Basic Guide to Blueprints: How to Read 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.

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.

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. 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. 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. 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.

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

1. 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. 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. 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. 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. 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. 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. 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. 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.
9. 9. Section line: Section lines indicate when the surface of an object in the sectional view is cut along the cutting-plane line. A sectional line consists of multiple short parallel diagonal lines.
10. 10. Break line: Architects use break lines to shorten the view of long uniform sections of an object in order to conserve drawing space. Short break lines are thick, solid freehand wavy lines, while long break lines are thin, solid ruler-drawn lines with interspersed freehand zig-zags. Architects use break lines in both detail drawings and assembly drawings.

To ensure that blueprints stay in order, architects label their drawings with a classifying letter code and a sheet number, e.g. A001. The below breakdown explains the letter code system and the order of drawings in a basic set of plans.

1. 1. G sheets (general sheets): General sheets contain the cover sheet, plan index, and plot plans.
2. 2. A sheets (architectural plans): Architectural drawings depict ceiling plans, roof plans, floor plans, building sections, and wall sections.
3. 3. S sheets (structural engineering plans): Structural drawings depict framing plans, foundation plans, and roof structure plans.
4. 4. E sheets (electrical plans): These plans show the location of all electrical fixtures, circuits, and panel boxes. Electrical schematics show the function of the actual electrical circuit, while wiring diagrams indicate the physical layout of the wires.
5. 5. M sheets (mechanical plans): Mechanical drawings contain information related to HVAC systems, refrigerant piping, control wiring, and duct work.
6. 6. P sheets (plumbing plans): Plumbing plans show the location and type of plumbing in a structure.
7. 7. Door schedule, window schedule, and finish schedule: Schedules describe the size, material, and style of the doors, windows, and other types of finishes.
8. 8. Specifications sheets: These sheets contain detailed descriptions of all the materials.

If you're new to reading blueprints and are preparing to work on a building construction project, familiarize yourself with these blueprint reading fundamentals. The tips here should provide you with a basic understanding of how to read blueprints, but if you want the knowledge of a construction professional, it may be worth looking into a hands-on blueprint reading course.

1. 1. Begin with the title block. The title block is the first piece of information you'll see in construction site plans. It contains important details like the project's name, plan number, drawing date, location information, contact information for the architect, company name, and the required government approval information. Lastly, it contains the plan index, which is a reference list of all the drawings contained in the entire set of plans. Any changes made to the blueprints are listed in a revision block that's typically located in the title block or in the top right corner of the actual revised drawing.
2. 2. Study the plan legend. The legend is your key to decoding and understanding basic symbols in the drawings. For example, electrical drawings have symbols that indicate the placement of an outlet and a roofing plan may have symbols showing the placement of skylights. There are industry-standard symbols for specific types of projects, but some architects and construction companies use their own custom symbols. Familiarizing yourself with the legend right off the bat will make understanding the blueprint symbols easier.
3. 3. Find the blueprint's scale and orientation. All blueprint drawings are drawn to scale. A drawing scale indicates the difference between the size of the finished structure and the size of the drawing. For example, one common drawing scale for a quarter inch in the drawing to equal one foot in the finished project. If anyone involved in the construction process uses the incorrect scale, there will be serious problems when materials come in the wrong sizes. In addition to the architect's scale, you'll want to look for a north arrow or a compass symbol that establishes the orientation of the drawings. You'll typically find the blueprint orientation near the plan legend, and the scale should be indicated on each separate drawing page.
4. 4. Look for notes from the architect. Architects may include general notes to provide additional context on aspects of the blueprints that would be difficult to interpret otherwise. Be on the lookout for these notes, which are written directly onto the drawings or attached in a separate document.

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