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3.2 Production specification content

3.2.1 Preliminaries and general conditions

The purpose of preliminaries is to describe the works as a whole, and to specify general conditions and requirements for their execution, including such things as subcontracting, approvals, testing and completion. SMM defines the content for projects with bills of quantities. NBS defines the content in greater detail for all the commonly used forms of contract.

3.2.2 Specification by performance or prescription

The specification process can be considered as two stages:

Ascertaining the performance required of the particular element, system, assembly or component.
Determining the design, products and workmanship needed to meet the performance requirements, and any special conditions for carrying out the work.

The second of these stages is traditional prescriptive specification. If the project specification identifies only the performance requirements, leaving the manufacturer or constructor to determine the form and dimensions of the construction and/or the products and workmanship, then this is known as performance specification. Specification by performance thus requires the manufacturer or constructor to complete the design process.

This Code is concerned with production information, which by definition must be based on a substantially complete design for the building. Production specification defines construction mainly in prescriptive terms, describing the products to be used and the important aspects of workmanship. The Code does not cover the full (pre-design) performance specification of the spaces and functional elements of whole buildings.

However, within the context of a substantially complete design it is often appropriate for some types of work to be specified at least partly by performance, to use the technical design skills of specialist constructors, e.g.:

Building fabric: piling, structural steelwork, precast concrete decking, precast concrete cladding, curtain walling, raised access floors.
Installations and services: lifts, escalators, low temperature hot water heating, air conditioning.

Performance specification and prescriptive specification each have several practical limitations, and the following questions should be asked in relation to each type of work:

Performance specification:

Is there a suitable industry or trade Standard, setting out a framework for specification by performance, that can be invoked by reference?
Are reliable, economic and practical methods of test available? Do the relevant manufacturers/constructors have appropriate existing test results for their construction systems?
Can the specified standards be achieved at an acceptable cost?
Are any of the specified requirements likely to be in conflict with each other in practical terms?
Can the constructor's design be integrated satisfactorily with the rest of the building? What are the design interdependencies, and can they be resolved in the context of the design programme?
Can subjective requirements such as appearance be defined adequately?
Is the constructor/supplier able to respond fully - has he enough skill and experience? What is his track record? Does he have appropriate quality accreditation?
Can the constructor's design responsibility be covered in the contract conditions, is it practicable to obtain a design warranty from him, and will he be adequately insured against design liability?
Can the cost of responding (especially if competitive bids are invited) and establishing compliance be justified when set against the scale of the work?

Prescriptive specification:

Is the design the most practical and economic solution to the problem?
Will what has been specified function properly?
Can it be verified that what has been specified has been provided?

It is important to adopt an approach that takes account of these questions and provides effective quality control. The best approach for many types of work will often be a mixture of performance and prescriptive specification. Typically, such specification sections will require compliance with appropriate performance Standards or industry quality schemes, identifying relevant options and alternatives. Aspects of quality not adequately controlled by the reference Standard can be covered by prescriptive specification, taking care to avoid practical conflicts with the specified performance requirements.

Where the design for the building is substantially complete the specification of building services by performance is heavily constrained by the need to achieve integration between systems and with the building fabric. It will invariably be necessary to predetermine the type of system, the main distribution routes, and the sizes of ducts, ceiling voids, plant rooms, switchboards, etc., so that the constructor's design contribution is limited to choice of products, sizing of conduits and equipment, and other practical details. Clearly, this is a very limited application of performance specification compared with a full design and build contract, where all elements and systems of the building can be designed and coordinated at the same time.

Requirements for the provision of evidence of compliance are a key part of performance specification. These may include calculations, reference to previously constructed buildings, records of previous tests, tests for this project, provision of samples, mock-ups and production control units. The procedures and timescale for submission of design proposals, comment, resubmission, etc. should also be specified.

The responsibilities of the parties are quite different where work is specified mainly by performance rather than by prescription. The two approaches are likely to co-exist on most projects, and there should be clear, practical boundaries between the different 'spheres of responsibility', i.e. between:

One type of performance specified work and another, and
Performance specified work and work specified by prescription.

Where performance specification is used for some sections of the specification, the remainder being prescriptive, use of the Common Arrangement of Work Sections (CAWS) is recommended (see Section 4.1.2). CAWS has work sections of an elemental nature for types of work that are commonly specified mainly by performance. Use of CAWS as the primary arrangement for the specification will provide clear boundaries between types of work with different design responsibility.

