When the floor slopes the wrong way: gradient failures

Of all the things that go wrong in a bathroom, the most common is also one of the most basic: the floor does not slope correctly toward the drain. It sounds trivial. It is not. A floor with the wrong fall holds standing water exactly where the room is most exposed, and over time that water finds every small weakness in the waterproofing.

What "fall to the drain" means

A wet-room floor is never meant to be level. It is built with a slight, continuous slope so that every drop of water runs to the floor drain and away. When that slope is too shallow, reversed, or uneven, water pools in low spots and around the edges instead of draining. Puddles sit against the membrane and the drain seal, dry slowly, and keep the area wet far longer than it should be.

Why it happens

Gradient failures usually come from rushed or unskilled substrate work before the waterproofing and tiles go on:

• The screed or levelling layer is laid flat, or sloped the wrong way.
• The fall is created only near the drain, leaving flat "dead" areas in the corners.
• A wall-adjacent drain is set at the wrong height.
• Large-format tiles are used over an inadequate slope, so water sits in the grout valleys.

None of this is visible once the tiles are down and dry. It shows up later as standing water, discoloured grout, and — eventually — moisture in the structure.

What the standards demand

Correct floor gradient is a recurring requirement across the Swedish wet-room rules. The waterproofing rules (GVK) and the ceramic tiling rules (BBV) both make proper fall to the drain a core condition of a compliant floor, and the 2026 tiling edition specifically sharpens the floor-gradient requirements. The slope has to be built into the substrate, verified before the membrane goes on, and preserved through the tiling.

Catching it before it is buried

This is exactly why an inspection of the substrate and waterproofing before tiling matters so much. A gradient problem found at that stage is corrected in the screed for very little. The same problem found after the room is finished means lifting tiles — or living with a floor that never quite drains. A simple check with a level and a bucket of water at the right moment saves a great deal later.

How M5 gets it right

We build the fall into the substrate across the whole floor, not just around the drain, set wall-adjacent drains to the correct height, and check the slope before the membrane and tiles cover it. Where the design uses large tiles, we plan the fall so water still runs cleanly to the drain. It is an unglamorous detail that decides whether a bathroom stays dry for a decade — so we treat it as one of the most important things we do.