Don't knock 'em

Main contractors have, shall we say, a less than complimentary attitude towards their demolition counterparts. The average construction manager views demolition as noisy, dusty, simple work that gets in the way of their efforts, carried out by halfwits who wouldn't have the first clue about construction.

But is this reputation deserved? With advances in technology, so demolition has advanced. Demolishing, particularly on a crowded city centre site or in a listed building is not just a case of getting out the wrecking ball.

It seems that antagonism exists on both sides. One demolition project manager claims that main contractors see his profession as second rate and a hindrance. "Most builders try to work round us," he says. "It doesn't work. The trouble is they all think they can do demolition, that anyone can knock a wall down, but it's just as specialist as any other discipline. There are certain jobs where we've been respected, but not overall."

Main contractors often aren't aware of the specialist advice demolition experts can provide, he adds. "They don't want to take advice from us. We are just expected to act on their decisions, even if we know there is a better way to do things."

Expert advice
Kevin O'Driscoll, a construction manager for Try Construction says he is happy to receive advice from demolition contractors and has consulted renowned demolition experts on his current job at King William Street in the City of London.

"It's very easy to knock demolition, but they've got a job to do as well. We have spoken with Keltbray, our demolition contractor, at length about the methodology of this job, it is the specialist after all. We try and buy in as much expertise as we can."

But he does admit that relations can become strained between construction managers and demolition contractors. "Demolition is a different frame of mind to us. They knock things down, we build them. They aren't always worried about keeping the noise and dust down or relationships with the client and the council because they're only around for a few weeks. We're then left to maintain the peace."

Roy Gibbons, managing director of London-based demolition contractor Linguard admits that his trade is "a dirty, messy business," but insists demolition firms do their best to minimise it. "There are machines available now that spray water to damp down the dust while demolition is going on, so we try to reduce the inconvenience."

He says that the industry has changed dramatically in the last 20 years. "Man power has been drastically reduced, which is a good thing in terms of health and safety. Because of the increasing sophistication of machines, instead of needing 10 men and a machine, now you only need two. For example, there are high-rise machines with munchers on the end, that reach up to 40m, so there is no need for scaffolding when taking down tall buildings."

There are also more crowded sites that require demolition, says Gibbons, so there is a need to be more precise. "The wrecking ball is very rarely used now. You can be more accurate with an excavator, so there is very little need for it."

"Demolition is a field of engineering in its own right," he asserts. "There are lots of calculations to make when knocking down a building, it's almost reverse construction. You have to know what you are knocking down. You have to know the volume of the building, the material, what type of material it is, if it's concrete whether it's stressed or not. If you cut through pre-stressed concrete, it explodes outwards, so you have to be very careful when taking it down.

The average construction manager views demolition as noisy, dusty, simple work that gets in the way of their efforts, carried out by halfwits who wouldn’t have the first clue about construction

"Most of the buildings that are coming down now are reinforced concrete buildings from the 1960s," he adds, "and they are more difficult to take down than the 1940s brickwork structures that were being demolished 20 years ago. The National Federation of Demolition Contractors (NFDC) provides guidance on how to demolish concrete, so we keep up to speed with developments that way."

And if you want proof that demolition is more engineering than destroying, look no further than the Erith Group's dismantling of a steel docking yard in East London. The pre-stressed concrete crane rail beams hangover the Thames, which means when taking it down there is no room for error or it falls into the river. And because the beams are pre-stressed, it's not just a case of cutting them into sections and lifting them down.

"Because of the tension wires in the concrete, if we just cut the beams, the whole lot would fall down," explains Jim Hollands, contracts manager for Erith. "The beams have to be heated up to de-stress the concrete before we can cut it."

The size of the beams has also caused problems. "To lift the sections of concrete down in the size we wanted to originally, it would have meant using two 1000 tonne cranes," says Hollands. "This area is residential and the access isn't very good, so it would have meant chaos on the road and for the residents, with the amount of lorries needed to bring in the weights for the cranes. So we decided to lift smaller pieces, meaning we only need one 1000 tonne crane, which will cause substantially less disruption for the residents." So it seems not all demolition contractors are careless of their environment.

"This has been an engineering job as well as demolition. We've consulted pre-stressed concrete experts and engineers to get it right," adds Hollands.

Invited in
Dave Darsey, contracts director at Erith, says it considers itself a principle demolition contractor and is often consulted directly by clients. "We are asked more and more by clients to be part of their professional team and are invited into pre-tender discussions."

But he says that main contractors aren't so respectful. "Main contractors are not so likely to consult with you. They will tell you how long you need to do a job, not ask you how long it takes. We would rather work directly for a client. We have our own in-house safety and site managers, so we can provide the management that a main contractor does."

Darsey says that to be sure of getting a demolition contractor that does respect the environment and provides a high quality job, you should look for signs of quality.

"Any demolition company that is affiliated to the NFDC, the Institute of Demolition Engineers or a member of the Considerate Contractors scheme has to be of a certain quality. The standard to get into the NFDC, for example is very rigourous," he says.