Skanska stirs up porridge

In Edinburgh Prison, inmates always have an audience, even when they're squatting on the chamber pot in the corner of their cell. But the curtain is finally coming down on primitive toilet facilities and overcrowded cells. Inside Edinburgh's boundary wall, Skanska has just finished building the biggest prison block in Scotland. Even when the number of inmates peaks (there's a surge every March and April), only a quarter of the 225 new cells will be shared. And shared or single, all cells have their own en suite toilet, bringing an end to the early-morning slopping-out parade.

The £18m block is the seventh PFI prison Skanska has built in as many years – four in England and three in Scotland. Thanks to modular construction, the company has delivered the Edinburgh block within budget and well ahead of schedule, and is now sitting pretty to win the contract from the Scottish Prison Service for its next two blocks.

Security risks?
By casting the modules that make up the block in a concrete factory in Peterborough, Skanska delivered a fast-track programme and consistent quality. Speed was critical because running a construction site within the grounds of a working prison presented an obvious security risk. Most obvious of all was the large hole punched in the outer wall to allow lorries to drive onto the site. That hole, a big 'over here' sign for would-be escapees, will be bricked up again only after site works end. "The shorter the time there's a breach in the wall, the better," says Derek Gunn of the Scottish Prison Service. "Reducing time on site is a massive win for us."

Skanska is handing over the new block three weeks early, allowing the prison to move the 300-odd inmates in the old blocks across to the new one well ahead of schedule. The old blocks (sound 1920s-built structures but difficult and costly to refurbish) will be demolished and a new one erected next year to double the prison's capacity.

John Rourke, Skanska project manager, says the rapidity of modular build gave the team more time to spend on the fit-out and finish. "We're handing it over with zero defects," he says. "It has to be that way because we can't go back to set things right when inmates are in there."

While it satisfied the client's main demand, speed wasn't the only reason Skanska built the block out of factory-cast modules. "The rates for on-site labour can be horrendous," says Rourke. "Modular is all about labour. Streamlining in a factory is the most efficient way to manage it."

In the Peterborough factory of module maker PCSL, a resident Skanska construction manager controlled quality round the clock, effectively acting as a clerk of offsite works. PCSL cast the four walls and ceiling of each module as one, building in conduits, service runs and openings for the door and windows before pouring a self-compacting concrete on top of a reinforcing steel mesh.

Stacking up
To build the two wings of the new block, Rourke poured a concrete foundation slab on site and then stacked up 80 modules (their weight alone holding them in place) either side of an association corridor wide enough to take tables and chairs. The first module went in in the second week in August, the final one in the last week of September, a process that took seven weeks from start to finish. Since then it's been about installing the doors and windows, putting on the steel and concrete roof, building the off-the-critical-path external brick cladding, sliding in the toilet pods, and doing extensive M&E work.

We’re handing over with zero defects. we can’t go back and put things right when the inmates are in there

John Rourke, Skanska

Most of the modules are four-cell units, with each cell holding a single prisoner, but each two-cell unit contains a pair of bunk beds in each cell. Prison numbers fluctuate markedly and predictably during the year, and the shared cells allow the prison to cope easily with peaks without overcrowding and without lots of empty cells when the prison population falls. The shared cells have 9sq m of floor space, compared with 7sq m in the single cells – allocations that exceed the existing regulations.

Surprisingly, given the supposed primacy of repetition in modular construction, only three of the 80 modules at Edinburgh Prison are identical. Modules differ according to whether they're four-cell and two-cell, the varying position of windows (which shift to suit the special furniture in suicide-watch cells), and slight variations in the wiring for the doors. While such extensive customisation no doubt demonstrates that modular isn't all about vast numbers of identical boxes, the point, profit and proliferation of modular construction surely depends on a greater degree of standardisation.

With the new block built within the walls – on the old recreation ground, now replaced by two five-a-side football pitches – the prison regime provides an unmissable backdrop for construction workers. The site is blocked off by a towering barbed-wire-festooned fence, loaded with so much high-tech escape-foiling gadgetry that assembling it took four months.

Then there's the no fraternisation rule. "Prisoners will always try to see what they can get out of you," says Gunn. "When someone new comes along, they're onto them straightaway." So if you're walking past the wire fence and a prisoner on the other side shouts something over, even responding with a 'what?' results in instant dismissal. It's happened, says Rourke, who recommends keeping well away from the windows of the old blocks to stay out of range of the barrage of rubbish and used toilet paper that inmates dump onto the unwary.

Gunn likes modular construction because it allows the prison service to capture and recycle prison design expertise. "It takes a lot of experience and governors' time to build a prison," he says. "We don't want to reinvent the wheel each time." At Edinburgh, the design of the new block maximises safety and security and will be repeated at the Scottish Prison Service's next two cell blocks. For example, PCSL cast the modules with rounded internal corners so inmates could not scrape out hiding places between walls, floors and ceilings – a favourite spot for cacheing drugs.

Keeping an eye out
Likewise, floors consisting of Porridge-style landings with a large central lightwell are out because they leave guards overlooked by inmates. Instead, the new L-shaped block arranges the cells over two wings – one of four storeys and the other of three – with guards stationed in a central core where the wings meet. The core (like the corridor, made of precast concrete panels rather than modules, and containing interview rooms) gives guards an unbroken view of what's going on in both wings, but prevents inmates seeing beyond their own wing. That way, if trouble breaks out, it's easier to stop it spreading.

And trouble is one of the drivers of Britain's prison upgrade programme. In the 80s and 90s there were spectacular instances of rioting inmates trashing UK jails. The Scottish Prison Service's £110m prison upgrade and building programme does two things: better facilities reduce the grievances that fuel riots, while the superior design improves security. The new block at Edinburgh, for example, incorporates hidden features to allow guards and police to wrest back control quickly should prisoners seize a wing or a landing.