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Introduction

Sport and leisure swimming is highly dependent on good-quality, accessible infrastructure. Professional swimmers need to train in large, deep pools in order to get experience of the conditions they will face during competition. Compared to other countries in the European Union, the UK has few 50 m pools. However, most recreational swimmers find such pools too long and too deep, so facilities have to be designed with flexibility in mind if they are to attract enough users to pay the bills.

In addition to the demand for high-quality facilities for competitive sport, swimming pool providers in the public sector have to respond to significant changes in demand and expectation. The promotion of swimming as an ideal low-impact exercise has led to an increase in levels of activity. However, much of this demand has been soaked up by private leisure clubs.

In the public sector, the existing stock increasingly represents a liability in terms of maintenance and fitness for purpose, so it is not surprising that some local authorities have sought to rationalise their facilities, closing pools with the greatest problems and focusing resources on new, larger facilities that are more popular, less costly to run and that can support a wider range of pool users.

Most of these pools have been a great success, providing flexible facilities for a diverse client base. However, there have been some notable failures, which have encouraged clients to adopt tried-and-tested solutions delivered by experienced design and construction teams for their new developments.

Credit: Charlotte Wood, courtesy of S&P Architects

Booms and movable floors are used to make the 50 m pool at Crawley Leisure Centre suitable for a mix of leisure, teaching and fitness swimming

Demand for pools

Pools are a key part of the UK's health infrastructure and an important aspect of the country's recreational and sporting investment. Some 12 million people are regular swimmers, mostly engaged in "purposeful" swimming related to sport, health and fitness or education.

To support competitive swimming and to secure a diversified income base, pools need to be designed to support a wide range of uses. Flexibility features such as booms and movable floors can make a major contribution to maximising the use of the facility, its value to the community and the revenue it can generate. In addition, changes in the way that pools are used have affected detailed specification. Most noticeably, public expectations of the quality of facilities have risen, driven mainly by competition from the private sector.

Unfortunately, popularity does not guarantee financial success and pools represent a significant revenue risk to their operators. Public facilities, dependent on "per-use" income streams and required to provide low-cost access to address the social inclusion agenda, need substantial subsidy, which means a stand-alone pool development is rarely a viable option. Schemes that combine swimming with gym and sports hall facilities achieve a better balance of revenue generation and a diversified health and fitness offer. Unfortunately, it may not possible to combine these uses on a single site. In some instances, capital funding can also be secured as part of a larger commercial development, such as the King Alfred scheme in Hove.

The level of subsidy required and the financial liability represented by the existing pool estate is often the trigger for redevelopment. Given that new pools attract more users, are cheaper to run and have no maintenance backlog, the business case is not difficult to construct even though the new facilities will require a continuing level of subsidy.

Pools built in the 1950s and 1960s, for example, which can have major problems with their building fabric, may not be worth the investment in equipment renewal and refurbishment. By contrast, many pools built before the second world war and those developed in the mid-1970s are generally sound enough to justify continuing investment and may, if maintained properly, have an economic life in excess of 70 years - as long as the pool tank itself meets user needs in terms of size, width and so on.

As pool provision is rationalised, there is the risk that smaller swimming pool facilities will be closed to redirect demand to support larger combination pools. However, in less densely populated areas, travel distances may be too great to support a centralised pool and a scaled-down facility may provide the right solution.

The Swim25 system by S&P Architects and Arup is an example of a standardised system providing a low-cost solution for community-scale swimming. Designed with an optimum pool area-to-floor area ratio and cost-effective materials, Swim25 is targeted at providing accessible, local facilities that still meet the requirements for training and competitive swimming.

Economics and cost drivers of pools

Pools are among the most expensive public-sector sports buildings to build and maintain. They require ongoing subsidy, so both capital and operating costs will come under careful scrutiny. As a result, the typical pool is designed with spatial efficiency very much in mind, allowing little space for uses other than programmed activities. This means opportunities for architectural expression or spaces for incidental activities can be quite restricted on these projects.

