Parametric or Schematic Estimates for Construction

James A. Beal AVS, LEED AP

An integral element for a successful construction project is a parametric, or as often referred to, a schematic estimate.  The function of a parametric/schematic estimate is to transfer the information provided by the designers, architects and owners, prior to starting the design, into a detailed estimate.  This allows the entire team to review cost versus the budget without the expenditure of valuable time.  Major changes can be made at this stage. 

What constitutes a detailed estimate at this point in the project?  By employing a systems format, the estimator objectively reviews structure, exterior closure, roofing, conveyance systems (i.e. stairs, elevators, escalators), fire protection, plumbing, mechanical, electrical, security, alarm systems and site work.  An experienced estimator’s expertise ensures these systems are in place.  The following information is necessary:

• Type of exterior skin

• Basic geometry of the building

• Number of floors and floor heights, length to
  width ratio and total square feet of the building

• Type of mechanical system  - Chilled water system, direct expansion on the roof, split system, etc.

• Basic criteria for electrical (i.e. lighting allowance and power required)

• Main transformer – will this be supplied by the
  Owner

• Emergency generator – size and amount of fuel
  supply required

• Size of the site and required parking

• Garage information

• Landscaping allowance

• Size of required detention pond

• Any modifications needed for roads or utilities, including if the utilities are in close proximity to the site.

The estimator’s task includes gathering information from the owner, architects and engineers.  The architect, and often with the Owner’s input, provides the estimator with information on the interior finishes for the project.  The estimator uses detailed interior information from similar projects to produce the estimated cost. 

What may not be available at this stage of the parametric/schematic estimate is various costs.  Once the estimate is complete, the estimating team confers with the design team for any necessary revisions.  Major design changes can then be implemented. 

The design team and the estimating team need to further confer on assumptions.  For example, the amount of steel required.  Variables must be considered:  steel at suspended floors may be eight pounds per square foot, and the roof steel may need five pounds per square foot.  The structural engineer’s input is necessary and the estimate may require adjustments accordingly. 

Another integral component of the parametric/schematic estimate, structural fill or type of foundation.  Since a soil report is not required at this phase, an experienced estimator may offer an opinion based on previous experience in the geographic area. In addition, the structural engineer may have similar projects in the geographic area which  will allow the estimator to refine the estimate. 

Some projects are afforded estimating models which can be changed to reflect the changes in design. Many school districts find this as a flexible tool when considering a typical design standard for a school. Variables used are student population, the number and type of classrooms, cafeteria and kitchen size, various offices and the respective sizes, bathrooms, media center (library), and the multipurpose room size.  By using this estimating model, the district may discern how may administrative offices are needed in the building.  Given the student population count, and prediction for future growth, the district may need to change the size of the building.  Included in this would be assuming added hallways and additional square feet which then would affect the cost per square foot for mechanical and electrical.

Using an estimated model approach for an estimate is time consuming and requires the use of an estimating staff to assure that estimates reflect any changes.

A parametric/schematic estimate follows the Owner’s intent and budget.  If the budget doesn’t meet the Owner’s vision, discovering this at an early stage sets the parameters for the design.  Best practice alleviates anguish which can occur once the project has bid and it is declared to be out-of-budget.