James Feltham recently spoke to Michael Donnelly from ENDS Report about Wrenbridge’s Oxford scheme, Nova, achieving a 100% BREEAM rating.
In Oxford, remediation works helped to clean up land for the construction of a complex that has now been awarded a 100% BREEAM rating score – a reported first in the UK. How was this achieved and what are the lessons for other projects?
Once a familiar site in the urban landscape, gasholders have become something of an architectural curio.
While a handful of the derelict structures have been retained and integrated into new developments, many more have been demolished, making way for new homes or offices.
However, while the structures may be easy to dismantle, the contaminated land legacy of many such sites is often less straightforward, adding to the complexity of the development process and cost for developers.
New lease of life for gasholder
In Oxford, one such challenge was faced by the developer of a former gasholder, which sought to remediate the site and construct an exemplar green building.
The former gasholder at Cowley, in the south east of the city, had occupied the 0.68-hectare site since 1960 before being decommissioned and put up for sale by its owners, gas distribution firm SGN.
Developer Wrenbridge and its funding partner Buccleuch successfully bid for the site, attracted by its position close to the Oxford Science Park and Arc Oxford campuses. Ahead of the purchase, and to assist with due diligence of the site, Wrenbridge commissioned remediation firm TRC.
Adam Sokolowski, director of UK and EU operations at TRC, said former gasworks sites can be “up there as some of the most challenging in terms of brownfield restoration”. However, with this specific site a great deal of information was already available from a pre-existing probe into potential contamination and a data archive that SGN provided, Sokolowski said.
Based on an analysis of this insight and a site visit, TRC produced a report that reassured Wrenbridge enough to purchase the site. The developer submitted a planning application for the construction of a 4,000-square-metre commercial building with “flexible” uses from offices to warehouse space.
Planning consent for the Nova Oxford development was then granted, featuring a requirement that the building should not be occupied until ground remedial works were carried out and validated by the local authority.
De-sludging, de-watering, de-oiling
As a first phase of works, demolition contractors TDS were commissioned to carry out de-sludging, de-watering and de-oiling of the gasholder ahead of its demolition.
Following this, TDS excavated a series of trial pits within the footprint of the former gasholder under supervision from a TRC engineer. Soil samples were then collected by TRC to assess underlying soil conditions alongside groundwater samples from four monitoring wells.
Sokolowski explained that on a “coal to gas manufacturing site you’d expect to see [contaminants such as] tars, heavy metals, various hydrocarbon products [and] oxides”. However, he added, that as this site had been primarily for the storage, and not manufacture, of gas, there wasn’t the usual “cocktail of contaminants and remnant features”.
On a coal to gas manufacturing site you’d expect to see [contaminants such as] tars, heavy metals, various hydrocarbon products [and] oxides … but because this site was primarily for storage … there wasn’t the usual cocktail.
Adam Sokolowski, director of UK and EU operations at TRC
While verification soil sampling did identify some contaminant concentrations, including asbestos fibres, heavy metals and hydrocarbons, no exceedances were identified when screened against assessment criteria.
Consequently, the TRC verification report concluded that soils on-site did not pose a “significant risk”. The firm did find “elevated carbon dioxide concentrations” in the soil, but deemed this to be “low risk”. In addition, TRC said it was “unlikely” that the site would pose a significant risk to controlled waters.
Consultations with the Environment Agency as remediation begins
Low risk assessment or not, remediation works were carried out ahead of construction, including the installation of a ground gas membrane in sensitive ground-level spaces such as offices, and soft landscaping across the site with clean imported material.
The TRC report said the firm “considers that human health risk pathways are no longer valid due to the presence of hardstanding (building footprints and externally paved areas), engineered capping in landscaped areas, which will provide an engineer barrier for dermal contact, ingestion and inhalation pathways”.
All concrete and tarmac arisings generated from the demolition were crushed on-site to be reused as part of the subbase material for the new development. According to Sokolowski, some “construction-related arisings” were taken off-site. This was done in accordance with a voluntary waste code of practice – that of construction waste charity CL:AIRE – which helps builders to decide whether excavated materials are waste or not, promoting material reuse.
As part of that process, Sokolowski said the team had to consult with the contaminated land officer at the local authority, as well as with the Environment Agency (EA). “Both of them have a consultation period to either approve it or to make comments on it, or request [additional details], [or] they could deny it as well,” he said.
According to him, a surprise during the remediation process was the realisation that building occupants would face a noise nuisance from gas transmission infrastructure on a section of the site that would remain in use by SGN.
This, Sokolowski said, became apparent at the due diligence stage, with TRC taking some “preliminary noise measurements”. The problem was resolved by SGN installing “acoustic housing” around the equipment.
Project aims for outstanding BREEAM rating
With the remediation works on the site completed, construction work began in the summer of 2023. Alongside this, the scheme aimed to be certified under BREEAM, a rating system run by building standards body BRE to recognise developments that are built and operated sustainably.
