Except as otherwise provided in this part, in reviewing and acting upon applications for certificates of appropriateness, the historic properties commission shall apply the same standards and take into account the same considerations as set forth in section 7-147f for use by historic district commissions in reviewing applications for certificates of appropriateness affecting historic districts. In passing upon the appropriateness of alterations to earthworks or sites of historic or archaeological importance, the commission shall consider, in addition to any other pertinent factors, their value and significance, size, design, arrangement, texture and materials. In its deliberations, the historic properties commission shall act only for the purpose of controlling the erection or alteration of buildings, structures, objects, sites or parking that are incongruous with the historic or architectural aspects of the historic property.