A bill of quantities contains an itemized list of work items to be executed with a detailed description of the unit rate tied to it.

Where some work items cannot be measured and described according to the standard method of measurement in use, they are allocated sums in the bills of quantities.

In this article, we are going to look at the three main sums that are very common in a bill of quantities. They include provisional sums, prime cost sums, and contingency sums.

1. Provisional Sums in a Bill of Quantities

These are sums included in the contract bills for the execution of work which cannot be entirely foreseen, defined, or detailed at the time the tender documents are issued.

At the time of issuance of the tender documents, the works being described as provisional cannot be fully described or measured by the rules of the standard method of measurement being used.

Provisional items broadly fall into two sub-groups:

  1. Defined work items – Here, a description and an indication of the amount of work can be given. Although it is not as detailed as the other well-defined work items, the contractor can rely on the information to make an allowance in programming, planning and pricing the preliminaries.
  2. Undefined work items – Here, the full extent of the work cannot be accurately determined and detailed. In this case, the contractor is not expected to make allowances for the undefined work items in his programming, planning and pricing of the preliminaries.

There are reasons why works may not be fully defined during the tendering stage. It could be because it has not been fully agreed on the scope of work to be executed or the drawings have not been developed and detailed to allow for a detailed measurement of the works for incorporation in the bills.

In the post-contract stage, these details will be availed. Therefore, the contract value of the provisional sums is adjusted during this stage after the works have been detailed and executed on-site.

2. Prime Cost Sums in a Bill of Quantities

A prime cost sum (also known as PC Sum) is a sum included in the contract bills of quantities for works or services to be executed by a nominated sub-contractor, statutory or other authority, or for materials and goods to be obtained from a nominated supplier.

The provision for these sums does not include any profit to be made by the main contractor. The common practice is for the main contractor to add his profit following the prime cost sums. This is factored in as a percentage of the total sum for the prime cost items.

Also, the term includes specialist work carried out by persons other than the main contractor and for materials or components to be supplied to him by persons nominated by the architect.

Further, where a nominated sub-contractor is engaged, the main contractor needs to provide attendance on them. Attendance items such as the use site office, provision of power, storage of materials, protection of works and provision of scaffolding, may be included in the preliminaries section of bills of quantities.

However, where the sub-contractor attendance items are not included in the preliminaries section of the bills, a provision to add on as a percentage of the sum of the prime cost items is made in the contract bills.

3. Contingency Sum

This item refers to unforeseeable costs likely to be incurred during the contract.

Contingency sums can be put into two main groups:

  1. Those referring to a particular item. That item is not contained in the bills of quantities but some work of its nature is envisaged.
  2. Those allocated to any item within the bills of quantities are to be expended at the discretion of the contract administrator or the architect.

In Conclusion

We have seen that bills of quantities are prepared according to an established standard method of measurement. The work items are itemised, adequately described and a cost per unit tied to them.

Also, other items in the bills are described as either prime cost items, provisional items and contingency items.

This depends on the level of detail achieved during the tendering stage and whether a sub-contractor or statutory authority will be executing the works.

The three main sums in a bill of quantities arise as sums allocated to the items described above. As discussed, they are the provisional sums, prime cost sums and contingency sums.