This PVC vent terminal is commonly referred to as a bird cage in the building trade. It sits on top of the vent pipe to prevent birds from entering or nesting within the soil pipe, causing a blockage of the vent pipe which in turn would prevent the drainage system from operating correctly due to pressure imbalances. The terminal is fitted over the outside of the soil pipe. Whilst this fitting does not prevent rainwater from entering the vent pipe, rainwater will not cause any harm. However if you prefer the vent pipe to be protected from the elements we would suggest using an SP310 vent cowl.