What factor could trigger the necessity for existing plumbing systems to be updated to comply with the IPC?

An enlargement of the structure is a key factor that may necessitate updating existing plumbing systems to comply with the International Plumbing Code (IPC). When a building is enlarged, it often requires a reassessment of the plumbing system to ensure that it can adequately support the increased demand for water supply and sewage disposal. This could involve additional fixtures, which would need to be properly accommodated within the existing system to maintain efficiency and compliance with safety and health standards established by the IPC.

Plumbing codes, such as the IPC, are designed to ensure that systems are safe and effective for the users. An enlargement of a structure can change the load on the plumbing system significantly—either by increasing the number of fixtures or by altering how the plumbing interacts with the building layout. Therefore, updating the plumbing system may be necessary to ensure it meets the current code requirements and maintains proper function and safety for the building's increased capacity.