Apr 16

4 Common Estimating Methods Used by Quantity Surveyors and Construction Cost Engineers

 

estimating_methods_recommended

Preliminary estimates also known as conceptual estimates are done in the design and planning stage of a construction project. There are several methods of estimating, some of which are obsolete and some which are highly recommended and used by Quantity Surveyors today. The following is a list of estimates that a Quantity Surveyor can prepare depending on the available information. Of all these estimates, the Elemental Estimate and Approximate Quantities are highly recommended, but if you don’t have sufficient information to perform these estimates, you should start with basic forms of estimating such as the Superficial Floor Area and Unit Method:

Recommended Methods:

  1. Unit Method*
  2. Superficial Floor Area Method**
  3. Elemental Estimate***
  4. Approximate Quantities***

Notes***Highly recommended

Obsolete Methods:

  1. The Cube Method
  2. Storey Enclosure Method
  3. Superficial Perimeter Method

Recommended Cost Estimates

Unit Method – This estimate is done in the early stages when design plans are not available. The Estimator can work out a rough figure based on the number of personal units required by the client:

Number of Personal Units x Cost Per Unit = Total Cost of Building

These personal units come in various forms. They can be:

  • The number of people who will occupy the building
  • The number of rooms or bedrooms in a building
  • The number of desks in a classroom
  • The number of keys or beds in a hotel
  • The number of beds in a hospital
  • The number of parking bays in a basement car park
  • The number of cows on a dairy farm facility
  • The number of beds in a prison
  • Number of tables in a restaurant
  • Number of stalls in a marketplace
  • Number of seats in a movie theatre or cinema building

 

Superficial Floor Area Method – Once sketch designs with floor areas are available, the Estimator can measure the internal gross floor area of the building and multiply the same by the construction cost per m2. According to data provided by local municipalities, building societies, property developers and consulting quantity surveyors, the construction cost per square metre differs by region, location and type of building.

Internal Gross Floor Area of Building x Cost Per M2 = Total Cost of Building

Elemental Estimate – This estimate requires more information other than floor areas. To use this method, drawings with enough information are required i.e. wall elevations, structural frame, roof structure, ceilings, foundation cross sections, floor construction, external works, wall and floor finishes. The document contains detailed information broken down into Building Elements. A project can have up to 21 Building Elements depending on the specifications and scope. To calculate the total cost, the Quantity Surveyor has to price the component items which are grouped together based on similar areas or length. An elemental estimating guide with measurement rules has to be followed.

Total Cost of Building = Total Cost of All Building Elements

Approximate Quantities – This estimate requires advanced drawings because sufficient information is required for building up composite rates. It’s a faster method of producing un-standardized Bills of Quantities, although it’s not really a BOQ but an approximate preliminary estimate. In this method, the Quantity Surveyor combines items from a Bill of Quantities into groups that can be quickly measured using the Group unit of measurement. A composite rate is created for each group, and thus this estimate takes a long time to prepare than other methods, although it’s a more reliable estimate. The total cost of a project is obtained by adding up the subtotals of the groups.

Total Cost of Building = Total Cost of All Work Groups