Chapter 2: How to Learn to Read Blueprints

Cary Flanigan

2 Chapter 2: How to Learn to Read Blueprints

Cary Flanigan

Blueprint Basics

Blueprints are 2-dimensional architectural design drawings that indicate the size of a planned building, the materials to be used in its construction, and the placement of its features. Learning to read blueprints is essential not only for construction workers but also for the people who hire architects to draft them.

The title block’s first section lists the blueprint’s name, number, as well as the location, site, or vendor. If the drawing is part of a series this information will also be listed. This section is largely for filing and organizational purposes.
The second section comprises bureaucratic information. Approval dates and signatures are located here. If you find a blueprint that interests you and want to know more, this information can be invaluable.
Section three of the title block is the list of references. This lists all other drawings that are related to the building/system/component, as well as all blueprints that were used as reference/inspiration. Similar to the second section this can be incredibly helpful if you are to begin your own blueprint.

If you are looking over the drawings with a team or partner and can’t physically point to the location you’re discussing, grid systems are very useful. This could be the case if you working online from different locations, or the other person/people simply isn’t in the room with you.

Step 2 Read the revision block.

Step 3 Read the notes and legend.

For projects that actually begin construction it is even more important to read the notes. It’s possible practical information like, “Do not begin working until 8am,” will be listed.

Step 4 Determine the view.

Plan: A bird’s eye view of planned work. Usually this is done on a horizontal plane at 30″ above the floor. This perspective allows precise mapping of width and length.
Elevation: A view of planned work from the side. These drawings are usually oriented from the north, east, west, or south. Composing an elevation map allows for detailed planning of height dimensions.
Section: A view of something as if it were cut through. This perspective is generally imaginary, and is used to show the inner workings of how something will be built.

Step 5 Establish the scale in your mind.

Architectural scales are used for the construction of building exterior and interiors; for establishing doors, windows, and walls. Many are presented in fractions: 1/4″ = 1′ (one-fourth inch equals one foot), 1/8″ = 1′ (one-eighth inch equals 1 foot).
Engineer scales, or civil scales, are used for public water systems, roads and highways, as well as topographical endeavors. They use whole-integer ratios like 1″ = 10′ (one inch equals 10 feet) or 1″ = 50′ (one inch equals fifty feet).
There are a variety of scales that might appear on blueprints. Common scales in the US include 1/4″=1′ and 3/32″=1′.

Step 6 Inspect the grid system.

Step 7 Locate any doors and windows.

The blueprints should always include a door and window schedule. This will state the style, size, and material of each door and window.

8. Fridges, toilets, sinks, ovens, stove-tops burners, and the like will be represented by simplistic representations that are readily recognizable. Take the time to consider whether they are located in an area where you want them. Although it may seem like their placement comes second the establishing walls, they can end up playing a more important role in deciding on design specifications.^{^[6]}
- You should see the finish schedule included. This will tell you what style or model each appliance is.

Blueprint Lines

Step 1 Look over the lines.

1. Although it can seem overwhelming when taken in all at once, lines are the language of blueprints. Lines often represent walls, door frames, and appliance exteriors; however they have many other purposes and are the primary characteristic of planned drawings. Depending on their thickness, whether they are straight or curved, dashed or consistent, lines have different schematic significance. The type of basic lines are as follows:^{^[7]}

Object Line
Hidden Line
Center Line
Extension and Dimension Line
Cutting Plane Lines
Section Line
Break Lines
Phantom Line

2. Object lines – or visible lines – are drawn the thickest of all on a blueprint. They represent what sides of an object are visible to the eye. Consider a simple drawn cube, the only lines seen are those visible. On a blueprint, these take on an added importance; thicker than all others, they became the reference point to compare the weight and composition of all other lines.

3. Hidden lines – or invisible lines – reveal surfaces that otherwise would not be visible to the eye. They are drawn at half the weight of object lines, with short, consistently spaced dashes. Consider the same drawing of a cube and how sometimes the otherwise invisible lines are represented in this same way.
- One rule of hidden lines is that they must always begin in contact with the line that is their starting point. The exception to this is anytime that first dash would appear to be a continuation of a solid line.
4. Dimension lines show you the distance between any two locations in a drawing. Whether that be walls in a house, or the space between wiring in an electrical outlet. They are drawn as short, solid lines, with arrowheads on each end. The line’s center point is broken, and here you will see the dimension (i.e. 3.5, 1.8, etc.)
- Dimension lines will help to envision a more 3D space and maintain correct spacing within a room or object.
5. Center lines establish the central axis of an object or part. You will most often see these with plans for circular or curved objects. On blueprints, they are drawn with alternating long and short dashes. Long dashes are on each end, and short dashes at points of intersection.
- Center lines are drawn with the same weight as invisible lines.
6. Phantom lines are used to illustrate different positions of an object. For example think of a switch in the off position. Phantom lines could be used to represent its possible appearance in the on position. On blueprints you will see them drawn with one long and two short dashes, with another long dash on the end – all evenly spaced.
- Phantom lines also show any detail that needs to be repeated, or even the location of absent parts.
7. Extension lines are used to precisely define the physical limit of any dimension. They are drawn as short, solid lines, and can be placed inside or outside of the dimension being defined. Extending from the object outline, they do not actually touch the object lines.
- Since dimension lines often have to hover above an object simply because there is no room on the paper, or they would overlap, extension lines allow for more definite end and beginning points.
- Dimension lines are drawn with the same weight as invisible lines.
8. Leaders lines are solid lines ending typically in an arrowhead; these indicate any part or area of a drawing that is associated with a number, letter, note, or other reference.
- Desks, bookcases, and other furniture that don’t come pre-assembled are a common reference to remember leader lines. In the instruction manual, lead lines are frequently used to define parts (i.e. “Place slot A into hole B”).
9. Break lines are used any time a part is removed in order to reveal what lies immediately beneath. In architectural drawings they are often used when a long section of drawing have the same structure; this reduces the drawing size and saves paper.
- Short break lines are done freehand and resemble a solid, thick sin wave.
- Long break lines are long, thin ruler-produced lines interspersed with freehand zig-zags.

Tips

When first learning how to read blueprints, take your time reading them. Look over individual words and symbols to understand their purposes before moving on to other parts of the blueprint. You may want to highlight individual parts as you figure out their meanings.

This chapter is an excerpt from a Wikihow article and was co-authored by Mark Spelman. Mark Spelman is a General Contractor based in Austin, Texas. With over 30 years of construction experience, Mark specializes in constructing interiors, project management, and project estimation. He has been a construction professional since 1987.

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Blueprint Lines

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