Here's the section that deals with "existing" conditions.............
"#4.1.6.(3) Special Technical Provisions for Alterations to Existing Buildings and Facilities:
(a) Ramps: Curb ramps and interior or exterior ramps to be constructed on sites or in existing buildings or facilities where space limitations prohibit the use of a 1:12 slope or less may have slopes and rises as follows:
(i) A slope between 1:10 and 1:12 is allowed for a maximum rise of 6 inches.
(ii) A slope between 1:8 and 1:10 is allowed for a maximum rise of 3 inches. A slope steeper than 1:8 is not allowed."