Tender addenda shouldn't cost you a night: how Estimator+ does it

Why does an addendum still wreck your week?

An addendum shouldn't cost you a night. In Estimator+ you drop it in the tender folder, tell Claude or ChatGPT it's there, and the AI does the document control: it works out which drawings changed and swaps them in. Your evening goes on what the changes do to the price.

You know how it goes. It's Thursday arvo, the tender closes Tuesday, and Addendum 02 lands with six revised drawings and a two-line transmittal. Now someone has to work out which sheets changed, swap them in, check every quantity they touched and let the right subbies know.

None of that is hard. It's fiddly, though, and fiddly is where the mistakes hide. The expensive one is a takeoff or a subbie still working off Rev C after Rev D is out. That's how a wall the architect deleted on Thursday ends up in your price on Tuesday.

What happens when you drop it in the folder?

Estimator+ connects to your tender folder, the one on your computer. For most builders that's the company-drive folder synced to it, something like D:\Tenders\Riverbend Aged Care. When Addendum 02 arrives, you save it where you'd normally put it, say Addenda/Addendum 02, and tell the AI it's in.

It reads the addendum, matches each new revision to its old drawing, uploads the new drawings and supersedes the old ones. The takeoff and the subcontractors work off the current set from then on.

A couple of things it won't do. It never moves, renames or deletes your files, so Addendum 02 stays exactly where you saved it. The only place it writes is the _Estimator+ folders it keeps inside the tender folder.

If the addendum revises a spec section or a schedule, that stays on your drive too, and the AI reads it there with the rest of the specs. Estimator+ holds the sheet pictures, the measurements and the estimate.

How does the takeoff stay on the current set?

Before the AI measures a line, it reads the specification, schedules, general notes, contract terms, project scope and every addendum. Then it measures the current revision of every sheet, with each addendum applied first. So a wall Addendum 02 deleted never gets drawn, and a door that changed type gets counted as its new type.

Here's the bit that makes checking it bearable. The AI never types a quantity. Every quantity is a shape (an outline, a line, a dot) or a pin on a published sheet, and Estimator+ works out the number from that shape and the sheet's printed scale. After an addendum you're looking at shapes on Rev D, with each line's name sitting on the plan.

It also flags where two drawings disagree, which happens a lot with addenda. A plan gets reissued and the elevation showing the same window doesn't. The AI assumes, says what it assumed and keeps going, then asks you the open questions together at the end.

Example: Addendum 02 and its six drawings

This one's made up. A three-storey medical centre, closing Tuesday, and Addendum 02 revises six drawings. Each new revision gets matched to its old drawing and uploaded, and the old one's superseded. Here's what each change means after that.

Six trades get a revision note for their trade, on the link they already have. The W05 question goes in the list at the end, so you can send it to the architect with everything else.

Lump sum or rate: which one moves?

This is where an addendum actually costs money. Take that deleted partition. Say the wall linings line came to 412 m² on Rev C. The wall was 6.0 m long and 2.7 m high, lined both sides, so 32.4 m² comes out and the line measures 379.6 m² on Rev D.

Two plasterers priced it, ex GST. One gave you a lump sum of $19,776, worked out on the 412 m². The other gave a rate of $46.50 a m², which came to $19,158 on Rev C.

In Estimator+ a rate follows the live quantity, so the second quote now reads $17,651.40 on the 379.6 m². A lump sum stays fixed to the quantity it was priced on, so the first one still says $19,776 against 412 m². That's your cue to ring them. They might sharpen it, or tell you the wall was never in their number. Either way, the call's yours.

By the time you ring, they've already got the revision note on their Sendout link. Estimator+ never sends mail itself, so if you want them to hear about it this arvo, that's an email from your own inbox. The AI drafts reminders in your Outlook or Gmail and you press send.

What about revising your own price?

Sometimes the addendum lands after you've submitted, or the client comes back with questions and you put in a revised price. Your submission goes out as a branded PDF with a revision number on it, and every past revision stays open to you as a full workspace.

So when the client's QS asks why Rev 1 came in lower than Rev 0, you open Rev 0, see what changed and answer properly, without rebuilding the story from a pile of emails.

So what's the catch?

A few honest ones.

• You still tell it. The flow is: drop the addendum in the folder, then tell Claude or ChatGPT it's there.
• It reads PDF drawings, not CAD or BIM models. A revision that only turns up as a model file is one for you.
• It doesn't make the money calls. Which lump sum to chase, and whether to carry a subbie's old price, is still you.
• You check its work, right off the current sheet, where every shape carries its line's name.

If you want the rest of the tender picture, our posts on comparing subcontractor quotes and tender exclusions and qualifications pick up from here. And the AI takeoff post goes deeper on how the measuring works.

Got an addendum-heavy job on right now? Book a demo and we'll run the takeoff on one of your tenders, at your office or on Google Meet.