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88
Exercise 21
Wall Material Calculations
OBJECTIVE
The objective of this exercise is to correctly calculate wall
material quantities.
TEXTBOOK REFERENCE
Information related to this activity can be found in the
INTRODUCTION
Determining wall material needs requires calculating the
surface area of the wall to be built and information from
the manufacturer regarding how much surface area is
If the wall is variable in height over its entire length
(Figure 21–1B), use the following steps:
• Obtain the average height of the wall by taking
multiple measurements (where the wall is the
tallest and the shortest), adding measurements
• Add 1 foot to the height measurement to
accommodate a buried base, and multiply by the
length to obtain square footage of the wall.
If the wall is consistent in height except for a few small
sections, such as return or cheek walls (Figure 21–1C),
use the following steps:
• Add 1 foot to the height measurement to
accommodate a buried base, and multiply by the
length to obtain square footage of the wall.
If the project contains multiple walls, the square foot-
age of each wall must be measured and added to obtain
one unit (typical areas range from .5 SF to 1.25 SF). Divide
the wall square footage by the surface area of one unit to
obtain the number of total units required for the wall.
Segmental Unit Capstone Calculations
Capstones are usually ordered by the number of linear
97171_21_ch21_p088-091.indd 88 14/06/10 8:58 PM
Exercise 21 Wall Material Calculations 89
Tie/Timber Calculations
Calculations for ties and timbers require the same area
calculations just performed, but the area is divided by
conversion numbers to determine the number of ties and
timbers to order. Find the material being used in the fol-
lowing list, and then divide the square footage of the wall
divide by 3.7.
• Timber 6 feet long by 6 inches height: divide
by 2.8.
To calculate the number of ties/timbers required for
deadmen or verticals, divide the total wall length by 5.
Add the wall ties/timbers numbers to the deadmen or
Figure 21–1 Wall material calculations.
H1
H2
H3
H4
H5
Add 1' to
height for buried
course
A. Consistent height retaining wall
(H + 1') × L = SF
C. Variable height retaining wall
where wall ends in hillside
(same formula as B)
A.
Formulas: Examples:
(5' + 4' + 7' + 5')
(5.25' + 1') × 30' = 187.5 SF
4= ave. HT. of 5.25
30'
C.
5'
5'
4' 7'
L
© Delmar/Cengage Learning.
97171_21_ch21_p088-091.indd 89 14/06/10 8:58 PM
90 Exercise 21 Wall Material Calculations
vertical numbers to determine the number of ties/tim-
bers to order.
Backfill Calculations
To calculate the amount of free-draining angular fill
Drainage Tile Calculations
To obtain the linear feet of drainage tile necessary to
PREREQUISITE EXERCISES
Students should have successfully completed Exercise 1,
Construction Math, before beginning this exercise.
MATERIALS REQUIRED
• Wall construction plans, including plan view,
• Calculator
• Writing paper and instrument
EXERCISE DESCRIPTION—PART A
• Timbers (assuming timbers 8 feet long and
6 inches in height)
• Segmental wall units (assuming .9 SF per unit
drawing negates the need to add one foot to the height
measurement (for the buried base) when calculating the
surface area of the wall. Record answers in the worksheet
provided in Figure 21–3.
EXERCISE DESCRIPTION—PART B
Using construction documents provided by the instruc-
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Exercise 21 Wall Material Calculations 91
Segmental Units Units Conversion Factor Quantity Notes/Comments
Segmental Units Each 1 unit =
Stone Units Conversion Factor Quantity Notes/Comments
Dry-Laid Stone Ton 1 Ton =
Backfill CF Same as CF above
Drainage Tile LF Same as LF above
Drainage T’s EA Count
Drainage Caps EA Count
Ties/Timbers Units Conversion Factor Quantity Notes/Comments
Timbers Each 1 timber =
Sqare Footage of Wall: Length of Wall: Cubic Footage of Fill:
97171_21_ch21_p088-091.indd 91 14/06/10 8:58 PM
