What type of change occurs when the owner modifies the project affecting costs?

Choosing "consequential change" is appropriate because it encompasses modifications made by the project owner that directly impact the project's overall costs. In construction and project management, a consequential change typically refers to effects stemming from the contractor's or owner's decision that leads to additional costs, adjustments in scope, or impacts on the schedule due to changes in the contract or project requirements.

When an owner decides to modify aspects of a project, it triggers a chain reaction that can ultimately alter budgets and timelines. This reflects the essence of consequential changes, where the modifications made—regardless of whether they are planned or immediate—result in tangible results that affect the project's financial and logistical dynamics.

Other types of changes listed, such as unexpected or design changes, do not accurately capture the broader implications of the owner's modifications in terms of cost implications. "Contractual change" could suggest alterations that arise from formal agreement adjustments but do not encapsulate the overall impact on project costs in the way that consequential changes do.