Accessible Bathrooms to DIN 18040-2: What the Standard Really Requires

Hardly any term is used as loosely in the bathroom sector as “barrier-free”. Sometimes it stands for a level-access shower, sometimes for a grab rail next to the WC, sometimes for a bathroom that really is fully usable from a wheelchair. The standard behind it is called DIN 18040-2, “Barrierefreies Bauen – Planungsgrundlagen – Teil 2: Wohnungen”, the German standard on accessible construction, design principles, part 2: dwellings, and it is considerably more specific than everyday usage suggests. This article describes what the standard says, where its limits lie and what you should clarify before material is ordered. It is intended as orientation and replaces neither planning by an architect or specialist planner nor information from the responsible building supervisory authority.

What the Standard Governs and What It Does Not

DIN 18040-2 is a planning standard. It describes how dwellings and their associated sanitary rooms have to be designed so that they can be used without outside help and without particular difficulty. The internal division into two levels is important: the standard formulates a basic standard for accessible dwellings and, beyond that, additional requirements marked with an “R”. These R requirements apply to dwellings that are to be fully usable from a wheelchair. Anyone who mixes the two levels inevitably arrives at contradictory dimensions – that is the most common source of misunderstandings in consultations.

The legal status is equally important. A DIN standard is initially a private technical rule and not binding in itself. It only becomes binding when building regulations refer to it – specifically via the state building regulations and the respective administrative provision on technical building rules. In North Rhine-Westphalia, § 49 of the Bauordnung NRW 2018, the state building code, governs the cases in which dwellings have to be built to be accessible, and the VV TB NRW introduces DIN 18040-2 as a technical building rule. Which version applies, to what extent it has been introduced and which deviations are permissible can change and differs between the federal states. That information belongs with the building authority or the planning architect, not with the builders' merchant.

For the most common situation in existing buildings – a couple having their own bathroom in a single-family house converted for later life – there is generally no building law obligation to provide accessibility at all. The standard is then not a constraint but a very usable checklist: it describes dimensions that have proven themselves in practice and prevents a conversion failing after ten years because twenty centimetres are missing.

A third point concerns funding. Grant and loan programmes as well as benefits from long-term care insurance each define their own conditions, which may overlap with the standard but are not identical to it. Whether a particular project is eligible for funding is decided solely by the respective programme provider on the basis of the conditions in force at the time of application – and generally before the measure starts. We cannot and will not give any assurance on this; clarify it beforehand directly with the programme provider or with a housing advice centre.

Circulation Areas and Door Widths

The central dimension in the standard is the circulation area in front of the sanitary fixtures. For the basic accessible standard, 120 × 120 centimetres are to be provided in front of the WC, the washbasin and the shower. For the additional requirement “R”, that is unrestricted wheelchair use, this dimension grows to 150 × 150 centimetres. The difference sounds small but determines the entire floor plan: 150 centimetres corresponds to the turning circle of a wheelchair, 120 centimetres does not.

Circulation areas may overlap. That is the most important planning lever in small bathrooms: the area in front of the washbasin and the area in front of the WC do not have to lie side by side, they may overlap, as long as they actually remain clear. Clear means: not restricted by radiators, inward-opening doors, furniture or pre-wall edges. Between individual sanitary fixtures the standard also provides for minimum lateral distances – around 20 centimetres as a basic dimension, and for wheelchair use at least 90 centimetres on one side next to the WC so that transferring sideways is possible.

With doors, the most common source of error lies not in the standard but in confusing terms. What counts is the clear passage width, that is the dimension actually usable with the door open – not the door leaf width and not the nominal structural dimension. An element ordered as a “90 door” delivers noticeably less clear width depending on the frame and hardware situation. The standard states a clear passage width of at least 80 centimetres for the accessible standard, and at least 90 centimetres for the additional requirement “R”. Anyone planning within an existing building should have this value measured in the finished state, not taken from the catalogue.

The most important dimensions at a glance – in each case the basic standard and, where different, the additional requirement “R” for unrestricted wheelchair use:

• Circulation area in front of WC, washbasin and shower: 120 × 120 cm, with “R” 150 × 150 cm
• Clear passage width of the door: at least 80 cm, with “R” at least 90 cm
• Lateral distance between sanitary fixtures: around 20 cm as a basic dimension; next to the WC with “R” at least 90 cm on one side
• WC seat height including the seat: 46 to 48 cm
• Shower area: level with the floor, permissible step down no more than 2 cm, fall about 0.5 to 1.5 % and no more than 2 %
• Washbasin top edge: 80 to 90 cm, with “R” accessible underneath with the top edge at about 80 cm

This compilation does not replace a look at the standard itself. It contains further stipulations – for instance on controls, lighting and the reachability of fittings – and in individual cases deviating or additional requirements from building regulations may be added.

For sanitary rooms there is an additional functional requirement that is often overlooked: hinged doors have to open outwards, and the door has to be openable from outside in an emergency. Both have a simple reason – if someone falls in the bathroom, the door must not be blocked. Where there is no space outwards, a sliding door is the obvious alternative; it does, however, cost wall space and has to be taken into account in the pre-wall planning from the outset.

The Level-Access Shower as the Central Element

The level-access shower is the component on which an accessible bathroom most readily hinges – and the one that intervenes most deeply in the structure. The standard requires a transition level with the adjoining floor. Lowering the shower area by no more than two centimetres is permissible, a step upwards is not. Anyone planning this transition is planning the build-up height at the same time: drain, fall, waterproofing and tile bed all have to fit into the existing construction. This is exactly where projects in existing buildings fail if the check is carried out too late.

