In lightweight timber frame buildings, the horizontal stability against, for instance, wind loads is mainly ensured by shear diaphragms. These shear walls are typically constructed using a timber frame and a load- bearing sheathing layer on one or both sides of the framework. An atypical construction method uses double sheathing panels on top of each other, e.g. because of acoustic or fire safety reasons. However, no design rules are provided for such structures: the respective current and upcoming European standard (Eurocode 5 part 1-1) does not consider the structural contribution of both sheathing panel layers. Therefore, in this study, an experimental campaign is performed to enhance the knowledge of such double-sheathed shear walls, and two analytical calculation methods are proposed. The experimental campaign tests eight full-scale configurations through a racking resistance test with monotonic loading. Sheathing materials include load-bearing and non- load-bearing gypsum plasterboards and resinoid-bonded particle boards. All sheathing panels are connected to the fully anchored frames using staples. Results demonstrate that adding a second sheathing layer of the same material, with the same fastener disposition as the inner layer does not fully double the racking capacity and racking stiffness. Secondly, using a non-load-bearing gypsum plate as the inner layer creates a long plateau phase at the post-peak loading response, producing a less brittle failure behavior. The experiments are used as a benchmark to develop an analytical model based on Bla ss and Gebhardt's method for calculating the shear capacity of dowel-type connections with an interlayer. The proposed method introduces an interaction factor that takes into account that the connections of the outer sheathing layer, which pass through the inner sheathing layer, also contribute to the sheathing-to-framing connection of the latter. A simplified model is also presented, using a combination factor that aligns with the current Eurocode 5 design method for walls with sheathing panels on both sides of the framing. Different values for the respective interaction and combination factors are verified to determine a safe value for each tested configuration.
