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Lesson 1.2 Bill of Materials (BOMs)

Before any construction project is started, make out a BOMs to requisition building materials. However, you should first make a materials takeoff list and a materials estimate list, before making out the BOM.

1-3. Materials Takeoff List.

This list is the first step leading to preparation of a BOM. It is a listing of all parts of the building, taken off the plan. Table 1-3 shows a materials takeoff list for the building substructure shown in Figure 1-20.

Table 1-3. Sample materials takeoff list

Figure 1-20. 20- x 40-foot-wide building substructure

Note

Spreaders and closers are not shown in the drawing but are part of the materials takeoff list.

1-4. Materials Estimate List.

A materials estimate list puts materials takeoff list information into a shorter form; adds allowance for waste and breakage; and estimates quantities of materials needed (Table 1-4). The lumber required is listed by board feet (BF).

Table 1-4. Sample materials estimate list

1-5. BF Computation

A BF is a unit measure representing an area of 1 foot by 1 foot, 1 inch thick. The number of board feet in a piece of lumber can be computed using one of the following methods:

Rapid Estimate. You can estimate BF rapidly by using Table 1-5. For example, reading the table, you can see that if a 2-inch by 12-inch board is 16 feet long, your board feet would be 32.

Table 1-5. Board feet

 Arithmetic Method. To determine the number of BF in one or more pieces of lumber use the following formula:

Board feet = Number x

Thickness (in) x Width (in) x Length (ft)    
12

 

Note

If the unit of measure for length is in inches, divide by 144 instead of 12.

 

Board feet = Number x

Thickness (in) x Width (in) x Length (in)    
144

Sample Problem 1: Find the number of BF in a piece of lumber 2 inches thick, 10 inches wide, and 6 feet long (Figure 1-21).

1 x

2 x 10 x 6 = 120  = 10 BF    
12 12

Sample Problem 2: Find the number of BF in 10 pieces of lumber 2 inches thick, 10 inches wide, and 6 feet long.

10 x

2 x 10 x 6 = 1200  = 100 BF
12 12

Sample Problem 3: Find the number of BF in a piece of lumber 2 inches thick, 10 inches wide, and 18 inches long.

1 x

2 x 10 x 18 = 2 BF
144

Figure 1-21. Lumber dimensions

Tabular Method. The standard essex board measure table (Figure 1-22) is a quick aid in computing BF. It is located on the back of the blade of the framing square. In using the board measure table, make all computations on the basis of 1-inch thickness. The inch markings along the outer edge of the blade represent the width of a board 1 inch thick. The third dimension (length) is provided in the vertical column of figures under the 12-inch mark.

Figure 1-22. Essex board measure table

Sample Problem: To compute the number of BF in a piece of lumber that is 8 inches wide, 14 feet long, and 4 inches thick:

  1. Find the number 14 in the vertical column under the 12-inch mark.
  2. Follow the guideline under number 14 laterally across the blade until it reaches the number on that line that is directly under the inch mark matching the width of the lumber.

Example problem: Under the 8-inch mark on the guideline, moving left from 14, the numbers 9 and 4 appear (9 and 4 should be on the same line as 14). The number to the left of the vertical line represents feet; the number to the right represents inches.

  1. The total number is 37 1/3 BF. BF will never appear in a decimal form.

Example solution: 1" x 4" x 8' x 14'

1" x 4" x 8' x 14'  Feet Inches
                            9     4
                            4     4
                           36   16/12
                                  1 4/12
                                   36 + 1 1/3 = 37 1/3 BF

Note

1" x 4" = Always multiply the number of pieces by the thickness and multiply the feet and inches by the sum of pieces and thickness.

1-6. Estimating the Quantity of Nails Required.

The sizes and pounds of nails needed should be added to the list. To estimate number of pounds, use the following formulas:

  • For flooring, sheathing, and other 1-inch material:

Number of pounds = 

2d to 8d x BF
4 100
  • For framing materials that are 2 inches or more:

Number of pounds = 

10d to 60d x BF
6 100

where d = penny

1-7. BOMs

Information for the BOM is taken from the materials estimate list.  When preparing a BOM, follow the building sequence. For example, on most frame buildings, the first pieces of lumber used would be the footers; next would be floor joists, girders, subflooring, sole plates, and studs.

Figure 1-23. Sample BOMs

David L. Heiserman, Editor

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All Rights Reserved

Revised: June 06, 2015