Slip Resistance of Tiles: R Classes for Bathroom, Terrace and Commercial Use

“Which R class do I need for the bathroom?” is one of the most frequent questions in tile sales – and it already contains a fallacy. The R classes describe the behaviour of a floor covering under shoes and with oil as a lubricant. For a shower area that you step into barefoot and with soapy water, that is simply the wrong test procedure. For that there is a second system with the evaluation groups A, B and C. Both figures often appear side by side in the data sheet, but they cannot be converted into one another and cannot be substituted for one another. This article separates them cleanly – and names at the end what a test figure fundamentally cannot deliver.

Two Systems, One Misunderstanding

Both procedures work on the same basic idea, the inclined plane: a test person walks on a surface that is continuously raised until safe walking is no longer possible. The angle of inclination reached is the result. Everything else differs – and precisely in the points that matter.

In the shod procedure, historically tested to DIN 51130, the test person wears standardised safety shoes and motor oil serves as the lubricant. The target group is work rooms and operational traffic routes. In the barefoot procedure, historically to DIN 51097, the test person walks barefoot and the surface is continuously wetted with a soap solution. The target group is wet barefoot areas such as showers, poolside walkways and changing rooms. Different footwear, different lubricant, different case of use – which is why the sentence “R 10 is enough for the shower” makes no sense without further qualification.

The two systems in direct comparison:

• R 9 to R 13: shod test, lubricant motor oil, intended for work rooms and operational traffic routes
• Evaluation groups A, B, C: barefoot test, lubricant soap solution, intended for wet barefoot areas
• In addition to the R groups: the displacement space V 4 to V 10 for areas with larger quantities of slip-inducing substances
• No conversion: a covering can perform well in one system and weakly in the other – both values have to be checked separately

The fact that a covering carries both figures is therefore neither coincidence nor marketing, but the normal case for products used in bathrooms and wet areas. If one of the two figures is missing from the data sheet, that does not mean the covering performs badly – as a rule it means that no test exists for this system. For a surface whose requirement is defined precisely within that system, such a product then cannot be reliably justified.

In terms of standards, something has changed since the end of 2021 that is not yet reflected everywhere in data sheets. With the publication of DIN EN 16165, the national German test standards DIN 51130 and DIN 51097 were withdrawn; the test procedures are now found in the annexes of the European standard, and the classification into R groups and evaluation groups in its national annexes. The designations R 9 to R 13 and A, B, C therefore remain in common use, but their normative basis has shifted. At the same time, some sets of rules that lay down the requirements still refer in part to the withdrawn standards. For practical purposes this means one thing above all: check which standard and which version a figure in a specific data sheet refers to.

R Classes in Detail: R9 to R13

The R groups map the measured angle of inclination in the shod procedure in five steps. R 9 corresponds to an angle above 6 up to 10 degrees, R 10 above 10 up to 19 degrees, R 11 above 19 up to 27 degrees, R 12 above 27 up to 35 degrees and R 13 more than 35 degrees. The jump from R 9 to R 13 is therefore considerable – and it is not a pure gain in safety but a trade-off: the coarser the surface, the better the grip and the more demanding the cleaning.

In addition there is the displacement space, stated as V 4, V 6, V 8 or V 10. It describes the void volume beneath the walking plane – for instance through studs, grooves or an open structure – into which liquids and solids can escape. This figure is relevant where larger quantities of slip-inducing substances occur, for instance in food processing businesses or in outdoor areas with standing water. A covering can thereby combine a lower R group with a defined displacement space instead of relying solely on a coarser surface.

Which R group is required where is set out not in the test standard but in occupational safety law: in the German technical rule for workplaces ASR A1.5 “Fußböden”, on floors, and in the accident insurance rule DGUV Regel 108-003. Their annexes assign evaluation groups to work areas. Examples given there include internal entrance areas and toilet rooms with R 9, changing and washrooms as well as garages not exposed to the weather with R 10, outdoor areas and open-air parking surfaces with R 11 or R 10 with displacement space V 4, and commercial kitchens with R 12. The lists are not exhaustive; areas not listed are to be classified by analogy, and using a higher group is permissible. What counts is always the current version of the set of rules.

Not every form of slip resistance is created through the visible structure. With porcelain stoneware it is generally produced through the surface finish of the tile itself – textured, ground or with a corresponding glaze. Coatings or chemical treatments applied afterwards change the test result and are therefore also not covered by the product's original figure. Anyone having a surface treated afterwards should have the changed properties confirmed by the contractor rather than continuing to rely on the old data sheet.

One point is regularly overlooked here: these requirements apply to workplaces. For a private bathroom, a private terrace or a private utility room there is no corresponding statutory requirement. The tables are nevertheless useful there – as values based on experience, not as an obligation.

