4.2 Cost Estimating

Cost estimating is the process of predicting the financial resources required to execute a construction project. It evolves as project details become clearer, moving from rough approximations to highly detailed bids. The PE Construction exam tests your ability to distinguish between estimate types, classify costs correctly, and perform unit-price calculations based on production rates.

Conceptual vs. Detailed Estimates

Estimates are typically classified by their purpose and the level of design completion.

Conceptual (Preliminary) Estimates

Conceptual estimates are created during the feasibility or early design phases when limited drawings are available (typically 0% to 30% design completion). They help owners determine if a project is financially viable.

Common methods include:

• Square-Foot Estimates: Based on historical cost data per square foot of building area (e.g., $250/SF for a commercial office).
• Parametric Estimates: Use statistical relationships between historical costs and project variables (e.g., cost per hospital bed, cost per megawatt of power).
• Assembly/System Estimates: Pricing major building systems (e.g., HVAC, foundation) rather than individual components.

Detailed (Bottom-Up) Estimates

Detailed estimates are prepared when the design is 90% to 100% complete. The estimator performs a comprehensive quantity takeoff and applies specific labor, material, and equipment unit prices. This is the estimate used by contractors to submit firm bids. It has the highest degree of accuracy but is time-consuming to prepare.

Cost Classifications: Direct, Indirect, Overhead, and Contingency

Direct Costs

Direct costs are expenses that can be specifically tracked and attributed to a single construction activity or work item. The three main components are:

• Materials: The physical items incorporated into the final structure (e.g., concrete, steel, lumber).
• Labor: The wages and benefits paid to the craft workers performing the physical work (e.g., carpenters, ironworkers).
• Equipment: The cost of the machinery used to perform the activity (e.g., cranes, excavators, bulldozers).

Indirect Costs and Overhead

Indirect costs are necessary for project completion but cannot be traced to a single activity. They are generally split into two categories:

1. Job-Site Overhead (General Conditions): Costs incurred at the project site to manage and support the overall project. Examples include the project manager's salary, superintendent, temporary trailers, site fencing, portable toilets, and cleanup.
2. Home-Office Overhead (General and Administrative): The contractor's corporate costs allocated across all projects. Examples include corporate executive salaries, home office rent, accounting staff, and marketing.

Contingency

Contingency is a defined reserve added to the estimate to cover "known unknowns"—unforeseen circumstances, estimating errors, or minor design changes that are within the original project scope. It is not intended to cover major scope additions requested by the owner. Conceptual estimates carry high contingencies (15-20%), while detailed estimates have lower contingencies (3-5%).

Calculating Burdened Rates and Unit Prices

Burdened Labor Rates

The bare hourly wage of a worker is only part of their actual cost to the contractor. To price labor accurately, estimators must use a "fully burdened" labor rate, which includes:

• Bare Wage: The base hourly pay.
• Fringe Benefits: Health insurance, pension contributions, and vacation pay.
• Payroll Taxes: FICA (Social Security and Medicare), FUTA (Federal Unemployment), and SUTA (State Unemployment).
• Insurance: Worker's compensation insurance and general liability insurance.

Worked Example: Burdened Labor Rate A carpenter earns a base wage of $30.00/hour. Fringe benefits are $10.00/hour. Payroll taxes (FICA/FUTA/SUTA) total 12% of the base wage. Worker's comp insurance is $15 per $100 of base wage (15%). What is the fully burdened labor rate?

1. Base Wage: $30.00
2. Fringe Benefits: $10.00
3. Payroll Taxes: 12% of $30.00 = $3.60
4. Worker's Comp: 15% of $30.00 = $4.50
5. Total Burdened Rate = $30.00 + $10.00 + $3.60 + $4.50 = $48.10/hour.

Equipment Rates

Equipment costs are divided into ownership and operating costs:

• Ownership Costs: Incurred whether the equipment is working or parked. Includes depreciation, interest, taxes, insurance, and storage (DITIS).
• Operating Costs: Incurred only when the equipment is running. Includes fuel, oil, grease, minor maintenance, repairs, and tire wear.

Unit-Price Estimation and Production Rates

Unit-price estimating calculates the cost of completing one unit of work (e.g., $per cubic yard of concrete) based on crew productivity.

Formula: $\text{Unit Cost} = \frac{\text{Total Crew Cost per Hour} + \text{Total Equipment Cost per Hour}}{\text{Production Rate (Units per Hour)}} + \text{Material Unit Cost}$

Worked Example: Unit-Price Calculation A concrete crew consists of 1 foreman ($55/hr) and 4 laborers ($45/hr each). They use a concrete vibrator that costs $15/hr. Concrete material costs $120/CY. If the crew can place 25 CY of concrete per hour, what is the total unit price per CY?

1. Calculate total labor cost per hour: $55 + (4 \times 45) = 55 + 180 = $235/hr.
2. Calculate equipment cost per hour: $15/hr.
3. Calculate combined labor and equipment cost per hour: 235 + 15 = $250/hr.
4. Divide by production rate to get placement cost per CY: $250 / 25 = $10/CY.
5. Add material cost: $10/CY (placement) + $120/CY (material) = $130/CY total unit price.