In areas of high seismic activity it is important to provide Light Frame Timber Buildings (LFTBs) with enhanced levels of lateral stiffness and strength, as well as to prevent excessive levels of non-structural (NSC) damage. Chilean wood-frame shear walls are usually sheathed at both sides with OSB and covered by one/two-ply type X gypsum wallboard (GWB) fastened to the frame with narrow patterns of nails or screws. The result is a multi-layered strong shear wall (MLSSW), which is not considered as such by design codes and mechanical models. The objective of this paper is to report an experimental evaluation of typical Chilean MLSSWs, with emphasis on the influence of NSCs. Connection-level and assembly-level of 1:1 aspect ratio shear walls were evaluated through experimental tests. Results showed increments of 53% and 160% in elastic stiffness and maximum capacity, respectively, while keeping virtually the same deformation capacity and energy dissipation of equivalent bare (non-GWB finished) shear walls. It is postulated that such increases may arise from the high embedment strength of the GWB, and that the deeply screwed GWB may prevent nails from pulling out during hysteresis cycles. It is concluded that GWBs have a significant structural influence on MLSSWs, and such influence should be taken into account in structural design.