The following rehabilitation and maintenance standards shall be used by local review boards as minimum requirements for determining whether or not an historic property is eligible for special valuation and whether or not the property continues to be eligible for special valuation once it has been so classified:

(1) Rehabilitation.

(a) Every reasonable effort shall be made to provide a compatible use for an historic property which requires minimal alteration of the building, structure, or site and its environment, or to use an historic property for its originally intended purpose.

(b) The distinguishing original qualities or character of a building, structure or site and its environment shall not be destroyed. The removal or alteration of any historic material or distinctive architectural features should be avoided when possible.

(c) All buildings, structures, and sites shall be recognized as products of their own time. Alterations that have no historical basis and which seek to create an earlier appearance shall be discouraged.

(d) Changes which may have taken place in the course of time are evidence of the history and development of a building, structure, or site and its environment. These changes may have acquired significance in their own right, and this significance shall be recognized and respected.

(e) Distinctive stylistic features or examples of skilled craftsmanship which characterize a building, structure, or site shall be treated with sensitivity.

(f) Deteriorated architectural features shall be repaired rather than replaced, whenever possible. In the event replacement is necessary, the new material should match the material being replaced in composition, design, color, texture, and other visual qualities. Repair or replacement of missing architectural features should be based on accurate duplication of features, substantiated by historic, physical, or pictorial evidence rather than on conjectural designs or the availability of different architectural elements from other buildings or structures.

(g) The surface cleaning of structures shall be undertaken with the gentlest means possible. Sandblasting and other cleaning methods that will damage the historic building materials shall not be undertaken.

(h) Every reasonable effort shall be made to protect and preserve archaeological resources affected by, or adjacent to, any project.

(i) Contemporary design for alterations and additions to existing properties shall not be discouraged when such alterations and additions do not destroy significant historical, architectural or cultural material, and such design is compatible with the size, scale, color, material, and character of the property, neighborhood, or environment.

(j) Wherever possible, new additions or alterations to structures shall be done in such a manner that if such additions or alterations were to be removed in the future, the essential form and integrity of the structure would be unimpaired.

(2) Maintenance.

(a) Buildings and structures shall not be allowed to deteriorate beyond the point where routine maintenance and repair will return them to good condition.

(b) Buildings shall be kept in a safe and habitable condition at all times. Structural defects and hazards shall be corrected. Any condition which constitutes a fire hazard shall be eliminated.

(c) Buildings shall be protected against ongoing water damage due to defective roofing, flashing, glazing, caulking, or other causes. Moisture condensation resulting from inadequate heat or ventilation shall be eliminated if present at levels sufficient to promote rot or decay of building materials.

(d) Deteriorated exterior architectural features and any broken or missing doors and windows shall be repaired or replaced.

(e) Painted exterior surfaces shall be maintained and repainted as necessary to prevent a deteriorated appearance or damage to the substrate. Exterior masonry surfaces shall be tuck pointed where required to maintain the mortar in sound condition. Finished tuck pointing shall match the original mortar joint in hardness and appearance.