Built in 1864, the library of the Protestant Church of the Canton of Vaud is a Swiss cultural asset of national importance. After serving as a theological research centre for centuries, the impressive building was extensively renovated in 2011. We were able to preserve 17 original windows and double them with modern insulating glass. The remaining 27 windows were reconstructed and insulated according to historical models. After digitising the library collection, the imposing building now serves as the secretariat of the Protestant church.