With sustainability at the core of the brief for a multi-purpose building at the Royal Horticultural Society’s new garden in Salford, Hodder+Partners went to town with timber, with award-winning results. Roseanne Field speaks to Stephen Hodder
RHS Garden Bridgewater, the Royal Horticultural Society’s fifth national garden, sits on the site of the former Worsley New Hall in Salford – a 154 acre estate designed and built in 1850 and demolished shortly after World War II. Although there had been many attempts to redevelop the site, nothing had come to fruition until the RHS came across it during their search for a site to locate their fifth national garden on.
The RHS came to an agreement with Salford City Council and Peel Land & Property, which led to landscape architect Tom Stuart-Smith, vice president of the RHS and a former Best In Show winner at Chelsea Flower Show, designing a masterplan for a phased redevelopment. This included the regeneration of a large walled garden, together with a car park and visitor centre. In 2016, the RHS invited architectural firms to compete to design various elements including the visitor centre – which is now known as The Welcome Building.
After winning the project, Hodder+Partners worked to secure planning consent for the conversion of a horticultural services yard, visitor centre, and car park, as well as old stables and potting sheds. While designing the building, they continued work with Stuart-Smith on the immediate landscape, while the conversion of the outbuildings was managed in-house by the RHS.
Brief
Initially, the practice was given a “fairly cursory brief,” says Stephen Hodder, chair at Hodder+Partners, for “a membership area, retail area, and restaurant together with a glasshouse and outdoor plant sales.” The accommodation was to be “equally divided, and roughly 1,000 m2.”
The brief developed once Hodder had been awarded the project, with early discussions covering what the architect describes as “tricky site conditions.” There were also concerns about the garden becoming too popular, and managing the likely large visitor numbers. “There were a whole series of public consultations to allay concerns,” Hodder says. “We worked with the city council on a new entrance and sustainable transport strategies.” With the site being in the greenbelt, there were “many issues to address before we could actually start
on site.”
There was also a hurdle to overcome with the ground conditions – one of the reasons Hodder cites as making the site difficult to develop previously. “There’s a layer of organic matter which sits underneath, and in terms of carbon capture it was important to the RHS that that was not disturbed,” he explains. This meant the architects had to rethink not only the car park layout, but also the location of the horticultural services yard.
Sustainability is a fundamental within RHS policies, and was therefore an important consideration from the beginning. It was something that was developed significantly during the pre-construction design phase, but was also central to Hodder’s competition bid – “We had an initial idea about how it could underpin the RHS’ approach, but it was something that evolved during the design process.” Hodder says. “The systems we used are not unique, but I think the combination of this client and site meant that we could push the boundaries in a way we’d never been able to before.”
With this in mind, the practice intended from the outset to focus on timber, presenting a previous project of theirs – St Clare’s in Oxford – during the competition; a design that made extensive use of prefabricated CLT panels and glulam frames. Although predominantly driven by logistics in this case, Hodder felt such an approach could be transferred to The Welcome Building, not only in terms of materials, but also in that “it somehow captured the spirit and quality of space that we were trying to create,” he explains.
Timber ultimately made sense for the RHS’ fifth national garden for two reasons, says Hodder: “A timber pavilion sitting in a beautiful landscape was quite appropriate.” Simultaneously, the architects “were also developing the idea that sequestering carbon was really the right way to go, and very much supporting RHS’ sustainability policies.”
As well as predominantly using timber, the building cross ventilates, all rainwater is harvested, a ground source heat pump was installed, and permeable surfacing was used in the car park alongside swales and attenuation ponds. “Sustainability goes well beyond the building,” Hodder says.
The other key part of design development came following the practice’s examination of other RHS visitor centres, where demand was exceeding the buildings’ capabilities. The architects quickly realised the building would have to “flex with seasonal demands,” as Hodder explains. On the other hand, there were also a set of what he describes as “prescribed” components; classrooms (for both school children and adults as part of the RHS’ education programme), offices, and a kitchen serving the restaurant. “Our initial idea was the prescribed components being in their own buildings, and then the visitor centre being this flexible space,” he says. “We then spent a lot of time shuffling these components around, always with the idea that they would sit beneath the overarching ‘umbrella’ structure in which the membership area, shop, and restaurant would sit.”
Design
A key part of the designers’ context-focused site response was achieving a ‘horizontal composition.’ Although in part intended to help minimise the building’s impact on the landscape, it was predominantly inspired by the Bridgewater Canal which sits roughly four metres above the garden on the horizon, along with the site’s strong treeline. “We wanted this building to be a very delicate intervention within the garden, we didn’t want it to rise above the treeline; the horizontal form was responding to
that horizon.”
Although they wanted the building to be a discrete addition, it formed a key part of the overall masterplan, as an important reference point. To this end, the roof folds down at the main entrance to ‘signpost’ it for visitors. It’s visible from most points in the garden, which Hodder describes as a “happy accident; when you see it in the distance so you’ve always got that point of orientation.”
This kind of fortuitous outcome also happened with the design of a long lawn stretching out from the north of the building. The architect of the original estate, Edward Blore, had played with this ‘axis’ throughout the gardens, but it wasn’t until Hodder was standing on the lawn looking back towards the building that he realised “they were building on the axis Blore originally created.”
The garden inevitably remained a focus throughout, so design details were included to reflect that. As well as timber, the practice utilised glazing extensively to connect visitors to the garden (with timber louvres to mitigate solar gain). The wall directly ahead of visitors upon entering the building is fully glazed, allowing views along the meadow to the east, as are the north and south elevations. “The building needed to orientate visitors, but at the same time, it was about throwing your attention out into the garden,” says Hodder. At the north and south ends, the roof extends beyond the glazed curtain walling, the former being the entrance to the garden and the latter looking out into the outdoor plant sales area.
