Choosing a floor drain for a utility room or sauna washroom

Body size and flow rate, not the design

A floor drain is sized by how much water it can carry away per minute, not by how it looks in the catalogue. A washing machine on a fast spin cycle, or a sauna washroom where two people are rinsing off at once, pushes more water through than a single shower ever does. An undersized drain copes fine most of the time and then backs up exactly when you are in a hurry.

For a domestic utility room a body with a nominal diameter of 50 mm is usually the minimum, and many manufacturers rate their standard drains for a shower and one appliance combined. If the room drains a washing machine, a floor-mounted sink and a shower all into the same point, ask for the drain's rated flow in litres per minute and check it against the appliances feeding it, rather than trusting the box alone.

The outlet pipe underneath has to match. A generous drain body sitting on a narrow 40 mm pipe still backs up, because the bottleneck has just moved down one level. This is worth checking against the existing drainage layout before you commit to a model, ideally with the pipework still visible and not yet boxed in.

The trap — the part that keeps the smell out

Every floor drain has a water trap, a bend or chamber that holds a column of water and blocks sewer gas from coming back up into the room. The depth of that water column is what decides whether the room smells, not the grate on top. A shallow trap in a rarely used utility room can dry out between uses and the smell returns even though nothing is faulty.

For rooms used daily this is rarely an issue, but a sauna washroom used only at weekends, or a laundry in a holiday home, benefits from a trap with a deeper water seal, generally 50 mm or more, so it survives longer between uses before drying out. Some drains also include a dry trap or a spring-loaded seal designed specifically for infrequent use, which is worth asking for by name if the room stands empty for weeks at a time.

Whatever trap you choose, it needs to be removable for cleaning without lifting the grate and fishing blind. Hair, lint and soap residue collect there and a trap you cannot get a brush into will eventually cause the same smell it was meant to prevent.

Grate material — the part underfoot

The grate is what gets stood on, mopped, and occasionally dropped a bucket on, so it needs to survive the room it is in rather than just look right in the shop. Stainless steel is the standard choice for wet rooms because it does not corrode and takes a scrubbing without marking. Cheaper chromed plastic grates look similar new but scratch and dull faster underfoot.

In a sauna washroom, check the grate is rated for the temperatures involved and will not warp near the sauna room threshold. In a utility room, a grate with a slotted or fine mesh pattern collects less lint than a wide-holed one, which cuts down how often the trap needs clearing out.

• Stainless steel grate, satin or brushed finish, for durability and easy cleaning
• Slot width narrow enough to stop small items and lint passing through
• A grate that lifts out without tools, for regular cleaning
• A frame that sits flush with the finished tile height, agreed before tiling starts
• Load rating suitable for the room — heavier for a garage or workshop floor

When a linear drain along the wall suits better

A linear drain is a long, narrow channel usually set against a wall or under a shower screen, rather than a point drain in the middle of the room. It suits rooms where the floor falls in one direction only, which is often simpler to build than a four-way fall to a central point, particularly in a small sauna washroom or an awkward-shaped utility room.

It also suits rooms where you want the floor to look uninterrupted, since the channel sits at the edge rather than as a visible circle in the middle of the tiling. The trade-off is a slightly higher cost for the drain body itself and a fall that has to be got right in one direction along its whole length, which is a job for whoever is laying the screed and tiles, not something to leave to chance.

What the drain does not solve — that is a flooring question

No drain, however well chosen, fixes a floor with the wrong fall. Water has to be guided towards the drain by the slope of the screed itself, typically around 1–2 % towards the outlet, and that fall is built before a single tile goes down. A drain sitting in a flat or badly sloped floor leaves puddles no matter how good the grate is.

This is where the drain choice and the floor build meet, and it is worth deciding both together rather than choosing a drain and hoping the floor accommodates it. We take on flooring work, including screed falls to a drain, from 15 € per job, and tiling from 35 € per job, both quoted once we have seen the room or your photos and measurements.