Forms of specification

3.3 Different forms of production specification

3.3.1 Introduction

Section 3.1 defines the functions and attributes of production specification. Although these apply generally it cannot be assumed that a single form of documentation will be suitable for all types and sizes of project.

Large and small projects are very different in respect of the size of the design and construction teams, the range of specialist skills employed, and the time taken for their design and construction. The scale of production documentation for large and small projects can be in the ratio of 1000 to 1. Whilst the basic principles are largely common, the conditions and procedures for producing and using documents are different, and have a significant effect on the form and content of those documents.

Logical forms of documentation can be defined for large and small projects, but deciding the optimum form of documentation for medium size projects will often require careful consideration.

3.3.2 Larger projects

The large number of drawings means that measurement of the project for pricing is a major task. Where competitive tenders are to be sought, a bill of quantities with measured and aggregated quantities complying with SMM is therefore invariably provided in order to avoid the wasteful effort of each constructor doing his own measurement. Where other forms of procurement are used the constructors will normally be expected to take their own quantities.

The descriptions in bills of quantities are specification information but, being prepared specifically for pricing, often before the detailed design is complete, they can be unreliable as production specification.

The annotations and notes on drawings are also specification information. On a large project they can be produced by many people, often resulting in inconsistency.

The same thing may be described in the specification, on say six drawings and in three places in the quantities. The potential for discrepancies and divergences of specification information within the complete set of documents is therefore very great.

If substantial (but incomplete) specification information is given on the drawings or in bills of quantities, the constructor may be tempted to proceed without checking the project specification.

In view of these problems it is recommended that full specification information be given only in the project specification, so that when questions of quality arise there is a single authoritative place to look. The drawings and any quantities should then identify the different kinds of work, but not specify them. This should be by using a few carefully chosen words (the minimum necessary for unique identification) with, as appropriate, a reference to the relevant clause or section of the project specification. Such disciplined separation of drawn, measured and specification information assumes and depends on the documents being arranged and cross-referenced in a way that makes it easy to read them together (see Section 4.1.5).

Where the method of procurement involves the production of discrete subsets of documentation for 'work packages' the specification for each package may include only one or just a few sections. The drawings annotation should identify the relevant type(s) of work and cross-refer to the specification as described above.

3.3.3 Smaller projects

There are usually only a few drawings, so measurement is far less onerous and time consuming. It is realistic to expect constructors to take their own quantities, and bills of quantities are not normally provided. But a pricing and price adjustment document is still needed on most small projects, and schedules of work, listing the various items of work to be done, are widely used for both new and alteration work.

Schedules of work are often seen as bills of quantities without the quantities. But there is an important difference in that the descriptions are produced by the designers as part of detailed design. Schedules of work are therefore used as an instructional specification document for purchasing, construction and quality control, as well as for pricing and price adjustment.

Alteration and repair work is often best described rather than drawn in detail, it being assumed that the constructor will visit the site before tendering. Many parts of new work can be described, enabling a reduction in the amount of detail on the drawings. It is therefore likely that less time will be needed to produce the drawings.

It is normal for the item descriptions in the schedule of work to include only variable specification information, i.e. potentially varying job to job, to enable them to be concise. Standard specification information (not varying between jobs) is then included in a largely standard reference specification that requires only simple editing for each project. Both schedules of work and reference specifications are specification documents - see definition at 3.1.1.

The overall structure in use of such small works documentation is generally as follows:

• The drawings give an overall appreciation of the project, the location and dimensions of the elements and types of work, and assembly details where needed.
• For both estimating and management of construction the main or 'spine' document is the schedule of work, which refers, either explicitly or implicitly, to the drawings and/or locations in the existing building for dimensions and context.
• The items in the schedule of work refer to the reference specification.
• The drawings refer to the relevant schedule of work descriptions.

The overall package of information described is simple, relatively economical to produce and effective in use for smaller projects. Example documentation for a small project is provided in Appendix S3.

3.3.4 Medium size projects

Sections 3.3.2 and 3.3.3 above describe sets of documentation for use on larger and smaller projects. There is no equivalent widely used form of documentation specifically for medium size projects, and in practice a choice between 'large project' and 'small project' types of documentation must be made. The factors that may influence choice include:

• Value of the project: 'Medium size' cannot be defined precisely, but probably lies within the range £250,000 to £1,000,000 contract value (2002).
• Complexity of the project: In particular, how time-consuming would measurement of the project be for the tendering constructors?
• How much of the project will be let or sublet to specialist constructors without the need for detailed measurement? The remaining portion of the project may be relatively small.
• Number of tenderers: If there are several, all of whom would be involved in a significant amount of measurement, a bill of quantities may be desirable.
• New works or alterations: Alteration work usually needs to be described in detail, and will tend to be more suited to a schedule of work approach.
• General workload: People who specialise in smaller projects may prefer to use a schedule of work for the occasional medium size project. People who usually carry out larger projects may prefer to use a traditional bill of quantities, or an alternative method of procurement.