When is bill of approximate quantities contract used?

This approach means that the bills used in tendering are approximate in content,

although representative of the project. The whole of the works is remeasured as

executed, but priced at the rates in the original bills, or rates derived from them. The

method is useful when the conditions just indicated apply, that is, uncertainty

initially. It is particularly helpful when time is tight, because it saves on pre-contract

time and allows overlapping between design and construction. It tends to higher

pricing by tenderers, as there are uncertainty factors about the reality of the quantities.

This is not something which is entirely resolved by the final remeasurement

producing the correct quantities. Tenderers must always price quantities with some

regard to which items are for larger or smaller parcels of work, which affects their

interaction, the use of common resources and other organisational and programming

matters. Even though these conditions are taken into account in settlement to a

degree, a margin still tends to be allowed.

Approximate quantities undoubtedly save time, although how beneficial this is will

depend on whether design then keeps ahead of construction. They may, as a

byproduct of this, allow options to be kept open until a later date. Because they are

less precise, they do not offer the same cost control, but this may be obtained from a

good cost plan or other control estimate set alongside the bills and remeasurement

and modified in price level in the light of these data. If firm quantities are subverted

by extreme variations, their control value is often lost.

The degree of approximation has no strict limit and may be conditioned mainly by

time or information available. It is possible to base bills on quite close design, saving

a margin of time by somewhat loose attention to accuracy. At the other end of the

scale, it is possible to produce bills by starting from broad estimates of cost based on

sketch drawings and a reasonable indication of the type of construction and materials.

The actual quantities are then produced by dividing up the estimates and feeding in

detailed item descriptions and quantities which are anticipated as a result. There is

never any virtue in greater approximation for its own sake, but much can be achieved

when needed. It is always necessary to describe the site conditions, character of the

works and other overall features fairly accurately, so that overheads and general price

frameworks are not thrown too far out.

So far as fees go, firm quantities with extensive variations are likely to cost about the

same as approximate quantities with remeasurement. Often approximation should be

used as more realistic in all the circumstances.