Margin rarely disappears in one dramatic event. It leaks through the same five gaps on job after job.
1. Unclear demolition scope
Selective demo is almost never fully drawn. If the extent is not defined, price what is drawn and exclude the rest in writing.
2. Missing blocking and backing
Every wall-mounted item needs something behind the drywall. It appears on details, not plans, and it is routinely left out of framing bids.
3. Firestopping and rated assemblies
Penetrations through rated walls carry real cost. The wall types legend tells you where they are; the trade drawings usually do not.
4. Temporary work
Shoring, protection, temporary power, dust walls and site fencing are real line items that live in Division 01 and get skipped.
5. Final clean and punch
The last two percent of a job takes far more than two percent of the effort. Carry it.
Every one of these is cheap to catch during takeoff and expensive to discover in the field. A written exclusions list attached to your bid is the single highest-return document in estimating.