28 CFR Part 35 Title II Notice of Proposed Rulemaking (NPRM) (published 2008)

(v) Series of smaller alterations. 

(A) The obligation to provide an accessible path of travel may not be evaded by performing a series of small alterations to the area served by a single path of travel if those alterations could have been performed as a single undertaking.

(B)

(1) If an area containing a primary function has been altered without providing an accessible path of travel to that area, and subsequent alterations of that area, or a different area on the same path of travel, are undertaken within three years of the original alteration, the total cost of alterations to the primary function areas on that path of travel during the preceding three-year period shall be considered in determining whether the cost of making that path of travel accessible is disproportionate.

(2) Only alterations undertaken after the effective date of this part shall be considered in determining if the cost of providing an accessible path of travel is disproportionate to the overall cost of the alterations.