Components for a respiratory treatment apparatus that is capable of providing a humidified respiratory treatment permit a reduction in condensation in a patient interface and/or its gas delivery tubing. In some embodiments, a rainout valve that may be an integrated component of a humidifier output aperture, or coupled thereto, may reduce condensation with a vapor barrier operable to selectively block and permit humidified gas transfer from the humidifier. For example, the barrier may be operable to open in response to a flow of pressurized breathable gas that may be generated by a flow generator of the respiratory treatment apparatus. In the absence of such a generation of pressurized flow, the barrier may prevent a transfer of the humidified gas such as into a conduit for a patient interface by retracting to a closed position. Example vapor barriers may include a resilient membrane, cover, bellows, flap, shutter or other suitable valve.