blueprint Set

Most buildings are built by a combination of professionals, each with a specific area of expertise — foundation, framing, mechanical, electrical, plumbing, roofing, etc. To coordinate how all these features should work together, each set of blueprints contains specialized drawings called “sheets.” 

Types of Sheets in a Blueprint Set

Each sheet is classified with its own letter code to help different contractors easily find the information they need. Sheets are typically organized in a blueprint set from the most general to the most detailed. Some common types of sheets and their designations include:

  • G sheets (general sheets) — These often begin with a cover sheet and plan index listing the sheets to follow. One main feature is the construction site plan, showing the placement of the building in relation to property boundaries, fences, setbacks, landscaping, and driveways, plus power, sewer, and other utility lines.
  • A sheets (architectural plans) — These include floor and roof plans, as well as elevation views that show how the building will look from the front, sides, and rear when completed. They also might include detail drawings with close-up views of various elements. Architectural plans provide critical dimensions, wall layouts, door locations and swings, etc. They also may specify dimensions for the roof, plus sheathing and roofing materials to be used. 
  • S sheets (structural engineering plans) — While architectural drawings show how a building is supposed to look, structural drawings show how to construct it. Created by an engineer based on the architect’s drawings, S sheets include plans for the foundation, footings, framing, roof structure, load-bearing walls, steel rebar concrete reinforcements, and other elements of structural integrity.
  • M sheets (mechanical plans) — These depict the layout of the HVAC (heating, ventilation, and air conditioning) appliances and ductwork, as well as exhaust elements, fire protection systems, and other mechanical equipment.
  • E sheets (electrical plans) — These show where circuits, wiring, outlets, breakers, and panel boxes will be located, as well as built-in ceiling fans and light fixtures. E sheets also govern fire-protection systems, smoke alarms, interior and exterior lighting, standby power, and wiring for built-in appliances.
  • P sheets (plumbing plans) — These show where the internal and external piping will go for hot and cold water, sewer and storm drainage, as well as irrigation piping for lawn watering and other systems. If the building will use gas, P sheets also feature plans for natural gas piping.
  • L sheets (landscape plans) — These detail areas outside the building to specify where trees, shrubs, plants, and hardscape items will be planted or installed.
  • Schedules — Other sheets can feature “schedules,” or material plans for specific features, such as door schedules, finish schedules, window schedules, etc. Usually formatted as a table or matrix detailing a single portion of the project, identifying the material, color, thickness, etc., of every instance of that item.
  • Specifications sheets — These include detailed descriptions of all the materials to be used for a particular element of the building.

Each sheet has its own numbering convention that represents three elements: The discipline designator determines the first letter (or two) in the sequence (A for architectural, G for general, etc.). 

Next, a numeral represents the sheet type (0 for general info, 1 for plans, 2 for elevations, and so on). The final numerals signify where the sheet number falls in the entire sequence. 

By this system, a sheet numbered A204, for example, would contain the fourth sheet of architectural elevations. EL103 would contain the third sheet of the electrical lighting plan.

4 Common Perspectives in Blueprints

Blueprints will often show a project from many different angles. These might include not just a floor plan, but also pages showing the project from the following perspectives:

  • Plan views – Floor plans, foundation plan, roof plan
  • Elevation views – Right, left, front, and rear elevations
  • Cross-section views
  • Isometric views

Plan view

Plan View

The plan view is a bird’s-eye view of a structure from above. It’s probably the most recognizable form of blueprint to most people: a two-dimensional or “flat” view drawn as if the walls were cut in half on the horizontal plane. Each floor of a building gets its own plan view drawing. 

Elevation view

Elevation View

Elevation drawings show how a building will look from the front, rear, left, and right sides. They can show interior elevation or exterior elevation views. They’re drawn on a vertical plane, depicting one side of a building the way it would look if you were standing and looking directly at it.

Colorful, detailed artist’s renderings of an elevation view are often displayed in model-home offices to show how different tract-home designs will look when they’re finished. They’re also often supplied to media outlets to give the public an idea of what public buildings like shopping centers and university buildings will look like.

Cross-section

Cross-Section

This is a drawing of the completed building as if it were sliced in half vertically. It helps the viewer understand the relation between floor heights, rafter lengths, stairway designs, and other structural elements. Note how, in the example, the stairs appear as they would from the side, similar to a sawtooth.

