Yeah, “addendum” is a fancy word, derived from Latin. The Latin background is the reason the plural is “addenda.” But really, what’s important is that it means something that’s added. In construction, it’s something added to or deleted from the contract, or something that revises the contract. Remember, the contract includes the contract documents – the drawings, the specifications, the agreements, etc.
The Project Resource Manual – CSI Manual of Practice, published by the Construction Specifications Institute, says that addenda are “written or graphic instruments issued to clarify, revise, add to, or delete information in the procurement documents or in previous addenda.” It goes on to say that “it is imperative that participants to the construction process properly account for these changes by posting or documenting the appropriate addenda information in the affected areas of the drawings and specifications.”
So, what is the proper procedure for design professionals when issuing addenda?
Remember that you are MODIFYING THE CONTRACT DOCUMENTS. The easiest way to think about this is to put yourself in the shoes of the people building the project. They are going to take your addendum, cut out the additions from the paper document of the addendum, and tape them over the things in the originally-issued documents that changed. They will strike through the things that your addendum deletes. When you, the design professional, issue addendum changes (or ANY modifications to the contract documents, actually) you NEED to actually MODIFY THE DOCUMENTS. If an Addendum item changes something about the contract documents, you have to actually modify the documents. You can’t just answer bidder questions without actually modifying your documents, the contract documents, to back up the answer to your question.
If you can’t put yourself in the shoes of the contractor, put yourself in your own future shoes. How does it feel when a question comes up late in the project, and you think that you may have changed something a while ago, but now you can’t remember what changed, and there is no official documentation of that modification? Feels bad. Looks bad to your client.
Do yourself, and your clients, and the contractor, a favor. Issue proper and complete addendum modifications. Change the actual documents, and, even if you don’t issue a whole drawing, document exactly what the change is, so that the intent is unambiguously communicated to all the participants in a construction project. You’ll probably thank yourself later!
Comments From a Spec Writer 
I forgot to mention the best way to think about every modification that you issue: Put yourself in your future shoes again, and think about those electronic RECORD DOCUMENTS that you may need to prepare after the project is completed.
Don’t just answer questions from bidders with short answers – track every single modification back to a specific portion of a specific document.
For example, if one of the bidder questions is, “What is the material of the interior window sills?” DO NOT issue an addendum item that reads “Window sills are to be plastic-laminate.” Instead, respond with a few addendum items. One should read someting like, “Revise Specification Section 06 40 23 Interior Architectural Woodwork to add plastic-laminate window sills as indicated in the attached revised specification section.” (And then, of course, issue the revised spec section with the addendum.)
You’ll need at least one addendum item for the drawings, probably one that modifies a detail. For example: “Revise Detail 8/A-512 to add a note pointing at the window sill that reads, ‘Plastic-laminate window sill.'”
Yes, it takes more time to do this than to answer questions with brief Addendum items. And, yes, during the bidding period we have less time than at any other. However, it really pays off to spend a little extra time up front in this way. And it’ll help a lot if you do have to do those electronic record documents at the end.
A follow-up:
Substitution Request Forms are NOT Contract Documents.
The proper procedure for approving a Substitution Request prior to the bid is to modify the documents and issue an Addendum that notifies ALL BIDDERS of the modification.
The proper procedure for modifying the documents is in the post above – track every single modification back to a specific portion of a specific document. Don’t say something like “Substitution Request from So-and-So is approved.” That is NOT modifying the contract documents.
Frequently I am asked to reissue specifications for construction that include Addenda revisions. The question always comes up as to how to indicate Addendum revisions in the Issued for Construction Project Manuals. Sometimes I am asked to use bold-underlined text for added text and strikeout for deleted text, each of which is followed by a parenthetical reference to the Addendum that promulgated the revision. But sometimes I am requested to just change the Issued for Construction Project Manuals to indicate the Addendum revisions as plain text because they are now included as part of the Contract Documents. Another variant is the bold-underlined text is revised to plain text followed by the parenthetical reference to the applicable Addendum. Where text is deleted by Addendum, then the text is removed and replaced by the parenthetical reference to the applicable Addendum.
Are you aware of an industry-accepted method of indicating Addendum revisions in Issued for Construction Project Manuals?
Hi, Steven, I wish I knew of an industry-wide commonly-accepted method for showing changes when issuing specifications for an Issued for Construction set! Like you, I have done this in a variety of ways. Some of the direction I’ve received has come from the owner, and some has come from the architect. Sometimes I’ve been left to my own devices.
One thing that I think we should all be able to agree on is that whatever we do in the specs should be aligned with what we do in the drawings. For example, if in the drawings, the revision clouds are removed, but revision deltas remain, then it would make sense in the specs to change all added text to plain text and actually delete the struck-through text that represented deleted text, but keep a parenthetical reference to the specific addendum number. In another example, if all revision clouds and deltas are removed from the drawings, then in the specs we should change all added text to plain text, delete the struck-through text, and delete parenthetical references to addendum numbers.
I’m curious to know if anyone knows of published standards (by any organization, not necessarily an industry-wide thing) for this.