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Does Rain Actually Make Floors More Slippery?
Yes, rain can make floors more slippery, but how much depends on the floor. Water forms a thin film between the sole of a shoe and the surface, which reduces friction. Some floors lose little grip when wet, while others lose a lot, and you cannot tell which is which by looking at them.
The short why
Grip comes from friction between the shoe and the floor. Water gets in the way of that contact. On a floor with good texture, water can be pushed aside or channelled away. On a smooth or worn floor, a film of water stays in place, and friction can drop sharply.
Is it the rain, or the floor?
Both. Rain is the trigger, but the floor decides the outcome. Two floors that look almost identical can behave very differently once wet. A textured surface that channels water away performs differently from a polished one that holds a film of moisture on top.
Rain also rarely stays outside. It comes in on shoes, coats, umbrellas and luggage, and spreads across entrances and main routes. Most of the risk is therefore not outdoors, but on the indoor floors people walk onto next.
Why doesn’t a floor that looks fine in the dry tell you much?
This is the belief worth challenging directly. A floor that looks clean and dry is not necessarily a floor that is safe. Grip is invisible, and a dry reading says very little about how a floor will behave in the rain.
A floor can look spotless, feel fine underfoot in your own shoes and still have poor slip resistance once wet. Years of footfall can also wear a surface smoother, particularly along the busiest routes, without any visible change. The way to know is to test.
What else affects how slippery a wet floor is?
The CHIMES framework helps explain why the same rain has different effects in different places:
- Contamination: rainwater is often mixed with mud, leaves or grease, which can make it worse
- Heel: wet-weather footwear varies hugely, and worn soles hold less grip
- Individual: people hurry, carry umbrellas and bags, and look at the floor less
- Maintenance: mopping adds moisture, and the wrong product can leave a residue that lowers grip
- Environment: slopes, ramps, steps, poor lighting and the move from outside to inside all matter
- Surface: the floor material and its measured slip resistance
Rain makes contamination the headline, but the surface and maintenance often decide how bad it gets.
Why isn’t a mat or a sign enough?
Entrance matting helps by drying feet before people reach the main floor. But it only works if it is large enough, in good condition and covers where feet are wettest. In our work, we have seen a major station with three metres of entrance matting where the floor was still wet well beyond the end of it on a rainy day.
Signs have a similar limit. A wet floor sign warns people that a hazard exists. It does not make the floor less slippery. If a sign is out every time it rains, it is a symptom of a problem that is not being fixed.
How do you find out how your floors perform in the rain?
By measuring them wet. Slip resistance is assessed using pendulum testing, the method preferred by the HSE and relied on in UK slip litigation. It swings a rubber slider across the floor to mimic a heel strike and produces a Pendulum Test Value (PTV). A PTV of 36 or above is generally regarded as low slip potential. Below that, risk rises as the number falls.
Testing wet is what tells you how a floor will behave in rain. A single reading is also only a snapshot, because floors change with wear, cleaning and footfall.
Slip Safety Services has found that organisations who measure first and then act on what they find see a 57%+ average reduction in slip incidents. The improvement comes from fixing real causes in the right places, rather than relying on signs and mopping.
What to do about it
Start with the places where rain comes in: entrances, lobbies, doorways and the routes leading from them. Find out when each was last tested, and whether the test was done wet. Where there is no recent, dated reading, treat that as the first gap to close.
Check that entrance matting is large enough and in good condition. Ask your cleaning team or contractor which products and methods are used, and make sure floors are dried properly after mopping. Then fix what the readings show. In many cases, a floor can be treated to improve its grip without being replaced.
This is general information, not legal advice, so check what applies to your estate with your health and safety adviser.
Next step
If you are not sure how your floors perform when it rains, the Slip Prevention Scorecard takes under four minutes per building and gives you a clear starting point, with a score for each of the six CHIMES factors. For the fuller method behind measuring, improving and proving floor grip, Slipology by Christian Harris covers the process in depth.
Related questions
- Why does slip risk increase in winter months?
- How do facilities teams prepare floors for winter?
- Wet vs dry slip resistance: why does testing both matter?
- How much entrance matting do you actually need in winter?