Two fire experiments have been conducted to study sprinkler system extinguishing performance in a compartment (13 m2) with an adjacent corridor (12 m2), both with exposed cross-laminated timber (CLT). Four nozzles were installed in the corridor and two in the compartment. In Experiment 1, the sprinkler system was fully functional and successfully controlled a concealed fire. In Experiment 2, nozzles in the compartment were disconnected, while the corridor nozzles were operative, giving flashover after 5 min with large flames emerging into the corridor, rapidly worsening evacuation conditions. Despite four activated nozzles in the corridor, the temperatures remained high, and flames spread through the corridor along the CLT ceiling and the upper parts of the wall, an area that was not effectively protected by the nozzles. After flashover, the compartment temperatures remained stable at ∼1000 °C until experiment termination at 96 min. This continued fire in the compartment can be explained by water from the corridor sprinklers not reaching this area, extensive radiative feedback by the CLT surfaces and delamination of CLT elements of the 20 mm layers. The charring rate was ≥1.1 mm/min for large parts of the exposed CLT wall and ceiling in the compartment during the fire.