Specification by performance involves the constructor in detailed design, and this should be reflected in the conditions of contract, e.g. by use of the JCT Contractors Design Portion supplement and/or Clause 42 of the JCT Standard Form of Contract. Design warranties should normally be required.

An example section of performance specified work is provided in Appendix S1.

3.2.3 Specification by prescription: products

In this Code the term 'products; is used as defined in Uniclass 1997: 'Products, components and 'kits of parts' incorporated or intended for incorporation into buildings or other constructions, including furniture and fixtures'. The term is thus used to mean the things purchased for a project. The term 'material' is used only to refer to the substance from which a product is made, e.g. steel, timber, neoprene, wool. Certain terms, e.g. 'concrete', can therefore be used to mean a product, e.g. ready mixed concrete, or a material, e.g. concrete blocks.

Products are usually specified by reference to Standards or by proprietary name (referring implicitly to manufacturers' product descriptions). Both Standards and product literature are increasingly written in performance terms, which is helpful to the designer when choosing products for inclusion in the project specification. However, products are usually ordered by reference to Standards or by proprietary designation, with no design input by the constructor, and supplied as standard items, invariably off the shelf - whether the reference documents specify by performance or prescription makes little difference to the way in which the typical project specification is used.

Any lack of thoroughness in specifying products is likely to cause construction errors, claims for extra cost, and delays to the construction programme. The constructor should be able to order products correctly and precisely from the specification, and it is therefore important to:

Ensure that the product details are correct and up to date, particularly if information from a previous project is being recycled.
Specify clearly which of the available product options are required, using the designations and terms used in the Standard or by the manufacturer.
Specify any required product attributes not covered or covered inadequately by the Standard.

It is all too easy, when short of time, to defer a decision by specifying a product as 'to approval'. This practice should be avoided wherever possible because:

Overall, time is not saved, as the decision has to be made eventually.
The constructor cannot price the item except by guessing what may or may not be approved, and there is the consequent risk of subsequent dispute and extra cost.
Under JCT forms of contract the item will be 'a matter for the opinion of the Supervising Officer', affecting the conclusiveness of the final certificate and the position on long term liability.

Verification that products comply with the specification can usually be obtained by inspection of delivery notes and packaging. Compliance with a Standard can, where a suitable scheme exists, be assured by specifying that a product must bear a particular third party quality mark. Where manufacturing quality control documentation is needed to verify compliance with the specification (e.g. for ready mixed concrete) the product should be specified for supply by a member firm of an accredited industry quality scheme.

If more than one source of supply of a product is permitted, the constructor may be able to purchase at a lower price and with a greater degree of certainty that delivery dates will be met. Therefore, where design priorities allow, the specification should permit options or alternatives.

In most cases specifying to a Standard will ensure that alternative manufacturers or suppliers are available to the constructor. Some standard grades or types are available from only one manufacturer, and some are not obtainable. Specifying quality marking to a Standard may further restrict availability. In some cases alternative products can be allowed by stating the type of product and requiring that it be Agrément certified. Where the project specification has requirements additional to those specified in the Standard, this may also restrict availability.

Where specification of proprietary products by name is preferred, giving two or more as alternatives is desirable. However, finding alternatives that are acceptable in all respects can be difficult, and in some cases it may be considered worthwhile to obtain prices for alternative products in advance, and specify via the nominated supplier procedure.

Another approach is to specify a proprietary product followed by the phrase 'or equivalent' (or variants such as 'equivalent approved' or 'equivalent of approved appearance') but this should be used only for minor items, and only when the specifier is genuinely prepared to consider alternatives put forward by the constructor. There can be doubt about what is 'equivalent' (i.e. which attributes and properties are regarded as important), potentially leading to dispute between specifier and constructor. The constructor will be unable to price firmly on the basis of an alternative, defeating the whole object of the specified option. Firmly specifying two or more alternative products is to be preferred.

Specification of products by proprietary brand may be discouraged or prohibited by the client for certain types of project. In the absence of a suitable Standard, it is possible to specify the type of product and it's precise attributes, (taking these from manufacturer's literature) so that the constructor can choose from alternatives. At best this practice is unhelpful - identifying the proprietary brands that are known to comply would save time for the constructor. At worst only one branded product may comply, which would defeat the whole point of the restriction on method of specifying.