Cross-section drawings are often used for a building’s framing plan, to show how beams, girders, columns, and joists fit together. These are elements you won’t see once the walls are finished, with drywall and ceilings installed. 

Isometric drawing

Isometric Drawing

An isometric drawing is a three-dimensional representation in which the lines are drawn at 30-degree angles. This gives the impression that you’re looking down on the interior from one corner of the building. It can reveal internal features such as plumbing connections, machine assembly, room design, or more. 

The word “isometric” stems from a Greek term meaning “equal measure.” The method isn’t just used for architecture; it’s also been used to create infographics in media. And artists have used the technique to create illusions in famous illustrations, such as those by M.C. Escher, in which staircases appear to begin and end on the same level.

8 Types of Blueprint Lines and What They Mean

A quick way to begin understanding blueprints is to get familiar with its lines. Lines represent walls, door frames, appliance exteriors, dimensions, ranges of motion, etc. 

Depending on their thickness, whether they are straight or curved, dashed or solid, lines signify different schematic purposes in a drawing. These are some of the most common lines you’ll encounter on a blueprint and their uses.

Object lines show the outer surfaces of objects that would normally be visible in a finished building. They’re the thickest and most common lines on a blueprint.

Object Lines

Hidden lines represent surfaces that would not be visible in a finished building because they’re on the far side of a wall, appliance, or other object. Also known as “hidden object lines,” these are typically used with isometric drawings.

Hidden Lines

Dimension lines are arrow-headed lines that indicate distance, from the measurements of walls to the spaces between wires in an electrical outlet, etc. 

Dimension Lines

Center lines define the central axis of a symmetrical object. They’re often used to distinguish circular features like holes, arcs, or cylindrical objects.

Center Lines

Phantom lines show different possible positions of a movable object. They can describe the “on” and “off” positions of a switch, the range of a door when it opens, and so forth. 

Phantom Lines

Extension lines mark the outer boundaries of dimension lines when greater clarity is needed. They do not touch the dimension lines, only indicating where they end.

Extension Lines

Leader lines, simply put, are “arrows” that point to features of a drawing that need more explanation. In general, they’re drawn at 45-degree angles to the feature they’re describing.

Leader Lines

Break lines are used to save space by shortening the drawing size. Depending on their length, they can look like wavy or sharp zig-zags. Either way, they indicate that a section has been removed.

Break Lines

Tips for Reading Blueprints

When reading blueprints, start with the title block to familiarize yourself with the basics, then study the legend. You’ll need to refer back to it repeatedly during the project, but committing key symbols to memory at the outset will give you a good head start.

It’s important to know what kinds of plans you’re dealing with, and what you need for each project. Each one will involve many of the same elements discussed above, but each one is unique, too, so it’s important to know how to read and interpret plans. 

You’ll want to be clear on which elements of a project come first in the process. You don’t want to get ahead of yourself and have the drywall up before you lay in the electrical wiring. Those are the kinds of mistakes that can make a project late and over budget.

It’s also important to know who you’re dealing with, from architects to engineers, electricians to carpenters, to make sure everyone’s on the same page.

Blueprints aren’t blue anymore … but they used to be

Blueprints were created by British scientist Sir John Herschel in 1842. He soaked thin paper in a chemical called cyanotype, attached it to white paper, and exposed it to light. The “Prussian Blue” shade seeped through, leaving white lines on the blue background.

The method remained in use until the mid-20th century. Most architects don’t draw blueprints by hand anymore. Instead, they use software to create blueprints digitally. But the name “blueprint” stuck, even centuries after the prints weren’t blue anymore.

Conclusion

Blueprints come first, before any work is done on a building project. They’re the foundational element of any construction project. They provide a picture of how a project is expected to look upon completion, plus a detailed road map for how to get there.

Whether you’re talking about property grading, structural layout, plumbing, electrical, or carpentry, you’ll need to provide specifics for how everything will fit together. Blueprints give you a way to do that. With their help, you can create a home or other building project to be proud of — and one that will stand the test of time.

Full infographics:

8 Types of Lines on Blueprints and What They Mean

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