ASI, ASD or Bulletin
It can be confusing what to do when you're in construction but see something that needs to change. Whether that's a code or client compliance issue or a design decision, you'll need to document it officially in some way. That's where ASI's, ASD's or Bulletins come into play. Each are a little different but they all serve similar purposes; to communicate design changes outside of formal document submissions.
So what's the difference? It all comes down to costing and timeline.
ASI's (Architect's Supplemental Instructions) aren't meant to have cost implications and are therefore often used in Design Build contracts with a Guaranteed Maximum Price (GMP).
ASD's (Architect's Supplemental Directive) are a contractual entitlement for architects in certain contract formats that's meant to be done to keep delays in the project from occuring as the client and contractor decide who gets to pay for it and is almost always a result of contractor error or client changes after bidding.
Bulletins are used when a change needs to occur that will impact cost or project timeline. Sent to the contractor to determine if a change order needs to occur. This usually does lead to a change order (unless the cost change is neutral) but doesn't direct the contractor to proceed.
The differences are subtle and they're often used interchangeably depending on the client, contractor, region or building type, but let's break it down so you know the correct term each time and how to use it.
The first major distinction is what type of contract you're using. Design-Build is a lot more collaborative between the GC and Architect and so there's often a bit of leeway with design changes in order to expedite the total construction schedule. ASI's are typically used in Design-Build contracts because they occur only when a change order is not expected. If you're using Design-Bid-Build, you likely won't be able to use an ASI. Even if you don't expect the design change to incur a change order, it'll still need to be documented as a Bulletin so the contractor can determine cost implications.
The next deciding factor is if the change is critical for the project timeline. Ultimately, the GC is responsible for the project timeline and hitting milestones on time, but if a change made by the architect or client occurs, it gives the GC room to shift the blame on others. If you have time and the contract type is Design-Bid-Build, then you'll use a Bulletin to let the GC and all of the subs know that a change is likely coming and to prepare a change order. If the change is critical to the timeline and the GC doesn't have enough time to create a change order or there isn't consensus on who should pay for it, then an Architect's Supplemental Directive is used to direct the GC to go forward with the change and decide who pays for it later. The contractor is contractually (under the AIA contracts) obligated to accede to the architect's directive so this should only be used in very special circumstances where it is absolutely needed.