While there are many ways to develop estimates for concrete construction projects, the choice today is between spreadsheet-based estimating and database system estimating. Which method you choose is really a matter of personal preference. In this article, I will describe spreadsheet-based estimating and its benefits.
An advantage of spreadsheets is that most contractors are conversant with spreadsheet programs, such as Microsoft Excel. Once a basic spreadsheet template is created almost anyone can be taught to use it in a short time.
Properly oriented, a spreadsheet template will provide every bit as much accuracy as a database estimating system. Spreadsheets are simply easier to learn and use for most estimators.
Every good estimate starts with a method of quantity takeoff. In the past few years the construction industry has largely switched to digital media versus printed plans. Architects and engineers routinely post drawings on their websites and use download platforms that are quick and easy to use.
There are several good software systems that allow estimators to download plans and to easily measure and track quantities for almost every aspect of construction. The need for pencil and paper tracking has been virtually eliminated. Quantity totals can also be calculated via spreadsheet.
The best set-up for estimating uses two screens, one for the plans and the other for the digital takeoff sheet. A spreadsheet template can be created and used as the takeoff sheet.
All concrete shapes can be quantified with six measurement columns: Depth, Width, Length, Quantity, Square Feet, and Cubic Yards. A column to the left can be used to describe each individual activity such as spread footing, continuous footing, and rebar template. An additional column can be used to note detail reference and other notes.
Activities are itemized in rows; quantities are extended using the six columns described above. Simple formulas can be written to convert feet and inches to the decimal system used in Excel. To convert inches to feet, take the number of inches and divide by 12. Thus, 2 inches equals 0.17 feet and 4 feet 2 inches is 4.17 feet.
There are simple methods to convert fractions to their decimal equivalent as well. I’ve found the simplest way is to create a chart of all the fractions in 1/8-inch increments. So 1/8-inch is 0.125 inches and ¾-inch is 0.75 inches. Add this to the full inches then divide by 12. Thus, 4 feet 2 ¾ inches equals 4 feet plus 2.75 inches/12 = 4.23 feet.
With usage, an Excel-based quantity takeoff sheet becomes fast and easy. More importantly, a digital record is created making it easy for others to spot check your work and to see how quantities were derived. Transparency and accountability are important parts of the estimating process. Estimating review is made more efficient by using this method as well.
In business, anything can be as simple or as complicated as you’re willing to make it. The same is true for spreadsheet formulas. Simple formulas work well when creating self-calculating spreadsheet templates.
For instance, when calculating spread footings in the 6-column format, the formula is width times length times quantity equals square feet. Then square feet times depth equals cubic feet, which divided by 27 equals cubic yards. The formula for continuous footings is width times length equals square feet. Then square feet times depth divided by 27 equals cubic yards.
Often, one type of calculation can be useful when preparing totals for other phases. In the above example, the total square feet of footings can be used when calculating thickened concrete over footings in the slab phase. In the footing phase the total square feet of footings will equal the amount of surface to be covered by spray-on curing compound in the footing phase.
Properly designed, spreadsheet-based estimates are easy to read, easy to understand, and easy to teach and learn. Excel uses tab formatted workbooks making it easy to have several different worksheets grouped into one overall estimating template, each displayed on its own tab. Each tabbed worksheet can segregate information within the estimating template for different purposes such as building concrete, site concrete, alternates, budget, schedule of values, and so on.
A useful tool provided by Excel is the hyperlink command. Hyperlinks allow the user to link information from one worksheet to another. This is especially useful in linking subtotals from each work phase to an overall summary worksheet or other related worksheets.
Estimating Basis and Work Phases: Individual work phases are typical to concrete estimating. As an example, using a relatively simple two-story steel-frame office building as a model, the work phases might include Mobilization, Foundations, Elevator Pit, Slab On Grade, Brace Frame Closures, Slab On Deck, Pan Filled Stairs, and General Conditions. Other phases may occur as well.
In a typical estimating template, the individual work activities within each work phase are shown in rows; cost categories are shown in columns. Typical columns might include Quantity, Unit Of Measure, Production Rate, Material Cost, Labor Cost, Total Man-Hours, Equipment Cost, and Subcontract Costs.
Work activities within each phase are typically listed in the order in which they occur. In the case of the steel frame building mentioned above, the foundation phase activities might include layout, excavation, fine grading, off-haul of footing spoils, footing formwork, rebar templates, column templates, setting of embeds, concrete placement, concrete pumping, and curing.
