Rehabilitation projects must meet the following Standards, as interpreted by the National Park Service, to qualify as “certified rehabilitations” eligible for both the Federal and Maine tax credits. The Standards are applied to projects in a reasonable manner, taking into consideration economic and technical feasibility.

The Standards apply to historic buildings of all periods, styles, types, materials, and sizes. They apply to both the exterior and the interior of historic buildings. The Standards also encompass related landscape features and the building’s site and environment as well as attached, adjacent, or related new construction.

A property shall be used for its historic purpose or be placed in a new use that requires minimal change to the defining characteristics of the building and its site and environment.
The historic character of a property shall be retained and preserved. The removal of historic materials or alteration of features and spaces that characterize a property shall be avoided.
Each property shall be recognized as a physical record of its time, place, and use. Changes that create a false sense of historical development, such as adding conjectural features or architectural elements from other buildings, shall not be undertaken.
Most properties change over time; those changes that have acquired historic significance in their own right shall be retained and preserved.
Distinctive features, finishes, and construction techniques or examples of craftsmanship that characterize a historic property shall be preserved.
Deteriorated historic features shall be repaired rather than replaced. Where the severity of deterioration requires replacement of a distinctive feature, the new feature shall match the old in design, color, texture, and other visual qualities and, where possible, materials. Replacement of missing features shall be substantiated by documentary, physical, or pictorial evidence.
Chemical or physical treatments, such as sandblasting, that cause damage to historic materials shall not be used. The surface cleaning of structures, if appropriate, shall be undertaken using the gentlest means possible.
Significant archeological resources affected by a project shall be protected and preserved. If such resources must be disturbed, mitigation measures shall be undertaken.
New additions, exterior alterations, or related new construction shall not destroy historic materials that characterize the property. The new work shall be differentiated from the old and shall be compatible with the massing, size, scale, and architectural features to protect the historic integrity of the property and its environment.
New additions and adjacent or related new construction shall be undertaken in such a manner that if removed in the future, the essential form and integrity of the historic property and its environment would be unimpaired.

Guidelines for Rehabilitating Historic Buildings

The Guidelines from the National Park Service assist in applying the Standards to rehabilitation projects in general; consequently, they are not meant to give case-specific advice or address exceptions or rare instances. These Guidelines are also available in PDF format.

The Guidelines on Sustainability for Rehabilitating Historic Buildings stress the inherent sustainability of historic buildings and offer specific guidance on “recommended” rehabilitation treatments and “not recommended” treatments, which could negatively impact a building’s historic character. These Guidelines are also available from the National Park Service as an interactive web feature.