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How to Read Blueprints

Before explaining how to read blueprints, it may be valuable to understand what blueprints are. It is quite difficult to build a structure to scale when the scale you are working from is very small. To make things easier to read, architects and designers complete their drawings on large scale vellum sheets of various sizes; probably the most common sizes for residential structures is 18" x 24" or 24" x 36". Twenty years ago, we didn't have the technology that we do today where most plans are drawn on computerized equipment. Plans 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 light and ammonia. This exposure to ammonia and light causes the blueprint paper to develop and the drawings are transposed in a dark blue color.

The Vellum drawings were very valuable since it represented hours and hours of work that the architect put in to creating the drawing. These days, house plans are most commonly created using computer aided drafting software. Once complete, the drawings are plotted (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 plan, 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 construction.

The Basics of Reading Blueprints

Scale: Home plans are drawn to scale so that if any specific dimension needed is missing, the contractor can scale the drawing to determine the right measurement. The main floor plans are generally drawn to ¼" scale which means that every ¼" on the plan equals 1' in actual length. Other details like framing layouts or built-in details may be drawn at another scale like 1/8" or even ¾". The scale of each drawing is usually called out beneath the drawing or somewhere on the page, usually next to the title.

Elevations: Elevations are a non-perspective view of the home. These are drawn to scale so that measurements can be taken for any aspect necessary. Plans include front, rear and both side elevations. The elevations specify ridge heights, the positioning of the final grade of the lot, exterior finishes, roof pitches and other details that are necessary to give the home its exterior architectural styling.

Basement Floor Plan: The basement or foundation plan delineates the location of bearing walls that will support the structure. It also identifies locations of footings, steel (rebar) placement, hurricane strap placement and other structural elements that are required to support the loads of the upper floors.

The Floor Plan: Floor plans are actually quite easy to understand. A floor plan layout on blueprints is basically an overhead view of the completed house. You'll see parallel lines that scale at whatever width the walls are required to be. Dimensions are usually drawn between the walls to specify room sizes and wall lengths. You'll also see on the floor plan locations of fixtures like sinks, water heaters, furnaces, etc. Among the walls and dimensions you will often find notes to specify finishes, construction methods, or even symbols for electrical or to reference cross sections.

Electrical Layout: Electrical layouts are sometimes on a separate page to make reading them a little easier. The layout will show locations of light fixtures, fans, outlets, light switches etc. There is usually a legend on the page which explains what each symbols represents. For illustration purposes we have included such a legend below. There may be such legends for heating systems, door swings and sizes, or even to specify certain finishes.

Framing Drawings: The framing drawings are also drawn to scale and outline the layouts of items such as floor joists and trusses, beam locations and other structural requirements. Framing layouts don't usually get into the details of each stud location in the walls since framing contractors are required to follow certain rules and regulations to assure that the home meets the required building code specifications. Though there are often cross section within the plan pages that outline the general methods of wall construction or floor assembly.

Plumbing and mechanical systems:
These systems are generally not covered extensively on the blueprints other than locations of fixtures and main service lines. If you are going to the expense of more complicated heating systems like in floor radiant heat or even an engineered forced air system, these drawings need to be completed by a heating or plumbing specialist.

Cross Sections and Details: Overhead views or floor plan views of the structure don't always provide enough information on how the home is to be built. Often times cross section or details will explain certain special conditions more appropriately. A cross section is basically a view of the home if it were sliced down the center. This allows you to view the home from the side and understand a little better the relativity of varying floor heights, rafter lengths, and other structural elements.

Plot Plan: Plot Plans are drawn to determine the placement of the home on the building lot. A plot plan again is an overhead view of the construction site and the home as it sits in reference to the boundries of the lot. Stock house plans usually do not include plot plans since they are drawn specific to the site where it will be built. Plot plans can be drawn by a local professional draftsman, architect or engineer. Plot plans should outline location of utility services, setback requirements, easements, location of drives and walks, and sometimes even topographical data that specifies the slope of the terrain.

These are the basics of reading a house plan; keep in mind however that what is included in plans will vary according to the designer who drew them. House plans are a very important part of the homebuilding process. It is crucial to purchase a plan drawn by a home design professional since they have a thorough understanding of how homes are built. If there were any terms on this page that you did not understand or would like a more thorough description of their meaning, please visit our construction terms glossary.


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