Office Sewerage: Design & Installation

Reliable office sewerage is a system you never notice while it works properly, but one that reminds you of itself instantly — with odours, blockages or leaks — if it is installed with mistakes. Its main task is to remove contaminated wastewater beyond the premises, and on a building scale, to drain rainwater from precipitation and snowmelt as well.

In this guide, Partner Create engineers explain how internal sewerage works, what its types are, why the vent stack matters and which mistakes occur most often during installation. It will be useful for business owners and managers planning to set up or update the engineering networks during an office renovation.

What internal sewerage is and what it consists of

Internal sewerage is a system that carries drainage from sanitary appliances to the external network. It consists of:

• sanitary appliances and wastewater receivers;
• socket-and-spigot pipes;
• connecting shaped fittings;
• network cleaning devices.

Sanitary appliances are the core elements of sanitary equipment: they connect to both the water supply and the sewerage networks at once. By purpose, they are installed in bathrooms and showers (washbasins, shower trays, floor drains), in toilets (WCs, urinals with flush tanks or valves) and in kitchens (sinks). Appliances are made of cast iron, ceramics, sheet steel, non-ferrous metals and alloys, or plastic, and are coated on the outside with vitreous enamel, glaze or galvanic coatings.

An important detail: each appliance is fitted not only with a tap or mixer, but with a siphon that has a water seal. It is this water seal that prevents contaminated air from the sewer network flowing back into the room — without it, the office will smell.

Types of sewerage: К1, К2 and К3

Internal sewerage is divided into three varieties — and in an office it helps to know which does what:

• К1 — household-domestic sewerage: carries drainage from restrooms, bathrooms and showers, kitchens, public toilets and other rooms. This is the main system for most offices.
• К2 — storm (rainwater) sewerage: drains water from the roof. To avoid water stagnating on the roof and destroying the covering, drain funnels (cap-type or flat) are installed to collect rain and meltwater and lead it out of the building via the pipe system.
• К3 — industrial sewerage: for technological drainage. Its distinctive feature is additional structures such as grease traps or pumping stations. Since industrial drainage is considered “contaminated” (unlike “conditionally clean” К1 and “clean” К2), К3 is best given a separate outlet from the building into a separate well, with the wastewater pre-treated.

In offices the basis is household-domestic sewerage К1. Elements of К3 may be needed if the office has a full kitchen or canteen — then, for example, a grease trap is installed.

How household-domestic sewerage (К1) works

Along the flow of wastewater, the К1 system consists of these elements: sanitary appliance → siphon (water seal) → outlet pipe → sewer riser → outlet network in the basement.

At the end of the network’s outlet pipe there is a cleanout — a tee with a screw plug, through which blockages are convenient to clear. An important standard applies here: counting from this cleanout, the length of the sewer outlet must not exceed 12 metres with a pipe diameter of 100 mm (per DBN V.2.5-64:2012). Exceeding this distance is one of the typical design mistakes that later complicates maintenance.

Sewer ventilation: the vent stack and vacuum valves

Special attention goes to the vent stack. Its job is to let air into the sewer system. This allows the network to transport large volumes of water quickly and remove unpleasant odours, and it also keeps the water seals in the siphons from breaking.

The height of the stack above the roof is taken per DBN V.2.5-64:2012 as no less than:

• 0.3 m — for flat non-operated roofs;
• 0.5 m — for pitched roofs;
• 3 m — for operated roofs.

The stack can be left without ventilation (not led above the roof) if its height does not exceed 90 internal diameters of the riser pipe. An alternative to the vent stack is vacuum valves: installed at top-floor level, they perform the same function. A vacuum valve can also be fitted to a floor outlet pipe to prevent odour spreading in a specific room. That said, for large multi-apartment buildings a vacuum valve is not enough — a full vent stack is better there.

Design and installation of office sewerage: what to consider

Sewerage, like water supply, is laid at an early, rough stage of a renovation — before finishing. It must be planned together with the water supply, since sanitary appliances connect to both systems at once. What matters:

• Pipe slopes. Drainage flows by gravity, so the correct slope is critical — without it, water stagnates and pipes clog.
• Placement of appliances and risers. The closer appliances are to the riser, the simpler and more reliable the scheme; long horizontal runs raise the risk of blockages.
• Access for cleaning. Cleanouts and inspection points must remain accessible even after finishing.
• System ventilation. A vent stack or vacuum valves are essential to avoid odours and broken seals.

Sewerage is best designed properly at the engineering design stage, while restrooms and the kitchen can still be placed optimally relative to the risers.

Common mistakes in sewerage installation

These are the mistakes that most often leave offices with odours and blockages:

• a sewer outlet longer than 12 metres from the cleanout with a 100 mm pipe;
• missing or insufficient system ventilation (no vent stack or vacuum valve) — which breaks water seals and lets odours in;
• insufficient or reverse slopes on horizontal runs;
• no grease trap where there is a kitchen or canteen;
• connecting industrial К3 drainage into a shared outlet with К1 without pre-treatment.

A contractor who runs the whole engineering complex and is accountable for the result helps avoid them. See examples of completed sites in our office spaces portfolio.

Office sewerage in brief

• Office sewerage removes wastewater; the key defence against odour is the siphon’s water seal.
• Types: К1 (household-domestic), К2 (storm), К3 (industrial); in offices the basis is К1.
• The К1 scheme: appliance → siphon → outlet pipe → riser → outlet network in the basement.
• The outlet from the cleanout is up to 12 m with a 100 mm pipe (DBN V.2.5-64:2012).
• Ventilation is provided by a vent stack (0.3/0.5/3 m above the roof) or vacuum valves.
• Sewerage is designed together with the water supply at an early renovation stage.

Frequently Asked Questions

Order sewerage design and installation from Partner Create

Well-designed office sewerage means no odours, blockages or emergency leaks. Partner Create will design and install the drainage in coordination with the water supply and other engineering networks, and take responsibility for the result.

Explore our work in the portfolio, read useful materials on the blog, or get in touch to discuss your project. Call +38 050 388 24 49.

We also recommend Office Water Supply: Design & Installation and Construction Works in the Office: Types & Stages — sewerage is always planned alongside the water supply.