What Is an Addendum in Construction?

Federal sealed bidding sets the model. Changes "in quantity, specifications, delivery schedules, opening dates, etc." or corrections to "a defective or ambiguous invitation" are made by amendment, sent before bid opening "to everyone to whom invitations have been furnished," and information given to one bidder goes to all of them as an amendment if they need it to bid or if lacking it would prejudice them (FAR 14.208). Before issuing one, the contracting officer considers whether to extend the bid date.

Acknowledgment matters. A bid that fails to acknowledge an amendment is excused only if it clearly shows the bidder had it, or if the amendment has "either no effect or merely a negligible effect on price, quantity, quality, or delivery" (FAR 14.405). Otherwise, on federal work, the omission is not a minor informality that can be waived; on private work, the bid may not cover the changed work.

See how to write an ASI and change order vs. change directive for the after-award side. The step-by-step for a GC issuing addenda to its trade bidders sits with how to send an invitation to bid.

In Conflo's trade bids, you issue numbered addenda to a package. The bidder sees the trade addendum to acknowledge before bidding, and the Bidders tab warns when a bid is missing one.

An addendum is the only clean way to change bid documents before bids are due: numbered, in writing, to every bidder.

Check every bid's acknowledgments before you level, because a bid that missed an addendum may not price the changed work.

See how trade bids handle addenda

1. FAR 14.208, Amendment of invitation for bids — Acquisition.gov, U.S. General Services Administration. Read October 22, 2026.
2. FAR 14.405, Minor informalities or irregularities in bids — Acquisition.gov, U.S. General Services Administration. Read October 22, 2026.