Dallmer develops innovative sanitary technology designed to improve drainage performance, reliability, and design in contemporary architecture. This technical guide outlines the key considerations for planning a bathroom renovation, with a focus on refurbishment constraints, accessibility, and reliable drainage solutions.
Bathroom renovation projects often take place under uncertain conditions, as existing pipe routes, floor structures, and waterproofing layers are not always fully documented. As a result, early technical assessment and close coordination between architects, planners, and contractors are essential to avoid costly adjustments during construction.
Bathroom refurbishment represents a significant portion of renovation activity and is frequently driven by the need for spatial upgrades or age-appropriate, accessible design. The following steps provide a structured framework for planning and executing a technically sound bathroom renovation.
1. Define the extent of refurbishment
Begin by determining whether the project involves partial replacement or a full refurbishment. Comprehensive bathroom renovations typically require removing existing sanitary fixtures, surface finishes, and technical installations.
The location of pipes largely determines where new elements such as showers, bathtubs, and washbasins can be installed. If a level-access shower is planned, additional factors such as floor structure, drainage system selection, slope formation, and waterproofing must be assessed early on.
2. Assess existing pipework and connections
In refurbishment projects, the layout of sanitary fixtures is often constrained by existing installations. Unlike new-build projects, pipe routes cannot always be freely repositioned.
Start by evaluating:
- The location of the water supply and wastewater pipes
- The overall condition and remaining service life of the installations
This assessment helps determine whether fixtures can be repositioned or whether adaptations are required. Drainage systems designed for refurbishment, such as the DallFlex drain body, support this process by offering multiple outlet options, allowing connection to existing wastewater pipes with greater flexibility.
| DallFlex drain body |  |
3. Decide whether pipes need replacing
As a general guideline, copper and steel water pipes have a service life of up to 40 years. Even if they are still functional, replacing ageing pipes during renovation is often advisable.
If replacement is required, select the appropriate installation method:
- Install additional connections between sanitary fixtures and the downpipe
- Connection pipes must be laid horizontally and designed with a minimum slope to ensure proper drainage
- Avoid horizontal cuts in masonry to preserve structural stability. Connection pipes are typically installed using a front-of-wall system
- Front-of-wall installation
Front-of-wall installations route pipes in front of the existing wall and conceal them behind a stud structure. This method is widely used in renovation projects because it is faster, more economical, and offers greater design flexibility.
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- Wastewater pipes are laid with a minimum slope of 2%
- Hot and cold water distributors are routed to individual tapping points
- The stud structure is closed with suitable boards and prepared for waterproofing and tiling
- Half-height front-of-wall installations can also provide additional storage or shelving
Concealed installations route pipes within the wall and require extensive demolition. This approach is more complex and is only permissible if the structural integrity of the masonry can be maintained. Structural verification in accordance with regulations is therefore required.
| HT / SML pipe couplings from Dallmer for a reliable and quick connection for various pipes |  |
4. Waterproof pipe penetrations and connections
All newly installed pipes and connection points must be integrated into the bonded waterproofing system in accordance with applicable standards, such as DIN 18534.
- Use approved sealing tapes and sealing sleeves
- Ensure pipes extend beyond the waterproofing level to allow proper sealing
- Compensate for insufficient pipe length by using spacers of up to 5 mm, particularly in concealed installations, where this issue occurs more frequently
- In front-of-wall installations, the correct connection lengths are defined by the construction
Careful detailing at this stage is critical, as defective waterproofing can lead to significant consequential damage.
5. Ensure proper ventilation of drainage pipes
Adequate ventilation of drainage systems is essential to prevent negative pressure from emptying siphons and allowing sewer gases to enter the bathroom.
In renovation projects, air-admittance valves are often a space-efficient solution. Follow this general outline for their installation:
- Check that the valve is allowed for the type of building that is being renewed
- Install the valve in a vertical position only
- Ensure a continuous supply of fresh air
- Maintain permanent access for inspection and maintenance
- Position the valve at least 10 cm above connecting pipes or 60 cm above the highest branch in the case of downpipes
- Protect the valve from contamination during the construction phase
- Install valves below the backflow level only if the drainage pipe is adequately protected against backflow
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| In the case of negative pressure in the pipe system, the ventilation valve opens, and the incoming air equalizes the pressure. | In the event of overpressure, the ventilation valve seals the system.
No sewer gases can escape. |
6. Assess the feasibility of a level-access shower
If a shower tray was previously installed, water connections are often already positioned appropriately. When replacing a bathtub, connections can usually be relocated and raised.
