Architecture Blueprint
An architecture blueprint is a reproduction of a set of drawings made on blue paper with white lines, and it is the name that stuck to the working drawings of the discipline of architecture even after the blue process was replaced by the digital one. The term now means any set of construction drawings, but the blue line on the white or the white line on the blue is still the image people have of the document a building is built from. This page defines the term, contrasts the blue process with the modern drawing, and explains how to read a blueprint.
What a blueprint is and where the name comes from
A blueprint is a copy of a drawing made by a photographic process that was the standard way of reproducing architectural drawings from the 1840s until the 1990s. The process used a sheet coated with two chemicals that, when exposed to light through a transparent original, left the drawn lines white on a deep blue background, and the process is named for that blue. A blueprint was made by tracing the original drawing onto a transparent sheet and exposing the coated paper to light, and a set of blueprints for a building ran to as many sheets as the original set, 30 to 60 for a house. The blue line on white, or the white line on blue, was easy to read and cheap to make, and it became the standard document that the builder worked from. The process was replaced by the digital plotter and the laser printer in the 1990s, but the name blueprint stayed, and it is still the word for the working drawings of a building.
The blue process and the modern drawing
The blue process and the modern drawing are the same document made by two different methods, and the difference is in the making, not in the content. The blue process made the drawing by light and chemistry, a physical sheet that could not be changed without making a new one. The modern drawing is made on a computer, a digital file that can be changed and reprinted, and the set is stored as a file rather than as a stack of paper. The content is the same, the plans, the sections, the elevations and the details, and the symbols are the same, the wall, the door, the window, the dimension. The modern drawing is sharper, because it is plotted by a machine rather than by a chemical, and it is cheaper to change, because a change in the file is a change in every copy. The table gives the two methods and the difference that matters to the reader.
| Feature | Blue process | Modern digital drawing |
|---|---|---|
| Made by | Light and chemistry | A computer plotter |
| Background | Blue paper, white lines | White paper, black lines |
| Change cost | A new sheet | An edit in the file |
| Stored as | Paper sheets | A digital file |
| In common use | Until the 1990s | Now, standard |
The shift from the blue process to the digital drawing was part of the larger shift in the discipline to computer aided drawing and to building information modeling, and it changed how the drawings are made and how they are changed. A modern set of drawings is a file that is updated as the design changes, and the builder works from the current file, which means the drawing and the building stay in step. The blueprint, in the modern sense, is that file, printed when it is needed, and the discipline's skill in the drawing is now in keeping the file true and the change controlled.
How to read a blueprint
How to read a blueprint is the same as how to read a set of architecture drawings, and the reader follows the set in a fixed order. The reading starts at the title block, the corner of the sheet that names the project, the drawing number and the scale, and moves to the plan, which shows the layout, and then to the section, the elevation and the detail. The reader reads the symbols, the wall as a thick line, the door as an arc, the window as a thin line, and the dimensions on the lines outside the drawing. A blueprint is read at the scale printed on it, and the dimensions are the measure, not the length of the line on the paper. The reader of a blueprint, the builder or the code reviewer, reads the set to answer 3 questions, what is to be built, where it is to be built, and how it is to be built, and the drawing answers all 3 if it is a complete set. The skill in reading the blueprint is in knowing the symbols and the order, and once those are known, the drawing of the building is as plain to read as a map of it.