Short answer: The governing standard since 2017 is DIN 18534 for interior rooms. It assigns every surface to a water exposure class W0-I to W3-I, and the class determines whether waterproofing is needed and with what. In a domestic bathroom the rule is generally: wall surfaces at the shower and bathtub W1-I, the floor of a level-access shower W2-I. The waterproofing is a bonded waterproofing – it lies beneath the tiles and is firmly bonded to them. Height: at least 20 cm above the highest tap outlet. And the sentence that causes most water damage: even with a shower enclosure, the floor waterproofing must not be omitted.
Why waterproofing is necessary
Tiles are waterproof, but the covering as a whole is not. Cement grout absorbs water and passes it on, silicone joints are maintenance joints with a limited service life, and hairline cracks form on their own through shrinkage and temperature changes.
What arrives behind stays there. Screed, plaster and drywall boards no longer dry out under a tight tile covering. The damage only shows years later – as a damp patch in the next room, as a musty smell, as a swelling door frame or as mould behind the pre-wall.
Waterproofing is therefore not an extra but part of the build-up: the water-carrying layer beneath the covering, in the trade jargon bonded waterproofing (AIV, Abdichtung im Verbund).
The standards since 2017
Until 2017, DIN 18195 governed all structural waterproofing together. It was split into five independent standards, with DIN 18195 itself remaining as a terminology standard.
| Standard | Applies to |
|---|---|
| DIN 18531 | roofs, balconies, loggias, access balconies |
| DIN 18532 | trafficable surfaces made of concrete |
| DIN 18533 | components in contact with the ground |
| DIN 18534 | interior rooms – bathroom, shower, kitchen, commercial |
| DIN 18535 | tanks and basins |
The main novelty of DIN 18534 is the water exposure classes, which replace the former stress classes. The system is simple: W for water exposure, 0 to 3 for the level of load, I for interior.
The four classes
| Class | Exposure | Typical surface | Waterproofing |
|---|---|---|---|
| W0-I | low – infrequent splash water | wall at the washbasin in a guest WC, floor without a floor drain | usually no area waterproofing required |
| W1-I | moderate – frequent splash water | walls at the shower and bathtub in a domestic bathroom, floor areas outside the shower | bonded waterproofing |
| W2-I | high – frequent splash and service water, temporarily ponding | floor of the level-access shower, wall surfaces in intensively used showers | bonded waterproofing |
| W3-I | very high – long-lasting exposure, intensive cleaning | commercial showers, commercial kitchens, swimming pool surrounds | tested system, usually waterproofing slurry |
The class is not a feeling but an assignment. In practice, the domestic bathroom can almost always be classified with two questions: how often and how intensively does water hit the surface, and can water pond on it?
How to classify your bathroom
Bathtub with hand shower and shower enclosure
Wall surfaces in the bathtub area: W1-I. Floor: W1-I. Despite the shower enclosure, floor waterproofing cannot be dispensed with – water reaches the floor when getting in and out and over the edge of the bathtub.
Shower tray with glass wall
Wall surfaces of the shower: W1-I to W2-I depending on intensity of use. The shower tray itself is a watertight component, but its connection to the wall is not – sealing tape and a properly executed connection joint belong there. Remaining floor area: W1-I.
Level-access shower
Shower floor: W2-I, because water can pond there. Wall surfaces of the shower: W1-I to W2-I. With effective splash protection – that is, a fixed enclosure instead of a shower curtain – the remaining floor area in a domestic bathroom may be classified as W1-I. Without a fixed enclosure, not.
Guest WC with washbasin
Wall behind the washbasin: W0-I. Floor without a floor drain: W0-I. As a rule, no area waterproofing is required here – a properly executed splashback on the wall is enough.
The heights and dimensions
The class says whether to waterproof. How far follows from these rules:
- At least 20 cm above the highest tap outlet. This is the normative base value; in practice, work is often done up to 25 cm above the shower head, because the dimension then still suffices even if the fitting height is changed later.
- At the sides at least 20 cm beyond the splash zone, measured from the edge of the shower or bathtub.
