An addendum is the formal written instrument through which the architect modifies the bidding documents after they've been issued but before bids are received. Once bid documents go out, anything that changes them, adds to them, or corrects them must come through an addendum. There is no other mechanism.

This matters because the bid documents define what contractors are pricing. If a contractor bids on outdated information because they didn't receive an addendum, their bid doesn't represent what the project actually requires. That creates a contract dispute before construction even starts. Or it creates a situation where the apparent low bidder priced something different from everyone else, and the comparison isn't apples-to-apples.

For the ARE, this topic is squarely in Objective 1.3: analyzing aspects of the contract or design to adjust project costs. Addenda are the primary tool for cost adjustments during bidding. They can correct errors in the documents (which may add or reduce cost), respond to pre-bid questions (which may clarify scope), or issue formal VE alternates (which directly affect the contract sum). Understanding when to issue them, how to distribute them, and what happens contractually when they arrive close to bid day is essential.

The key distinction: an addendum changes the bidding documents and becomes part of the contract. It's not a courtesy correction. It's a legally binding modification. Every bidder must acknowledge receipt of every addendum in their bid, or the bid may be considered non-responsive.