Measurement

[edit] Introduction

Note: This article refers to the measurement of quantities for construction works. For articles about more general measurements, see the list of articles in the measurement category.

The measurement of quantities for construction works involves the transformation of drawn information into descriptions and quantities. This process is undertaken to value, cost, and price construction work, as well as enabling effective management of the design and construction process. The measurement process is not restricted to the quantity surveyor producing a bill of quantities for contractors to price during tendering. It is also used in both pre- and post-contract work, helping assess the likely cost of the works, and determining what contractors and subcontractors should be paid for work that has been completed.

The contractor may use measurement for:

The quantity surveyor may undertake measurement for:

The degree of detail to which construction work can be measured varies according to its use and the stage in the project. In the very early design stages, there is not much detail available, so estimates are based on general parameters, such as:

Functional unit: For example, cost per school pupil, cost per theatre seat, cost per hospital bed, and so on.
Floor area: Cost per sq.m.

As the design progresses and more information is known, estimates can become more detailed, such as elemental estimates (for walls, floors, roof, frame, etc.).

During the later stages of the design, the work required to construct the building may be measured by:

Itemised specification: A detailed cost plan which is broken down into a series of elements. Initially, the elemental cost plan will simply be the total construction cost for the project divided into elements on a percentage basis.
Approximate quantities: A first attempt to measure defined quantities from the drawings (or to take them off from a building information model (BIM)). This should be accompanied by a schedule of assumptions made.
Bills of quantities: The work is measured in detail, usually in accordance with a standard method of measurement.

NB: Bills of quantities are normally only prepared on larger projects. On smaller projects, or for alteration work the contractor may be expected to measure their own quantities from drawings and schedules of work. Schedules of work are 'without quantities' instructional lists that allow the contractor to identify significant work and materials that will be needed to complete the works and calculate the quantities that will be required.

It is important that there is a uniform basis for measuring building works for industry-wide consistency and to allow benchmarking, encourage the adoption of best practice and help avoid disputes.

Provides a structure for the information that should make up the descriptions.
Defines the unit of measurement for each item - m, m2, m3, number, tonnes, and so on.
Provides rules as to what is included within each item.
Defines the terms used to avoid disputes.
Allows familiarity to develop, so measurement becomes easier and quicker.
Provides a clear system for structuring other project information and cross-referencing specification information with bill of quantity information.

NRM provides a set of detailed measurement rules for the preparation of bills of quantities or schedules of rates for the purpose of obtaining a tender price. It also deals with the quantification of non-measurable work items, contractor designed works and risks. Guidance is also provided on the content, structure and format of bills of quantities, as well as the benefits and uses of bills of quantities.

The term ‘taking off’ refers to the process of identifying elements of construction works that can be measured and priced. Those elements can be measured in number, length, area, volume, weight or time, then collated and structured to produce an unpriced bill of quantities. This process is sometimes referred to as ‘working up’.