A head of claim that is often made by contractors against employers is for prolongation costs, i.e., those costs sought by a contractor for having to remain on site longer than it originally anticipated due to the actions of an employer.

Much has been written about the recoverability of head office overheads and, more specifically, whether such claims can be proven by way of reliance on a formula or whether actual cost data is required.

However, an important aspect of prolongation claims that is often not addressed by commentators on construction claims is the basis and evaluation of claims for additional preliminaries (or job site overheads as they are known in the United States). In short, preliminaries are comprised of fixed costs, time related costs, activity related costs and value related costs.