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Sustainable construction: Wolseley UK Ltd

A sustainable shop window

28 January 2010

How easy is it for the construction industry to specify sustainable materials? Wolseley's answer was to build its own showcase of low-carbon products and technologies - using its own supply chain. Mark Elton reports

With the establishment of the Code for Sustainable Homes, the increase in demand for assessment against BREEAM for non-domestic buildings and the regulation of Site Waste Management Plans, the responsible sourcing of construction materials has never been higher on the mainstream agenda. But just how easy is it for designers, contractors, developers or even DIYers to specify sustainable materials, confident in the knowledge that they are appropriate, obtainable and affordable?

This was the question Wolseley UK Ltd was considering in 2004 and quickly realised it had a responsibility - and an opportunity - to become part of the solution. As the world's largest heating and plumbing merchant and a leading supplier of building supplies across Europe and North America, Wolseley recognised the need to embrace more sustainable building products, in preparation for a future of non-fossil fuel technology and low-carbon materials. It conceived the idea of the Sustainable Building Center (SBC), a venue to showcase 'green' construction solutions under one roof and, early in 2005, selected a design partner for the project, ECD Architects. The 632m2 building was completed in 2008 and now forms Wolseley's interactive shop window for its 'green' construction supply chain, targeted at everyone involved in environmentally-friendly development, from the jobbing builder to the major housebuilders and developers.

Figure 1: The SBC juxtaposes heavyweight thermally massive construction with lightweight timber construction

The initial brief for the project was very loosely defined, suggesting a building of 600-700m2 internal area over a maximum of two floors. The primary purpose of the building, to demonstrate low-carbon products and technologies, was to be achieved through the provision of product display galleries, supported by an audio-visual theatre seating 40 people, staff office facilities, a cafe/seminar room and washroom facilities. Wolseley was looking for an exemplar building that was 'futuristic' in appearance yet shared some connection with the other buildings on the site at Wolseley's campus in Leamington Spa. The building also had to meet the exacting BREEAM Excellent standard.

Greening the supply chain

So to what extent can a builder's merchant facilitate sustainable design? Since almost all the components used in its construction can be obtained from Wolseley's own supply chain, the SBC is living proof that they can have significant impact. However, there are many different criteria by which products may demonstrate a degree of sustainability and when making the choices for the SBC specification it was clear to ECD that some are more suited to a large merchant than others.

Figure 2: The upper gallery will be populated over time by product displays; interactive pods give real-time information on supply chain availability

So where to start? Wolseley UK had an extensive supply chain already, incorporating a number of key suppliers of sustainable materials and technologies to the construction industry. However, the SBC team was also interested in products outside of its existing portfolio, either currently distributed through niche eco-merchants or perhaps not yet available in the UK market. ECD was therefore given a wide remit to select from those products currently offered by Wolseley but also to identify others that would be appropriate to incorporate into the building. ECD compiled a comprehensive database, covering the entire building process - each product, material or technology had characteristics that would contribute to an overall sustainable approach for the Center, whether that was through:

  •  the use of natural materials
  •  having low embodied energy
  •  delivery of operational energy benefits
  •  provision of a low-toxicity alternative to conventional materials
  •  incorporation of recycled or by-product content
  •  having exceptional lifespan or durability
  •  being readily recycled or reused at the end of its design life
  •  generating renewable or low-carbon energy.

These credentials were typically evaluated through existing tools or guidance such as the BRE's Green Guide to Specification and Greenspec

There were other important influences on the final choices, not least of which was a product's suitability and 'scale-ability' for distribution across Wolseley's national network of merchants - rammed earth and straw bales were never likely to feature highly. Using the database, Wolseley contacted prospective new suppliers to explain the SBC concept and investigate their suitability for a long-term relationship.

Figure 3: The technologies supplying heat and hot water to the building are periodically switched but always supply an array of thermal stores and cylinders all of which are on permanent display in the galleries

Element by element, specifications fell into place and the SBC's design was fine-tuned to take each product into account, occasionally accepting that less-than-perfect solutions still contributed towards the end goals of reducing emissions, waste, carbon usage or finite natural resources; for example, the pre-cast concrete panels have significant embodied carbon but help to stabilise internal temperatures through their exposed thermal mass.

Key existing suppliers, such as Finnforest for the engineered timber products and Hanson for the pre-cast concrete components, were established early in the process and had some involvement in the design proposals, while other materials were only identified at tender stage, often selecting products new to the UK. The final scheme incorporated over 170 products and, for the first time, it brings together information about 7,000 sustainable products that are available through Wolseley's branch network.

