Bill of quantities
A bill of quantities (BOQ) is a document used in tendering in the construction industry in which materials, parts, and labor (and their costs) are itemized. It also (ideally) details the terms and conditions of the construction or repair contract and itemises all work to enable a contractor to price the work for which he or she is bidding.
Bills of quantities are prepared by quantity surveyors and building estimators, and “Indeed the bill of quantities was the raison d’etre for the development of quantity surveying as a separate profession.”.
Bills of quantities are prepared by a “taking off” in which the cost of a building or other structure is estimated from measurements in the Architects, Structural Engineers, and other building consultants drawings. These are used to create a cost estimate such as in regard to the square area in meters of walls and roofs, the numbers of doors and windows, and systems as heating, plumbing and electrics. Similar types of work are then brought together under one item, a process known as "abstracting".
Estimating books provide the relevant costs of the materials and labour costs of the operations or trades used in construction. As the rates for materials and labour change due to inflation, these books are frequently republished.
The practice historically of estimating building costs in this way arose from non-contractual measurements, taken off drawings to assist tenderers in quoting lump sum prices.
There are different styles of bills of quantities, mainly the Elemental BOQ and Trade Bills.
A Contingency sum is an item found within a Bill of quantities (BoQ).
The item refers to unforeseeable cost likely to be incurred during the contract.
There are two types of contingency sum. The first refers to a specific item i.e. 'additional alterations to services when installing said shower unit'; where an item for alterations to existing services is not contained within the BoQ but some work is envisaged.
The second type of sum is where money can be allocated to any item, within the BoQ, in the same way as the above example or used as 'additional work to be undertaken by the contractor, at the request of the contract administrator'.
The first is usually approximated by the client’s PQS and the second by the contractors QS (or commercial manager).
Additional requirements is referred as Bill of materials (BOM).
Bills of quantities compounds labour and material costs by combining them into a single rate that iss then adjusted in regards to material quantities. They also do not consider all the main costs incurred by contractors such as construction plant, temporary works, and payments made on an interim bases in regard to work completed. Thus they do not actually model real costs. An alternative form of cost document that accounts for these costs was developed at Building Research Establishment and called an operational bill.
They impair transparency in regard to changes and costs “It has suggested that the reason why bills of quantity still find favour with contractors “is the opportunity it provides for creating a smoke screen around the contractor's original intentions. Thus, front end loading may go undetected, and new rates may be negotiated almost from scratch”. 
A Bill of Quantities does in fact consider all costs and is transparent in relations to all costs. Where information is missing at the time, sums based on ad hoc schedules or know rates will be entered, but this will of course depend on the contract being used. Traditional routes, where time is not so much an issue add better cost certainty. From inception to completion and beyond Bills of Quantities cover all aspect of work and this includes all work, materials and any cost related aspects supplied by the contractor. This is done in the preliminary stages of the Bill and it is then up to the contractor to enter rates against the items mentioned. (The description previously edited here is misleading and untrue.)
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