This Practice Note provides an introduction to cumulative impact claims and considers how multiple variations instructed on a construction project may effect the contractor’s ability to progress the unchanged work and cause a loss of productivity, the court’s and tribunals’ approach to such claims, the potential impact of contractual provisions on such claims, how and when to quantify claims and practical tips on how to succeed in a cumulative impact claim. What is a cumulative impact claim? Variations on construction projects are extremely common and occur for many reasons, for example, where a contract is signed prior to the design or scope of works being finalised, where the employer wants to make changes on the project as building work progresses, where there are inconsistencies in the contract documents that require resolution, or unforeseen physical conditions on site which need to be addressed. The direct impact of variations, in terms of the cost to carry out the varied work and the effect on work connected to the change is usually straightforward to ascertain. However, on large and complex projects,