Hembuild, part of the Limetec Group, was asked to supply a 198,000sqft retail store near Chester built to M&S Plan A requirements for optimal sustainability and energy efficiency. UK’s largest retail store and largest M&S store in Europe, taking seven years to build.
Hemclad was selected for all non-glazed areas of the envelope as its thermal mass and inertia properties were calculated, by extensive thermal modelling, to provide savings to M&E plant (heating & cooling) at construction stage, plus reduced energy in-use.
2600m2 of Hemclad “infill” panels applied into a primary/secondary frame by others. This frame was a mix of steel and glulam elements. Hemclad panels made at approx. 3.8m x 2.4m complete with pockets for installation by telehandler, as crane installation was not possible due to eaves overhang already in place. Panels have 0.12U-value using a twin-stud arrangement to minimise thermal bridging – overall 400mm deep with 200mm Hemcrete factory-cast and 200mm Breathable hemp-fibre quilt. Specification chosen after extensive thermal modelling to provide the best balance of thermal mass to suit retail store thermal dynamics and optimisation of heating/cooling plant.
80T of CO2 locked-up during the growth of hemp insulation material and sequestered into panels. Projected saving of 340T of CO2 by building in this material compared with conventional infill.
Continuous monitoring of the building provides data that currently indicates energy-in-use values are less then thermal modelling had predicted. Plan A targets have been exceeded.
Generic illustration of a Hemclad panel
Findings from the study, which was funded by the Technology Strategy Board’s (TSB) building performance evaluation (BPE) grant, included:
• Energy: 42% reduction in energy use compared to an equivalent store, against a target of 30%. The store used 21% less electricity and 60% less heating fuel than initial estimates
• Carbon emissions: 40% fewer carbon emissions than an equivalent store, against a target of 35%
• Biomass boiler: the biomass boiler supplies nearly three-quarters of the store’s heating, reducing its comparative heating demand by 66%.
• Insulation: a high standard of insulation was achieved through careful detailing in design and construction and the use of bio-composite Hempcrete panels. Building airtightness was found to be 70% better than required by Building Regulations, with less than 1°C of heat lost overnight in winter, compared to 9°C in other store environments
The most successful sustainable elements at the BREEAM Excellent-rated learning store have already become part of the standard specification for new M&S outlets. The retailer opened four learning stores during 2014, in Epping, Slough, Oswestry and Heswall in Merseyside. All are currently being evaluated and successful innovations rolled out to other stores.