Are deflection heads always the solution to interior movement in buildings? Here Rob Judd asks what steps architects should take to manage partition deflection.
Deflection is a collective issue in the building industry, but it’s not on a level playing field, says Rob Judd, Managing Director of Optima Contracting Ltd, one of the largest installers of partitioning systems incorporating deflection heads.
Optima cannot dismiss deflection. The fact is, it exists and we have to address it. But not everyone is prepared to specify a solution to protect interior fittings from stress. Together, we need to understand deflection, accept that it’s there and work collectively to accommodate it.
It’s naive to believe that deflection heads are being over-specified, particularly in large London offices. It’s important to be aware of the need for deflection heads. They are accepted as an unavoidable expense because quite often they are.
The Problem with Deflection in Building Interior
As the UK’s market leading partitioning specialists, Optima has worked on some of London’s most iconic structures. Almost all of the ceilings on these high-end projects are rigid – either plasterboard soffits or substantial steel ceilings suspended on rods or steel straps. This means they cannot absorb the deflection if the building moves, and will simply transfer some of the movement as a load onto the partition. Most partitioning systems, particularly glazed systems, are not defined as load bearing and can, quite literally, crack under the pressure.
Partitioning systems also have to accept deflection caused by loads imposed on the floor plates through desks, storage and personnel. As a result of floor slabs being loaded, deflection can occur in both upward and downward directions; movement of either the floor where the partitioning system is installed, or the level above. The ceiling can deflect downward, effectively compressing the partition – “minus”, or the floor can deflect downward, effectively putting the partition in tension – “plus”. Non-rigid suspended ceilings, by their very nature, can absorb movement, but no ceiling can deflect upwards movement relative to the partition, because the fixings would be pulled loose.
In older buildings with short spans between columns, deflection heads might not be necessary, although this should always be checked with a structural engineer.
Modern buildings however are incorporating greater spans between structural columns and this can result in movements of up to plus/minus 40mm. The design of partitioning systems needs to allow for this. The entire range of Optima’s partitioning systems can accommodate such levels of movement whilst maintaining the structural stability of the wall.
It should be noted that as the use of ever larger floor plates continues in modern building design, real live load deflection will inevitably increase. Optima is currently involved in a few projects where a plus/minus 50mm deflection head will be needed.
At Optima, we physically see our deflection heads working on a number of sites where they are in use. As partitioning specialists, we must continue to invest in such deflection innovations, meeting the needs of Architects, Interior Designers and Structural Engineers.
Actions for the Design Team
Architects should establish the true degree of deflection to be accommodated and specify accordingly. It’s important to determine the live load deflection range from Structural Engineers’ statements, as opposed to the range of deflection that the building could stand before it falls down.
Ultimately, deflection specification should be left to the specialists. If the Structural Engineer calculates the likelihood of live load deflection then the Architect or Interior Designer should take heed of the advice and design the partitioning system accordingly.
Deflection Heads in a Nutshell
Our advice to Architects and Interior designers is:
- Work with your Structural Engineer.
- Establish the true degree of deflection to be accommodated.
- Check what capabilities your partitioning system has.
- Specify according to your needs.
- Use your partition manufacturer’s design expertise to assist.