Constructors will often put forward alternative products for consideration even when this is not envisaged by the specification. This practice is often regarded by specifiers as unwelcome, usually because of the additional time taken in investigating the suitability of the suggested alternatives. However, such alternative products may, on occasion, be superior to what is specified, or offer a reduction in cost to the client. It is likely to be helpful to the constructor if he knows in advance the general attitude of the supervising officer to this practice. A preliminaries clause can be included stating that, except where the submission of alternative products for approval is specifically permitted by the specification, any alternative product put forward by the constructor:

May be rejected without giving a reason, but equally, at the discretion of the supervising officer, may be accepted, or
Will not be accepted.

Specification of products usually involves direct or implied reference to Standards or manufacturer's literature. Recommendations on specification by reference are given in Sections 3.2.5 and 3.2.6 below.

An example section of work specified by prescription is provided in Appendix S2.

3.2.4 Specification by prescription: workmanship

The achievement of good standards of workmanship is generally considered to depend, to a considerable extent, on the employment of constructors with quality assurance and/or a reputation for the quality of their work. However, procurement procedures, selection of constructors and choice of type of contract all lie outside the scope of this Code.

The main problem with specification of workmanship is to know how much detail to give, particularly with traditional trades where designers often have considerable practical knowledge. Competent constructors should know all aspects of good construction practice, and should follow these as a matter of course. But if something considered by the specifier to be important is not provided or performed the constructor may decline to agree that it is essential, and allege that he had not included it in his pricing. If the matter is not covered by the specification the specifier may have to concede the point.

Workmanship should not be specified by blanket references to Codes of Practice which the specifier has probably not read, and which the constructor is unlikely have on site. Most Codes of Practice are concerned mainly with design guidance rather than workmanship, and are not sufficiently definitive for contractual purposes. Site personnel should not be left to resolve (or ignore) the options and doubts that are often left open by such documents. It is normally preferable to specify workmanship by direct description in the project specification.

Where manufacturers' published sitework instructions exist and are of good quality, they can reduce the need for detailed workmanship clauses in the specification, and it is wise to include a preliminaries clause requiring compliance with manufacturers' written recommendations. However, particularly where choice of product brand is left to the constructor, this cannot always be relied on. For those types of work not known to be covered by good quality manufacturers' information it will normally be appropriate to provide a relatively full specification of workmanship requirements.

Specification of workmanship should seek to define the important characteristics of the finished work rather than how to achieve them. However, this is not always practicable, e.g. finishes to screeds are best described as 'steel trowel', 'wood float', etc..

Published specification library systems that comply with this Code and are widely used can be used to ensure:

A degree of industry standardisation on how far to take the workmanship descriptions;
Economy of language so that the workmanship specification is not too bulky.

It is difficult to specify fully the appearance of many kinds of finished work e.g. brickwork, concrete finishes, rendering. The products to be used, joint profiles, depth of exposure of aggregates, etc. can be specified with precision, but the finer qualities of colour, texture, consistency, etc. usually defy meaningful description. Reference can be made to existing samples and buildings, but these should be easily accessible. Where justified by the scale and importance of the work it is good practice to specify the construction of samples on site for approval of appearance before the remainder of the work is executed. Such samples, which may be special mock-ups or part of the finished work, should be of adequate size and incorporate important features so that they are meaningful and helpful in establishing acceptable standards of appearance.

The arrangements and procedures that apply before, at and after completion should be specified fully and clearly (in the appropriate work sections or preliminaries and general conditions as appropriate), including:

Commissioning of services systems, including balancing and calibration.
Instruction of employer's operation and maintenance personnel.
Safekeeping and handover of spare parts and products.
Completion and handover of as built and maintenance information.
Arrangements for access, handover of keys, security codes, etc. at practical completion.
Final cleaning and polishing.
Arrangements for access, etc. for making good defects.

To ensure that these items are properly carried out they should be priced individually and adequately (e.g. by specifying a minimum amount against relevant items in the tender documentation).

3.2.5 Specification by reference to Standards

Referring to Standards and other published documents can considerably reduce the size of the project specification and save much time and effort. This applies to both performance specification (e.g. testing of hardened concrete to BS 1881-124) and prescriptive specification (e.g. natural slates to BS 680-2).

