Sandwich panels
Designing a swimming pool roof to limit condensation and corrosion
A roof over a heated pool has to withstand warm, humid air and the chemicals used to treat the water. Specify the facings, fixings and seals for those conditions. PIR insulation can reduce heat loss, but the roof also needs corrosion protection and the building needs ventilation. Assess the whole assembly, from the internal lining to the drainage, before deciding on a core thickness. A seasonal cover for an outdoor pool and a heated indoor pool are different design tasks. For an indoor pool, establish the air temperature, humidity and pattern of use. The exposed water surface, number of swimmers and periods when the pool is closed all affect the load on the building services and conditions at the roof.
In this guide
Which conditions should the design allow for?
Include the intended water treatment chemicals and surface cleaning methods in the design brief. Use that information to select the facings, coatings and fastener materials. A description such as ‘moisture resistant’ tells you too little. A product suitable for a dry warehouse may be unsuitable inside a pool hall.
Why is condensation such a concern?
Water condenses when humid air meets a surface below its dew point. A fixing, rooflight or poorly insulated roof-to-wall junction can provide just such a cold spot. Repeated condensation keeps the surface wet and can accelerate deterioration. Looking only at the centre of a panel misses the risk at these details.
The roof must also be airtight on the room side. Warm air leaking through a gap can carry moisture into colder layers. Specify junctions and service penetrations for the expected indoor conditions. Before using a seal designed for an ordinary industrial building, check that it is suitable for pool use.
What can PIR insulation contribute?
The low thermal conductivity of PIR provides a high thermal resistance at a relatively modest thickness. That can be useful on a roof where flashing heights and the weight of the assembly matter. Select the board and its facing to suit the layers immediately above and below it.
PIR insulation alone does not waterproof the roof. Water can enter at gaps, edges and faulty joints. Provide a continuous barrier against rain and design the drainage accordingly. Also consider fire requirements and service loads, including planned access routes for maintenance.
Are sandwich roof panels suitable above a pool?
A sandwich panel combines facings with an insulating core and can help enclose a building quickly. Above a pool, use a version approved for that environment. Check the internal coating, fixings, seals and treatment of cut edges. A standard roof panel is not necessarily suitable.
The drawings and installation instructions should show how to seal the panel joints and connections to flashings. Pay particular attention to ventilation openings and rooflights. Provide access to inspect the underside of the roof. Even a suitable material may deteriorate unnoticed if critical details cannot be reached.
Include the supporting steelwork in the material selection. A panel coating does nothing to protect purlins, hangers or other components underneath, although they may face equally demanding conditions. Specify compatible materials and a cleaning method that protects the coatings on adjacent surfaces.
How should the roof, ventilation and dehumidification work together?
The envelope limits heat loss and protects the structure, while the building services maintain indoor conditions. Design them together. A warm inner roof surface does not remove the water vapour released by the pool. Equally, increased ventilation cannot repair a thermal bridge or a damaged coating on a steel member.
Specify how the systems will run when the pool is closed. A temperature change or a lower air change rate can affect condensation. Allow for humidity monitoring and access to vulnerable areas. At commissioning, verify actual airflows and control settings as well as the installed equipment.
What maintenance will the roof need?
Schedule inspections of seals, fixings, coatings and drainage. Investigate staining, corrosion, peeling coatings or recurring condensation. Find the moisture source before painting over a mark. Choose cleaning products to suit the coating and the pool environment: an unsuitable chemical can damage a previously sound surface.
Keep records of operating conditions and inspections. If the water treatment process or indoor temperature changes, check whether the original material choices still suit the new conditions. The life of a pool roof depends on the materials, junction details, building services and continued maintenance working together.