The implementation of innovative materials for energy saving is a main focus in the building sector. In this context, aerogels are often indicated as really promising materials. In particular, aerogel blankets have already shown potential in many retrofitting projects while the development of glazing systems with aerogel is still at the research stage. This paper describes the development of double pane glazing systems with monolithic silica aerogel in their cavity. The results of a multi-disciplinary analysis, including thermal and lighting tests, are reported. This new monolithic aerogel window is then used in the retrofitting project of an educational building completed in the 1960s. A level 3 energy audit was conducted through measurements of the envelope transmissibility, the building air-tightness, and several indoor environmental parameters. The energy audit provided data for an accurate energy model and to perform a detailed analysis of the energy consumptions of the building. Several energy saving measures for the case study building were then investigated. Lighting and energy simulations allowed comparisons of different designs of the aerogel window with the intent to guarantee sufficient daylight, clear perception of the external environment, and high energy saving. Finally, this paper provides a sensitivity analysis of the investigated retrofitting strategies in different climates, with the intent to show where aerogel windows may represent a valuable retrofitting choice. (C) 2015 Elsevier Ltd. All rights reserved.