Bill of quantities
The bill of quantities (sometimes referred to as 'BoQ') is a document prepared by the cost consultant (often a quantity surveyor) that provides project specific measured quantities of the items of work identified by the drawings and specifications in the tender documentation. The quantities may be measured in number, length, area, volume, weight or time. Preparing a bill of quantities requires that the design is complete and a specification has been prepared.
The bill of quantities is issued to tenderers for them to prepare a price for carrying out the works. The bill of quantities assists tenderers in the calculation of construction costs for their tender, and, as it means all tendering contractors will be pricing the same quantities (rather than taking-off quantities from the drawings and specifications themselves), it also provides a fair and accurate system for tendering.
The contractor tenders against the bill of quantities, stating their price for each item. This priced bill of quantities constitutes the tenderer's offer. As the offer is built up of prescribed items, it is possible to compare both the overall price and individual items directly with other tenderers’ offers, allowing a detailed assessment of which aspects of a tender may offer good or poor value. This information can assist with tender negotiations.
The priced bill of quantities will also:
- Assist with the agreement of the contract sum with the successful tenderer.
- Provide a schedule of rates assisting with the valuation of variations.
- Provide a basis for the valuation of interim payments.
- Provide a basis for the preparation of the final account.
 Preparing bills of quantities
It is very important that bills of quantities are prepared according to a standard, widely recognised methodology. This helps avoid any ambiguities or misunderstandings and so helps avoid disputes arising through different interpretations of what has been priced. In the UK, bills of quantities for general construction works were until most commonly prepared in accordance with the Standard Method of Measurement, currently in its 7th Edition (SMM7). However, a new standard, the New Rules of Measurement became operative on 1 January 2013 and replaced SMM7 on 1st July 2013.
NB Other methods of measurement are used for civil engineering works (Civil Engingineering Method of Measurement) currently in its 3rd Edition (CESMM).
SMM7 adopted the Common Arrangement of Work Sections (CAWS), a standard method for categorising the works. This is also the categorisation of work that is used for the National Building Specification (nbs):
- A - Preliminaries and general conditions.
- B - Complete buildings, structures and units.
- C - Existing site, buildings and services.
- D - Groundwork.
- E - In situ concrete and large precast concrete.
- F - Masonry.
- G - Structural carcassing, metal and timber.
- H - Cladding and covering.
- J - Waterproofing.
- K - Linings, sheathing and dry partitioning.
- L - Windows, doors and stairs.
- M - Surface finishes.
- N - Furniture and equipment.
- P - Building fabric sundries.
- Q - Paving, planting, fencing and site furniture.
- R - Disposal systems.
- S - Piped supply systems.
- T - Mechanical heating, cooling and refrigeration systems.
- U - Ventilation and air conditioning systems.
- V - Electrical systems.
- W - Communications, security, safety and protection systems.
- X - Transport systems.
- Y - General engineering services.
- Z - Building fabric reference specification.
However, this system is currently undergoing considerable change, with CAWS being incorporated into Uniclass, and Uniclass being replaced with Uniclass2 (see Uniclass for more information). In addition, NRM has moved away from the Common Arrangement of Work Sections (CAWS) to adopt its own system of indexing (see NRM2 for more information).
Bills of quantities can be prepared elementally or in works packages, by a process of 'taking off' which involves identifying elements of construction works that can be measured and priced. See Taking off for more information.
Bills of quantities are most useful to the contractor when they are prepared in work sections that reflect likely sub-contract packages. This makes it easier for the contractor to obtain prices from sub-contractors and is more likely to result in an accurate and competitive price.
The bill of quantities should identify the different kinds of work required, but should not specify them as this can lead to confusion between information in the bill of quantities and information in the specification itself.
Disputes can occur where there is discrepancy between the bill of quantities and the rest of the tender documents (for example where an item is included in the drawings and specification but not in the bill of quantities), or where there has been an arithmetical error. Generally the priced bill of quantities will take precedent, and the client will be responsible for their own errors or omissions, which may be classified as relevant events (or compensation events) giving rise to claims for an extension of time and loss and expense. However if an ambiguity or error is noticed by the contractor during the tender process, it is best practice for them to tell the client, even if there may be some commercial advantage to them not doing so.
Increasingly, software packages are available to assist in the preparation of preparation of bills of quantities, and building information modelling systems can be used to produce bills of quantities from information already contained within the model.
Bills of quantities are normally only prepared on larger projects. On smaller projects, or for alteration work the contractor can 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 to calculate the quantities that will be required.
An approximate bill of quantities (or notional bill of quantities) can be used on projects where it is not possible to prepare a firm bill of quantities at the time of tendering, for example if the design is relatively complete, but exact quantities are not yet known. However this will tend to result in more variations during construction and so less price certainty when the investment decision is made.
Some contracts allows for re-measurement of approximate quantities (for example, this is common on cut and fill on roadworks). Here, quantities are simply revised and payments made accordingly without the need to instruct a variation.
If an approximate quantity turns out not to have been a realistic estimate of the quantity actually required, this may constitute a relevant event giving rise to claims for an extension of time and loss and expense.
Approximate bills of quantities can also be used during the design process as a tool for controlling design. They are then sometimes included in the tender documents as a guide with a caveat stating that responsibility for measuring quantities lies with the contractor, and drawings and specifications take priority over any description in the approximate bills (see Approximate quantities cost plan).
 Related articles on Designing Buildings Wiki
- Approximate bill of quantities.
- Approximate quantities cost plan.
- Common Arrangement of Work Sections (CAWS).
- Comparison of SMM7 with NRM2.
- Computers in tendering.
- Construction work packaging.
- Contract documents
- Cost plans.
- Elemental cost plan.
- Firm bill of quantities.
- New Rules of Measurement.
- Prime cost sums.
- Provisional sums.
- Standard Method of Measurement (SMM7).
- Taking off.
- Tender documentation.
- Tender pricing document.
 External references
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