Bathrooms make an ideal candidate for prefabrication, being relatively small and self-contained units. Furthermore, sanitary and services provision is expensive. Bathrooms typically account for 6-10% of the capital cost of a hotel, so prefabricating them can mean significant savings.
With traditional building, a multitude of trades needs to be organised to realise the bathroom design. This requires a high degree of supervision and management on site to ensure correct sequencing and quality of work from plumbers, electricians, tilers, floor layers, sealant applicators, decorators, glaziers, carpenters and other specialists.
Modular bathrooms or bathroom pods do away with most of these issues and although the capital cost may not be less than site-constructed bathrooms, savings from waste and improved quality result in less snagging and better performance in use. More significantly, reduced construction times mean earlier income streams from the property.
Specification variation
There is no such thing as a standard bathroom pod; what you specify is what you get. However, there will be cost benefits in specifying to manufacturers’ “standards” or in large volumes. Depending on the complexity and manufacturer a minimum order of 10 to 100 pods may be required for a reasonable final cost. Larger quantities allow further spreading of set–up costs, for example, making a prototype and tooling up.
The range of options for specification are limitless, but it is worth bearing in mind that the capital costs of the bathroom pods are influenced by the structure, size, shape and quality of finishes and sanitaryware. Typically they include:
• Structure: this may be precast concrete panels, timber or steel frame, reinforced glass fibre or a composite panel system.
• Internal linings and finishes: wall finishes are typically ceramic tiles to BS EN 14411 on a moisture resistant or waterproof lining. Tanking may be an option. The floor to wall, bath edge and shower tray wall are the key junctions to resolve to prevent water penetrating the lining and structure.
• Sanitaryware: basins and WCs are typically vitreous china to BS 3402, baths enamelled steel to BS 1390. Shower enclosures are usually made from safety glass with an aluminium frame.
• Services: electrical and plumbing should be to the relevant standards complete with a commissioning certificate after installation.
• Distribution and waste pipework: these are normally plastic waste and supply pipework, or copper supply pipes.
• Fixtures and fittings: the range is vast and may include mirrors, soapholders and glass shelves.
Functional requirements
Keeping water – liquid and vapour – where it doesn’t harm the fabric is a key functional requirement but it is by no means the only consideration. The relevant sections of the Building Regulations apply with further guidance provided from national secondary documentation: approved documents, technical standards and technical booklets. One potential issue is when the pod is placed on the structural floor of a building, as this may result in a step to gain access, and could compromise accessibility and contravene.
Part M of the Building Regulations. One solution is to specify floorless pods.
Managing the off-site process
Early agreement and a freeze of the design is important. The design process works best where the supply chain is integrated and based on an audited quality control system to ISO 9001. Early freeze allows the factory enough time to schedule manufacture; the downside is that variations may be costly.
Building tolerances and allowances for site positioning are important to ensure the pods fit with other building elements and services connections. Additional structural provision may need to be made to accommodate the loads associated with the bathroom pods.
The protection, storage, transport, lifting and manoeuvring of the pods should be considered in the context of the time of year, programming and site access. Also, if pods are sourced from abroad, ensure that lifting provision is to the UK standards.
Pods in use
In theory the maintenance burden for a prefabricated bathroom should be no more, if not less, than a similar site-fabricated version. The key is to plan for easy access to the services. It should be possible to detect and remedy any leak before the underlying structure is affected.
Specification options
| Shower pods | Capital cost £/unit | Net present value for 60 years £/unit |
| Light weight galvanized low carbon steel framed shower room pod based on residential accommodation | 3500 - 4500 | 6,800 |
| Glass reinforced fibre monoblock structure shower room pod based on student accommodation | 2540 - 3260 | 5,200 |
| Glass reinforced fibre panel structure suited shower room pod based on student accommodation | 2450 - 3150 | 5,300 |
| Precast concrete to BS 8110 panel structure shower room pod based on hotel accommodation | 3540 - 4560 | 6,900 |
Table notes
A discount rate of 3% is used to calculate net present values.
Costs are indicative and are for supply and site installation of the pod. A minimum of 100 units is envisaged, approximately 2.5m x 1.5m. Pods include: basin and taps, WC, shower enclosure and flexible shower hose and head, mirror, towel and heating rails, extract ventilation, electrical socket, ceramic tiled wall finish, PVC slip resistant floor finish with upstand, door and ironmongery, mirror, loo roll holder, vanity shelf. Finishes to relevant British or European standards. Cost benefits from reduced construction times have not been evaluated.
Life cycle costs allow for component replacement, servicing and maintenance items, no allowance for cleaning. Churn or periodic major refit is not modelled. Average capital costs are used in the LCC analysis. Expected service life of structure 60 plus years.
A cost analysis based on project specific information is essential for a realistic best value appraisal.
First published in Building, 2008
Further information
BLP provides latent defect warranties for buildings www.blpinsurance.com
Further information contact peter.mayer@blpinsurance.com or telephone: 020 7204 2450