The electrical sub on a residential build typically prices a scope of work as a single line item: "Rough-in electrical, panel, fixtures — $28,000." The homeowner signs it. The manager records the estimate. Construction begins.
Three months later, invoices have come in for $34,200. The scope changed — a few times, in ways that seemed reasonable in the moment. A larger panel for the homeowner's EV charger. Extra circuits for the home office. Recessed lighting in the master that wasn't in the original plan. Each change was approved verbally. None were formally amended to the contract.
This is the most common financial surprise in residential construction. And it's almost always preventable.
The Creep Pattern
Subcontractor invoice overruns don't usually happen all at once. They accumulate in small increments: a change order here, an upgrade there, a "while we're at it" addition. Each individual invoice looks reasonable. The cumulative effect against the original estimate is not.
The problem is that humans are bad at cumulative tracking across time. You approved the panel upgrade three months ago. You approved the extra circuits six weeks ago. Today's invoice for fixtures seems normal. Nobody connected the dots.
What the AI Watches
BLT tracks three numbers for every subcontractor: their original estimate, total invoiced to date, and total paid to date. Every time a new invoice is recorded, the system updates these numbers and checks them against threshold rules.
At 80% of estimate: an informational alert. The manager sees where the sub stands and can review the remaining scope.
At 100% of estimate: a warning alert with the delta displayed. "Valley Electric has invoiced $28,400 against a $28,000 estimate. Two phases remain: fixtures and final inspection."
Over estimate: an AI-generated insight that includes context — which budget lines are affected, what the overrun amount is, and a note on pending scope if any remains.
The $14,000 Example
A BLT user managing a 2,800 sq ft custom home had their HVAC sub come in $14,000 over estimate. The sub had upgraded the system spec mid-project based on a conversation with the homeowner about zoning — a conversation the manager wasn't part of.
In the old workflow, the manager would have learned about this when the final invoice arrived. In BLT, the system flagged the HVAC sub at 87% of estimate when the third invoice was recorded — eight weeks before the project completed. That gave the manager time to have a direct conversation with both the homeowner and the sub about what was authorized, document the scope change formally, and adjust the project budget before it became a surprise at closeout.
The Conversation That Doesn't Happen Without the Alert
The most valuable thing the AI does isn't generating the alert. It's creating the occasion for a conversation that otherwise wouldn't happen until too late. Construction disputes almost always involve things that weren't documented when they should have been. Early alerts give you the chance to document while the memory is fresh and the relationship is intact.