The on-site assessment of dynamic properties of building envelopes is often necessary for accurate analysis of building performance. The main difficulty is that the experiment has to be carried out with unknown thermal loadings on the wall under test. We present a methodology able to address this difficulty: it consists in identifying all-at-once both the sought parameters; i.e., the heat conductivity and capacity, and the unknown thermal loadings. They are obtained as solutions of an inverse problem using only standard temperature measurements as input data. The numerical performance of the methodology, applied to homogeneous walls, is assessed.