One of the most active 鈥� and controversial 鈥� subsectors of the ground engineering industry is basement extension.
It鈥檚 active because in central London, where property prices are astronomical and space is at a premium, installing a basement or extending an existing one can be a practical way of adding value to your property. And it鈥檚 controversial because the technical challenges have proved too much for some of the architects and contractors employed to carry out the work.
The super-rich have been leading the march underground with ever-more ambitious schemes going three or four storeys deep and incorporating such features as underground cinemas, garages, swimming pools 鈥� and even climbing walls.
Not everybody鈥檚 a fan, though. Technical problems, such as flooding and subsidence, have combined with severe above-ground disruption from vehicle movements and noise to make the London borough of Kensington & Chelsea (where the basement business seems to be especially popular) introduce measures to discourage the practice.
Under proposed planning bye-laws, basement extensions in the borough would be banned from going more than one storey deep and could extend out to no more than 50% of the property鈥檚 garden area. Surprisingly, this is welcomed by Oliver Gentle, piling manager with Brentwood-based contractor Knightbuild, which specialises in groundworks including basement projects. 鈥淚t鈥檚 good news for us because it鈥檚 led to a rush of planning applications,鈥� says Gentle. Planning permissions granted before any revision of the regulations will remain valid for up to three years, he explains. So the borough鈥檚 announcement has effectively guaranteed three or more years鈥� work for the company. Last year, mainly on the strength of the basement market, Knightbuild set up its own in-house piling division to carry out this highly specialised work. 鈥淚鈥檝e been in piling for the past 20 years and I鈥檇 been doing Knight鈥檚 piling as a subcontractor up until last year,鈥� says Gentle. 鈥淭heir business is basements and concrete frames, so piling is important to them,鈥� he adds.
Now, with eight piling rig operators and five 鈥榩iling men鈥� on the team, Knightbuild鈥檚 piling division is working flat-out. 鈥淲e鈥檝e just finished eight big jobs and we鈥檝e got another eight just starting,鈥� says Gentle. 鈥淎t any time Knightbuild always has 12 to 15 projects on the go,鈥� he adds.
But although the new division employs more than a dozen people, it has no piling rigs of its own. Instead, it has chosen to hire all of its rigs from Cheshire-based hire and sales company Skelair, a company Gentle knows well from previous experience.
Skelair is the sole UK supplier of the German-made Klemm range of mini-piling rigs, which are perfect for the sort of work Knightbuild does.
鈥淗iring makes sense, especially when you consider we鈥檙e only just getting started,鈥� says Gentle. He reckons that owning enough rigs to satisfy the current workload would require an investment of at least 拢1m. Tying up that amount of money in capital equipment at this stage would be unwise: 鈥淥ur closest rival bought all their rigs; their piling division lasted nine months,鈥� he explains.
Being able to hire the equipment gives the company flexibility. At the time of writing it had two Klemm 709-2 rigs out on hire, including one on a major basement project which required a compact machine capable of installing 450mm-diameter piles to a depth of 30m.
Having access to high-quality rigs on longterm and flexible rental agreements is a cost-effective and scalable solution, especially for a business that, like Gentle鈥檚, is undergoing rapid growth.
Gentle has a particular liking for the Klemm machines, which he describes as typical examples of German engineering: 鈥渂uilt to last and simple to use. The workmanship is second to none,鈥� he says. They are compact but powerful, capable of installing piles up to 660mm in diameter and 30m deep. 鈥淭he job we鈥檙e on at the moment, we could use a 40 tonne rig for those piles,鈥� he says. 鈥淏ut there鈥檚 a listed gateway and some mature trees nearby. The sheer weight of a big rig would do too much damage; but the Klemm only weighs 14 tonnes.鈥�
Gentle does not rule out the possibility of Knightbuild eventually owning some rigs of its own although he says it鈥檚 certainly not going to happen soon. He鈥檚 happy to continue hiring from Skelair Having said that, with so much work around at the moment, there would be no need for any machine owned by Knightbuild to stand idle. Why not buy some machines and offer specialist foundations services to third parties? 鈥淲e have discussed this and it wouldn鈥檛 necessarily be a problem,鈥� concedes Gentle. But it鈥檚 still early days, he reminds us; the division was set up specifically to satisfy the parent company鈥檚 requirements and it鈥檚 too soon to consider turning it into a specialist contractor in its own right. 鈥淚n any case, we are so busy with our own work at the moment that there鈥檚 no time for third party work. We haven鈥檛 got a spare week this side of Christmas.鈥澛�
Give a dog a bad name
Three months ago, the Health & Safety Executive made a series of unannounced visits to domestic basement projects in London. Nearly half of them failed the inspections.
Such is the demand that a growing number of unqualified builders have been tempted to try their hand at basement extensions without the first idea of how to manage the technical challenges and without the services of a professional structural engineer.
You don鈥檛 have to look far to find the inevitable horror stories 鈥� such as the Victorian house in Barnet that had to be demolished in April after shoddy basement work resulted in the building literally splitting in two.
The basement business is developing an image problem, admits Oliver Gentle. And it鈥檚 a major frustration for companies like Knightbuild.
鈥淭here鈥檚 plenty of them out there: people trying to make a fast buck 鈥� no propping, no structural design,鈥� he says. Knightbuild, he points out, has an in-house team of six structural engineers and does all its own design work.
When the HSE carried out its safety blitz in March, five of the projects it visited were Knightbuild鈥檚. 鈥淣ot one was served with an improvement notice,鈥� says Gentle. All Knightbuild sites are registered with the Considerate Constructors scheme and the company has even come up with its own 鈥淪ee it; say it鈥� campaign to encourage site staff to report anything untoward. Employees are encouraged to fill in cards and drop them in boxes located on site. 鈥淓very week we award a 拢25 Marks & Spencer鈥檚 voucher for the best card,鈥� says Gentle.
This article first appeared in the June 2015 issue of聽Construction聽magazine. To read the full magazine online,
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