From energy-hungry supermarket to super-eco office

A tired 1980s building has gone from band G to B on the sustainability scale thanks to a slick refurbishment. Jan-Carlos Kucharek reports

Sitting at one end of the high street in Elgin, a town 40 miles along from Inverness on Scotland’s north coast, a disused supermarket has been given a new lease of life. Not in its former retail guise, however, but as the newly opened offices for Moray Council.

This £4m refurbishment is part of a larger regeneration initiative for the whole area; and while the idea of converting a redundant 1980s supermarket might seem small fry in a construction culture more intent with clearing away the old and the wholesale replacement with the new, the scheme, designed by Bennetts Associates in conjunction with engineer Buro Happold, could serve to show how our struggling high streets can be rejuvenated.

Project managed by Mace, the supermarket-to-Moray offices conversion comes in the wake of TV celebrity and retail guru Mary Portas’s recent report on how to revive our ailing town centres. Perhaps the Queen of Shops should go north of the border and take a close look at a building that has not only revivified the urban context, but done it in a way that has improved its sustainability credentials radically, taking it from an energy performance rating (EPR) of G to a B.

The former Morrison's supermarket (top) turned its back on the town to face its car park, while the office design now addresses the town

The proximity of the 3,000m² single-storey Morrisons supermarket, adjacent to the existing offices on the town’s high street made it the perfect candidate for consolidating the various Moray Council functions, which until now had been spread over 20 sites in the town. Bennetts Associates had been advising Moray on its bigger regeneration strategy, and when Davis Langdon proposed consolidation of the council’s various departments into one site as a cost-cutting exercise, it was the council, with an extremely tight budget, that proposed the reuse of the Morrisons site.

But as James Nelmes, Bennetts Associates project architect for the original proposal, explains, it was about more than mere convenience. “It was important for the county council to maintain a presence in the town centre, not just from a service delivery point of view, but symbolically,” says Nelmes. “They had budgeted for a basic refurbishment — in straitened times, a lack of ostentation was important for them — but we approached them and told them that we could do a lot more for the money.” On the strength of Bennetts’ proposal, Moray Council appointed the firm to work up a design and sustainability proposal to stage D+.

From a building that had an initial rating of G, that’s no mean feat, and all at a tad over £1,400/m². While admitting that it’s not the most glamorous project on their books, Mace project manager Martin Scott is keen to push the merits of the scheme. “It’s amazing that as part of the initial exercise, we actually looked at demolishing the structure and doing a new build, but instead we went for a ‘light touch’ approach. Moray Council should be applauded for having the vision to see beyond a 20-year-old supermarket, and to turn it into a contemporary and highly sustainable working environment” says Scott.

The existing supermarket was effectively a deep plan 5m high steel truss structure with load bearing ashlar masonry and glazed facades. Above the 3m high suspended ceiling was a 2m services void, packed with air handling units and ductwork.

The new 5m ceiling height drove the passive ventilation strategy, devoid of plant. Acoustic panels help to deal with resultant reverberation

The former supermarket had a 3m suspended ceiling above which was a plethora of plants and air handling units

Air conditioned meeting rooms are space planned to run along the central spine of the office, minimising service runs

Council tax, aisle 4

Bennetts’ Nelmes explains that the architect’s strategy was to create “quick wins” for the building. First, to cut plant costs by developing a natural ventilation proposal taking advantage of the building’s height; second, to pull natural light deep into the plan; third, as much as possible to augment the existing fabric to optimise its environmental performance; and fourth, to reorientate a building that was effectively facing a car park to face the street.

The building was procured under a traditional D&B contract with Mace as project manager, local firm Acanthus Douglas Forrest as executive architect, and Stewart Milne as contractor.

Tendered at the beginning of 2010, the refurbishment started on site in August of the same year, with Practical Completion in December 2011.

Mace was originally employed by Moray Council as technical consultant for its estate, but was keen to take up the sustainability challenge of the new council office project and offered its services. It was as much about the strip out as it was the installation. “There was a plethora of services above the suspended ceiling line to deal with the conditioning demands of the supermarket — to start we had to rip all of this out and strip the structure back,” says Mace’s Scott.

Being a single-storey structure, the exposed steelwork did not need intumescent coatings before the whole internal structure was stripped, cleaned and white painted.

Nelmes says the building’s revealed 5m height was critical to the natural ventilation strategy. “As an integral part of the natural ventilation for the open-plan offices we introduced eight wind chimneys into the roof in the centre of the building. We knew that if we reconfigured the facades to incorporate opening lights connected to a basic building management system (BMS), we could introduce natural air flows into the full depth of the building, allowing it to condition itself to 21^oC +/-2^oC without the use of plant,” he says. This margin had to be proved to be achievable, as British Council for Offices criteria state that internal temperatures cannot exceed 25^oC for more than 5% of the occupied hours, or 28^oC for more than 1%.

