FOREWORD Addendum a deletes the definition of ??alteration?? from Section 3 of Standard 90.4 and defaults to the definition used in Standard 90.1 (which is reproduced in Standard 90.4@ Annex 1). This change aligns Standard 90.4??s use of ??alteration?? with how the word is defined in codes. Specific requirements for alterations to data centers are addressed through existing language in Section 4.2.1.3 on a general basis and in Section 6.1.1.3 for mechanical systems. These requirements remain unchanged and are included her to provide context. Criteria for alterations to electrical systems in existing data centers are added through Section 8.1.4. Criteria for additions to electrical systems in existing data centers will be added by addendum b to Standard 90.4. A new Section 8.1.3 is created here as a placeholder for that content. Note: In this addendum@ changes to the current standard are indicated in the text by underlining (for additions) and strikethrough (for deletions) unless the instructions specifically mention some other means of indicating the changes.