The key areas where money is spent in pools - substructure and pool tank, roof, finishes, mechanical services and the pool installation itself - are difficult to value-engineer, as a base level of performance has to be high enough to guarantee trouble-free operation. In seeking to develop a cost-effective solution, the key drivers affecting the cost-value equation are:

• Pool size Pool size is the major development driver, determining the size of the pool hall, changing facilities and so on. Most of the expensive building work is associated with the pool so its size will have greatest impact on total cost.
• Area and depth Training pools require depths of between 1 m and 1.2 m, whereas pools designed for major competitions need to be 2 m deep. The pool width will be determined by the number of lanes, which are specified as being 2 m wide by Britain's Amateur Swimming Association.
• Volume Deeper pools designed for competition require larger filtration and heating plant as well as the larger tank.
• Ground conditions A high water table may result in the need for ground anchoring of the pool tank if water pressure is too high.
• Builders' work The installation of dry air duct systems, moving floors and booms drive up costs.

Pool hall size and volume

Pool hall size is broadly determined by the width of the pool surround, typically 2 m, and the height of the pool, taking into account requirements for spectator seating and diving platforms. These factors affect wall-to-floor ratios, air-handling volumes and heating loads.

Pool flexibility

Features such as booms and movable floors add considerably to the building costs and also require extensive builders' work to accommodate machinery and so on. Movable floors also require an additional zone of 400-700 mm below the maximum operating depth of the pool. However, the payback of these features is considerable as they substantially increase the flexibility available to the operator and the intensity of the pool's use.

Mix of wet and dry activities

Other facilities such as health and fitness suites and sports halls are significantly cheaper to build than the swimming areas. As a result, schemes with a high proportion of dry sports to wet will have a lower build cost on a £/m2 basis although the floor area and total cost will be substantially more than for a comparable wet-only scheme.

Design issues

Given the functional and environmental challenges posed by pool design, together with the significant risks associated with underperformance, it is not surprising that many of the main design issues concern the mitigation of operational risks. However, before detailed performance is considered, some big-picture issues need to be addressed.

Flexibility

The basic requirement in a pool complex is separate areas for teaching and "purposeful" swimming. The alternatives available are:

• A 25 m pool with a separate learner pool, possibly with moving floors to provide variable depth. This is the option with the lowest capital and operational costs, but with some limits on use for competitive swimming.
• A sub-divisible 50 m pool with booms and moving floors. A boom and moving floor at each end enables the pool to be split up for shallow water teaching, competitive training and diving. Since the award of the 2012 Olympics to London, more 50 m pools are being proposed as the best way to provide the right balance of facilities at the optimum capital and revenue cost.

Ancillary spaces

The arrangement of support spaces has a considerable impact on ease of use and the long-term cost-effectiveness of the pool. In addition to optimising area allocations, there are operational and safety issues to be considered, which may create challenges on a highly constrained site:

• Changing areas should ideally be adjacent to the shallow end of the pool
• Spaces for covers and so on need to be immediately adjacent to the pool tank
• Adequate space must be provided for the storage of equipment
• Plant rooms must be provided for filtration plant, movable floor control gear and other systems.

Credit: Charlotte Wood, courtesy of S&P Architects

The UK has a shortage of full-sized 50 m, 10-lane Olympic pools such as this one, the National Aquatic Centre in Dublin

ºÚ¶´ÉçÇø services solutions

ºÚ¶´ÉçÇø services installations in pools deal with large heating and ventilating loads in a highly corrosive atmosphere. Selection of the systems can have a significant impact on the base build design, operating costs and the management regime. Three areas to consider are:

• Design of the system to manage pollutants Pool environments are highly corrosive and the ventilation and extract system can be used to contain the zone of polluted air above the water surface, taking extract air through "dry ducts" incorporated into the pool overflow system.

This system also reduces the metal work in the pool hall by removing the need for high-level extract ductwork.

• Requirements for builders' work Dry duct systems have extensive requirements for builders' work that will increase the capital cost of the pool. However, the ducts can also be used as services distribution routes, which may lead to savings in capital and maintenance costs associated with the building services installation. More conventional systems that use high-level extract will require dedicated service routings around the pool tank.
• Heat recovery and energy efficiency Because of high air temperatures and humidity levels, there are considerable opportunities for energy recovery using both thermal wheels and heat pump technology. Combined heat and power systems can also be used to supply the constant heating and power needed. However, CHP systems are not always popular with users. Ease of use and reliability need to be addressed to ensure successful take-up of the technology.

