Thermal accumulation of transparent façade elements can be increased by the direct integration of solid-liquid phase change material (PCM) which brings uncertainties about their spectral transmittance and thermal response. Dynamic changes in the physical state of PCM modify the distribution of heat fluxes and daylight in an indoor environment to address the actual thermal and visual comfort needs of occupants. They have a non-linear nature under the incident solar radiation and heat accumulation process. The intensity of solar radiation is the most important factor due to triggering the phase transmission mechanism of PCM together with increasing the level of spectral transmittance. PCM was integrated into glass blocks as an internal part of a double-skin naturally ventilated façade and exposed to outdoor conditions and compared with reference façade samples (air-filled glass block, insulating double-glazed unit). Moreover, the spectral transmittance of façade test elements was investigated by spectrophotometric measurements in visible and near-infrared spectral ranges. The results revealed that the effect of PCM variously affects thermal and solar transmittance as a time-related function of their phase change.