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How to read a tender

Addenda on Ontario Tenders: How to Track Them and What to Do When a Closing Date Moves

Bid Scout · Tue Oct 27, 2026 · 7:08 AM ET

You register as a plan taker, download the drawings and start pricing. Then the addenda start arriving: a revised panel schedule, an answer to someone else's question, a new site plan, a closing date pushed back a week. On a busy job they can keep coming until just before closing.

Here's how addenda work on Ontario municipal tenders, what recent electrical bids show about them, and a simple routine so a late change doesn't sink your bid.

What an addendum is, and how you hear about it

An addendum is the buyer's written change to the tender documents. Thunder Bay's standard Information to Tenderers says any and all changes to the contract documents are issued as addenda and posted to the City's bidding system, and that verbal answers are only binding once they're confirmed by written addenda.

Oshawa's Bid Submission Procedure describes the notice side: an addendum is posted to the bidding system and an email goes out automatically to all plan takers. That's the practical reason to register as a plan taker rather than just reading the public listing. If you aren't on the list, nobody tells you.

How many addenda to expect

On some bids, one. On others, ten or more. The counts below come from the public document list on each buyer's bids&tenders page, checked on Monday, October 26, 2026:

The lesson from Newmarket: an addendum can land after you think you're done. Read the whole list, not just the newest file.

When the closing date moves

Closing dates move by addendum too. Oshawa's procedure says that when a closing date has to be extended, the City must allow time for bidders to review the new information and ask further questions. Recent electrical bids show how common it is:

A later closing date is extra time, but it usually means something in the documents changed. Before you relax, read what changed, and check whether the question deadline moved as well.

Acknowledge every addendum, every time

This is the step that knocks bids out. Thunder Bay's template says tenderers must acknowledge each addendum, and any applicable attachment, by checking a box in the bidding system before closing. A submission without that evidence is deemed incomplete and won't be accepted.

It goes further. If an addendum is issued after you've submitted, the system withdraws your bid and marks it incomplete. You have to acknowledge the addendum and resubmit before closing. Thunder Bay recommends checking for addenda right up until closing time.

A routine that works

  1. Register as a plan taker the day you decide to look at a bid, so the notices reach you.
  2. Keep a one-line log per bid: addendum number, date posted, what it changed, and who on your team re-priced it.
  3. When the closing date moves, update your calendar and re-check the question deadline.
  4. Go back to the bid page on the morning of closing, and again just before you submit.
  5. After you submit, keep watching until the bid closes, in case a late addendum pulls your submission back.

If the buyer page and your notes disagree, trust the buyer page.

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