Communities Achieving Sustainability Act - Directs the Secretary of Housing and Urban Development (HUD), during a 2-year period, to insure and make commitments to insure rehabilitation loans (including advances during rehabilitation) made by financial institutions in order to assist in the rehabilitation of 1- to 4-family structures used primarily for residential purposes.

Limits insurable rehabilitation loans to investors who do not intend to occupy the structure in question but obtain a rehabilitation loan for the purpose of appreciation or production of income with respect to the structure.

Allows mortgage insurance for up to four such structures during a calendar year.

Prohibits such mortgages from exceeding 90% of the appraised value of the structure in question.

Requires the single premium payment due at the time of insurance to be increased by 10 basis points for any mortgage insured under this Act.