Five real scale compartment fire tests, constructed of CLT slabs and glulam beam and column in accordance with current US product standards, were performed. The compartments had surface areas of exposed mass timber equal to up to two times the area of the floor plan. The 4 hours long tests showed that compartments with such quantities of exposed wood can exhibit continuous decay to hot-spots and embers after flashover. The tests indicate that the presence of two exposed wall surfaces in one corner should be avoided to ensure this.