Blueprint – The Meaning of Symbols

Graphic symbols are often used on building plans to show elements such as gas and water service lines and window types as well as to list drawing notes and identify finishes and revisions. The same graphic can be used for more than one purpose. For example, the same symbol is used for every revision; it is the number within the graphic that carries specific information. Trade-specific symbols are included for the electrical, HVAC, and plumbing trades.

One of the most important symbols to use right at the beginning of a new job is the directional symbol. This symbol, which is usually an arrow labeled “N” for north, enables the reader of a construction drawing to orient it. However, there are numerous variations of the “North” point symbol, depending on the designer's fancy (Figure 8.2). Whichever symbol is decided upon, a drawing is properly oriented when it is held so that the north arrow shown on the drawing is pointing toward north. The drawing must be properly oriented so the reader can relate the information on it to the surrounding area.

The following figures show some of the most common standard symbols; during the course of your work you will likely see many other types as well. For various reasons, some of the symbols on a drawing may not be standard. Many times you will figure out what a symbol means by analyzing it and thinking about what it looks like. The legend on a drawing should show any nonstandard symbols and their meanings. Occasionally a symbol for a particular component or device may have been specifically created by the architect or engineer who developed the drawing.

Reading blueprints requires a good understanding of line types. For example, on a plot plan some of the information shown will include property lines, rights-of-way, easements, topographic features, and a north arrow. Line types are discussed in greater detail in Chapter 3. Figure 8.4A and B show various door, window, and wall symbols used in general construction.

Material symbols are used to represent materials or contents on floor plans, elevations, and detail drawings. Different symbols may be used to represent the same item on these drawings. The outline of the drawing may be filled in with a material symbol to show what the object is made of. Many materials are represented by one symbol in elevation and another symbol in section. Examples of this are concrete block and brick. Other materials look pretty much the same when viewed from any direction, so their symbols are drawn the same in sections and elevations as seen in Figure 8.5.

When a large area is made up of one material, it is common to only draw the symbol in a part of the area. Some drafters simplify this even further by using a note to indicate what material is used and omitting the symbol altogether (Figure 8.6).

Throughout the remainder of this text, material symbols are presented as they appear in plan and elevation views. Many symbols are designed to approximate the actual appearance of material. This is especially true on elevation drawings, as shown in Figure 8.6. Because of the complexity and space required, many symbols do not have any graphic relationship to the items they represent. These must be memorized if drawings are to be consistently interpreted. When material symbols are similar, always look for a notation, different view, detail, or specification for information about the material.

8.4 electrical symbols

electrical drawings—like other types of building-construction drawings—must be prepared by competent electrical drafters in a given time period to avoid unnecessary delays. Symbols are used on electrical drawings to simplify the drafting work for both the drafters and the workers interpreting the drawings. It should be noted that electrical symbols are not standardized throughout the industry, which is one reason why electrical drawings typically have a symbol legend or list.

Many electrical symbols are used to show the desired lighting arrangement. Switch symbols are usually placed perpendicular to the wall and read from the right side or bottom of the sheet. Figure 8.7 shows two lists of electrical symbols currently in use on most electrical drawings. The lists represent a good set of electrical symbols in that they are easy to draw, easily interpreted by workers, and sufficient for most applications.

The electrical system for a small property would typically include wiring as well as devices such as switches, receptacles, light fixtures, and appliances. Wiring is indicated by lines that show how devices are connected. These lines are not shown in their actual position. They simply indicate which switches control which lights. Outlets (receptacles) and switches are usually shown in their approximate positions. Major fixtures and appliances are shown in their actual positions. In Figures 8.8, 8.9, and 8.10 we see examples of receptacle symbols, alarm symbols, and other electric symbols.

Some of the symbols listed contain abbreviations, such as TV for television outlet and WP for weatherproof. Others are simplified pictographs, such as the symbol for an electric meter. One way to develop the ability to interpret a drawing and its symbols is by first learning the basic form of the different symbols. This is because many symbols are similar (square, circle, etc.), and the addition of a line, letter, or number determines the specific meaning of that symbol.

8.5 PLUMBING SYMBOLS

One must differentiate between industrial and residential or commercial piping. Industrial piping is generally designed to carry liquids and gases used in manufacturing processes. In heavy construction steel pipes have welded or threaded fittings and connections. Piping used in commercial and residential applications is generally termed “plumbing” and is designed to carry fresh water, liquid and solid wastes, and gas. These pipes can be made of plastic, copper, galvanized steel, or cast iron. In preparing a plumbing drawing, all pipe fittings, fixtures, valves, and other components are represented by symbols

In residential applications, plumbing information can often be provided on the floor plans in the form of symbols for fixtures and notes (for pipe sizes, slope, etc.) for clarification. Other plumbing items and information to be shown on the floor plans include water connections, floor drains, vent pipes, and sewer connections. Floor drains are shown in the approximate location on the plans and sections, with notes indicating the size, type, and slope to drain. Sewer and water-service lines are located in the position in which these utilities enter the building. Service lines are normally indicated on the site plan. Vent pipes

ELECTROMAGNETIC TYPE DOOR HOLDER OUTLET.

