Definition
An addendum is an official amendment to the bid documents — the plans, specifications, quantities, or instructions to bidders — issued by the party soliciting bids after the package goes out but before the bid deadline. On a heavy-civil package, addenda revise pipe materials, adjust pay-item quantities, clarify ambiguous details, push the due date, or answer a question one bidder raised that every bidder now sees. Each addendum is numbered in sequence (Addendum 1, Addendum 2, and so on) and becomes part of the contract once bids are submitted.
The acknowledgment requirement is what makes addenda matter to you as the general contractor reviewing the bids you receive. A subcontractor is expected to confirm in writing — usually on the bid form — that it priced every addendum issued. A sub that fails to acknowledge an addendum may have bid an outdated scope, and depending on the rules of the procurement, that omission can render the bid non-responsive.
A worked example
Say you have a storm-drainage package out to five subs, and three days before bids are due you issue Addendum 3, which changes a 36-inch pipe run from reinforced concrete pipe (RCP) to high-density polyethylene (HDPE). The change drops the installed cost from about $420,000 to about $355,000 — a $65,000 swing. Four subs acknowledge Addendum 3 and price the HDPE; their bids cluster between $348,000 and $361,000. The fifth sub returns the apparent low bid at $338,000 but its form shows no acknowledgment of Addendum 3, and its line items still carry RCP. That bid priced superseded documents. It is non-responsive, and the real low responsive bid is the $348,000 quote — not the $338,000 number on top of the stack.
Why it matters when you evaluate sub bids
Missed addenda quietly poison a bid tab. The bid that ignores an addendum is almost always the apparent low number, because it is priced against the cheaper or smaller scope the addendum replaced. If you rank on raw totals, you reward the sub that bid the wrong documents and set yourself up for a change order the day you hand off the corrected plans. Before you score price or pick an award, you have to confirm that every bidder priced the same, fully amended scope — a bidder that didn't acknowledge an addendum is not responsive and cannot be leveled against the ones that did. Catching it is the difference between an honest apples-to-apples comparison and a tab built on bids that never measured the same job.
How Bid Reasoner handles it
Bid Reasoner reads each bid PDF and levels the line items to your scope of work, so when one sub still carries RCP after Addendum 3 moved the run to HDPE, that shows up as a scope-coverage gap, listed by pay-item code. The two-way gap analysis surfaces both the line a sub is missing and the line it priced that no longer belongs, and, if the sub bid through the bidder portal, the Bid Inbox shows it has not acknowledged every addendum (Addenda 2/3, say), a count the AI also sees when it judges the compliance score. The total-bid rule won't catch this one on its own: at about 5% under the median of the five bid totals, the RCP bid sits well inside the rule's 20% band, which is why the scope and acknowledgment checks matter. You see the off-scope items listed against that bid and decide whether it is non-responsive. If your award differs from the recommendation, the award page asks for a category and a reason, and both print in the award memo — one of the 15 Word documents the award page builds, alongside 3 Excel reports and a PDF packet.