Due to concerns about potential airborne chemical and biological (chembio) releases in or near buildings, building owners and managers and other decision makers are considering retrofitting buildings to provide some degree of protection against such events. A wide range of technologies and approaches are being proposed with varying levels of efficacy and cost, as well as varying degrees of applicability to particular buildings and ventilation systems. This document presents the results of an effort to evaluate chembio retrofit options for buildings. A number of retrofit options are identified, and their potential to protect building occupants from a number of generic contaminant releases is evaluated using building airflow and contaminant transport modeling. In addition, a case study is presented in which specific retrofit options were considered for two actual buildings and pre-installation designs and cost estimates were developed. Based on the analyses performed, the results of the case study and other available information, guidance on the application and effectiveness of various retrofits are presented. An economic analysis software tool employing life cycle cost analysis techniques was developed as part of this project, and its use is described in an appendix to this report. The retrofit options considered fall into two categories, the first being stand-alone technologies or devices such as enhanced particulate filtration that are installed and implemented as purchased. The second category includes retrofit approaches that employ operational strategies or building modifications to increase building protection, such as outdoor air purging or building envelope airtightening.