Ventilation assembly for a wearable drug delivery device

A ventilation assembly for a drug delivery device reservoir unit, the ventilation assembly comprising:

• a reservoir unit housing defining an interior volume separated from an exterior, the reservoir unit housing comprising a bottom wall forming a base plate on an outside thereof;
• an adhesive patch assembly comprising an adhesive layer and a release liner;
• an adhesive mounting tape fixing a top side of the adhesive layer to the base plate, wherein the bottom wall forms a recessed surface in the base plate creating a cavity in-between the recessed surface and the top side of the adhesive layer and the bottom wall forms one or more through holes fluidly connecting the cavity with the interior volume of the reservoir unit housing;
• and
• a waterproof and breathable pressure compensation membrane sealingly attached to the bottom wall wherein all of the one or more through holes are overlaid by the pressure compensation membrane,
• wherein the cavity leads to an opening to the exterior, the opening rimmed by the recessed surface and the top side of the adhesive layer, and
• wherein the cavity accommodates a spacer structure configured to be permeable.