A full-polarimetric radar system for non-contact, non-destructive high-resolution imaging and inspection of wooden buildings damaged by earthquakes is developed. The stepped frequency continuous wave system is based on a network analyzer and employs a multi-channel antenna array consisting of four linearly polarized Vivaldi antennas operating in an ultra-wideband ranging from 1 GHz to 20 GHz. The signal processing methods for high-resolution 3D imaging and polarimetric analysis are introduced in this paper. We conducted two-dimensional scans on damaged wooden wall specimens in the laboratory. The measurement is carried out at a five mm step. The results indicate that the microwaves up to 20 GHz can penetrate the wooden walls. Cracks and deformations of wooden structures inside the wall, as well as of metal nails and bolts can be clearly imaged. The observed radar signatures related to the damaged wooden structures are discussed. Our findings demonstrate that the polarimetric radar technique is able to provide richer information than conventional single-polarization subsurface penetrating radar.