Build height is the vertical space the channel body and its trap need under the finished floor, and it is the figure that stops projects. Manufacturers publish it; low-profile versions exist for exactly this reason.
Why it is the first number
A renovation over a concrete slab often has 6 cm to work with once tile and adhesive are counted. A channel needing 9 cm cannot be made to fit by any other choice — the length, the grate and the finish are all changeable, the height is not.
What the height is made of
The channel body, the outlet, and the trap, whose water seal depth is part of it. Shallow traps buy build height out of seal depth, and a shallow seal in a shower used twice a week is what dries out and smells.
The other two figures
Stated drainage rate in litres per minute, which has to exceed what your shower delivers rather than match it. And the outlet diameter and direction — horizontal outlets save height, vertical ones are simpler to connect.
What is genuinely worth paying for
A trap you can lift out to clean, and a grate that comes up without tools. Both are used far more often than the drainage rate is tested.
Questions people actually ask
Is a point drain lower than a linear one?
Often, and it is the usual answer when build height is tight. What a linear channel buys is a single fall direction across the floor instead of four, which is easier to tile and easier to walk on.
What drainage rate do I need?
More than your shower produces. Add the stated flow of the head and any body jets at your pressure, and compare. Most domestic showers sit well under what a channel is rated for; multiple outlets are where it matters.
Last reviewed 5 September 2026