A per-project aggregate endorsement modifies your general liability policy so that the aggregate limit applies separately to each project rather than to all projects combined during the policy period. Without this endorsement, your $2 million aggregate limit is shared across every job you work on during the year. If one large claim on a single project consumes most of your aggregate, you have little coverage left for claims on other projects.
For roofing contractors running multiple jobs simultaneously, a per-project aggregate is critical. Consider a scenario where you have a $1 million per occurrence and $2 million aggregate policy. Without a per-project aggregate, two $1 million claims on different projects would exhaust your aggregate for the entire year. With a per-project aggregate, each project gets its own $2 million aggregate, so a claim on one project does not reduce your available coverage on another.
Most general contractors on commercial projects require a per-project aggregate as a standard insurance specification. The endorsement ensures that their project has a full, dedicated aggregate limit regardless of your claims activity on other jobs. The cost of adding a per-project aggregate endorsement is modest, typically adding 5% to 10% to your CGL premium. Given that it is almost universally required for commercial work and provides significant protection for your business, it should be a standard part of every roofing contractor's insurance program.