FIRE ALARM TERMINAL CASINET.

POST INDICATOR VALVE.

FIRE ALARM TRANSMITTER (BASE LOOP) NUMERALS DENOTE CODE,

FIRE ALARM TROUBLE TRANSMITTER (BASE LOOP) NUMERALS DENOTE

CODE.

CITY FIRE ALARM MASTER STATION MTD 5′-6″ [1676mm] AFF

UNLESS NOTED.

FIRE ALARM RECORDER.

FIRE ALARM BATTERIES

BATTERY CHANGER,

FIRE ALARM CENTRAL CONSOLE,

When plumbing drawings are prepared, they are not usually shown on the same sheet as the architectural floor plan. The main plumbing items shown on the floor plans are the fixtures. Drainage, vent, and water systems are drawn with thick lines using symbols, abbreviations, and notes.

The main function of HVAC drawings is to show the location of the heating, cooling, and air-conditioning units as well as the piping and ducting diagrams. Graphical symbols on HVAC drawings are similar in pattern to those used for plumbing. In Figures 8.12A and B we see examples of typical HVAC symbols in current use in the United States and Europe.

It should be noted that on some HVAC drawings one sees two types of symbols. The main duct may consist of a rectangle to represent the actual size of the ductwork—including reductions. However, the

THERMOSTATIC TRAP

Figure 8.12B Examples of heating symbols in general use.

branches are shown by a single line with the dimensions of each noted adjacent to the lines. Both methods are used on HVAC drawings throughout the building-construction industry, either singly or in combination (Figure 8.13A and B). A number of custom HVAC CADD programs are currently available to help improve drafting productivity and efficiency.

8.7 MISCELLANEOUS SYMBOLS

Component symbols represent such items as furniture, fixtures, and appliances. Many component symbols are similar to the actual item represented in plan/elevation view.

Specialist Symbols

There are many specialist trades, such as welding, that have their own specific symbols. Figure 8.14 shows examples of basic and supplementary weld symbols and the standard location of elements of a welding symbol. Figure 8.15 and Figure 8.16 are further examples of specialist type symbols.

Indexing Symbols

To summarize, when reading symbols on a blueprint, the following should be remembered:

Placement of symbols on floor plans and elevations may be approximate unless they are dimensioned.

Do not scale a symbol to determine its size. Specific information should be obtained from relevant details, schedules, or specifications.

A symbol's size may vary according to the scale of the drawing.

Symbols drawn to represent surface materials may cover only a representative portion of an area.

Abbreviations are often used in place of a graphic symbol in order to reduce drawing time and space. A list of architectural/construction abbreviations is given in the Appendix.

Symbols for the same items are usually different in plan, elevation, and section drawings.

Some symbols may use the same or similar graphic treatments in elevation. Check notations, detail drawings, and specifications for identification.

TELECOMMUNICATIONS DUCT POWER DUCT

EXTERIOR FLOOD LIGHT

DUAL POWER & TELECOMMUNICATIONS MANHOLE

PADMOUNT TRANSFORMER – NUMERAL INDICATES KVA SIZE SWITCHGEAR – SUBSCRIPT DENOTES SUBSTATION HIGH-VOLTAGE SWITCH ON CONCRETE PAD LOW-VOLTAGE SWITCH ON CONCRETE PAD

SWITCHBOARD

EXISTING CONDUIT IN PLACE – REMOVE EXISTING WIRES AND INSTALL NEW WIRES AS INDICATED

EXISTING CONDUIT AND WIRE TO REMAIN EXISTING CONDUIT AND WIRE TO BE ABANDONED OR REMOVED CONNECTION OF NEW CONDUIT TO EXISTING CONDUIT W/APPROVED TYPE COUPLINGS – INSTALL NEW WIRES CONDUIT SEAL FOR EXPLOSION PROOF INSTALLATION

PLACED ADJACENT TO DEVICE SYMBOL DENOTES EQUIPMENT SHALL BE REMOVED AND OUTLET BLANKED

PLACE ADJACENT TO DEVICE SYMBOL DENOTES EQUIPMENT SHALL BE REMOVED