Waterproofing Details for Bathrooms and Wetrooms

Types of Waterproofing

1. Flexible sheet waterproofing
2. Watertight board waterproofing
3. Liquid applied waterproofing

Each type of waterproofing has its own advantages and disadvantages. Above all else, it is essential to ensure that the chosen system is coordinated with the wall and floor design, so that they all work together in line with the system manufacturers requirements. It is recommended to source all waterproofing elements from a single manufacturer to ensure their compatibility. This way, all of the products will be designed to work together.

1. Flexible Sheet Waterproofing

Flexible sheet waterproofing involves the application of waterproof membranes to the surface of the wall or floor before tiling. The sheets are cut to fit and fixed to walls and floors using an adhesive. The seams are sealed with a waterproof sealing tape or they are bonded using overlaps to create a continuous watertight barrier. Pre-formed seals and tapes are used for the corners between walls / floors and for any penetrations through the sheet (such as at the shower head and mixing valve). It is critical to follow the manufacturer’s requirements for fixing, jointing and sealing using their compatible products. Once installed, tiles can usually be applied directly on to the membrane.

Considerations:

• Requires a flat substrate
• Requires precise installation and careful seam sealing 
• Can be more expensive than liquid waterproofing

Example manufacturers:

• Schluter – KERDI
• Wedi – Subliner

2. Liquid Applied Waterproofing

Liquid applied waterproofing involves the application of a brush on, roll on, or spray on waterproof coating that dries into a seamless, flexible membrane. Pre-formed seals and tapes are used for corners between walls / floors for any penetrations through the wall (such as at the shower head and mixing valve). The waterproofing liquid is usually applied in multiple coats onto a primed surface. It then dries to form a flexible waterproof membrane that prevents water penetration. Once dry, tiles can be installed on top.

Considerations:

• Easy to apply, but can be uneven if not done carefully
• Usually requires multiple coats with drying time between applications
• Creates a seamless waterproofing layer
• Can be more affordable than sheet membranes

Example manufacturers:

• Aquaproof – Wetroom tanking
• Intelligent membranes – Poseidon

3. Watertight Board Waterproofing

Watertight boards are structural building boards which have waterproof properties. Boards can be installed as part of the wall or floor build up in lieu of other board types. The joints between boards are sealed using waterproof tape and adhesive. Tiles are applied directly to the boards, making them a structural and waterproofing solution.

Considerations:

• Can be faster to apply than other waterproofing methods
• Can be more expensive than liquid applied and sheet waterproofing methods
• Requires proper sealing at joints

Example manufacturers:

• Wedi building board
• Schluter – KERDI board

Quality Standards for Bathroom and Wetroom Waterproofing

There are a couple of references and best practice standards that should be considered when specifying the design for wet areas.

Bathroom waterproofing is featured within BS 5385-1 (wall and floor tiling in normal internal conditions). It recommends that bathrooms and wet rooms (areas subject to frequent wetting) be waterproofed before tiling, in both commercial and domestic projects. Without waterproofing measures, moisture could be absorbed through the tile grout and adhesive bed and pass into the adjacent substrate. If the substrate was subjected to moisture it would be at risk of damp and mould issues.

The National House Building Council (NHBC) has technical requirements and performance standards for the design and construction of new homes registered with them. Guidance for the waterproofing of bathrooms and wetrooms is provided within their technical guidance note number 9.2/06. The guidance details the extent of bathroom waterproofing required in different types of location, the suitable substrates and the performance requirements of the waterproofing system itself. The guidance is very useful, even in cases where the project may not be registered with the NHBC. This is because it provides an indication of what the largest warranty provider in the UK expects as standard.

Key Considerations for Bathrooms and Wetroom Detailing

Specify the type – Consider which type of waterproofing is best suited to the project. Factors affecting the decision could be ease of installation, cost and contractor experience (if they’re involved at this stage).

Consider the substrate – The substrate for the waterproofing (the wall and / or floor build up) must be compatible with the waterproofing type and product. The flatness of the substrate must also be compatible. Remember to consider the wall and floor performance as a whole – note that they may have acoustic / fire performance requirements and that in that case any alterations to the build up for waterproofing purposes must not affect other areas of performance.

Specify the products – Research products from reputable manufacturers. NBS source can be a useful guide to begin product selection. Factors affecting the decision could include product guarantee, warranty requirements (such as NHBC), EAD certification, BBA certification, presence of VOCs, sustainable credentials, product thickness, water vapour permeability etc.

Specify the extent – Communicate the extent of waterproofing that’s required on drawings and within specifications. The extent will be affected by the bathroom / wetroom layout. Follow best practice guidance such as that within NHBC technical guidance note 9.2/06.

Design the junctions – Walls, floors and any junctions between them or penetrations through them are critical interfaces (or weak points) that require particularly careful consideration. Drawing the junctions accurately, in line with manufacturers installation details is critical to ensure that the design intent is achieved.

Make sure the tiled finish is compatible – Note that some waterproofing systems may restrict the size of tiles that can be applied to the waterproof surface. Ensure that the chosen tiles are suitable and also ensure that the substrate can take the weight of the chosen tiles.

Meet any new build warranty requirements – if the project is required to achieve an independent warranty, ensure that any technical guidance is followed to ensure compliance.

Consider decoupling the tiled floor finish – note that some waterproofing products for floors can provide both waterproofing and decoupling in one. This can prevent the tiles cracking or lifting if the substrate below moves.

Consider ways to reduce moisture in the room – Adequate ventilation is key to removing excess moisture from the room and preventing mould growth. Consider enhancing any purge ventilation through extracts and opening windows where suitable. Note that the ventilation must meet building regulation requirements as a minimum.

Communicating the Design

Regardless of the project size, it is useful to provide as much information to the contractor as possible to avoid any misunderstandings on site and to ensure that the waterproofing details are coordinated with the rest of the design.

The following can be useful to include:

• Room elevations and floor plans indicating the extent of waterproofing required. A variety of these drawings are available on the Detail Library and they can be adapted to suit a specific project
• Construction details (plans and sections) showing the key junctions between the waterproofing and other finishes / fittings (e.g wall to bath or floor to wet room shower tray). A variety of these coordinated construction details are available on the Detail Library and they can be adapted to suit a specific project
• Performance specification notes 
• Notes on partition types plans to highlight the walls where waterproofing will affect the wall specification
• Notes on floor types and / or floor finishes plans to highlight the floors where waterproofing will affect the floor specification

Conclusion

Well designed waterproofing is essential for creating bathrooms or wetrooms that are free of moisture problems. Providing robust design information such as coordinated construction details and detailed specifications can ensure that best practice is followed and avoid any misunderstandings on site.

A variety of bathroom waterproofing details have been added to the Detail Library’s vast collection of construction details. The details are available for download in a number of formats (including DWG, RVT & SKP). They include examples of flexible sheet / liquid applied and watertight board waterproofing details. Does your next project include a bathroom or wetroom? Why not see how much time the Detail Library details could save you.

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Resources

Related Reading

References and Useful Resources

https://www.nhbc.co.uk/builders/products-and-services/techzone/nhbc-standards/technical-guidance

BS 5385-1 (wall and floor tiling in normal internal conditions)

https://eu.schluter.com/en-GB/waterproofing-224.html

https://www.altsystem.wedi.net/uk/products/building-systems/building-board/

https://wetroomexperts.co.uk/shop/wetroom-tanking/