36 C.F.R. § 67.7 – Standards for rehabilitation.

(a) The following Standards for Rehabilitation are the criteria used to determine if a rehabilitation project qualifies as a certified rehabilitation. The intent of the Standards is to assist the long-term preservation of a property's significance through the preservation of historic materials and features. The Standards pertain to historic buildings of all materials, construction types, sizes, and occupancy and encompass 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. To be certified, a rehabilitation project must be determined by the Secretary to be consistent with the historic character of the structure(s) and, where applicable, the district in which it is located.
(b) The following Standards are to be applied to specific rehabilitation projects in a reasonable manner, taking into consideration economic and technical feasibility. (The application of these Standards to rehabilitation projects is to be the same as under the previous version so that a project previously acceptable would continue to be acceptable under these Standards.)
1. (1) 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.
2. (2) 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.
3. (3) 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.
4. (4) Most properties change over time; those changes that have acquired historic significance in their own right shall be retained and preserved.
5. (5) Distinctive features, finishes, and construction techniques or examples of craftsmanship that characterize a historic property shall be preserved.
6. (6) 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.
7. (7) 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.
8. (8) Significant archeological resources affected by a project shall be protected and preserved. If such resources must be disturbed, mitigation measures shall be undertaken.
9. (9) 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.
10. (10) 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.
(c) The quality of materials and craftsmanship used in a rehabilitation project must be commensurate with the quality of materials and craftsmanship of the historic building in question. Certain treatments, if improperly applied, or certain materials by their physical properties, may cause or accelerate physical deterioration of historic buildings. Inappropriate physical treatments include, but are not limited to: improper repointing techniques; improper exterior masonry cleaning methods; or improper introduction of insulation where damage to historic fabric would result. In almost all situations, use of these materials and treatments will result in denial of certification. 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 will result in denial of certification. For further information on appropriate and inappropriate rehabilitation treatments, owners are to consult the Guidelines for Rehabilitating Historic Buildings published by the NPS. “Preservation Briefs” and additional technical information to help property owners formulate plans for the rehabilitation, preservation, and continued use of historic properties consistent with the intent of the Secretary's Standards for Rehabilitation are available from the SHPOs and NPS WASO. Owners are responsible for procuring this material as part of property planning for a certified rehabilitation.
(d) In certain limited cases, it may be necessary to dismantle and rebuild portions of a certified historic structure to stabilize and repair weakened structural members and systems. In such cases, the Secretary will consider such extreme intervention as part of a certified rehabilitation if:
1. (1) The necessity for dismantling is justified in supporting documentation;
2. (2) Significant architectural features and overall design are retained; and
3. (3) Adequate historic materials are retained to maintain the architectural and historic integrity of the overall structure.
  Section 47 of the Internal Revenue Code of 1986 exempts certified historic structures from meeting the physical test for retention of external walls and internal structural framework specified therein for other rehabilitated buildings. Nevertheless, owners are cautioned that the Standards for Rehabilitation require retention of distinguishing historic materials of external and internal walls as well as structural systems. In limited instances, rehabilitations involving removal of existing external walls, i.e., external walls that detract from the historic character of the structure such as in the case of a nonsignificant later addition or walls that have lost their structural integrity due to deterioration, may be certified as meeting the Standards for Rehabilitation.
(e) Prior approval of a project by Federal, State, and local agencies and organizations does not ensure certification by the Secretary for Federal tax purposes. The Secretary's Standards for Rehabilitation take precedence over other regulations and codes in determining whether the rehabilitation project is consistent with the historic character of the property and, where applicable, the district in which it is located.
(f) The qualities of a property and its environment which qualify it as a certified historic structure are determined taking into account all available information, including information derived from the physical and architectural attributes of the building; such determinations are not limited to information contained in National Register or related documentation.