Mark Bowman of Marmox provides expert advice on how to successfully design and install large and small bathrooms

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From the Supreme Court of America to smaller council chambers across rural England, issues regarding the creation of shared or ‘gender neutral’ washroom facilities for public use have proven to be a legal as well as a political hot potato, with the debate set to continue for the foreseeable future. For architects and interior designers, however, there are many other technical considerations that must be considered if their work is to meet users’ expectations. For example, whatever the size of the bathroom or washroom being created, it is essential that the background structure and substrates to the room are fit-for-purpose in terms of strength, durability and resistance to moisture. Other requirements, including thermal and acoustic performance, as well as the need to provide access for the less able bodied, are addressed by parts of the Building Regulations.

Ever since the emergence of the Egan Report, offsite construction and prefabrication have been gathering momentum across the industry, with fully fitted bathroom pods playing a pivotal role in the rapid delivery of student accommodation, hospitals, hotels and commercial buildings. Whatever the scale, from an individual en-suite to a large washroom with multiple facilities, they enable building services work to be completed off-site, reducing time and improving quality. While some pods feature reinforced concrete bases, the weight penalty sees the majority assembled using a light-gauge steel or engineered timber frame, with a range of board products providing the substrate for fittings and finishes.


It is worth noting that despite using concealed steel frames with sizeable securing bolts, the increasingly popular wall-hung toilet bowls and urinals normally transmit a proportion of their load to the wall itself. So whether the specifier selects a decorative laminate or a tile-backer board, such as Marmox Multiboard, the fixture will have to be installed over a 15mm (or thicker) sheet of plywood to prevent flexing. Tile-backer boards do, however, provide good compressive strength, as well as a number of other positive physical characteristics, making them a popular choice for building either in-situ or offsite.

Employed in wall or floor build-ups, tile-backer boards can sustain a distributed load of 40 tonnes per square-metre, making them fully able to support the weight of pedestrians, wheelchairs and even mobility scooters when covered by appropriate floor tiles. Performance stems from their construction, which comprises an extruded polystyrene core, bonded between two layers of glass-fibre reinforced polymer concrete. The combination of a rigid outer shell and XPS core absorbs lateral movement, allowing the board to serve as an effective decoupling layer.


This structure not only earns an ODP score of Zero and a Class O rating for flammability under BS EN 476, but the XPS also delivers excellent thermal characteristics. The insulation provides a thermal conductivity of 0.034 W/mK, and with the tile-backer board being available in thicknesses of up to 60mm, it can make a significant contribution to achieving Part L requirements.

Furthermore, the ability to reduce heat loss also helps to combat condensation and associated mould growth. This can be particularly beneficial on refurbishment projects, where the energy performance, as well as the physical condition of the walls is generally a concern.


High-performance tile-backer boards are regularly employed on social housing contracts, where kitchen and bathroom renovations have to be completed to a tight timescale with the residents still occupying the building. They can be screw-fixed to blockwork and brickwork, or bonded using a cement-based adhesive across uneven substrates, including existing ceramic tiles. Top-end bathroom specifications often incorporate wetrooms or steam-rooms, which is where the fully waterproof performance of XPS and reinforced polymer concrete comes to the fore. Rooms such as these can be effectively ‘tanked’ by applying the special waterproofing tape to all joints and other details, including corners, prior to tiling or plastering.

Given the UK’s temperate climate and the increasingly exacting design aspirations of developers and specifiers, choosing the right materials for the construction of bathrooms or other washroom facilities is paramount. With the endorsement of the Energy Saving Trust, CE marking and all other necessary accreditations, XPS based tile-backer boards (Marmox Multiboards) make a powerful argument for inclusion.

Contact details
For more information please contact the Marmox website (, email or call 01634 835290.