- If only the floor area is waterproofed, it must be turned up at least 5 cm at adjoining and rising components – the later skirting covers this area.
- At the washbasin, 50 cm to the sides and 20 cm above the tap are usually enough.
All corners, edges, pipe penetrations and movement joints receive a sealing tape or a collar irrespective of the class. They are not optional accessories but part of the tested system.
Which system for which class?
| System | W0-I | W1-I | W2-I | W3-I |
|---|---|---|---|---|
| Liquid membrane (wall and floor) | – | yes | yes | wall yes, floor limited |
| Mineral waterproofing slurry | – | yes | yes | yes |
| Waterproofing sheet with hybrid adhesive | – | yes | yes | yes |
| Sealing tape, collars, corner pieces | – | mandatory | mandatory | mandatory |
What matters is that the components come from one system. Waterproofing, primer, sealing tape and adhesive are matched to each other and tested in this combination. Combining a liquid membrane from one manufacturer with the sealing tape of another is exactly the kind of improvisation that, in the event of damage, falls to the cost of the contractor.
How the application works in practice is described in our guides Waterproofing a bathroom with liquid membrane and Applying waterproofing slurry.
The build-up in section
From bottom to top, a bathroom floor that complies with the standards consists of these layers – each has a function, and none replaces another:
| Layer | Function |
|---|---|
| Structural slab | carries |
| Impact sound and thermal insulation | decouples, insulates |
| Screed, with fall in the shower | load-distributing layer, leads water to the drain |
| Primer | consolidates, regulates absorbency |
| Waterproofing with sealing tape and collars | holds the water back |
| Tile adhesive C2 | bonds covering and waterproofing |
| Tile | wearing surface, appearance |
| Grout and silicone joints | closes the surface, maintenance joints |
The key insight from this: the silicone joint at the very top is not the waterproofing. It is a maintenance joint with a limited service life. When it tears – and at some point it will – the layer beneath catches the water. That is exactly what it is there for.
Which substrate may go in the bathroom?
| Substrate | W0-I / W1-I | W2-I / W3-I |
|---|---|---|
| Cement-bonded building board | yes | yes, first choice |
| Concrete, sand-lime brick, clay brick | yes | yes |
| Cement plaster, cement screed | yes | yes |
| Impregnated plasterboard | yes | no |
| Normal plasterboard, gypsum plaster | only outside the splash zone | no |
| Calcium sulphate screed | with primer | limited |
| Wood-based boards | no | no |
For new builds and renovations in the shower area, cement-bonded building board is almost always worthwhile. The extra cost compared with impregnated plasterboard is negligible against the risk – and in W2-I, plasterboard is no longer permitted anyway.
Retrofitting waterproofing in existing buildings
In an existing bathroom without waterproofing there are three routes, and all three have their price.
Tiles out, rebuild. The clean solution: old covering off, check and prepare the substrate, waterproof to the standard, tile anew. Laborious and involving downtime, but afterwards the build-up is right.
Waterproof over the existing tiles. The existing tiles stay, are degreased, sanded and pre-treated with an adhesion primer; the waterproofing and a new covering go on top. Prerequisites: all tiles are firmly bonded, old silicone joints are removed completely, and the build-up height of about 15 to 20 mm is available at doors and drain. How this works in detail is explained under Waterproofing a bathroom with liquid membrane.
Secure only the weak points. Not a build-up to the standard, but better than nothing: renew connection joints, back the bathtub edge with sealing tape, seal pipe penetrations. For a bathroom that will be renovated anyway in a few years, a defensible interim solution – as a permanent state, not.
Document while it is still visible
Once the tiling is done, it can no longer be determined whether and how waterproofing was applied. So take photos of the finished waterproofing build-up before the covering goes on: the surfaces, the corners with the sealing tape laid in, the collars at pipe penetrations and drain, plus the product labels.
That takes five minutes and is worth its weight in gold in three situations: when selling the property, in a dispute with a tradesperson and with the insurer if damage occurs elsewhere in the house. For commissioned work, the measurement record with the heights as executed and the system components used also belongs in the documents.
