What is a vereveningsleiding (pressure equalisation pipe)?

A vereveningsleiding is a pipe in Dutch building drainage that balances the air pressure in one or more discharge stacks and to which no branch pipes from appliances are connected. That is how the Dutch standard for building drainage, NEN 3215, defines it. The pipe runs alongside the stack (Dutch: standleiding) and is connected to it at several points. In English terms it is a form of secondary ventilation, similar to a relief vent.

Why is it needed?

Water falling down a stack drags air with it. Where the stack changes direction, for example at an offset or where it has several horizontal sections, the water can briefly seal the pipe. Above that point negative pressure builds up, below it positive pressure. These swings pull water out of the traps or blow it out, giving gurgling drains and sewer smells indoors. The vereveningsleiding gives the air a route around the obstruction.

How is it connected?

The Dutch Wavin handbook on building drainage states that each vertical section of the vereveningsleiding connects to the matching section of the stack with a 45 degree downward-pointing branch, that its diameter is at least 0.8 times the largest diameter of that stack section, and that connection-free zones of at least 1 metre apply around the joints. The rules for these connections in NEN 3215 were revised in 2018. These are Dutch requirements; elsewhere, follow your national drainage regulations.

Connecting a vereveningsleiding to the stack: Dutch requirements

45 degree downward-pointing branch: Each vertical section connects to the matching section of the stack with a 45 degree downward-pointing branch.
Diameter at least 0.8 times the stack: At least 0.8 times the largest diameter of that stack section.
Connection-free zones of at least 1 metre: Applies around the joints between the vereveningsleiding and the stack.

Connection requirements as stated in the Dutch Wavin handbook on building drainage. These are Dutch requirements; the rules for these connections in NEN 3215 were revised in 2018. Elsewhere, follow your national drainage regulations.

Not to be confused with

Omloopleiding (bypass pipe): same function, but appliance branches that may not join the stack in its connection-free zone are connected to it.
Vent stack above the roof: the continuation of the stack through the roof, which provides primary ventilation and relieves both negative and positive pressure.
Air admittance valve: a valve that only lets air in. It does not relieve positive pressure and does not replace a vereveningsleiding.
Equipotential bonding conductor: in Dutch also called vereffeningsleiding, but an electrical cable linking metal pipework to earth. Same word, completely different trade.

Application

You mainly find it in apartment blocks and high-rise buildings, and wherever a stack has to dodge a beam or duct. A house with a straight stack rarely needs one.

Tips

Avoid offsets: a straight stack is the best solution. If an offset is unavoidable, use bends of no more than 45 degrees.
Connect nothing to it: a basin or shower on the equalisation pipe disrupts the pressure balance.
When remodelling: if you reroute a stack, for example for a new upstairs bathroom, have a plumber check whether extra ventilation is needed.

Related terms

Discharge stack
Soil vent pipe
Air admittance valve
Drain trap
Upper floor
Earthing network

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