A framework for schools
Component-based steel frame buildings, first developed in the 1950s, are enjoying a revival. Jan-Carlos Kucharek visits Great Denham, a school being built using the Scape Technology system
Love them or hate them, everyone’s talking about standardised school building systems. And the system that’s picking up the majority of contracts is Scape, the successor to the CLASP system developed in the 1960s and 70s to deliver the UK’s urgent need for schools to serve a growing population. The Scape system is a component-based steel frame, designed to allow for any kind of cladding specification and suitable for schools and mid-sized health service buildings.
The Scape System Build company, jointly owned by Derby City, Derbyshire County, Gateshead, Nottingham City, Nottinghamshire County and Warwickshire County Councils, acts either as a design and procurement consultant to public sector clients or — via its Sunesis joint venture with Willmott Dixon — offers a turnkey design and construct option. Its marketing claim is that Sunesis can reduce typical build costs by up to 30% and programme by an average 20 weeks.
The Scape system, having learned lessons from its CLASP heritage, has managed to rationalise the structure to a marked level of finesse
Simple 3D visualisation of Bond Bryan’s Great Denham school. The single-storey “race track” of classrooms gains most of its rigidity from the double-height hall structure
The Great Denham school site, view of the structure looking north-west
In light of government cuts and last year’s James Review for Education, Scape is making some big promises for standardised construction, claiming to “cut the costs, risks and protracted timescales of bespoke design, while providing the flexibility to personalise your buildings”. That offer is helping it secure contracts to design and deliver projects UK-wide, most recently with £100m of public works with one of the partners, Nottinghamshire County Council.
Meanwhile, Sunesis is the vehicle through which any public sector body can procure construction works, ensuring compliance with OJEU regulations. Marketing itself as a one-stop-shop, it not only promises leaner processes and programme, but, critically, a fixed price. For the client its website is also tantalisingly interactive — in a few clicks, it seems possible for a prospective purchaser to design their own school.
Bedford Borough Council commissioned Scape for its 420-pupil Great Denham primary school and nursery on the outskirts of the town, appointing Bond Bryan as its architect and Willmott Dixon — which is also sole delivery partner in the Scape national contractor framework — as contractor.
The school is a textbook example of the system in action. Due for occupation this September, its steel frame, with two single-storey courtyards of classrooms sitting on either side of a double-height central hall, had to be erected within a tight 30-week programme. Having broken ground less then six weeks before CM’s visit, progress so far has been impressive. “We are in the ninth day of steel erection, with the steel columns and beams of the main hall up in less than two days,” says Wilmott Dixon project manager Mark Pinder. “The intention was to have all the structure up in 18 days, but we’ve had two days of downtime due to high winds, but we should still be complete within four working weeks.”
Standardised components means using a spacing of square columns, generally at 3.6m, hidden within the perimeter cladding zone. Any internal columns are likewise tucked inside classroom partition walls. The pervading solid thin steel sections only become deeper where columns are “dropped”. If larger sections are necessary, such as in the hall, the design defaults to perforated, deeper sections; any roof penetrations that break the steel rafter centres are achieved using parallel flange channels. The thinner steelwork sections are due to the fact that these are low-rise structures.
Great Denham’s main hall is a double-height space, but Scape design director Tom Ridley-Thompson says that the system would never run above four storeys. It’s all about keeping the physical weight of the structure down and, being single-storey, here it doesn’t even require any fire-proofing.
And it shows. The most obvious thing about the system is its slenderness, something Scape virgin Pinder attests to. “I came from a retail background, and when I saw the structure first I thought it looked very thin, but I’m a convert,” he says. But this slenderness is an aspect that comes with provisos. “It’s important to educate the site team to the nature of this structure and its constraints, as stability is key. Erection, for instance, has to be done starting at the right location.”
In the case of Great Denham, the frame is being erected like a race track. The two-storey hall section, the structure’s most rigid element, had to be built first, with the fingers of single-storey classrooms coming off it. Every return then gives any “run” of structure greater stability. The figure-of-eight form is structurally efficient as each side is strengthened by its adjacency with another.
So is this super-optimised structure actually an exercise in engineering brinkmanship? Ridley-Thompson thinks not. “In its skeletal state, the structure really is quite stable, as every column has a four-bolt base connection, giving it column rigidity,” he says. But there’s a qualification coming. “Where care needs to be taken is when the cladding goes on, as that’s when the structure attracts wind loading, so at that point all the necessary bracing needs to be in place.”
Ridley-Thompson explains that unlike the cross-bracing of the past (see box), in today’s Scape system, “it’s the roof that gives the skeleton true rigidity. The stressed 7.4m long D60 metal deck roof and ply layer acting as a diaphragm, stitching it all together.” Vertical bracing is evident on all four sides of the main hall, but on the single-storey classroom blocks coming off it, there’s none at all.
Instead, Ridley-Thompson points out a detail where columns meet the edge beam, where there’s a double-bolt connection that stiffens up the whole structure. “Just this detail gives enough stiffness that could free up the whole perimeter elevation for glazing,” he says. Attention to detail is therefore everything — Pinder says that “the most difficult thing for the erector is the positioning of the column bolts ‘floated’ into the wet raft concrete, you have to ensure that they don’t move to make sure they keep the structure plumb”.