Is waterproofing mandatory?
There is no regulation that says in so many words “you must waterproof”. DIN 18534 is, however, a generally recognised rule of technology, and every tradesperson owes that to their client – even if it is not in the contract.
In practice that means: if a bathroom is built without the required waterproofing, there is a defect, regardless of whether water gets through or not. In the event of damage the contractor bears the costs, and insurers reduce payouts for demonstrably defective execution.
For DIY work the same technical yardstick applies, albeit without a contractual partner. Anyone waterproofing their own bathroom still has an interest in doing it right – and should be able to document how the work was done when the house is sold later. Photos of the build-up before tiling are the simplest means for that.
Four misconceptions that get expensive
The tile yes, the grout no. Cement grout absorbs water, and silicone joints only last a few years.
Water reaches the floor when getting in and out, when cleaning and through leaky cubicle profiles. Floor waterproofing is required even then.
A primer consolidates and regulates absorbency. It has no sealing effect – that takes the actual waterproofing layer in the required thickness.
All corners, edges and penetrations need a tape or a collar. That is exactly where the substrate moves most.
Frequently asked questions
Which DIN applies to bathroom waterproofing?
DIN 18534 “Waterproofing of interior rooms”, valid since 2017. For this area it replaced the former DIN 18195.
Must the bathroom floor be waterproofed?
As a rule yes. With a level-access shower, the shower area belongs in W2-I and must be waterproofed; the remaining floor area is classified as W1-I with effective splash protection and is also waterproofed. Only with W0-I – for example in a guest WC without a shower – can it be omitted.
How high must the waterproofing on the wall be?
At least 20 cm above the highest tap outlet and at the sides at least 20 cm beyond the splash zone. For a bathtub that is also used for showering, this usually results in a height of about 2.25 m above finished floor level.
What does W2-I mean?
High water exposure indoors: frequent splash and service water that can temporarily pond on the surface. The typical case is the floor of a level-access shower.
Is a shower enclosure enough as splash protection?
It allows the remaining floor area in a domestic bathroom to be classified as W1-I instead of W2-I – but only if it is a fixed enclosure. A shower curtain does not count as effective splash protection. The floor waterproofing itself must not be omitted in any case.
What is a bonded waterproofing?
A waterproofing that lies directly beneath the tile covering and is firmly bonded to it – abbreviated AIV. It replaces the waterproofing under the screed that used to be usual and stops the water at the surface instead of only deep in the build-up.
Does DIN 18534 also apply to DIY work?
As a standard it is addressed to those carrying out the work, regardless of whether anyone is paid for it. Legally you have no obligation towards yourself – technically the same yardstick applies. And when the house is sold later, the question of how the bathroom is built can very well become relevant.
What does bathroom waterproofing cost?
On the materials side it is the smallest item in the whole bathroom renovation – primer, waterproofing, sealing tapes and collars are, for an average bathroom, in the low hundreds of euros. The effort lies in the working time, above all for the corners and penetrations. Measured against the cost of moisture damage in the storey below, both are negligible.
Is a water-resistant tile enough as waterproofing?
No. The tile itself is watertight, the covering as a system is not – joints, connections and hairline cracks pass water on. Waterproofing is a layer of its own beneath the covering and cannot be replaced by anything on the surface.
What is the difference between DIN 18534 and DIN 18195?
DIN 18195 governed all structural waterproofing together until 2017. Since then it has been split into five specialist standards; for interior rooms DIN 18534 applies. DIN 18195 continues as a terminology standard, but no longer contains execution rules.
Do I also have to waterproof the bathtub if it is tiled in?
The bathtub itself is a watertight component, its connection to wall and floor is not. Exactly there, a bath edge sealing tape and a professionally executed connection joint belong. With bathtubs that are built in or tiled in, this connection is the most frequent point of damage in the whole bathroom.
Who is liable if the waterproofing is missing?
For commissioned work, the contractor carrying it out, because the generally recognised rules of technology are owed even without an express agreement. For DIY work you bear the risk yourself – and may have to disclose it when selling later.
