What is Building Drainage?

• Roof drainage: gutters, downpipes and roof outlets collect the rainwater.
• Wastewater pipes in the house: branch pipes from kitchen, bathroom and washing machine lead into vertical stacks. These are vented through the roof so that flowing water doesn’t create a vacuum that sucks the traps dry.
• Underground drains: beneath the floor slab or in the ground, they collect everything and carry it on a gradient to the inspection chamber and on through the connection pipe to the public sewer.
• Basement drainage: perimeter drainage, floor drains, pump sump and lifting station for everything that lies lower than the sewer.

Several German and European standards apply: DIN EN 12056 for systems inside buildings, DIN EN 752 for outside, and DIN 1986-100 with the German additions for buildings and plots up to the property boundary. Operation and maintenance are covered by DIN 1986-3, inspection and renovation of existing pipes by DIN 1986-30.

Whether rainwater and wastewater are drained together or separately depends on the public sewer. In a combined system, both flow through one sewer. In a separate system, there are two sewers, and rainwater must not go into the foul sewer. What applies to you, and whether you should let rainwater soak away on your plot, is set out in the municipality’s drainage bylaw.

This matters for the basement. According to the federal flood protection guide, it is above all combined sewers that can be overloaded in heavy rain. Rainwater and wastewater then push back through the property drainage into every unprotected drain below the backflow level. A common fault in older houses is misconnections, such as a downpipe connected to the foul sewer in a separate system.

Everything above the backflow level may drain into the sewer by gravity. Everything below it has to be protected against backflow, either by a backflow valve or by a lifting station with a backflow loop. The municipality sets the backflow level; where it hasn’t, the top of the road at the connection point applies.

Two rules are often overlooked. First, only drainage points below the backflow level may drain through the protective device; water from above doesn’t belong there. Second, a single central backflow device for the whole house is not permitted, because it hinders the venting of the sewer system. Otherwise, during backflow, wastewater from the upper floors would also end up in the basement.

More under sewer backflow and backflow protection.

• Blockages: fat, wet wipes and food scraps clog branch pipes and underground drains. The first sign is slow-draining basins, often on the lowest floor first.
• Gurgling and sewer smell: if the roof vent is missing or blocked, draining water sucks the traps empty.
• Damage to old underground drains: cracks, displaced joints and root ingress. You often only notice from recurring blockages or damp patches in the basement.
• Missing or unserviced backflow protection: it only shows up in the next heavy rain.
• Pump failure: lifting stations and basement drainage pumps rarely run. A fault then only shows when they are needed.

The owner is responsible for running the building drainage. DIN 1986-3 gives owners and operators rules for inspection and maintenance. For the systems in the basement, operator rules based on DIN 1986-3 state:

• Backflow valve: operate the emergency closure monthly; servicing by a qualified person every six months, according to the federal flood protection guide
• Lifting station: monthly test run over at least two switching cycles; servicing annually in a single-family home, every six months in an apartment building, quarterly in commercial premises
• Drains: keep traps filled, empty sludge buckets

There is no uniform interval for underground drains. Whether and when a leak test is mandatory is regulated differently by the German federal states and municipalities; the technical basis is DIN 1986-30. Ask your local sewer authority. Regardless of any obligation, a CCTV pipe survey is worthwhile when buying a house, after recurring blockages or before renovating a basement.

Drainbee monitors one point of the building drainage, not the whole system: the water level in a pump sump or lifting station. It only sees a blocked underground drain or a leaking joint under the slab if the water collects where the probe hangs.

What Drainbee does cover is exactly the spot where a failure gets expensive fastest: the basement pump, which rarely runs and therefore rarely gets noticed. The app shows level, pump cycles and inflow; alarms go off on threshold, power outage and WLAN loss.