ºÚ¶´ÉçÇø performance issues

Pool design involves a number of technical challenges and the consequences of defects can be more severe than for many other public buildings. However, there are many successful projects from which lessons have been learned and a risk-adverse approach to design is likely to be in the best interests of the client. Areas to focus on include:

Control of condensation

Condensation and corrosion are inherent problems in swimming pool design, where control of condensation has become more challenging as pool temperatures have risen in line with user expectations. To avoid condensation, air temperature must be kept 1°C above the water temperature. Air in swimming pools is also very humid, so if there are failures in either insulation or the vapour barrier, the consequences can be severe. Design measures include using stable insulation, use of low conductivity materials such as glulam timber in the pool hall and the design of the heating and ventilating system to direct warm, dry air over the internal surface of the facade to minimise condensation. Use of pool covers outside of opening hours also helps to control both evaporation and condensation and lowers water heating bills.

Leakage from pool tank and surround

Leaks can come from failures in the casting of the concrete tank shell or from applied waterproof coatings. Steel tanks tend to be more reliable and are used in high-risk locations such as pools on upper floors. The pool tank itself should be tested for integrity before backfilling operations and so on. Two additional sources of leak risk are the pool surround and steam rooms. In the case of pool surrounds, monolithic construction offers the best long-term solution. With steam rooms, the challenge is to ensure full integrity of the enclosure, regardless of build technique.

Glare and pool hall safety

Natural light is an important feature in pool design - to provide contact with the outside world and visual interest for swimmers and to reduce lighting costs. Most natural lighting can be provided from high-level rooflights and presents only a limited risk of glare. Side lighting, an increasingly popular design feature, can create glare and unwanted reflection, which can result in risks to users, such as not being able to distinguish the pool edge. The risk can be addressed by considering the extent of glazing, its orientation and control of contrast.

Dimensional tolerance

Pools designed for any level of competition need to meet closely defined dimensions. These can be difficult to achieve with insitu concrete work. Final dimensions depend on the thickness of tiles and backing and the tolerances of the tank wall. Although it is possible to correct the dimensions of an over-sized tank with a thicker lining, undersized tanks are harder to correct because of the need to retain adequate concrete cover over reinforcement in the tank wall.

Operating costs

Key issues in controlling operating costs include:

• The selection of the filtration system Until recently, ozone was the market leader. Because of high water turnover rates, ozone-based systems are widely believed to provide the highest quality water. However, they need larger plant rooms and have the highest operating costs, partly because of the need to generate ozone on site. UV systems are also highly rated and, because they need very low levels of chlorine, cause little swimmer discomfort.
• The design of surfaces and selection of easy clean materials An effective cleaning regime is important in pools, not only to maintain good appearances but for health and safety reasons. Careful selection of non-slip tiles and the specification of falls that balance public safety and effective cleaning are important.
• Avoidance of high maintenance materials These include exposed architectural concrete, porous masonry and ceramics, structural glass and certain grades of stainless steel.

Safety and security of users

Key safety issues include:

• Providing clear sight lines for supervisory staff in the pool hall
• Avoidance of circulation pinch points, level changes and trip and catch hazards in all public areas
• Adequate provision for safe storage of equipment and teaching aids.

Personal security concerns users more and more so the design of changing areas and glazing has to take into account the prevention of antisocial behaviour. New risks - and public awareness of these risks are always emerging and pool design must respond to these.

Credit: Visual courtesy of S&P Architects

The Swim25 system has been designed to provide a simple low-cost pool that can be built as a stand-alone pool or combined with dry sports facilities

Procurement of specialist equipment

The key areas of specialist procurement of pools are related to filtration systems and other installations including booms and moving floors.

The long-term performance and operating costs of a pool are strongly influenced by the selection of the filtration system. The market for these systems and the consultants who design and specify them is quite small. As a result, clients need to be careful in their pre-selection and tendering procedures. There is a range of quality and performance in the supply chain and the client must ensure that the procurement route secures the interest of the appropriate supplier for the grade of pool specified.

Given that European procurement directives usually apply, accountable tendering procedures also have to be followed.

Attention should be given to the following:

Capacity

This is particularly important among the high-end suppliers that can match the most stringent performance requirements for competition pools.

Co-ordination of filtration and equipment specialists

A high degree of co-ordination between systems is needed, and many specialists operate in strategic alliances, which can narrow the tender list.

Drafting of performance standards

Pool performance standards are open to a degree of interpretation so it is important to draft the specification to cover a full range of operational circumstances. This needs to address:

• Overall system capacity
• Performance at different rates of throughput
• System resilience and back-up capacity.

The preselection of a list of filtration and pool equipment subcontractors by the client before the tender for the main contractor is advisable, either as part of a single- or two-stage procurement process.