This project studies the HPD Design Guideline for Preservation in order to build a retrofit index that separates substantial rehab from gut rehab in existing housing. I translate HPD triggers such as share of units under work, percent of envelope replacement, interior reconstruction scope, and needed EGC or LEED v4 Gold certification into clear quantitative thresh- olds. The resulting index becomes a tool to classify case study renovations by depth of intervention and estimate their impact on energy performance, tenant relocation needs, and long term building preservation.