in conjunction with an electrical plan to denote specific equipment. Figure 5-24 illustrates an electrical legend in conjunction with additional electrical notes.
Although there are many commonly recognized legends and graphic symbols, the drafter should always include the specifics of what is being shown. Legends should be concise and graphically presented: as small as possible on the sheet, yet easily readable in the field by the builder.
Dimensioning involves incorporating numerical values in a drawing to accurately locate and size various objects and assemblies in buildings and interiors. Dimension lines and arrows (or tick marks) are used to identify exactly where the dimension begins and ends, as shown in Figure 5-25. Dimensions are grouped, where possible, and ordered in a hierarchical manner. First the overall, or outside, dimension of a space or object is indicated, then the dimension of smaller details within the space are noted, as illustrated in Figure 5-26.
Dimensions are required on all construction drawings and must be accurate, complete, and readable. At the present time, most construction drawings are dimensioned in the English or metric systems, using feet and inches, or meters.
When feet and inches (English system) are used for dimensioning, the symbol (') is used for feet and (") for inches. Dimensions less than 12" are specified in inches, with no zero before them. Dimensions 12" or above are specified in feet and inches, with a dash placed between the feet and inches, such as 2'-6". If a dimension is an even number of feet, the inches are generally shown as a zero, such as 5'-0". However, some firms prefer to leave the inch
es off when they are zero, such as 5'. If a distance is a fraction of an inch without a whole number before it, some prefer to put a zero before it for clarity, such as 0'-%". In most drawings using the metric system, all dimensions are in millimeters, such as 5 mm.
Dimensioning should remain consistent with respect to how materials and assemblies are measured, whether to subsurface or finish surfaces. For example, if a wall is dimensioned to the finished face, subsequent walls should also be dimensioned to their finished faces. A note should be placed on the drawing to denote
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how items are to be measured. If there are any exceptions to this overall rule, these should be called out on the sheet.
The most common method of dimensioning is the framing technique. The advantage of this system is that it most closely follows the construction sequence in the field and informs the particular trades of the dimensions most important to their area of construction. The framing technique is to the face of a stud, concrete, or masonry wall, as illustrated in Figure 5-27. With this technique, the builder first locates the framing or foundation wall, to which other assemblies or finish materials are applied at a later date. The dimension can be placed to either the face of the sub wall (depending on the location and how easy it is for the builder to make a mark), or to each side, with an indication of the total sub wall thickness.
For example, a wood stud partition wall on a plan with a layer of V2 inch (12 mm) gypsum board on each side is dimensioned as 3V2 inch (88 mm). This is the actual stud width, and not the total wall thickness, which would be 4V2 inch (100 mm). This way, the builder who is erecting the wall does not have to be concerned with the finish materials at this time and mentally subtract these thicknesses to arrive at the exact location for the wall stud. However, if there is indeed a critical dimension that needs to be maintained relative to the finish material, typically for fit with another object (such as a wall or cabinet to be installed later), a note can be added to the dimension stating it is a "clear" or "face of finish" dimension, as shown in Figure 5-28.
The other method of dimensioning involves locating the centerline of a wall. In this case the builder must subtract from the centerline to find where to run the face of the wall studs, or make a center mark on the stud. This takes extra time and introduces the
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possibility of errors. However, this method is appropriate in a plan where one wants to locate a wall in the exact center of a space, or in the center of a structural frame gridwork.
Dimension standards discussed here primarily apply to the floor plan. Different drawings, such as elevations, ceiling plans, details, etc., have their own unique dimension standards, but are similar to the floor-plan font size, style, and units. These other drawing types might be dimensioned to the frame member or the finished face of a material. In the field of kitchen design, specialized cabinetry is almost exclusively dimensioned only in inches (or millimeters) instead of feet and inches, to the finish faces (Figure 5-29).
Although many plans are dimensioned using the English system (feet and inches), the metric system is slowly replacing it as the preferred method. In the metric system, units are based on the standard meter, which is then subdivided by tenths to arrive at decimeters, centimeters, and millimeters. This system is simple to use, as the decimal can simply be moved to the right or left to change from one unit to another. There are no fractions to memorize or convert when adding. In architectural drawings, the meter or millimeter is used more than the decimeter or centimeter.
Figure 5-27 An example of dimensioning to face of stud, concrete, or masonry wall.
Figure 5-28 This example shows how dimensions are applied to the face of the finish where the "clear" opening is critical.
Figure 5-29 An elevation of cabinetry that is dimensioned in inches.
Figure 5-29 An elevation of cabinetry that is dimensioned in inches.
Converting from the English to the metric system can be done in several ways. The choice will depend upon whether one is dealing with elements still manufactured under the English system and on what accuracy is required in the final assembly, which will be a judgment call on the part of the designer or builder.
In the first and most accurate method, if a piece of metal is made at V2 inch thickness (as the manufacturer has not converted to the metric system), the V2 inch must be converted to metric by multiplying V2 x 2.54, which would equal 1.27 cm or 0.0127 meters.
Another method of converting is to estimate the number in the metric system according to a scale one is familiar with. Note that one inch equals 2.54 centimeters, and that V2 inch is a bit more than one centimeter. Also, 1/4 inch is more than half a centimeter, and 1/i6 inch is more than one millimeter. Using these rough guides, the final number in metrics can be estimated to a tolerance that is acceptable in the field during construction.
Another factor to consider when converting is whether the item or detail dimension can be rounded up or down to arrive at the metric number. For example, if the current spacing of some fastening anchors is 6'-0" on center, one cannot round up when converting into metrics, because then one will exceed the specified spacing. In this case, the dimension would have to be rounded down. Typically, when conversions are needed, one should round off fractions to the nearest 5 mm, inches to the nearest 25 mm, and feet to the nearest meter.
Buildings can be constructed using modular components that are manufactured in standard sizes. This process eliminates considerable waste of materials, labor, and time. Modules manufactured in the English system of dimensioning come in 16-, 24-, and 48-inch (40.6, 60.9 and 121.9 cm) sizes, as shown in Figure 5-30. Even brick and concrete block are installed on approximately 4-inch (101.1 cm) and 8-inch (20.32 cm) modular coursing.
A modular grid (based on common building material sizes) can be used in the design process to conform the floor plan (or section when working vertically) to a standard module. For example, if a small building is 28 feet (8.53 m) by 40 feet (12.19 m), its dimensions correspond to the 2-foot (.6 m) module. However, if the building is 27 feet (8.22 m) by 39 feet (11.88 m), it falls short of the module. In this situation, approximately one foot (.3 m) must be cut off the modular material, resulting in wasted material and increased labor costs for cutting.
During the construction drawing process, the modular layout should also be followed wherever possible. When dimensioning new spaces, walls, and other elements, it is preferable to set the dimensions on the module to avoid creating more work for the car-
penter and wasting material. For example, if a wall is to be located in a new space, it should be placed at 12 feet (3.65 m) from an existing wall rather than 11 feet, 10% inches (3.6 m).
It is good design practice to try to always design with a modular unit in mind. In the design of corporate spaces, the spacing of the windows generally sets the modular unit, which is generally 5'0" (1.52 m) or 6'0" (1.83 m).
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