Building modifications. The senior affordable housing project shall consist primarily of the adaptive reuse of an existing building whose primary portion is over 50 years old. The City Council, either in its zoning designation or in its special permit, may authorize modifications to the existing building to enhance its adaptive reuse for senior affordable housing including, for example, modification of the roofline to better accommodate residential units, provided that in no event shall the existing height of the building be increased by more than eight feet, and modification of the line of outer walls to accommodate better layout and light and air for dwelling units, or for the inclusion of additional common spaces. Authorized additions to the building(s) shall not exceed 10% of the gross floor area of the building(s). Exterior alterations shall comply with any applicable requirements for a certificate of appropriateness under Chapter 134 of the Code. In no event shall a senior affordable housing project include any new freestanding buildings housing residential units. The City Council may authorize the construction of outbuildings for accessory functions, such as garages, an exterior generator, maintenance shed(s), and the like.