Mass timber buildings are utilizing CLT for floors, walls and if permitted by regulations and codes, as exterior wall elements. In the United States, the IBC allows an exterior (external) wall to be load-bearing and constructed from Cross Laminated Timber, provided the exterior surface is protected with fire rated gypsum board and if located above 12.2m, passes an NFPA 285 fire test. Supported by a US Forest Service grant, two CLT based exterior wall assemblies have been fire tested to NFPA 285, a global first. This paper presents the design of the exterior walls, summarizes the required code path and provides the results of the fire tests. The fire test assembly includes a 3 ply CLT panel, fire rated gypsum board, a commonly used water resistive barrier and mineral wool. Both of the CLT based exterior wall assemblies successfully passed the NFPA 285 test and will enable greater use of mass timber in future buildings. All data, drawings and test reports will be made public to progress the acceptance of CLT for fire safe use in exterior walls.