Timber
The roof structure – spruce with a cross laminated timber deck, plus the larch external wall cladding and louvres, were all manufactured and supplied by HESS. Their calculations show the roof structure sequests 320 tonnes of carbon, and the cladding an additional 26 tonnes. “The use of timber was absolutely intrinsic to the approach to sustainability,” Hodder says.
The biggest challenges that came with the timber were around the structural ‘trees’ that support the 90 by 24 metre roof. Initially the building was designed utilising a portal frame, but when the structural engineers became involved it ended up increasing in girth beyond what the practice were happy with, hampering their desire for something more elegant. Hodder says he viewed the classroom, admin, and kitchen ‘pods’ as buildings in their own right, and that the overarching roof structure should be separate, and “should almost feel as if you’re outside; delicate with lots of natural light flowing in.”
To resolve this structural conundrum, the design went through a collaborative, iterative process which resulted in a diagrid structure initially with two-dimensional Y-frames, which slightly reduced the depth of the portal frame – but not enough. They then discussed looking at a more ‘three dimensional’ solution, and came up with the idea of using the structural trees.
Columns have four branches at the top, allowing each column to support a prefabricated six by six metre cassette. “There’s a hierarchy in the size of timbers within the roof, but nevertheless it’s much finer, more elegant,” Hodder says. As well as enabling the roof structure to be more refined, the branch approach also meant fewer columns were required, which allowed the designers to keep the main space in the building flexible. “You go through this process until you achieve what you want from the building,” says Hodder.
The structural trees, combined with the way the roof sits, have become design features in their own right, says Hodder. A triple glazed rooflight runs down the centre – helping conjure the ‘outside’ feeling – with the diagrid structure beneath creating a variety of shadows. With the building seeing an unprecedented number of visitors (currently operating at levels not predicted until its eighth year of operation) it can feel chaotic at times, but Hodder says that the oversailing warm timber roof helps visitors relax. “For me it’s calming; and it’s quite rewarding when you see people enter that building and the first thing they do is look up at the roof,” Hodder says. “Wherever you are in the building, the roof is that common reference point.”
There were further structural challenges. The ‘trees’ all sit inboard of the main roof structure, meaning the edges of the roof canopy are cantilevered, and therefore susceptible to additional movement, beyond what is normal with timber. So managing that movement within the design was “critical,” says Hodder.
The ‘trees’ were originally designed to include uplighting, but RHS director general Sue Biggs (who has since retired) didn’t feel it gave the interior the right quality of light. She instead wanted to use pendant lighting, but the clerestory-type high level glazing below the roof around the entire perimeter meant that no power was running to it.
The solution was to run cabling up through the mullions of the curtain wall glazing at the ends of the building. In between each timber cassette in the roof, connecting them together, is a flitch plate – which created a shadow gap. The cabling was run within these gaps to power the pendants which, asserts Hodder, “really added to the quality of the interior and elegance of the roof structure.”
Layout & landscaping
To the right of reception is the main retail area, which leads through into the restaurant, featuring an outdoor terrace protected by the extending roof. Beyond the restaurant is the glasshouse, housing indoor plants and equipment and leading out to the outdoor plant sales area. The ticketing and membership areas are to the left, beyond which is the entrance to the garden. Flanking that are the toilets and ‘pods’ containing two classrooms and offices.
While the main hall is six metres high, the pods are more intimate, and neutral. “There’s a contrast between the two,” Hodder says. The membership area, ticketing desks and other key areas are clad in terracotta, with the intention to clearly signal to visitors where to go, minimising the need for signage.
Although finding room for all the required elements wasn’t excessively taxing, deciding on the layout proved challenging. “We spent a lot of time shuffling the pods around to make sure the relationships were right,” Hodder explains.
The practice worked closely with Tom Stuart-Smith on the landscaping; “the shape of the new lake, the movement of people around the building, and the planting up against the building had to be really considered,” says Hodder. “He understood the building and what we were trying to achieve; the landscape and the building were seen as one.” The new lake connects to the original, restored lake (which sits slightly higher), via a stream.
Recognition
Completion was at the end of 2021, slightly delayed due to Covid, but the building has been a phenomenal success. Not only have visitor numbers far exceeded expectations, the project has also been shortlisted for and won a variety of awards, for its sustainability, accessibility, use of timber, and design.
“It’s a very special project,” Hodder says. The landscaping combined with the building’s wildflower roof has seen an improvement to the area’s biodiversity and the practice has received multiple compliments, from the RHS, visitors and fellow architects. “It’s a legacy project, it’s for the people of Salford,” Hodder concludes. “It’s just nice to go back and see people enjoying it.”
Awards
- MSA Design Award 2017
- Architect of the Year (Winner) – Structural Timber Awards 2020
- Cultural & Leisure Project of the Year (Shortlisted, Highly Commended) – BCI Awards 2021
- Environment & Sustainability Initiative of the Year (Shortlisted) – BCI Awards 2021
- MSA Design Award 2021
- Structural Award (Winner) – Wood Awards 2021
- Commercial & Leisure (Highly Commended) – Wood Awards 2021
- Building of the Year (Winner) – GMCC Excellence Awards 2021
- Civic Trust Award 2022
- RIBA North West Award 2022
- RIBA North West Sustainability Award 2022
- RIBA North West Building of the Year 2022
Project Factfile
- Architect: Hodder+Partners
- Client: Royal Horticultural Society (RHS)
- Contractor: BAM Construct UK
- Timber: HESS Timber
- Environmental/M&E engineers: Hoare Lea
- Structural engineers: RoC Consulting
- Quantity surveyor/cost consultant: Arcadis
- Landscape architect: Tom Stuart-Smith