Which party is fully responsible for all liabilities under a proprietary specification if an alternative does not perform?

In the context of proprietary specifications, the contractor bears full responsibility for all liabilities if an alternative does not perform as expected. This is because proprietary specifications typically outline specific products or systems that are to be used in a construction project. When a contractor chooses to use an alternative product or method, they assume the risk associated with its performance and adherence to the specified requirements.

The contractor is responsible for ensuring that the materials and methods they employ are suitable for the project and will fulfill the performance criteria set in the proprietary specification. If the alternative does not meet these criteria or fails to function as intended, the contractor is liable for any resulting issues, such as delays, additional costs, or damages.

The roles of other parties, such as the architect/engineer, client, and inspector, may involve oversight, design, or acceptance of the work, but they do not hold the same level of liability for the performance of alternatives selected by the contractor. Each of these parties has distinct responsibilities, and while they may influence project outcomes, it is ultimately the contractor who takes on the responsibility for any performance failures of the alternative materials or methods they choose to implement.