How to Read Blueprints

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There are three basic house plan blueprint views:

Floor plan

Elevation

Cross-section

When looking at house plans, most of the important details in understanding blueprints lies in the floor plan view. The image below shows a basic floor plan blueprint.

Floor Plans

When learning how to read blueprints, the best place to start is the floor plan view. The floor plan of a house blueprint shows the house from what is called "plan" view - looking at the house from above as though the viewer was in the sky looking directly down on the house with the roof removed. This view details each room, room sizes, fixtures such as appliances, bathroom fixtures and sometimes furniture. Some floor plans will also show electrical blueprint symbols such as lights, switches and plug outlets.

Let's jump right in and start learning how to read blueprints and the various symbols shown on the floor plan above.

But first, open blueprint symbols. The blueprint symbols glossary will open in a new window so you can toggle back and forth between the How to Read Blueprints tutorial and the blueprints symbols glossary as needed.

Let's start with the walls.

walls house plan blueprints

Walls are indicated by a double line. The thicker the wall, the further apart the two lines will be. An interior wall will usually consist of the wood framing covered on both sides with drywall. (Drywall is the common name for the inside walls of your house that are painted or wallpapered). Interior walls can also be made of bricks (adobe or concrete) or other materials. Exterior walls will typically be wider than the interior walls since the exterior walls help hold up the roof. The exterior wall could be wood or metal framing, concrete (perhaps with insulated forms), straw bale, rammed earth, cob, adobe bricks or anything that passes your local building code. The inside walls of the exterior walls are often covered with drywall or stucco and the outside walls covered with either stucco or sheetboard (either plywood or oriented strand board) which is then covered with some type of breathable waterproofing, then covered with exterior surfacing (wood siding, brick, stucco, etc.) Typically, the exterior walls will appear thicker than the interior walls on your blueprints.

Which brings us to scaling.

What Size Is It?

All blueprints are drawn to scale. This means that they are an exact representation of the real house as it will be built but they are scaled down to fit onto paper. Think of it as though you have drawn them full size and then used a massive photocopier to reduce their size by a reasonable percentage.

The reduction is not random however. The draftsperson or architect will draw them to a specific scale. An example of a scale could be one inch to one foot (written as 1":1'). So if the house was 40 feet long, the draftsperson would draw the house on paper as 40 inches long.

Now 40 inches would make for cumbersome blueprints so the scale that is more commonly used is 1/4 inch to one foot (written as 1/4":1'). So here we do the math, if we have a 40 foot long house and every foot will be represented by 1/4" we will draw it as 1/4 inches per foot X 40 feet which equals 10 inches. This will fit nicely on a piece of 11" X 17" paper. For framing details, 1/2":1' is often used. The same 40' long house would then appear on paper as 1/2 inch per foot X 40 feet which equals 20 inches. At this scale, the drawings are often on 18" X 24" or even 24" X 36" size paper.

The scale used on a set of house plan drawings will be listed somewhere near the page title block. Look on the page for 1/8":1', 1/4":1' or 1/2":1'.

To make reading blueprints and measuring your house dimensions easier, an architect's scale will come in handy. They are about the size of a standard ruler. Many office or art stores sell these. The scale is triangular shaped with two scales on each side. The side shown below shows a 1/4":1' scale going from right to left (on the other end of this side but not shown is the 1/8":1' scale).

Detail of Architects Scale

Look on the right-hand side of the scale in the image above. You will see the numbers 0, 2, 4 going from right to left. If you had house plans that had 1/4":1' written near the page title, you would use this part of the architect's scale. If you were to place the 0 on the inside line of an interior wall on your house plans, you could then measure across to the inside line of the opposite room wall. Simply read the number on the scale as though it were feet. So if the opposite wall of the room lay at the number 12 on the scale, the room is then 12' wide. The very fine gradations to the right of the 0 represent inches.

Elevation Drawings

The next step in learning how to read blueprints is understanding the elevation view. Typically a set of house plans will include four elevation drawings, one for each of the front, rear and two sides of the house. The elevation view is a completely flat view, in other words, with no artistic perspective. The elevation details the building height, the exterior materials used, including siding and roofing. It helps give the prospective owner an idea of what the home will look like but it is also used by the municipal planning office before issuing a building permit to ensure that the building meets the local zoning regulations. The elevation drawing is also used by the building trades when finishing the house exterior.

Below is a very simple elevation drawing.

Cross Section Drawings

The final view of the three house blueprint views is the cross-section. The cross-section shows a "slice" of the house. Imagine taking a doll house and then cutting it like a loaf of bread. If you took any one of the slices and looked at it from the flat face you would have a cross-section of the doll house. Below is an example of a cross-section through the stairwell of the same house which is shown above in the floor plan and elevation drawings.

The cross section could very well be the most difficult view in learning how to read blueprints since a large amount of detail and layers can sometimes be included. In our doll house example, imagine if the "slice" was very thick and included in it a few layers of walls, as well as some doorways, fixtures such as bathtubs and sinks, and details for a built-in cabinet. The residential designer or architect will often use the cross-section view to detail interior finishing such as built-ins, trim work and stairway finishing for the sub-contractors who will be doing this work. This view is also invaluable to the framers since it will give a better picture of how the house is to be built. Since the cross section also shows a slice of the exterior walls, information about the details of the wall layers , their insulation and exterior cladding is also included in this view. Often full house blueprints will include a few cross-sections. A more complicated and detailed house will require more cross-section drawings.

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How to Read Blueprints

Electrical Blueprint Symbols

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