Architectural concept

The design challenge presented to ECD was to exhibit a broad range of materials and components in a coherent and aesthetically exciting manner, yet one which still embodied the characteristics of sustainable design. The first phase of Wolseley's new HQ office building was well under construction by this stage with another outlined for the future to the south of the site. To the west, the enormous national distribution centre was being planned on a scale (33,000m2) that would dwarf the SBC. ECD therefore identified the southern boundary of the Wolseley masterplan as the ideal site as it gave not only a better public presence and a south-facing aspect but also easier access for construction.

The design solution deliberately juxtaposed two alternative approaches to low-energy architecture - the south wing taking an externally insulated, heavy mass approach; while the north wing took a lightweight, timber-framed stance. The former, a bow-fronted, two-storey gallery block, dominates the single-storey north wing but they are connected by the double-height east/west-aligned internal street.

The layout prescribes a visitor route that flows easily from entrance to audio-visual presentation; and from demonstration galleries on both ground and upper floors (including the external terrace) back down to the seminar room. To the rear of the gallery spaces, a structural spine forms the springing point for the butterfly roof form. This spine area also contains the platform lift, access/escape stair and vertical riser cupboard for services distribution around the building.

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Figure 4: The south wing extends over a covered courtyard, shading the west elevation and directing visitors to the main entrance

The upper floor connects visually with the main HQ building though the upper glazed screen and a bridge links the upper gallery to the external terrace where visitors will be able to view sedum roofing, sunscoops, roof-mounted photovoltaic panels and a solar thermal flat plate collector mock-up at close hand.

At ground level, the SBC is well integrated with the number of landscape features, including a planted rill water feature and swales on the east side adjacent to the existing landscape belt. Conceptually, the curved plan forms are intended to be a reflection of the dynamic nature of the environment - the leading edge of the gallery wing roof appears to track the arc of the sun as it passes to the south; the roof folds collect and channel the flow of rainwater.

Achieving planning permission for the scheme went without a hitch - in fact, it received enthusiastic support from the planning officer who was delighted to have an exemplar of sustainable design within their locality. The drawings were submitted in December 2005 and planning approval was received the following March.

Procurement process

At the detailed design stage of the project, Wolseley appointed project manager Edmond Shipway to oversee the implementation process. A two-stage tender arrangement was chosen as the preferred procurement method as it was felt that a main contractor's input would be highly beneficial to a building of such complexity. The initial scheme exceeded the £2.9m construction budget and, with finite funding coming directly from Wolseley's marketing budget, savings had to be made.

Components such as LVL (laminated veneer lumber) structural panels were substituted for stud solutions, the 'prow' of the single-storey was truncated and replaced with a pergola, the amount of photovoltaic panels was halved, and so on to bring it back on budget. The scheme was then re-tendered but, surprisingly, it proved difficult to find contractors interested in such a small yet complicated building despite the opportunity to engage with sustainable design methodologies. Eventually a local contractor, SOL Construction (which later became part of the ROK group), was selected and work began on-site in June 2007.

Performance matters

Insulation levels are high throughout the construction, typically 0.16 W/m2K for the walls and higher for the roofs (0.12 W/m2K typically), incorporating five varieties of low GWP (global warming potential) insulation product, including mineral wool, sheep's wool, glass wool, natural cork and wood fibre. The latter are used as external insulation to the south wing where the internal pre-cast concrete structure is left exposed to exploit its thermal mass.

Figure 5: Many parts of the SBC's interior are cut away to reveal the structure; in the seminar room Finnforest I-joists are left exposed at ceiling level

The raw material for the wood fibre insulation consists of softwood splinters and wood chips sourced as by-products in German/Swiss sawmills. The boards are interlocking on all four sides to eliminate gaps and are therefore quick and easy to install - they also eliminate the need for membranes or vapour checks. We used the boards in conjunction with a lime-based mineral render to provide a 'vapour open' construction, which, like sheep's wool, actively controls the level of moisture within the building's fabric. This in turn helps to ensure a healthy internal working environment for the building's occupants.

Korklite is made from Portuguese cork granules, steam baked and pressure-bonded into boards, using the cork's own self-contained resins as the binder. The raw materials are obtained from fully renewable and sustainable sources, i.e. cork trees harvested every nine years or so, and the manufacturers claim that production of the finished board consumes the lowest amount of embodied energy of any equivalent insulation type, despite the transportation from Portugal. There is a trade-off in reduced thermal performance however, particularly compared to, say, petrochemical-derived flat roof insulations - over 360mm of cork was needed to insulate the roof of the north wing underneath a sedum roof build-up.

