This is the most economical and widely used system. Ventilation is guaranteed by the extension of the waste stack to the roof; this end piece of pipe is defined as the waste stack vent header. As an alternative to the roof extension it is possible to use vent valves that guarantee the inlet of air into the stack but impede the discharge of foul-smelling gas into the room.
It is the most simple and economic system. The primary ventilation system eliminates the effect of siphonage aspiration but not compression siphonage. While the back pressure above the point of discharge is compensated by the inlet of air through the vent stack, the increase in pressure at the base of the stack cannot be compensated, therefore, other particular configurations in the waste manifold are necessary depending on the number of floors present in the building.
