Portland's Historic Preservation Ordinance does not review or restrict use. Your building does not have to look exactly the same after you have made alterations, as long as the changes have been approved. If your building will look exactly the same after you have done your w6rk, the project does not require review. The work would be considered maintenance. There ore many different materials and methods that may be used for most preservation projects.
Repair is preferable over replacement and is often less expensive.
A property may be considered historic if it is at least 50 years old and retains its distinguishing architectural character and design intent. A historic building need not be a pristine example of its architectural style, but should retain a significant portion of its character-defining elements. Character-defining elements include the overall shape of the building, its materials, craftsmanship, decorative details, interior spaces and features, as well as the various aspects of its site and environment. Alterations to non-contributing structures will be reviewed with same standards as those used for review of contributing structures. However the standards are applied more liberally by the Committee because there is little historic character to conserve.