Wastewater pipes, floor drains and wall-adjacent drains

Waste and drainage are where a wet room either sheds water cleanly or quietly traps it. The rules are detailed because the failures are expensive.

Wastewater pipes

A gravity sewer must slope along its entire length. Pipes cast into the floor are fixed with special fasteners before casting so they cannot move or twist, with fasteners at every branch and joint and no more than 200 mm from a floor drain. Direction changes use defined branch angles (generally 45°, up to 90° in specific cases). Cleaning access on horizontal collection pipes uses a 90° connection so the pipe can be rodded both ways; on a standing pipe the access sits with its bottom edge at least 400 mm above the floor. The installation needs at least one roof vent, sloped along its length and sealed to the roof's waterproofing.

Where floor drains are required

A floor drain is required in rooms with a bath or shower; rooms with a shower cubicle that has no overflow; rooms with a washing machine (unless it sits on a watertight surface with a leak breaker); rooms with drains lacking overflow or flood protection; rooms with water heaters or other equipment needing draining; and rooms cleaned with a hose. The 2026 edition extends this to more cases, including showers at a WC, bidet or basin, and rooms holding drainable equipment of five litres or more.

Installing the drain

A floor drain in a wet room sits so the distance from the wall waterproofing to its outer flange is at least 200 mm. It is mounted level, fastened to the joists with approved fasteners (mounting plates in timber joists), with the connecting waste pipe fastened no more than 200 mm from the drain in concrete joists. It must be set level to the finished waterproofing within a ±2 mm tolerance, fitted with a protective lid during construction, and any extension ring must be tested and approved for that drain.

Wall-adjacent and wall drains

A drain installed closer than 200 mm to a wall ("väggnära"), or a wall drain with its trap inside the wall, must be tested and approved together with the specific waterproofing system used — not mixed and matched. Approved drain-plus-membrane combinations are listed by Säker Vatten.

Old drains

Floor drains made before 1990, and any drain incorrectly installed in the floor structure, are replaced during a renovation — they are a known water-damage risk.

Official source: this is M5's plain-language summary, not the official text. For the full rules see Säker Vatten (sakervatten.se).