Table 5.14 – Visible Alarms and Alterations to Existing Facilities
Current Guidelines:  
4.1.3  Accessible Buildings: New Construction.
Accessible buildings and facilities shall meet the following minimum requirements: . . .

(14)  If emergency warning systems are provided, then they shall include both audible alarms and visual alarms complying with 4.28. . . .

4.1.6  Accessible Buildings: Alterations.
(1) General.  Alterations to existing buildings and facilities shall comply with the following: . . .

(b)  If existing elements, spaces, or common areas are altered, then each such altered element, space, feature, or area shall comply with the applicable provisions of 4.1.1 to 4.1.3 Minimum Requirements (for New Construction). . . .
Final Revised Guidelines:  
202.3  Alterations.  Where existing elements or spaces are altered, each altered element or space shall comply with the applicable requirements of Chapter 2.

215.1  General.  Where fire alarm systems provide audible alarm coverage, alarms shall comply with 215.
Exception:  In existing facilities, visible alarms shall not be required except where an existing fire alarm system is upgraded or replaced, or a new fire alarm system is installed.
Model Codes & Standards
IBC 2000:  Section 907.9.1 has an equivalent exception for visible alarms in alterations to existing facilities.

IBC 2003:  Section 907.9.1 has an equivalent exception for visible alarms in alterations to existing facilities.