Evaluation Groups A, B and C for Wet Barefoot Areas

The second system has only three steps and a clearly defined field of application: surfaces walked on barefoot and wet. The evaluation groups correspond to minimum angles of inclination in the barefoot procedure – group A from about 12 degrees, group B from about 18 degrees, group C from about 24 degrees. A is the lowest requirement, C the highest.

The assignment to fields of application is found in DGUV Information 207-006 “Bodenbeläge für nassbelastete Barfußbereiche”, on floor coverings for wet barefoot areas. Group A applies there to largely dry barefoot walkways, communal rooms and changing rooms. Group B is intended for shower rooms, poolside walkways and sauna areas that are not predominantly dry. Group C concerns the most critical surfaces – steps leading into the water, sloping pool edge areas and footbaths. This system comes from swimming pool construction; it is therefore tailored to public and commercial facilities and is not mandatory for private bathrooms.

Even so, it is the more sensible reference value in a private bathroom than any R class, because it reflects actual use. Tellingly, the standard for accessible dwellings also states both figures for the shower place – evaluation group B for the barefoot area and R 10 for use with footwear. If you are planning for accessibility, you will find the related connections in our article on the accessible bathroom to DIN 18040-2.

Which Class Makes Sense Where

For a private bathroom the question can be answered by zones. The dry area of the bathroom – in front of the washbasin and the WC – is usually finished with coverings at the lower end of the scale; here good cleanability takes priority, because the risk of slipping on a dry floor is low. For the shower area itself, a covering with a stated barefoot rating is the obvious choice, because that is where you walk barefoot, wet and with soap. Anyone wanting to combine both in one continuous surface has to make the compromise consciously: a surface that offers safe grip in the shower is noticeably harder to clean throughout the bathroom. You will find suitable floor coverings for both zones in our range of floor tiles.

Outdoors the logic shifts. Terraces, balconies and paths are walked on with footwear but are exposed to rain, leaves, frost and algae growth. For workplaces, the set of rules typically places open-air traffic and parking surfaces at R 11 or R 10 with displacement space V 4 – a usable guide value for private terraces too, without any obligation existing there. Just as important as slip resistance outdoors, however, are the frost resistance of the material and the build-up beneath it; we have written a separate article on frost-resistant tiles for terraces and balconies about this. A selection of suitable formats can be found under terrace slabs.

In a commercial property the question is no longer one of taste. Anyone operating a workplace has to assess the hazard and select the floor accordingly – documented, and in the version of the set of rules applicable at the time. The sales area, kitchen, cold store, delivery area and sanitary rooms of a single property can end up in quite different groups. The contacts here are the occupational safety specialist, the specialist planner and the responsible employers' liability insurance association, not the material supplier.

A practical detail here is the transition between surfaces with different slip resistance. Where the covering changes – for instance from the outdoor area into the entrance or from the sales area into the kitchen – a hazard arises at precisely this edge, because the grip underfoot changes abruptly. It is therefore customary to defuse the transition with a zone of increased slip resistance, with barrier matting or with a sufficiently long transition stretch, rather than letting two very different coverings meet directly. That is a planning detail, not a product detail – and in the materials list it only stands out if you look for it specifically.

What a Recommendation Cannot Deliver

A test value describes a laboratory result on a new, clean sample under defined conditions. It does not describe the floor on which someone slips in three years' time. Between the two lie factors that no data sheet can cover: the cleaning agents actually used and whether they leave a film, the cleaning intervals, falls and drainage, the users' footwear, dirt brought in from outside, wear of the surface over the years and, outdoors, algae and moss growth. In many cases of damage the problem is not the choice of material but the maintenance.

The reverse therefore also applies: a higher class is not automatically the better decision. A heavily textured covering holds dirt, needs more intensive cleaning and can – if that cleaning is not carried out – perform worse in everyday use than a smoother covering that is kept clean. For surfaces used barefoot there is the added point that coarse textures are perceived as unpleasant. The right choice is the one that suits realistic use and realistic maintenance.

The format also plays a part, and independently of the tested surface. Joints break up a closed film of water and give the foot an additional edge – in wet areas a small-scale covering is therefore often more favourable than a large, continuous surface with the same figure. That is one of the reasons why shower areas are traditionally executed in small formats or mosaic. A test value alone does not reflect this effect, because it is determined on a single sample and not on the laid covering.

One last but important point: on slip resistance we pass on exclusively the figures that the manufacturer states for the respective product. We cannot and may not give any assurance that a particular covering is suitable or safe for your specific case of use – assessing the individual case rests with the planner, the operator and the employer. If you need the data sheets for specific series for a project in the Kreis Mettmann or the Düsseldorf area, or want to make a preselection based on specified figures, get in touch with us. Bring the requirement that comes from your planning – then we will look for the material to match.