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CONSTRUCTION PREFABRICATION


buildings, or parts of them, is said to offer better build quality and shorter project times. So why has this process so far apparently only had limited impact in the industry? Alistair Gibb, professor of construction


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and engineering management at Loughborough University, estimates that prefabrication, in its many forms, is used in no more than 10% of construction projects. Gibb, who previously had a career in engineering and project management with John Laing, Taylor Woodrow and Sir Robert McAlpine, backs the use of prefabrication, but says its adoption has been held back by cost issues and the recession. ‘There was a significant increase [in the


use of prefabrication] a few years ago, but it has been severely disrupted,’ says Gibb. ‘What tends to happen is there is an increase in off-site solutions during boom periods when labour is cheap and people need things doing quickly – some of the earliest uses of toilet pods were in the commercial building boom of the late 1980s. ‘But when labour prices come down, it’s


not uncommon for the quantity surveyors, or people bidding for work, to say they can buy labour for less than the factory costs.’ Gibb also claims that many project teams


When you go off site, all the reconditioning, the snagging and all the rest of it, is done in the factory


simply ‘do not know how to accurately assess the cost’ of prefabrication versus traditional methods. While many say that off-site is 5% more expensive, Gibb argues that these comparisons are based on first price rather than outturn costs, and ignore the extra expense of problems that occur with traditional on-site methods, such as ‘rework, interface coordination problems, delays and disruption’. These are left out of bid prices on


the assumption they will be covered in subsequent claims for variations. But, says Gibb, ‘when you go off site, all the reconditioning, the snagging and all the rest of it, is done in the factory.’ Gibb adds that the stop-start nature of


the private housing market has also worked against prefabrication, because factories need long-term commitments from buyers to invest in production facilities. ‘I wouldn’t argue that off-site is the answer for every situation, but it deserves a bigger share of the market than it’s getting at the moment, without a doubt. I think the reason is people can’t work out the real value of it.’


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n the face of it, prefabrication is a no-brainer. The off- site manufacture and quick installation of whole


Model approach Despite the industry’s apparent record of resistance, there are signs that the ‘prefabricators’ are beginning to win the argument. Two major developers say they definitely expect to use more prefabrication once the market picks up. ‘Previously, the cost may have been


higher than doing the work on site, but perhaps what hasn’t been properly recognised is the efficiencies achieved,’ says Neil Pennell, head of sustainability and engineering at Land Securities. ‘The prefab shops have improved


over time; they’ve got larger and they’re using more productive processes. They are providing a wider range of solutions and they do the work in the best possible conditions to achieve higher quality.’ Pennell has toured the construction


site of the 310-metre Shard at London Bridge and been impressed by the use of prefabrication by the contractor, Mace. Tall buildings face potential problems in having to move large numbers of workers around the site quickly and efficiently, especially before the lifts are installed. Mace has reportedly reduced the number of men installing equipment on the site from an estimated 400 to just 80, thanks to prefabrication of items such as pump rooms, whereby water pumps for heating and chilled water are being brought into the site in pre-assembled groups, while risers are being dropped in several floors at a time. Pennell points out that this requires


careful planning, with walls left unbuilt until large items of prefabricated equipment have been brought inside. ‘What you’re fighting against is that the people who design the building don’t always think about how you’d get more prefabricated stuff in by leaving walls down – the people in charge of those processes are often a bit divorced from the building’s services.’ Mace declined to comment, but Pennell believes its approach at the Shard may point the way to the future: ‘There’s been quite a lot of interest from the industry in what they’re doing.’ Land Securities has begun piling work at its own 38-storey tower at 20 Fenchurch Street in the City of London, and various construction contracts are being tendered. It’s too early for specifics, but Pennell says: ‘There will probably be a lot of opportunities for prefabrication in the risers, a bit like the Shard’s approach.’ Pennell stresses that prefabrication is not


new, and almost every conceivable building item has been prefabricated in the past.


June 2011 CIBSE Journal 23


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