Part precast, part in-situ concrete, Pitman Tozer’s Farrimond House might just provide a template for estate regeneration. Tony Whitehead reports on the latest phase of Barking’s Gascoigne estate revamp – and the first to be zero-carbon in operation
As it entered the 21st century, the sixties-built Gascoigne East residential estate in Barking was already looking tired – a depressingly familiar mix of deteriorating high-rise towers, anodyne low-rise blocks, and bleak community space. To make matters worse, the area had also been plagued by a series of fires which, particularly after Grenfell, caused increasing concern.
Recent years have seen the start of real transformation. Failing blocks have been demolished, and to date some 1,400 highly efficient and affordable new homes have been delivered. The regeneration arm of the London borough of Barking and Dagenham, Be First, wants the new Gascoigne to be “a model of 21st century urban living”, but visiting the estate today it becomes clear that this is no showy silver-monorail vision of the future. There is little in the way of extravagant architecture and, at first glance, some of the developments have a touch of mid-century style about them.
The Pitman Tozer-designed Farrimond House is a good example. Four-to six storeys high and brick- clad, its 226 new homes are arranged around a central courtyard. Zoom in a little, however, and it quickly becomes apparent that this building offers considerably more than its predecessors. “It’s zero-carbon in operation,” says architect Luke Tozer. “It is fed by a district heating system, the roof is covered with PV panels, and it conforms to high standards of insulation and airtightness.”
Every home, he adds, is dual aspect, giving residents plenty of light and a variety of views: “This also saves on mechanical air-conditioning, allowing cross-ventilation to keep the flats cool. And vitally, it allows every flat to have two means of escape in the event of fire.” Fire risk was a key factor in choosing concrete for the structure: “For this kind of large-scale, affordable housing project, concrete is a very cost- effective structural solution,” says Tozer. “Add to that its inherent resistance to fire, and really concrete is the only material in town for projects like this.” Farrimond House occupies a 73m x 54m footprint with a spacious 45m x 30m central courtyard and play area.
This gives “wings” of 14m and 12m in depth, including the walkways, via which the apartments are accessed. It has a hybrid concrete structure, featuring in-situ reinforced concrete floor slabs with precast columns and The Pitman Tozer-designed Farrimond House is a good example. Four-to six storeys high and brick- clad, its 226 new homes are arranged around a central courtyard. Zoom in a little, however, and it quickly becomes apparent that this building offers considerably more than its predecessors.
“It’s zero-carbon in operation,” says architect Luke Tozer. “It is fed by a district heating system, the roof is covered with PV panels, and it conforms to high standards of insulation and airtightness.” Every home, he adds, is dual aspect, giving residents plenty of light and a variety of views: “This also saves on mechanical air-conditioning, allowing cross-ventilation to keep the flats cool. And vitally, it allows every flat to have two means of escape in the event of fire.”
Fire risk was a key factor in choosing concrete for the structure: “For this kind of large-scale, affordable housing project, concrete is a very cost- effective structural solution,” says Tozer. “Add to that its inherent resistance to fire, and really concrete is the only material in town for projects like this.” Farrimond House occupies a 73m x 54m footprint with a spacious 45m x 30m central courtyard and play area. This gives “wings” of 14m and 12m in depth, including the walkways, via which the apartments are accessed.
It has a hybrid concrete structure, featuring in-situ reinforced concrete floor slabs with precast columns and precast core walls. “Having decided on concrete for the structure, the question was how to make it as sustainable as possible,” explains Nathan Fieldsend, associate with structural engineer Elliot Wood. “In preplanning, we were looking at an all-precast structure: precast load-bearing walls spanned with precast planks. But when we compared that with an in-situ frame, we found the precast option initially came out slightly higher in terms of embodied carbon.”
Fieldsend says this was partly due to the concrete mix used to help speed curing and production in the factory. “For example, the columns went from C35/45 in-situ concrete to C40/50. That involves extra cement.” Carbon was not the only factor in the decision, however, and the team wanted to incorporate precast where it brought other benefits. “The client wanted to embrace MMC [modern methods of construction] as far as practicable, and the contractor was keen to use precast, mainly from a programme point of view,” says Fieldsend. “Being manufactured offsite in quality-controlled conditions helps maintain that speed of construction.”
The challenge was to find a sweet spot between carbon efficiency and buildability. Fieldsend explains that the desire for material-efficient structural simplicity drove the choice of in-situ slabs, rather than the precast planks originally envisaged. “Most precast slab systems span one way,” he says. “That would have created some difficulties with the column arrangements we have. We would probably have had to introduce beams, with all the extra material and carbon that would have involved. Reinforced concrete flat slabs were a simpler, more efficient option.”
Flat slabs made sense architecturally, too. “Beams would have meant downstands,” says Tozer. “Not only would that have created issues with our floor-to-ceiling heights, but they would also have got in the way of the MEP [mechanical, electrical and plumbing] services, many of which are carried above false ceilings.” To reduce the carbon content of the slabs, 30% of the cement in the in-situ mix was substituted with GGBS (ground granulated blast-furnace slag), and GGBS replaced 70% of cement in the concrete for the foundations. The precast concrete elements contained no GGBS, because of the impact on curing times.
So the team instead focused on reducing carbon further by slimming the total amount of concrete in the building. “A key way we did this was by regularising the layout,” says Tozer. “Often, with housing, you find that everything stacks, apart from the ground floor due to the presence of foyers or back-of-house spaces. Here, we’ve made an effort to avoid that. The homes sit neatly on top of one another all the way down, which enables the loading to go straight down to the foundations. And because everything stacks, there is no need for any transfer structures – strengthened slabs or beams that would have been expensive in terms of material and carbon.”
The next step was to remove material from the design. “We were able, for example, to take away some parapet walls – concrete upstands around the deck access. These were replaced with railings. But the main change was to switch from load-bearing walls to columns with stud walls. The columns use less material, and because of this the whole structure could become lighter and less material-intensive.”
The 250mm-thick RC slabs are supported by 450 precast blade columns. In section these are mainly 1,000mm x 200mm or 500mm x 300mm – making them slim enough to be concealed within the stud walling which now forms the majority of the partitions between rooms and flats.
The building also contains 420 precast wall panels, used to form cores around lifts and stairwells. Most of these are twin wall, and typically 4.5m x 3m. “Being twin wall, with a cavity between two slim panels, makes the panels lighter,” says Fieldsend, “so they are easier to transport and to crane around the site. Once the panels are in place, concrete is pumped into the cavities and this effectively stitches the panels together.”
Tozer adds that one advantage of precast wall panels was their factory-controlled appearance. “You don’t see much of the concrete in this building, but where you do – around the cores and stairwells – the precast wall units look very neat with a great finish.” Where there are openings in the cores, solid panels have been preferred to twin wall to create a visually acceptable cut-edge.
The team is clearly satisfied that the material choices they made back in 2019 have paid off, delivering a smart, practical and very efficient building within a limited budget. “The refinements to the original design reduced embodied carbon by 5-10%,” says Fieldsend. “If you think of the construction industry as having a carbon budget, then I would argue that buildings like this are exactly where you should be spending it – using concrete to create long-lasting, affordable and fire- resilient housing.”