An architect's supplemental instruction -- more commonly referred to as an ASI -- is similar to a contract addendum. Just as a contract addendum allows you to provide additional information or make small changes in a contract without entirely rewriting it, an ASI allows an architect to provide additional instructions or make minor changes without having to rework the entire construction plan.
Definition and Usage
An ASI is a document authorized for use by the American Institute of Architects under paragraph 7.4 of A201-1997. An architect can only use this form to resolve informational issues or make minor changes that do not affect a construction project's budget or alter the construction timeline. For example, the architect might realize that a drawing or photograph will make the instructions clearer, or might wish to provide more detail in an existing specification. However, use of an ASI would not be the appropriate way to include new specifications that alter the plan in any way.