Addendum (Construction Bidding)
A written change to the bid documents, issued before bids are due.
Quick Answer
An addendum is a written document that modifies the bidding documents after they are issued but before bids are due. It can revise drawings or specifications, answer bidder questions, change the bid date, or add alternates. Addenda become part of the contract documents, and bidders typically must acknowledge each one on the bid form.
The Full Picture
Bid documents often go out before the design is fully settled, and bidder questions reveal errors and gaps. The addendum is the formal way to fix the documents mid-bid while keeping the competition fair: every change goes to every bidder in writing, at the same time.
Mechanically, an addendum is numbered and dated, and it lists changes by document: revised or added drawing sheets, spec section edits, answers to bidder questions, schedule changes, and sometimes updated bid forms. Instructions to bidders usually set a cutoff for issuing addenda before the bid date. If an addendum is significant and lands late, the bid date is often extended so bidders can reprice.
In practice, a GC on a busy bid may receive several addenda in the final week. Each one must be read, routed to the affected trades, and reflected in both the GC's own estimate and the sub bids. A sub who bids off the original drawings instead of Addendum 3 is pricing different work, and that mismatch has to be caught in leveling.
For preconstruction, the hard part is finding what actually changed. A reissued sheet may carry a small cloud or none at all, and a single revised note can move scope between trades. Late addenda compress the time available to find those changes, which is when missed scope slips into a bid. Once the contract is signed, addenda are part of the contract documents and changes after award are handled by change order instead.
Real Examples
Common Misconceptions
People assume: An addendum and a change order are interchangeable.
Actually: An addendum changes the documents before the contract is signed and is priced by all bidders. A change order modifies the signed contract and adjusts price or time after award.
People assume: Acknowledging an addendum on the bid form is a formality.
Actually: On public work, failing to acknowledge a material addendum can make a bid nonresponsive. On any job, acknowledgment signals that the price includes the changes, which matters when a dispute arises later.
People assume: If a sheet is reissued, the changes are clouded.
Actually: Clouding practices vary, and unclouded changes are common. Reliable addendum review compares the new sheet against the previous version rather than trusting the clouds.
Does MeltPlan Solve This?
Partially — adjacentPartially — MeltPlan's Design Review handles drawing revision comparison, which is the hardest part of processing an addendum. It compares revised sheets against the prior set and flags what changed, including changes that were never clouded, so estimators can route them to the right trades. MeltPlan does not issue or distribute addenda; that remains with the design team and GC.
See what changed between drawing revisions →Frequently Asked Questions
What does a construction addendum include?
Typically revised or new drawing sheets, specification changes, answers to bidder questions, schedule or bid date changes, and sometimes new alternates or a revised bid form. Each addendum is numbered and dated.
Why must bidders acknowledge addenda?
Acknowledgment confirms the bid price includes the changes. Bid forms usually list addenda by number, and on public work a missing acknowledgment of a material addendum can disqualify the bid.
Can an addendum be issued right before the bid date?
Instructions to bidders usually set a latest date for issuing addenda. When a significant addendum is issued late, owners commonly extend the bid date so bidders have time to price it.
How should a GC handle addenda during bidding?
Read each one fully, identify every changed sheet and spec section, route changes to affected trades, confirm subs are bidding the current addendum, and update the GC's own estimate. Leveling should check that every bid acknowledges the latest addendum.