UNIT
Scales
Scale Drawings
Objectives
Because construction projects are too large to be drawn full size on a sheet of
paper, everything must be drawn proportionately smaller than it really is. For
example, floor plans for a house are frequently drawn 1/48 of the actual size.
This is called drawing to scale. At a scale of ¼” = 1’-0”, ¼ inch on the drawing
represents 1 foot on the actual building. When it is necessary to fit a large object
on a drawing, a small scale is used. Smaller objects and drawings that must show
more detail are drawn to a larger scale. The floor plan in Figure 3–1 was drawn
to a scale of ¼” = 1’-0”. The detail drawing in Figure 3–2 was drawn to a scale
of 3” = 1’-0” to show the construction of one of the walls on the floor plan.
The scale to which a drawing is made is noted on the drawing. The scale
is usually indicated alongside or beneath the title of the view.
After completing this unit,
you will be able to perform
the following tasks:
Identify the scale used on
a construction drawing.
Read an architect’s scale.
Reading an Architect’s Scale
All necessary dimensions should be shown on the drawings. The instrument
used to make drawings to scale is called an architect’s scale, Figure 3–3.
Measuring a drawing with an architect’s or engineer’s scale is a poor practice.
At small scales it is especially difficult to be precise. The following discussion
of how to read an architect’s scale is presented only to ensure an understanding of the scales used on drawings. The triangular architect’s scale includes
eleven scales frequently used on drawings.
Full Scale
3/32” =
1/8” =
3/8” =
1/2” =
11/2” =
1’ - 0”
1’ - 0”
1’ - 0”
1’ - 0”
1’ - 0”
3/16”
1/4”
3/4”
1”
3”
=
=
=
=
=
1’ - 0”
1’ - 0”
1’ - 0”
1’ - 0”
1’ - 0”
Two scales are combined on each face, except for the full-size scale, which is
fully divided into sixteenths, Figure 3–4. The combined scales work together
because one is twice as large as the other, and their zero points and extra
divided units are on opposite ends of the scale.
The fraction, or number, near the zero at each end of the scale indicates
the unit length in inches that is used on the drawing to represent 1 foot of the
actual building. The extra unit near the zero end of the scale is subdivided into
Scales 15
Figure 3–1. Portion of a plan view with a firewall.
Figure 3–2. Detail (plan at firewall).
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Figure 3–3. Architect’s scale. Courtesy of Alvin & Co., Inc.
Figure 3–4. Architect’s triangular scales.
twelfths of a foot (inches) as well as fractions of inches
on the larger scales.
To read the architect’s scale, turn it to the ¼-inch
scale. The scale is divided on the left from the zero
toward the ¼ mark so that each line represents 1 inch.
Counting the marks from the zero toward the ¼ mark,
there are twelve lines marked on the scale. Each one of
these lines is 1 inch on the ¼” = 1’-0” scale.
The fraction 1/8 is on the opposite end of the same
scale. This is the 1/8-inch scale and is read in the opposite direction. Notice that the divided unit is only half as
large as the one on the ¼-inch end of the scale. Counting
the lines from zero toward the 1/8 mark, there are only
six lines. This means that each line represents 2 inches
at the 1/8-inch scale.
Now look at the 1½-inch scale. The divided unit is
broken into twelfths of a foot (inches) and also fractional parts of an inch. Reading from the zero toward the
number 1½, notice the figures 3, 6, and 9. These figures
represent the measurements of 3 inches, 6 inches, and
9 inches at the 1½” = 1’-0” scale. From the zero to the
first long mark, that represents 1 inch (which is the same
length as the mark shown at 3) and four lines. This means
that each line on the scale is equal to ¼ of an inch.
Reading from the zero to the 3, read each line as follows:
¼, ½, ¾, 1, 1¼, 1½, 1¾, 2, 2¼, 2½, 2¾, and 3 inches. Do not
confuse the engineer’s scale with the architect’s scale.
The engineer’s scale uses feet and decimal parts of
a foot.
Scales 17
Figure 3–5.
CHECK YOUR PROGRESS
Can you perform these tasks?
Locate the scale notations on drawings.
Use an architect’s scale to measure objects drawn to
scale.
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ASSIGNMENT
1. What are the dimensions indicated on the scale in
Figure 3–5?
2. What scales are used for the following views of the
Duplex? (Refer to the Duplex drawings in the packet.)
a. Floor plan
b. Site plan
c. Front elevation
d. Typical wall section