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Whether you're a homeowner with a hands-on approach to home renovation or a professional contractor, knowing how to read blueprints is an essential skill.

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What Is a Blueprint?

A blueprint is a two-dimensional set of drawings that provides a detailed visual representation of how an architect wants a building to look. Blueprints typically specify a building's dimensions, construction materials, and the exact placement of all its components.

The word "blueprint" originated in the mid-nineteenth century when engineering drawings were printed on blue paper with white lines. In the modern construction industry, physical blueprints typically aren’t blue. Construction drawings, construction plans, building plans, house plans, floor plans, and working drawings are all types of blueprints.

Why Are Blueprints Important?

Blueprints put everyone involved in the construction process on the same page, including the contractor, construction workers, fabricators, the home or building owner, and building inspectors. You need blueprints to estimate the cost of labor and the bill of materials, to create a construction schedule, and to obtain building permits. A set of blueprints must show that your building design is in compliance with your local building codes, or the building inspection department won't approve your permit to begin construction.

3 Types of Views in Blueprints

When looking at a construction blueprint, it's important to understand the perspective of the viewing angle. There are three views that architects typically use to depict a structure in a technical drawing.

  1. Plan view drawing: A plan view is a drawing on a horizontal plane depicting a bird's eye view of a structure from above. Each floor in the building has its own plan view drawing.
  2. Elevation view drawing: An elevation view is a drawing on a vertical plane that depicts how the building looks when viewed from the front, back, left, or right side. There are both interior elevation drawings and exterior elevation drawings.
  3. Section view drawing: A section view is a drawing on a vertical plane that slices through solid space to depict the inside of a certain section of the structure. A cross-section view shows elements such as insulation, wall studs, and sheathing.

10 Types of Blueprint Lines and How to Read Them

Knowing what the different types of lines represent in a construction drawing is one of the most basic blueprint reading skills.

  1. Object line: Also known as visible lines, objects lines indicate the sides of an element that are visible when looking at the element in person. Visible lines are completely solid and are the thickest type of line.
  2. Hidden line: Also known as invisible lines, hidden lines show object surfaces that are not visible when looking at the object in person. Hidden lines consist of short dashes that the architect draws at half the thickness of object lines.
  3. Center line: This type of line indicates the central axis of an element. Center lines consist of alternating short and long dashes that the architect draws with the same thickness as hidden lines.
  4. Dimension line: Dimension lines indicate the distance between two points in a drawing. When dimensioning, the architect draws two short solid lines with a gap between them and two arrowheads pointing in opposite directions. The architect then writes the dimension number in the empty gap between the two lines.
  5. Extension line: These short, solid lines at each endpoint of a dimension line indicate the exact limit of the dimension. Extension lines always pair with dimension lines and should never touch the object lines.
  6. Leader line: A leader line is a finely-drawn solid line that labels a specific point or area with a note, number, or other written reference. Leader lines usually contain an arrowhead pointing to the area they are describing.
  7. Phantom line: This type of line indicates elements of an object that can move into alternate positions, or it indicates adjacent features of an object. For example, an architect might use phantom lines to draw how a closed door looks in the open position. A phantom line consists of one long dash that alternates with two short dashes.
  8. Cutting-plane line: A cutting-plane line is a U-shaped line with arrowheads on each end. It bisects an object to display its interior features.