Due to the need of good thermal performance, external wall insulation (EWI) is usually made of materials that are not fire resistant and sometimes flammable. That restricts its application to a particular circumstance such as limited building height. Hence, a material with good thermal insulation and fire resistance performance would allow EWI to be more widely applied. This paper introduces a novel material: a silica-based aerogel porous board, which differs itself from mainstream products available in the market because of its outstanding properties, such as low density, high surface area, low thermal conductivity and superhydrophobicity. Herein, its thermal insulation and fire-resistant performance were tested and compared with commercial products. The cone calorimeter analysis results indicated that the aerogel porous board could improve the fire resistance performance. Moreover, the evaluation of thermal insulation performance suggested that the application of an aerogel porous board on the external stone wall of existing buildings can decrease the U-value by 60%. Through the detailed insight into the case-study, it is quite clear that the carbon impact of building stock could be greatly reduced by means of a coherent set of building envelope retrofitting actions based on this innovative heat insulation material, without compromising the fire safety.