The BREEAM process scores developments on a range of sustainability themes, from energy to transport, health and wellbeing, land use and ecology, pollution and waste. The Nova Oxford scheme targeted an Outstanding BREEAM rating score, which – requiring a minimum rating of 85% – is the highest a development can achieve.
[Aiming for a 100% BREEAM score] is quite a difficult thing to do at this stage because the design is very early on, but on this project we had aspirations to do something special, and really pushed the boundaries.
Alistair Dunsdon, director of Wrenbridge
Alistair Dunsdon, director of Wrenbridge, walked ENDS through the milestones the project had to hit with regards to BREEAM. The process started, he said, with the appointment of green consultancy Eight Versa to pre-assess the site and the proposed design from a BREEAM perspective.
According to Dunsdon, workshops were convened with a range of stakeholders – technical teams, design teams and engineers from many fields – to examine what the project could realistically target. From the outset, he said, the team thought a high 90s score was achievable.
“It’s quite a difficult thing to do at this stage because the design is very early on, but on this project we had aspirations to do something special, and really pushed the boundaries,” he said.
The ‘buffer’ of early public engagement
Ultimately, BRE awarded the scheme a 100% BREEAM Outstanding rating score on its final stage certificate – a self-styled UK first.
According to Dunsdon, achieving this required “spinning quite a lot of plates”, the better to get all the sustainability dimensions right with the development. It became clear, he said, that it is important to earn as many of the credits that underpin the BREEAM rating score as possible early on “should any slip by the wayside” as construction begins and the numbers are revised.
One area that helped Wrenbridge build this “healthy buffer” of credits preconstruction was its decision to carry out a public consultation early on. It was important, Dunsdon said, to show that the developers had considered people’s views during the design process.
“You’ve got to show you’ve done that at an early stage because the feedback you get from that engagement feeds into the design,” the Wrenbridge director said, adding that it is not possible to do this at a later stage once construction has begun.
Gardens, ponds, solar panels and sun breaks
Public consultation aside, Nova Oxford’s 100% BREEAM rating score was achieved via features added to the building, including green-roofed cycle shelters, electric charging points for bikes and cars, and improvements to surrounding pedestrian and cycle routes, as well as the installation of a landscaped garden with a wildlife pond.
According to Wrenbridge, these and other measures helped to “maximise” ecological enhancement and biodiversity, with the project ultimately achieving a “significant net gain”.
In addition, energy improvements were made across the site. Cost-saving solar panels were installed across most of the roof, while heat pumps were added to drive efficient heating and cooling, and a sun-deflecting structure, known as brise soleil, was built all around the development.
I think some people probably thought that we were a bit silly when we suggested we would be able to achieve [100%], but we’ve done it now, and … we’re trying to apply [the lessons] where we can to other schemes.
Alistair Dunsdon, director of Wrenbridge
As part of the energy efficiency scoring, the team had to carry out thermographic surveys to determine if there was any heat leakage within the building. Based on the results of this, no additional work was required, Dunsdon said.
Waste management was another area where the potential number of BREEAM credits was “maximised”. Dunsdon explained that Parkway, the contractor, achieved those through “good waste management”, with “low waste consumption [and] high levels of recycling during the construction phase”.
‘It can be achieved’
After construction concluded in March, Dunsdon said Parkway had to provide “all of the evidence” to BRE for a final assessment of the scheme’s BREEAM score.
The BRE’s verdict can take months after construction, and sometimes sees the standards body “chip away” at the score on the final evidence, Dunsdon noted. He said Nova Oxford had already been granted a preliminary 100% BREEAM score at the design stage, but added that, during construction, “projects usually find that they might fall away about 5%”.
“[BRE] might come back and argue that some of the credits you’ve submitted and suggested you’re achieving [aren’t achievable],” he added. “So, there’s still that dialogue with the BRE, and you don’t know until you’ve got that final certificate. But we felt like we were in a good place.”
The standards body’s decision to award the scheme a 100% BREEAM Outstanding rating score also post-construction is proof, Duncan said, that “it can be achieved”.
He added: “I think some people probably thought that we were a bit silly when we suggested we would be able to achieve [100%], but we’ve done it now, and we’re taking those lessons learnt, and we’re trying to apply them where we can to other schemes.”
A 100% BREEAM score: Lessons learnt
Get personal
Sokolowski said that “having active engagement with the regulators up front, and actually having [a] site meeting was a really useful step in the whole process”.
He added that being able to get on site and meet people, communicating directly with them, understanding what their main concerns are was “a real winner”.
Keep a foot in the door
Following the building’s completion, a series of additional acoustic surveys were required to hit the BREEAM target. However, as Dunsdon explained, by that stage Wrenbridge had already “handed over the keys” to the building’s new owners, potentially threatening the ability to secure the required credits. But in the end, access was granted quickly thanks to good relations with the new owners.
“It sounds like a really small point, but it could have been the difference between achieving 100% or not,” he said.