In addition to pipe positioning, the following parameters must be evaluated
- Available structure height and screed build-up
- Expected water volume
- The presence or absence of shower partitions
These factors determine the choice of drainage system, slope design, and waterproofing strategy.
6.2 Assess floor structure and structure height
Structure height refers to the total thickness between the finished floor surface and the load-bearing slab, and typically includes insulation layers, screed, waterproofing, and floor finishes.
This information can often be obtained from architectural drawings. However, if these are unavailable, sample drilling may be required. Determining the available structure height at an early stage is critical, as it directly dictates which drainage systems and installation methods can be used.
| CeraFloor Select shower channel + DallFlex Plan drain body |
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| 1. Structure height, 2. Tiles, 3. Tile adhesive, 4. Bonded waterproofing, 5. Screed, 6. Thermal insulation, 7. Concrete surface |
6.3 Choose the installation system in the screed
Different installation methods are available depending on the existing structural conditions:
- Systems installed in the screed
The shower area is recessed into the floor, with the drain body positioned below floor level to allow for sloped screed. After fixing the drain body and connecting it to the drainage pipe, screed is applied, bonded waterproofing is integrated, and surfaces are tiled. Low-profile drain bodies are particularly suitable for refurbishment; for example, the DallFlex Plan drain body requires an installation height of 65 mm (standard: 90 mm).
| CeraWall Select shower channel + DallFlex drain body |
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| 1. First waterproofing layer, 2. Sealing sleeve, 100 mm all round, 3. All-round sealing tape, 4. Second waterproofing layer, 5. Safety tape with cut protection, 6. Tile adhesive, 7. Channel with cross slope, 8. Drain body |
- Systems with a shower underlay
Hard-foam shower underlays with an integrated slope and drain allow installation without forming a screed slope. Depending on site conditions, partial screed removal may be required. Compatibility can only be confirmed once existing fixtures are removed, as pipe height and position are decisive. Shower underlays must be tiled and fully integrated into the bonded waterproofing system. Tile size depends on the compressive strength of the foam; Dallmer shower underlays require tiles of at least 5 × 5 cm and are suitable for wheelchair-accessible bathrooms.
6.4 Implement bonded waterproofing
Reliable waterproofing is essential for long-term performance. Defective waterproofing can lead to significant consequential damage and must therefore be implemented in accordance with DIN 18534.
Level-access showers in private bathrooms fall under water exposure class W2-I, indicating a high water load. In these areas:
- Crack-bridging mineral slurries or reactive resins must be used, with a minimum dry layer thickness of 2 mm
- Sheet waterproofing systems may be applied
- Polymer dispersion coatings (minimum dry layer thickness: 0.5 mm) are permitted only in splash-water zones, such as wall areas, and must not be used on the shower floor
6.5 Plan partitions, transitions, and feed-throughs
Shower partitions may take various forms, including enclosed cubicles, doorless partitions, or niches. The chosen configuration must be defined before installation, as it determines the extent and detailing of the waterproofing.
Waterproofing must extend beyond wall and floor surfaces to include:
- Transitions between the screed and the drain body
- Connections using sealing tapes, fleeces, and sleeves
- Secure integration of the drainage system into the waterproofing layer
Systems such as DallFlex allow the sealing sleeve to be clamped directly into the drain body after bonded waterproofing is applied, ensuring a reliable and continuous seal.
Feed-throughs at the waterproofing level are particularly sensitive and should be avoided wherever possible. If unavoidable, they must be carefully planned and executed without damaging the waterproofing layer and should ideally be defined before waterproofing begins. For level-access showers, the entire bathroom floor area generally requires waterproofing.
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| The flexible DallFlex sealing sleeve for mounting bonded and sheet waterproofing as per DIN 18534 |
7. Plan and implement the sloped screed
The shower surface must be designed with a defined slope to ensure reliable gravity drainage. Channels or floor drains should be positioned at the lowest point of the shower area, directing all water toward the outlet while accounting for expected water volume and water level above the grate.
- Apply the correct slope geometry
- Use a slope of 2% when the outlet is centrally located
- Provide a slope of approximately 2 cm for a 1.5 m² shower area when the channel is positioned along the wall; increase to 2% for larger areas
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| Implemented slope of 2% |
- Prevent water migration beyond the shower area
- Extend a gentle slope across the bathroom floor if no partition is used
- Slope surfaces toward the drain and away from doors
- Avoid water transfer from waterproofed to non-waterproofed areas
- Install a raised threshold of approximately 1 cm where required, depending on water exposure
- Extend waterproofing into the door reveal and behind the frame in accordance with regulations
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| Slope of 2% in cross section | Slope of 2% in system section |
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