The Scape Technology system is designed ideally as a homogenised frame of similar beam spans. Where columns are missed, or loads increased, the penalty is thicker beams and increased cost
Perimeter columns are hidden in the cladding zone. With no cross-bracing, the perimeter could potentially be completely glazed
The main idea with the Scape system is that the steel is structurally independent of anything else in the build. Ridley-Thompson explains that even on their taller buildings, where there might be blockwork lift shafts, the structural design would still isolate the steel frame from other elements. “It was key that the system doesn’t rely on wet trades for its integrity, as typically coming later in the project, these would have programme implications.”
The lightness of the structure also simplifies site logistics. Les Carter, Willmott Dixon local account manager, says that crane access for lifting them in only needed to be from one side with a single 80-tonner. Carter says also helping is the fact that with the structure concentrated on the outside and with shallow excavations, “the pour is only constrained by the rate the concrete comes out of the pump. Here, the raft is 125mm thick, with a 450mm downstand — there’s only mesh reinforcing too; no rebar and no chairs or bending of steel”.
All these facts might contribute to the fact that the site seems oddly devoid of operatives “There’re only nine ground workers on site currently, four fabricators, four labourers and a crane driver,” says Pinder. By the time the fit-out starts, however, there’ll be upward of 60 operatives on site.
Getting architects on board early is key to project success, and here Bond Bryan worked with Willmott Dixon and Scape almost from the outset. “They hadn’t used it before and needed guidance,” recalls Ridley-Thompson. “So we showed them how to use the Scape grid and to employ simple rules of thumb to make sure the system worked for them.”
He stresses that it’s counter-productive to develop a design and then try to match the system to it. “With a traditional build the architect is king; they’ll design it and the engineer will model it. But if you want to get the benefits of the Scape system, you have to work with the grid and column positions. You don’t try to eliminate them to create larger spans, because then you’re having to beef up the structure, and that adds to the cost,” he says.
But for the build team, playing by the rules is everything. “If you’re not getting a structural compliance with the system in excess of 80% at design stage, you’re wasting both money and design time,” says Carter, adding: ”You don’t create a system to have architects break it — all the efficiencies are bound up in its standardised nature.” So to avoid exponential costs, the advice is: stay within the system.
Nevertheless, there have been some modifications at Great Denham: where internal columns have been dropped, such as in the kitchens and servery areas where a more open plan was needed, increased beam sizes are immediately obvious. That said, Ridley-Thompson acknowledges that “the world’s a messy place and sometimes you have to make client changes, but it’s not a system that likes structural changes at a late stage”.
In the time that Wilmott Dixon has worked with Scape it says there has only been one project overrun, with none going over budget. Not everyone is pleased about this, with Building Design magazine calling Sunesis schools a “one-size fits none” approach. But the team is unlikely to be troubled: the comment came in response to a positive review by Design Council CABE of two new Sunesis schools in Rugby and the Isle of Wight. Provided there was further client/design team liaison, it endorsed them as “a successful way to build new schools”.
The great Scape from CLASP
Tom Ridley-Thompson, design director at Scape, on continuity and change in its steel-framed system
Scape is nothing new. Its former guise, CLASP (Consortium of Local Authorities Special Programme), was set up in the late 1950s to meet a demand for school building.
It was always a steel frame but went through various developments, going from Marks 2-6, although its heyday was in the 1960s-70s with Marks 3-4, where it developed a definitive and recognisable aesthetic.
After 1979, when public sector building fell off a cliff, a lot fewer were built, but over that time it also became a less stylistically rigorous system, more flexible and open-ended. Pitched roofs came in and the use of traditional cladding. By the 1990s, a CLASP building was not recognisable as visually different from any other typical public sector building of the time.
The CLASP frame system went from a defined aesthetic in the 1950s and 60s to one that could incorporate any type of architectural style (below)
In a sense, Scape has carried that open-endedness and flexibility on, but has learned from the past and significantly simplified the steelwork design. CLASP buildings suffered from the intrinsic design problem of being riddled with internal cross-bracing bays, so that layouts were pretty much fixed and not easily remodelled. Now any bracing is limited to the external frame.
Also, production of the CLASP steel frame was reliant on a limited number of centralised fabricators, involving materials having to travel. Our system of standard universal beam and universal column steel sections can be manufactured by local fabricators — good news for local employment, as well as reducing carbon miles. Our aim is to make structure work as hard as possible, which also minimises use of resources.
Foundation design has also evolved. CLASP always used pre-cast raft foundations that could be as little as 100mm in depth, but they were historically more expensive to procure. We’re still using raft foundations, but in-situ cast ones, which are also a lot thicker to meet current codes and which again makes use of local skills. There’s no deep excavations, and they can be used on all but the poorest ground, where we’ll use piled foundations.
Any building procured through our framework agreement, such as Great Denham, uses an NEC contract, although outside the framework we can use traditional tendering — it’s all about client choice. Architects are also not locked into a pre-defined aesthetic. It’s best if we work with them from the outset, and while there’s a bit of a learning curve initially, we’ve successfully collaborated with the likes of Aedas and Bond Bryan to produce some really good buildings.