Over the past decades, the seismic vulnerability assessment and strengthening of existing reinforced concrete buildings with masonry infills have been topics of great interest for engineers worldwide. Often, such buildings have been designed disregarding lateral loads and the influence of masonry infills on the local and global response, resulting in severe structural damage or collapses in earthquakes. In the context of improving the seismic performance of old reinforced concrete framed buildings, a seismic retrofit scheme based on cross-laminated timber panels is studied herein. The effectiveness of the proposed retrofit method has been previously investigated by the authors through advanced numerical modelling. This paper presents the results from a preliminary experimental campaign on materials (e.g., diagonal compression tests on wallettes) and connections (e.g., timber-to-timber and timber-to-concrete connections) carried out to improve the predictive accuracy of the numerical models in simulating the coupled behaviour of old reinforced concrete elements, masonry infills and retrofitting materials. The results of the updated numerical analysis appear promising, showing that the proposed retrofit scheme considerably improves the seismic behaviour of reinforced concrete framed structures.