Cladding materials were selected for their low embodied carbon content, their durability and ultimately their recyclability, including heat-treated timber cladding and steel standing seam roof sheeting. Innovative products incorporated include Cobiax floor slabs (which reduce the volume of concrete needed in a slab structure by 35% using void forming recycled plastic spheres atop a prefabricated soffit plank), Aluzinc steel roofing, krypton-filled triple-glazed windows (prototyped specifically for this project by JELD-WEN), photovoltaic brise-soleil, phase-change board and LED lighting. Within the specification, detailed attention was paid to the avoidance of materials associated with off-gassing for example, zero VOC (volatile organic compounds) trade paints and clay-based dry-lining to walls.

The gallery spaces are designed as flexible office-like rooms so a raised flooring system was specified that uses only FSC-certified chipboard in its core. Carpet tiles contain a high recycled yarn content with a PVC-free backing. Elsewhere, linoleum floor finishes were used since they are derived from natural materials such as cork, wood flour and linseed oil. In the internal street area, a terrazzo-like screed called Ttura was laid, which comprises recycled glass chips in a solvent-free resin to provide a beautiful and eco-friendly floor finish.

Figure 6: Double-height spaces allow the transfer of displays to the upper gallery but also aid the natural ventilation strategy

The building purposefully demonstrates the wide range of low and zero CO2 technologies available from Wolseley through their active use in the building, including solar thermal collectors, photovoltaics, ground source heat pump and a biomass boiler. Part L2 calculations show a 64% reduction in CO2 emissions from compliance requirements (TER (Target Emissions Rate) 15.91 KgCO2/m2, BER (Building Emission Rate) 5.71 KgCO2/m2). Eleven per cent of the reduction is achieved through the high standards of building insulation and airtightness. The remaining 53% is achieved through the use of the aforementioned technologies. The significant use of refrigerants was avoided and NOx (nitrogen oxide) emissions are estimated at only 20mg/kWh (the lowest benchmark to receive credits for low NOx emissions under BREEAM is 100mg, the highest benchmark (i.e. maximum points) is 40mg). Performance of both the building as a whole and the individual technologies involved will be monitored by the SBC team via a BMS system.

Water demand was minimised through the use of efficient sanitaryware, including waterless urinals, infrared sensor taps and WRAS-approved 4/2.6 litre dual-flush WCs. Mains water use was reduced through rainwater harvesting to flush the WCs. A leak detection system was also specified, as has a water meter attached to the BMS. The aerated shower specified reduces water flow rates by 75% and, together with a rack and lockers, encourages cycling to work. Harvesting, combined with the extensive use of infiltration and retention sustainable urban drainage systems (SUDS), all but eliminates the discharge of rainwater to municipal systems, so the development does not add to the risk of flooding.

In addition to the permanent displays integral to the building itself, visitors to the SBC will have access to real-time displays and touch-screen interactive kiosks providing background information on the installations. Though the SBC has been designed to fulfil its purpose as a sustainability showcase, it has also been planned to be adaptable for future reuse as a speculative commercial office space, for example, with open plan spaces and flexible raised floor voids in the two-storey wing and non-structural partitioning in the single-storey wing.

Figure 7: A double-height corridor connects the two halves of the building and its monopitch roof carries photovoltaics and solar thermal collectors at the optimum performance angle

Power of example

The building was opened in June 2008 by Red or Dead founder Wayne Hemingway, who described the building as making sustainability 'sexy', and it has subsequently won awards including Best Sustainable Construction Project at the Edie Awards in 2008 and a shortlisting for the RICS Awards 2009. But the project's real success has to be measured by its influence on the mainstream construction industry - to date there have been in the region of 8,200 visitors to the building including a recent trip by Environment Secretary Hilary Benn and Michael Ankers, Chief Executive of the Construction Products Association.

Experts have often identified that making sustainable and natural building products available to the industry via mainstream sources is key to their widespread use and Lord Stern himself has highlighted the 'power of example'. It is hoped, therefore, that this project will continue to inspire and facilitate other developments to follow its sustainable principles.

Figure 8: The south facade is partially shaded by a bank of louvres which incorporate photovoltaic cells on their upper surface

Mark Elton is Associate Director and Head of Sustainability at ECD Architects and was both Designer and Project Leader of the SBC

Further information