For the fall, the standard states a narrow corridor: about 0.5 to 1.5 per cent, no more than 2 per cent. The reason is the dual function of the surface. It has to lead water safely to the drain and at the same time remain trafficable and safe to walk on. A steeper fall drains more quickly but is no longer comfortable to use with a walking frame or wheelchair. Whether the fall is realised via point drainage or a linear channel is also a tiling question: a fall from four sides towards a point drain sits poorly with large, stiff formats, a channel with a single-axis fall considerably better.

On slip resistance the standard is more specific than many expect: for the shower place it refers to evaluation group B for wet barefoot areas as well as to R 10 from the set of rules for areas used with footwear. That two different systems stand side by side here is not an editorial error but reflects actual use – barefoot in the shower, in shoes when cleaning and providing care. What these figures mean and why they cannot be converted into one another is explained in detail in our article on R classes and evaluation groups.

When selecting products, a distinction has to be made between two construction methods. A tiled shower with a drain and site-applied waterproofing allows any shape and size, but requires careful waterproofing planning. A level-access shower area as a prefabricated element – for instance from our range of shower trays – reduces the number of interfaces between trades and delivers a defined surface with documented properties. Which variant is the right one depends on the substrate; in existing buildings the screed build-up is often the decisive criterion, as our article on tiling over old screed also discusses.

For the enclosure the rule is: it must not permanently restrict the circulation area. Fixed glass elements are permissible provided the required area in front of the shower remains clear; outward-opening or fully retractable elements from the shower enclosures range are often the more practicable solution in tight floor plans than a door that swings into the room. Here too it is the specific floor plan that decides, not the product type.

Sanitary Fittings: Grab Rails and Seat Heights

For the WC, the standard states a seat height of 46 to 48 centimetres including the seat. That is considerably higher than with standard ceramics and the reason why, in many existing bathrooms, a noticeable improvement can be achieved simply by changing the ceramic or adjusting the pre-wall height. It is important that the height is meant including the seat – the top edge of the ceramic alone is not the relevant dimension.

For the support rails at the WC, the standard is unusually detailed: hinged support rails on both sides are provided for, with their top edge about 28 centimetres above the seat height and a clear distance between the rails of 65 to 70 centimetres. The rails have to be able to bear body weight safely. From this follows a requirement that has to be met long before the rails are bought: the walls of sanitary rooms have to be constructed on site so that horizontal and vertical support and grab rails can be fixed to them. With pre-wall installations and lightweight walls that means built-in cross members or continuous boarding – and this decision is made during the shell construction, not when fitting out.

The washbasin should be designed so that it can be used while seated. The standard states a top edge in the range of 80 to 90 centimetres for the accessible standard; for wheelchair use the washbasin has to be accessible underneath, with sufficient knee space and a top edge at about 80 centimetres. In practice this means: a flat surface-mounted or concealed trap, no cabinets in the leg area and a tap that can be reached while seated – single-lever or touchless taps have the advantage here over two-handle mixers.

For the mirror, the standard adds a requirement that is easy to implement and makes a lot of difference in everyday use: it should be at least one metre high and start directly above the washbasin, so that it can be used both seated and standing. Towel rails in the washbasin area should be designed to withstand a load – if it comes to it, they will be used as a grab rail whether they were intended for it or not.

For the shower place, the standard provides for a seat as well as grab rails, and the tap has to be reachable from the seat. The principle of preparation applies here too: even if a shower seat is not fitted initially, it makes sense to prepare the wall for it. Retrofitting later is hardly possible without intervening in the tiled surface – and a subsequent intervention in the waterproofing layer of the shower is fundamentally delicate.

What to Clarify Before Implementation

The first question is always the legal one: does an obligation to provide accessibility apply to your project at all, and if so, to what extent? That depends on the type of building, the number of dwellings, whether it is new build or existing stock, and on the state building regulations. This information is provided by the responsible building supervisory authority or the planning architect. A builders' merchant cannot replace it, and nobody should derive it from a brochure.

The second question is the constructional one. Level-access showers require a certain build-up height for the drain, the fall and the waterproofing; in existing buildings this height is frequently the bottleneck, particularly with timber joist floors or thin screeds on insulation. The route of the drainage, the load-bearing capacity of the walls for support rails and the question of whether doors can be re-hung or converted to sliding elements also have to be clarified. These points belong on the table before tiles, shower element and ceramics are selected – not afterwards. With owner-occupied flats there is the added point that interventions in the waterproofing, the screed and the risers frequently require the consent of the owners' association; that too is to be clarified before ordering material and not afterwards.

In existing buildings the realistic answer is often a partial conversion anyway. Not every bathroom can be converted in compliance with the standard – sometimes the square metres for a circulation area of 120 × 120 centimetres are simply not there. That is no reason to do nothing at all. A level-access shower, a raised WC ceramic, walls prepared to bear loads and a door that opens outwards improve usability considerably, even if not every dimension is achieved in the end. All that matters is to name the difference clearly: such a bathroom has been converted for later life, but it is not accessible within the meaning of the standard – and that distinction is relevant wherever a certificate is required.

The third question is the personal one, and it is the one most often skipped. A bathroom built to the standard is a bathroom for a generally defined case of use. A bathroom for a specific person with a specific impairment may sensibly deviate from it – for instance in reach height, in the preferred transfer direction at the WC, or in the question of whether a bathtub is wanted in spite of everything. Where there is a permanent care situation, involving occupational therapy, housing advice or a care service in the planning is usually more valuable than any additional figure from the standard.

And finally the sequence: planning, then review by those involved, then material. We supply tiles, shower elements, enclosures and sanitary ceramics to trade businesses and clients in the Kreis Mettmann and the Düsseldorf area and are happy to match the product selection to a plan that already exists. If you are at this point, get in touch – ideally with a floor plan and details of the existing floor build-up.