Which of the following is an essential item that might be included in a client's checklist during warranty services?

Including maintenance items in a client's checklist during warranty services is essential because it helps ensure that the client understands the ongoing care necessary to maintain the integrity and performance of the building or structure. Maintenance items can encompass a variety of tasks that need to be performed regularly, such as HVAC system checks, roof inspections, and landscaping upkeep. This not only prolongs the lifespan of various components but also prevents small issues from escalating into significant problems that could result in costly repairs or warranty claims.

By having this checklist, clients are better equipped to monitor and assess their property's condition post-completion. It encourages proactive management of building systems and surfaces, thus aligning with the intent of the warranty service period, which aims to respond to and rectify any issues that arise due to construction deficiencies.

The other options, while relevant to different aspects of a project or its ongoing management, do not specifically pertain to the immediate needs and responsibilities tied to warranty services in the same direct manner as maintenance items do. Cost estimates may relate to budgeting for future repairs rather than the current warranty period, legal documents pertain more to contractual obligations than to maintenance tasks, and design changes typically fall outside the scope of warranty services unless they relate directly to recognized deficiencies.