The ten Secretary's of Interior Standards for Rehabilitation are to be applied to specific rehabilitation projects in a reasonable manner, taking into consideration economic and technical feasibility.
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 be 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. Click here to access pdf documents on cleaning historic materials.
Significant archeological resources affected by a project shall be protected and preserved. If such resources must be disturbed, mitigation measures shall be undertaken.
New addition, 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 manner that if removed in the future, the essential form and integrity of the historic property and its environment would be unimpaired.
As stated in the definitions of the Treatments of Historic Properties the treatment "rehabilitation" assumes that at least some repair or alteration of the historic building will be needed in order to provide for an efficient contemporary use; however, these repairs and alteration must not damage or destroy materials, features or finishes that are important in defining the building's historic character. For example, certain treatments—if improperly applied—may cause or accelerate physical deterioration of historic building.
This can include using improper re-pointing or exterior masonry cleaning techniques, or introducing insulation that damages historic fabric. In almost all of these situations, use of these materials and treatments will result in a project that does not meet the Standards. Similarly, exterior additions that duplicate the form, material, and detailing of the structure to the extent that they compromise the historic character of the structure (confusing the viewer with what is historic and what is new) will fail to meet the Standards.