Are deflection heads over-specified or under-appreciated? Can designers’ demands for futureproofed partitioning and drywall systems be accommodated without drastically altering the installation process? Paul Thompson reports on a few of the specification challenges facing specialist contractors in the industry.
As the economy continues its tentative emergence from recession, both the commercial and residential sectors are witnessing surging sales. Demand for new build and refurbished office space in our city centres is starting to claw its way back to pre-recession levels, while across the country more high-density residential schemes are finding their way into the order books of specialist contractors. Even the fast turnaround world of shopfitting seems to be further accelerating away as firms on the high street vie to grab more of our newly disposable income.
This spirited economy is a welcome relief to hard-hit contractors, but with it comes the increased pressure of trying to make money on historically low tender values while input, labour and material prices rise, mirroring the upward trend of the economy. With order books bulging most contractors are anxious to strip out any waste and improve their operational efficiency.
One area that frustrates specialists is that of over specification. Being required to use costly materials or methods that experience suggests will not be needed. Deflection heads are a constant source of frustration. Designed to help non-loadbearing partitions and drywall absorb any movement caused by the loading of floor and ceiling slabs, deflection heads are specified on the back of a theoretical maximum deflection calculated by the structural engineer.
Often, though, these theoretical maximums are so far over the likely norm that by the time rounding up and a factor of safety have been added on, the specialist drywall and partitioning contractor is being asked to install deflection heads that can accommodate as much as ± 32mm, yet not all partitions require any deflection heads, especially those under suspended ceilings.
“It can be frustrating. The design and installation of these deflection heads is expensive. Generally you will be asked to install a system to accommodate 15-25mm deflections, but I have seen instances where a ±65mm has been required. If that level of deflection is needed I would have thought the building’s owner would have more to worry about than a few cracked partitions,” described one frustrated drywall and partitioning contractor.
There are some advantages in the use of larger deflection heads, as they can provide flexibility in some systems allowing them to become relocatable and not just demountable.
“Glass in glazed partitioning is cut to such high tolerances that it can be impossible to relocate, because the floor to ceiling height will vary and the toughened glass cannot be cut to suit a new location, when there is a need to reconfigure the office for instance. That deflection head can become a ‘tolerance’ head helping to alleviate some of the issues caused by an uneven slab,” explained Joe Cilia, technical manager at AIS FPDC.
And the current trend for exposed soffit slabs, helping developers use the thermal sink properties of concrete to meet energy efficiency targets, means that because they are open to view, the deflection head details are getting ever smaller, tidier and more intricate.
But because the deflection heads are likely to be exposed, the architects are driving the requirement for more aesthetic details and, in turn, prompting manufacturers to produce them.
Manufacturer SAS International has developed a system that can integrate both drywall and glazing as well as offering deflection protection of 25mm. It can also accommodate material from all the major plasterboard manufacturers.
Andrew Jackson at SAS International explained: “Partitioning integration with drywall is very often overlooked by contractors, even though it offers up to ±25mm deflection and seamless drywall to glass integration. The System1000-Drywall+ is a so-called aesthetic detail and offers performance guarantee in accordance within the specification and application as well as the standard product guarantee. The part drywall, part glazed installation gives it a modern clean aesthetic while offering high performance.”
Other manufacturers including British Gypsum and Knauf boast an array of standard details for deflection heads and these are only guaranteed for compatible drylining systems, allowing contractors to provide performance certification when required.
“We stick with one manufacturer through 90 per cent of what we do,” said Peter Baker, commercial director at Stanmore’s. He added: “Some manufacturers have streamlined and value engineered the number of standard deflection head details they offer which can save some money although I would still only ever use one manufacturer’s board on any single scheme.”
But it’s not just the vertical loading on partitioning and drywall systems that can cause issues. Horizontal and applied loading from wall-hung cupboards, TV’s and bookshelves can create problems, particularly for those working in the residential sector.
Traditionally extra noggins are designed into the stud frame, particularly in kitchens where wall-hung cupboards will be located. But in future years the occupier might want to change the layout and hang cupboards from walls that are not designed to be able to take that loading.
Futureproofing these areas has become an increasing demand from designers. Board manufacturers are striving to develop systems that will address these futureproofing concerns without drastically altering the installation process for contractors.
British Gypsum’s ‘Lifestyle Wall’ is a fibre-reinforced plasterboard, more dense and more robust than standard boards, that enables homeowners to fix directly into it, cutting out the need for specialist fixing systems and taking out the mystique of drywall systems for the end user, according to Sarah White, residential market manager at British Gypsum.
“It has been developed with the idea that homeowners
and end users should be free to be able to alter their own houses however they want to. This board helps temper their fears about understanding and using drywall systems,” she commented.
As more contracts are let under design and build packages, there are fears that specialists could be pressurised into providing design advice for the main contractor, leaving them open to possible claims should anything fail in the future.
Ultimately the responsibility for specifying which deflection head, if any, should be used or if more robust boards need to be specified, lies with whichever party has the design responsibility, but specialists can still offer advice.
“Specialist contractors should be aware of the specification they are working to and can offer clients advice on the back of their experience. But it does all come down to whoever has design responsibility,” concluded Mr Cilia.