Buro Happold’s proposal used centrally positioned chimneys running down the central spine of the building with opening dampers. Both these and the high level opening windows around the perimeter of the office are fitted with actuators and connected to a highly sensitive BMS. Internal heat build up engages the actuators and dampers, creating the air crossflows from the perimeter to the centre that allow the building to “breathe”. Each one of the eight chimneys is also fitted with punkah fans to try to deal with high heat scenarios, as touched on above, without resort to air conditioning.

The depth of the plan also provided the engineers with challenges regarding providing the necessary levels of natural daylight. “With the space as deep as it is we knew that with only the available perimeter glazing we were never going to meet the strict BCO criteria on daylighting,” admits Buro Happold’s Peter McCallum. “We needed a better spread of lighting to give us the 2% daylight factor we needed and that was only going to be achieved by installing north-facing roof lights, which would allow the requisite light in without exposing the building to further solar gain.” All the 12 new rooflights were fitted with solar control glazing sealed units with a solar gain “g” value of <0.41, thus reducing internal heat build-up.

Daylight studies drew attention to the need for light to be drawn into the depth of the plan

The new rooflights required secondary structure set over cuts directly into the existing steel roof section. The existing slate mansard hides them from the street

Looking due west past the refurbished supermarket on the left to the town centre

Mace found the condition of the original roof to be in good order so decided to build the new, better-insulated roof on top of it. “To get the daylight values, 60% of it had to be opened up to install the new rooflights, involving cutting holes directly through the steel roof section. Once we had formed the new secondary rooflight steelwork truss structure, we then added a 150mm rigid insulation and finished with a single-ply bituminous membrane laid directly over the existing one — the only thing we needed to deal with was modifying the perimeter drainage interfaces,” recalls Scott.

Scott adds that optimising the sustainability of the building also led to some key decisions on the internal fit-out. “We decided to run ductwork directly through the middle spine of the building, putting the dedicated conditioned spaces like meeting rooms in the deepest part of the building, meaning general desk areas are placed more towards the perimeter to benefit from the natural ventilation. This also minimised ductwork runs, bringing its own material savings,” says Scott.

Some demolition was necessary. For example, the original entrance facing the car park was demolished and a new high-performance glazing installed along the rest of the east facade for the staff relaxation areas. The former rotunda cafe facing the street was converted to become the new entrance, creating a more active and accessible street presence.

Elsewhere on the facades, insulation the existing ashlar-faced elevations was done by adding layers internally, reducing net internal areas, but increasing performance significantly. Scott says: “We were set air tightness criteria of 5m³/hr/m², which is very onerous for a building over 20 years old. We increased the build up internally by adding 150mm of internal rigid insulation, combined with extensive plasterboard detailing. Some specific interfaces, such as wall/roof were reviewed to ensure that they would meet the increased air-tightness demands.

Taken together, the modifications have completely changed the environmental performance of the building. It has yet to be proved in operation, but it’s anticipated the offices will consume 100kWh/m², resulting in a building emissions rating (BER) of 25kgCO₂/m², compared to 27kgCO₂/m² for the current target emissions rating (TER), based on the 2007 edition of the Scottish Building Standards. This gives the redesign an EPR of B, and its BREEAM “excellent” rating was confirmed last month.

Moray Council’s new offices may never end up gracing the pages of the architectural monthlies. But in terms of its sustainability performance, its reduced carbon footprint and its considered attempt to both re-use and regenerate, this exemplar refurb should be stopping the presses.

A model green building

Environmental consultant engineer Buro Happold carried out thermal modelling of its proposed ventilation strategy to check what could be achieved, based on the principle that the 5m soffit height of the ceiling would be enough to allow for “stratification” of air within the space.

Cross ventilation is achieved using high and low-level openable glazing lights running along all the perimeter facades — low ones would be controlled manually and high-level openings with building management system (BMS) actuators.

In conjunction with the chimneys with adjustable dampers, operated from a BMS system responsive to temperature changes of +/-0.5 degrees, sufficient air flow rates through the space can be ensured.

Each chimney is fitted with a “punkah” fan which, on still summer days, will be used to mechanically draw air up and out to avoid the build-up of exhaust air in the heart of the building.

In winter mode the fans will be reversed to redistribute heated air back down and around the open-plan office. In this scenario, trench perimeter heating is powered by low temperature hot water from two 125kW low NoX condensing gas boilers operating at up to 98% efficiency.

Buro Happold engineer Peter McCallum says that while the general rule was to naturally ventilate, there were exceptions — notably in meeting rooms, which required privacy, and the data room, which had to deal with far greater heat loads.

But even here, efforts were made to improve sustainability. “With highly conditioned environments like data rooms, it’s hard to avoid energy-intensive strategies,” says McCallum. “Here, we supplied the room with two dedicated chillers. We would have liked to have linked the exhausted air back to a heat exchanger, but the budget simply didn’t allow for that.”

In the meeting rooms, variable air volume air feeds were connected to movement detecting sensors, ensuring that when they were unoccupied, air conditioning would default to “background” air supply levels.