Reading and Interpreting Drawings - Introduction
In order to read and interpret the information on drawings, you need to learn the special language used in construction drawings.
This section of the module describes the different types of lines, dimensioning, symbols, and abbreviations used on drawings.
Lines Used on Drawings
Many different types of lines are used to draw and describe a structure. Lines are drawn wide, narrow, dark, light, broken, and unbroken, with each type of line conveying a specific meaning.
Lines Used on Drawings
• Object lines
• Dimension and extension lines
• Center line
• Cutting plane
• Break line
• Leader line
• Hider lines
• Phantom line
• Stair indicator line
• Contour lines
Symbols Used on Drawings
Symbols are used in architectural plans and drawings to pictorially show different kinds of materials, fixtures, and structural members. Symbols used on drawings generally:
Categories of Drawing Symbols
Click on each button to find out more:
Typically, materials are shown on drawings in two ways.
1. Here, the material is presented as you would see it when looking down on it.
2. Here, the symbol shows the material roughly as it would look when you are facing it.
Window and Door Symbols
Usually shown with only a center line measurement to locate them from some reference point, window and door symbols are shown on drawings as either elevation or plan views.
These symbols are used to show the electrician the location of outlets and switches. They are also used for showing auxiliary hardware such as buzzers, telephones, and computer hookups.
They show all of the hardware and fixtures required for the building. (Floor plans usually indicate only where the different fixtures should be located and plumbed.)
Symbols for Heating, Ventilation, and Air Conditioning (HVAC) systems are also used to show the direction of movement of the hot and cold air in the system.
Plot Plan and Survey Symbols
Plot/site plans show the position and sizes of all relevant structures on the site as well as the features of the terrain.
Structural Member Symbols
Structural steel shapes have a system of identification by the use of symbols.
Symbols for welding provide a means of conveying complete welding instructions from the designer to the welder. Weld symbols are used to indicate the type of welding to be performed.
Dimensions given on drawings show actual sizes, distances, and heights of the objects and spaces being represented. Dimensions may be from outside to center, center to center, wall to wall, or outside to outside.
Many written instructions are needed to complete a set of construction drawings. Normally, the title sheet in a drawing set contains a list of abbreviations used in the drawings.
Guidelines for Reading Drawings and Specifications
To know more about the general procedure suggested as a way to read a set of drawings for maximum understanding, click on each button:
Acquire the complete set of drawings and specifications, including the title sheet(s).
Read the title block. The title block tells you what the drawing is about.
Find the North arrow. Always orient yourself to the structure.
Always be aware that the drawings work together as a group.
Check the list of drawings in your set, and note the sequence of the various plans. Some drawings have an index on the front cover. This should state the categories of drawings contained in the set: architectural, structural, mechanical, etc.
Study the plot (site) plan to determine the location of the building to be constructed, the various utilities, roadways, and any easements.
Check the floor plan for the orientation of the building.
Check the foundation plan.
Check the plans for floor and wall construction and other details relating to exterior and interior walls.
Study the features that extend for more than one floor.
Study the plumbing and mechanical plans.
Study the electrical plans.
Check the notes on various pages.
Recognize applicable symbols and their relative locations in the plans.