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Building Better Cost Estimates

Achieving greater accuracy by filling your estimating toolbox
[ Page 3 of 5 ]        
Sponsored by Gordian
By Peter J. Arsenault, FAIA, NCARB, LEED AP

Step 2: Quantity Takeoff

Some cost estimates are prepared with the thought that a quantity takeoff is the beginning step, but as just explained, it should only be started after the scope is clearly understood. In that way, the quantity takeoff information can be used together with the scoping information and pricing cost data to create a more accurate final estimate.

Quantity takeoffs are basically a measurement of “how much” of each of the relevant parts of construction are included in the project. In the early phases of budgeting and design, a quantity takeoff may mean little more than quantifying square footage of the building or the size and extent of the systems and assemblies. However, ultimately, a detailed quantity takeoff of materials and products will likely be undertaken as part of a full unit-pricing cost estimate. Therefore, clarity is needed on defining “what” is being measured (i.e., square feet, systems, assemblies, individual units, etc.) and recognizing where they do or do not get used in a project. The definition of those items needs to be clear as well as they relate to available specifications or notes that describe the quality and makeup of the items being measured. With these things understood, accurately measuring and calculating the relevant quantities of those items should be fairly straightforward based on a dimensioned set of drawings. Preparing quantity takeoffs with this level of understanding and attention to careful calculation is a critical step in producing accurate construction cost estimates.

Learning from experienced cost estimators, a number of best practices have been identified to help with greater accuracy and reliability.

As with the scoping process, there are a number of best practices that cost-estimating professionals use to improve outcomes of quantity takeoffs, including the following:

  • Use standardized forms. This is all about standardizing the quantity takeoff process to create consistency and reliability. Such forms can be in-house creations or obtained from third parties. Either way, it is more important that something consistent is used that works for the estimator than the details of what those forms are.
  • Organize takeoffs. Randomly getting quantities from drawings does not serve the purpose of an accurate cost estimate. Rather, reviewing the information at hand and systematically going through it in an organized manner will not only help create a better takeoff, but it also will likely make it easier to go back and check or revise something if needed later on.
  • Track takeoffs. As progress is made, there should be an easy way to keep track of what is completed and what is still yet to do. This can be a visual cue on forms or drawings or a checklist based on specification sections or similar work breakdowns. This way, duplication of effort is avoided and the chance of missing something is decreased.
  • Abbreviate. This is a time saver and can also be important for communication. Cost estimators may be reluctant to write out “square feet” repeatedly but can easily add in “sq ft” or “s.f.” after a quantity to be clear about what is being measured. Standardized forms can have some of that pre-printed where appropriate but the point is to be both concise and clear about the takeoffs.
  • Verify units. Different materials, assemblies and products are commonly quantified in different ways. Cubic yards is the norm for concrete and stone, while cubic feet is used for some insulation and other products. Still others are indicated on an individual-piece basis. It is important then to make sure that the correct unit is verified and attached to the quantity so that the correct pricing calculation can ultimately be made. In some cases, that may mean converting the information available on the drawings to the needed units, such as taking the square footage of a concrete slab and factoring in its thickness to determine the cubic yardage required.
  • Convert dimensions to decimals. If the project drawings are shown using metric dimensions, this step is likely already done. Otherwise, most projects in the United States use imperial measurements (feet and inches) for the dimensions, which are less conducive to multiplication in a cost estimate. Therefore, converting the imperial dimensions to decimals is a needed step in a quantity takeoff in order to be useful. Some are easy (i.e., 10 ft 6 in. = 10.5 ft) but others may require some calculations or the use of a standard conversion table. It may be prudent to limit the number of decimal places to one or two as well (i.e., 10 ft 4 in. = 10.33 ft, not 10.33333…).
  • Reuse calculations. If you have a standard calculation process that is universal in its application, consider reusing it on quantity takeoffs. This can be useful in making unit conversions or other standardized tasks to allow for consistency across estimates.
  • Double check math. No one intends to make a math error, but that doesn’t mean they don’t happen. Go back and double check the math on the quantity takeoff to make sure that nothing got entered incorrectly. In cases where a computer is doing the math, make sure the correct formulas or commands are entered where the quantities are inserted and that they are recognized properly by the computer software.
  • Use dimensions, not scales. There is typically a note on the drawings: “Written dimensions take precedence over scaled dimensions. Do not scale the drawings.” In this case, heeding that advice can make a crucial difference, particularly if the drawings are smaller scale (18 in. = 1 ft or less) or if the printing/display of the drawings is not accurate. The project will be built to the written dimensions, so that is what should be the basis of the quantity takeoff and cost estimate.
  • Avoid rounding until final tabulations. There is a natural temptation to think that each small item can be rounded as the quantity takeoff is done. But all of those small adjustments can add up quickly, especially on a large project, throwing the total estimate out of whack. It is better to accurately record each individual quantity takeoff, and then when final tabulations are made, round the totals if there is a need to do so. This will help assure greater accuracy.

Following these guidelines, quantity takeoffs can be managed and carried out very effectively in a more efficient manner.

 

[ Page 3 of 5 ]        
Originally published in Engineering News-Record

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