Change orders document changes that arise during construction: owner-requested upgrades, unforeseen conditions (rock encountered in excavation, unmarked utilities), design errors, or scope clarifications.
Pricing a change order: trade unit prices × quantity changes, plus markup for overhead and profit. Most contracts specify markup percentages for change-order work (e.g. 10% O&P on labor, 15% on subcontract work, 5% on materials).
Document every change order with its own quantity takeoff. Reference the original bid item, the change, and the difference. Keep change-order tickets with the project file.