Each of these activities is then subdivided by the above listed cost category. In the Quantity and Unit of Measure columns the totals shown are taken directly from the takeoff sheet. The takeoff sheet can be used as a shorthand version of the estimate. Activities listed in the takeoff sheet flow in the same direction as the estimating pricing sheet.
Estimating Basis, Composite Man-Hour Rate, and Unit Costs: Establishing the composite man-hour rate is essential to creating a spreadsheet template. The composite man-hour rate is the average cost per man-hour for a work crew. The composite man-hour rate should include base pay, employer burden, employer contributions, and union benefits, where applicable.
As an example, a seven-man formwork crew might include a foreman, an assistant foreman, three carpenters, and two laborers all with different rates of pay. The total of their fully burdened hourly rates divided by seven equals the composite man-hour rate.
Unit costs are used to establish the cost of materials, labor, equipment, and subcontract costs. In formwork for instance, unit costs can be developed for lineal feet, square feet, or other commonly used denominators.
Establishing a unit cost for lineal feet of formwork, as an example, is quite straight forward. The total cost of lumber, string, stakes, and nails divided by lineal feet equals the unit cost. The same principle is true for every formed shape. Throughout the spreadsheet, the unit cost times the quantity equals total dollar value for any given line item and cost point.
Establishing a Unit Cost for Labor: Establishing a unit cost for labor involves formulating three components: production rate, price per unit of measure, and total man-hours. All three work in concert with the established quantity for each activity line item.
In a well-designed spreadsheet, the production rate column fits next to the quantity column. A unit of measure column fits next to the quantity column, for example linear feet (LF), square feet (SF), each (EA), or other common units of measure. Likewise, a unit of measure column fits next to the production rate column per man-hour (MH), for example, LF/MH, SF/MH, or EA/MH.
Production rate is defined as the rate per man-hour any given quantity takes to produce. Methods of establishing accurate production rates are typically derived as part of job costing wherein a cost code is established for a work activity. The total number of man-hours assigned to that cost code divided by the quantity equals the production rate.
A good cross-check is to have the superintendent track selected items and report how many man-hours an activity line item takes. The benefit in cross-checking is that it helps the superintendent think along the same lines as the estimator and helps keep costs under control.
As an example, to show how the above works in an estimate, we’ll use 1,250 lineal feet of slab edge form. An established production rate for forming and stripping edge forms might be 16 LF/MH (for my company, we know it takes 1 MH to form 12 lineal feet plus 1 MH to strip 20 lineal feet equals 32 total LF divided by 2 MH equals 16 LF/MH average). Each company’s production rates may be different, of course.
The production rate unit cost is established by dividing the composite MH cost rate by the rate of production. For example, if the established composite man-hour rate is $45.00 per MH and the slab edge form production rate is 16 LF/MH, then the labor unit cost equals $2.81 per LF.
Again, using the above example, 1,250 lineal feet of slab edge form times $2.81 equals $3,516 labor cost. Total man-hours are calculated by dividing the total cost by the composite man-hour rate. Thus, $3,516 divided by $45.00 equals 78.13 man-hours. Showing all three components is important in a well-designed spreadsheet estimate. Simple formulas can be written to provide the information.
Establishing a Unit Cost for Equipment and Subcontracts: Equipment cost units and subcontract cost units work in the same way as everything discussed above. Cost divided by quantity equals unit cost. That said, most major equipment that is rented by the month is better represented in a General Conditions phase group. Examples of monthly rented equipment might include grading equipment, water trucks, forklifts, and man lifts.
Examples of equipment that might be included in an individual work phase group might include company owned equipment such as generators, concrete saws, gang-box power and distribution systems. A unit cost can be established to amortize the replacement value of these types of equipment.
Subcontract costs are typically included as lump sum figures within a phase group. Reinforcing, when subcontracted, is a good example. It is also important to calculate related expenses when subcontracting work. Related expenses for reinforcing might include coordination, hoisting, and cleanup. These should all be included in the work phase group.
A well-designed spreadsheet template is easy to use and will provide very comprehensive detail that’s understandable and easy for others to review. As a final note, Excel allows the user to create a color scheme for each template as well. The use of colored headers and selected columns makes information stand out in a very useful way. Much more can be said about organization in a spreadsheet, but the above will provide the basic framework necessary for creating a quality concrete estimating template.