24 CFR §990.260

1. (a)PHAs that own and operate 250 or more dwelling rental units under title I of the 1937 Act, including units managed by a third-party entity (for example, a resident management corporation) but excluding section 8 units, are required to operate using an asset management model consistent with this subpart.
2. (b)PHAs that own and operate fewer than 250 dwelling rental units may treat their entire portfolio as a single project. However, if a PHA selects this option, it will not receive the add-on for the asset management fee described in § 990.190(f).