Until explaining how to read blueprints, it may be good to understand what blueprints are. It is quite difficult to build a house to scale when the scale you are working from is very small. To make things easier to read, architects and designers complete their blueprints on large scale vellum sheets of various sizes; probably the most usual sizes for residential houses is 18" x 24" or 24" x 36". Today most plans are drawn on computerized equipment. House Blueprints were drawn by hand on a semi-transparent film called vellum. Blueprints are made by overlaying the vellum drawings on top of blueprint paper, which is then run through the blueprint machine, which exposes the paper to intensified ammonia and light. This exposure to light and ammonia causes the blueprint paper to develop and the drawings are transposed in a dark blue color.
The Vellum drawings were very expensive since it represented hours and hours of work that the architect put in to creating the drawing. Today, house plans are most commonly created using computer software. Once complete, the drawings are printed on a large-scale printer called a plotter. If the vellums are accidentally destroyed the architect has the plans on file to re-plot. As consumers often have minor changes to personalize their home blueprints, vellums are quite commonly purchased rather than a package of blueprints. Consumers can then draw any changes onto the vellums before making Photostats or blueprints. Vellums generally cost more since it gives the consumer the opportunity to make as many blueprints as desired for a single house.
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