Who should own the integration seam on a critical-infrastructure build?

The integration seam is the highest-risk surface on a critical-infrastructure project and the most commonly orphaned one. Without explicit ownership, the BMS contractor blames the EMS contractor, neither owns the data model, and nobody signs off the converged operation.

Three viable models

Master Systems Integrator (MSI) as a separate scope. An independent integrator under direct client contract, accountable for the seam from RIBA Stage 2. Best for projects with three or more disciplines integrating.

Lead BMS contractor with integration scope written in. Works when one vendor's BMS is the centre of gravity and the other systems hang off it. Cheaper; risks the lead contractor underweighting integration that doesn't benefit their own platform.

Client-side technical advisor with delegated authority. Common in pharma and government. Slower decision cycles; strongest for compliance-heavy estates.