Insulating a basement containing two swimming pools was key to meeting stringent thermal performance standards at Spelthorne Leisure Centre in Surrey
With many leisure centres teetering on the brink of closure due to rising energy bills, some councils are turning to Passivhaus construction to keep energy consumption in check and meet pressing sustainability targets.
Exeter City Council's trailblazing St Sidwell's Point project became the UK’s first ever Passivhaus leisure centre and public pool when it opened last year and now Spelthorne Borough Council is following suit with a wet and dry leisure centre in Staines-upon-Thames designed to deliver energy and cost savings of up to 60% compared to a standard newbuild.
Due to complete later this year, Spelthorne Leisure Centre was designed by GT3 Architects and Passivhaus specialist Gale & Snowden Architects. It features a health club with a large gym, exercise studios, competition-standard and learner swimming pools, a ‘mini spa’, sports hall, soft play area, a climbing facility and a café with poolside viewing.
Leisure facilities are typically high energy consumers, with space heating and hot water loads higher than any other building type, and they can also be prone to comfort and overheating issues.
Josh Wardle, senior architectural technologist and certified Passivhaus designer at GT3 Architects, said: ‘Leisure centres are one of most energy intensive building types so the opportunity to reduce energy use is large. The challenge comes as they have more interacting systems, compared to a non-pool building, such as water filtration, evaporation and ventilation, which all affect each other and the overall energy intensity.’
Designs for Spelthorne were amended at RIBA Stage 3 to achieve Passivhaus certification, which according to GT3 involved reorienting and relocating of layouts and plant rooms, improving air tightness, integrating air handling units and optimising the domestic hot water system and pool filtration. The building will use up to 50% less water than a standard leisure centre, further reducing its impact on the environment.
A key concern was insulating the enormous basement – which contains an eight-lane, 25m pool with spectator seating, a 20m by 10m learner pool and a filtration room. It demanded a product with sufficient compressive strength, thermal conductivity and thickness.
The originally specified insulation boards were found to be unsuitable, so main contractor Willmott Dixon turned instead to Ravatherm XPS X 700 SL, by Ravago Building Solutions, which could be simply glued and surpassed the thermal performance of the original product.
Nathan Good, technical sales manager, at Ravago Building Solutions UK, said: ‘The originally specified insulation boards turned out to be incompatible with the fastening methods needed to install the pool walls. Airtightness is a key consideration for Passivhaus construction and requires comprehensive photographic evidence of the lack of air gaps. Our boards could be shiplapped and fastened with adhesive bonding, limiting heat loss through nail holes.’
Two 250mm layers of the moisture-resistant insulation were applied to the underside of the pool slab and three 360mm layers to the vertical sides to achieve a U-value of 0.08W/m2K, a 20% improvement on the project's original target of 0.10W/m2K. Passivhaus recommends 0.15 W/m²K or less for buildings heated to 20°C.
‘The fact that Ravatherm could simply be glued on was a huge tick,’ said Wardle. ‘It makes life so much easier to have that flexibility in application, particularly for Passivhaus, where you have to account for heat loss even through the fixings.’