Despite the inherent advantages, specification by reference to Standards has been characteristic of much bad practice, notably reference to out of date documents and blanket references to Codes of Practice (see Section 3.2.4 above). Before deciding whether to specify by reference to a Standard or other document, the pros and cons should be considered:

What is the status of the reference document? Is it authoritative (in the sense of being technically sound rather than just having an official endorsement)? Is it current (in the sense of reflecting sound up to date practice rather than still being available)?
How readily available is the document? What does it cost? Will the constructor have a copy, or can he reasonably rely on his product supplier to have a copy?
How suitable is the document for use by the constructor and others? Is it couched in clear instructional terms? How much text is involved and is it easily identifiable in the document? If not, restating the relevant requirements in the project specification may be more convenient and effective.
How much of the document does the specifier wish to invoke? It is undesirable to invoke a document and then make specific exclusion of major parts. In principle it is better to refer specifically to the parts that apply or, in very complex cases, restate the information in the project specification.

In general, it is preferable to specify products by reference, as estimators, purchasers and suppliers should have access to the relevant documents. Site operatives do not need detailed specification of products, just simple identifications to make sure they install each product in its correct location in the building.

IIt is usually preferable not to specify workmanship by reference (see Section 3.2.4). To be suitable for use on site, documents need to be uncomplicated, definitive and readily available.

The main principles to follow when specifying by reference to Standards are:

Refer to a document substantially or not at all. Acquisition of Standards can be costly and time consuming for the constructor, so do not invoke just a small part of a substantial document.
Identify the document precisely, giving title, publisher, date, reference number as appropriate.
Be thoroughly familiar with the contents of the document - otherwise the references are likely to be over-generalised, inappropriate or contradictory.
Be helpfully precise, stating the part, chapter, type, grade, class, group, quality, section, table, column, material, finish, clause, appendix, code, weight, size, number or other designation(s) that apply. A clause should be included in preliminaries stating that where a reference is given to a specific part or designation of a Standard, the relevant general parts of that Standard also apply.
Specifically (and prominently) describe any permitted or required departures from the Standard.
Do not specify by reference to two documents that have a confused or contradictory relationship.
Ensure that supplementary specification does not duplicate or contradict the reference document, e.g. specifying minimum cement content for a BS 5328-2 RC40 designated concrete mix.

The dates and revisions of Standards are frequently specified in a generalised way, e.g. by requiring them to be those current at (say) the date of invitation of tenders. This avoids the considerable chore of updating references to Standards and their amendments, and permits considerable simplification of the specification text - compare the following alternatives:

Draining taps (screw-down pattern): to BS 2879: 1980 + AMD 3715, AMD 4595, AMD 5477
Draining taps (screw-down pattern): to BS 2879

In theory it is best practice to check on all amendments to every Standard referred to in the specification, and to give the date and amendments in full, but in practice this is a counsel of perfection. At any given time a high proportion of the Standards referred to in the Building Regulations are out of date. Many Standards give out of date references to other Standards. Most amendments to Standards are of low import and unlikely to have practical significance for the project in hand.

Provided the specifier knows what he is specifying by invoking a Standard, and is confident that it is readily available, the most important consideration is to establish, for contractual purposes, the exact dates and amendments that apply. A suggested preliminaries clause is set out below, which should enable the vast majority of Standards to be specified only by number, but leaves open the option of giving details of brand new Standards and amendments where required:

'REFERENCES TO BSI DOCUMENTS are to the versions and amendments listed in the BSI Catalogue 200_ and any subsequent versions and amendments specifically referred to.'

3.2.6 Specifying by proprietary reference

In specifying proprietary products, the manufacturer, the precise product designation, and any available options that are required should be identified.

When specifying products by proprietary reference it is advisable to avoid also specifying compliance with a Standard - nothing is gained, and if it transpires that the branded product does not comply with the Standard there can be a dispute over which specification prevails. Similarly, it is advisable to avoid stating separately a product attribute that is implicit in the manufacturer's designation.

Where a proprietary product that is not generally known in the industry is specified, it is helpful to give the manufacturer's postal address, telephone number and e-mail address.

In general it is unwise to refer to specific items of manufacturer's literature because of the general uncertainty about identification of editions and amendments, and doubts about what is current.

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