Chapter 2 Arithmetic and Principles of Measurement

1. Chapter 2Arithmetic and Principles of Measurement

2. How is Work Measured in a Takeoff? • Work is measured in five different kinds of units: • By counting the number of pieces; for example, the number of doors • By measuring the length of an item such as a pipe • By measuring an area of a material; for instance the area of floor sheathing • By measuring the volume of a material such as concrete • By measuring the weight of materials such as structural steel beams

3. Calculating Number of Items • Enumerated items are often counted from the drawings, but sometimes you need to calculate the number. Examples: • How many bolts spaced at 24" are required on a 13'-0" wall (the end bolts are 2" from the end of the wall)? • Answer: 13'-0" - 4" = 12'-8" (12.67') 12.67' / 2.0'= 6.3 (round up to 7) + 1 for the end bolt = 8 • How many studs spaced 16" are required for a 21'-0" wall? • Answer: 21.0'/ 2.0' = 10.5 (round up to 11) + 1 for the end stud = 12

4. Length Calculations • Usually the length of an item is obtained directly from the dimensions on the drawings. • Scaling lengths is not recommended but may be necessary when dimensions are lacking. • Many buildings have perimeter walls. The volume of concrete in a perimeter wall is obtained by multiplying the centerline length of the wall, the width of the wall, and the height of the wall. • The centerline length may also be used to calculate a number of other items: forms for walls, trenching, concrete, and forms for wall footings.

5. Perimeter Calculations • The perimeter length of the basement wall shown of Figure 2.3 is calculated in this way: 2 x 42'-0" = 84'-0" 2 x 26'-0" = 52'-0" = 136'-0" Less 4 x 8" = <2'-8"> 133'-4"

6. Calculating Areas • Most areas in estimating will be rectangles, but triangles, circles, and other shapes sometimes have to be calculated. • The area of the building (to outside of walls) shown on Figure 2.12 is calculated in this way: 42.0' x 38.5' = 1617 + π x 21.0'2 / 2 = 692 2309 sf

7. Calculating Volumes • To calculate the volume of concrete in a continuous footing to the perimeter of a building use this formula: • Volume = centerline length x width x depth • Example: If there is a footing size 2'-0" x 1'-6" under the wall shown on Figure 2.4, what is the amount of concrete in this footing? 2 x 25.0 = 50.0 2 x 16.0 = 32.0 less 4 x 0.5 = <2.0> = 80.0 volume: 80.0 x 2.0 x 1.5 = 240 cu. ft. = 9 CY

8. The Quantity Takeoff • A quantity takeoff is the process of measuring the work of the project. • The document that is produced in this process is also called a takeoff. • A takeoff is a series of quantified items that correspond to the tasks required to construct the project. • A takeoff item comprises a description and a set of dimensions that define the quantity of the item. • Items are measured according to standard rules of measurement so that all estimators measure the same kind of items in the same way. • For example, the standard units for measuring concrete footings are cubic yards.

9. What is Measured in a Takeoff? • A takeoff for an estimate is more than a materials takeoff because additional information is required for pricing. • For example: “160 square feet of ½″ G1S ply” is fine for a material takeoff, but is to be applied to walls or floors? This information is needed for pricing. • Also, some items do not involve materials such as: “hand troweling.”

10. Rules of Measurement • Dimensions are entered onto the takeoff in this order: length, width, and depth (or height). • Dimensions are written in feet to two decimal places, thus, 5'-10" would be written into a dimension column as 5.83. • Deductions listed with the dimensions are written in red or enclosed in brackets and noted as deductions. • Extensions (the result of multiplying dimensions together) are calculated to the nearest whole number whether it is linear feet, square feet, or cubic feet. • Totals in the extensions column are rounded off to the nearest whole number. • See text for a full list of measurement rules.

11. Takeoff Order and Strategy • The order of the takeoff generally follows the sequence of the work on the project. • Strategy for larger projects: • Divide the project into manageable parts • Takeoff one part at a time • Within each of these parts, measuring the work as a sequence of assemblies • Where an assembly is a collection of related items

12. Wall Assembly Example • Items included in a wall assembly: • The concrete in the wall • The forms to the sides of the wall • The forms to openings and blockouts in the wall • The rubbed finish on the exposed concrete of the wall • The reinforcing steel in the wall

13. Computer Estimating • Use of computers can increase the efficiency of the process. • The computer can perform all the arithmetic to determine total net quantities from the dimensions input. • Items are automatically sorted and recapped into the required order. • Items can be automatically priced from the database. • Keeping backup notes on paper is recommended. • It provides a record of how the estimate was prepared. • It enables the takeoff to be checked to ensure that all the work has been measured as required.