What an addendum is
An addendum is a written change to the bid documents, issued before bids are due. It can revise drawings, revise the spec, answer bidder questions or move the bid date. It becomes part of the contract. You are bound by it whether you read it or not.
Steps to take
- Download the addendum and every attachment.
- Read the narrative from start to finish, not only your section.
- Check for a new bid date or time.
- Find the reissued sheets. Compare each to the sheet you counted.
- Find the spec changes. Read the new text against the old.
- Read the answers to bidder questions. Some change scope in one sentence.
- Update the takeoff. Mark each changed line with the addendum number.
- Update the price and the supplier quotes.
- List the addendum in your proposal.
Where changes hide
- A change to another trade's sheet that moves or removes your item.
- A revised schedule with no cloud on the plan.
- A substitution approval that adds an acceptable manufacturer.
- A changed alternate.
- A new sheet added to the set.
- A pre-bid meeting answer that reassigns work between trades.
Do not trust the clouds alone
Revision clouds show where the designer says the sheet changed. Sometimes a change is not clouded. On the sheets that matter most to you, compare the old sheet and the new sheet side by side.
Late addenda
Addenda often arrive in the last days before the bid. Check the plan room each morning in the final week, and again on bid day. If one arrives after you send your number, tell the GC in writing whether your price changes.
Naming the addenda in your proposal tells the GC what your number covers. On many public bid forms, the GC must acknowledge every addendum. A sub bid that names them all is easier to use.
Bidding and estimating · Updated 11 Nov 2026