Approximate Quantities Method of Estimating (Measurement Groups) Advantages and Disadvantages [Building Construction]

Structural Frame - Building Element

The Approximate Quantities method of estimating the cost of a construction project is regarded as the best because it’s more accurate and more reliable than other methods of estimating. This estimate is based on measurement groups where Bill items with the same dimensions (in metres or square metres) are grouped together. This essentially means that items occupying the same area or perimeter are measured together at once using a Group unit of measurement.

If you are familiar with an Elemental Estimate, you should know that Building Elements consist of major Elemental Items which are composed of items occupying the same area or length. Items which cannot be mapped to the Group area or length (Elemental area or length) are measured separately, for example reinforced concrete columns, bases, staircases, door steps, windows, doors, eaves, flashings, downpipes, cornices, built-in cupboards, kitchen fittings, sanitary fittings, cold water supply, hot water supply, geysers, steel balustrade and sundries. Most of these items are enumerated (measured in number), but as long as the surface area or linear dimension cannot be mapped to the Group area or length, it will be measured separately regardless of how it’s measured. Just like major items, separate items should be linked to associated items as much as possible, for example Eaves should include fascia board, gutters and painting. Doors should include door frame, ironmongery, painting on door, plaster/paint to reveals and adjustments for wall openings. Windows should include cills, lintels, glazing, painting, plaster/paint to reveals and adjustments for wall openings.

The same concept can be applied to Approximate Quantities, however the difference is that the grouping of Approximate Quantities is much more flexible, it should not necessarily follow the Elemental format. For example, in an Elemental Estimate, you cannot group Roofs with Ceilings & Soffits, but in the Approximate Quantities method, you are free to group the two. The Structural Frame (Slabs) cannot be grouped with Ceilings & Soffits, but you can group them together in the Approximate Quantities method.

Since this estimate is based on a group of items which are combined together, the rate for each group (composite rate) is also a combination of individual item prices. These component items are BOQ items. In this estimate, the procedure for building up composite rates will take a large part of the Quantity Surveyor’s time, and therefore it requires more work than the Superficial Area method. However, although you will spend the initial period building up rates for a project, most of the rates can be applied to a new project which is similar in nature, so you will only be required to do minor rate adjustments and editing.

Composite Rate Build Up Procedure

There are principles that you have to follow when building up composite rates for Approximate Quantities. We are going to illustrate a composite rate build-up for Foundations:

Excavate trench 600mm wide and 700mm deep, with 200mm thick concrete footings, 230mm foundation brickwall 800mm high and facebricks on plinth 300mm high.

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