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The Elephant in the Roof
Paul Trace from Stella Rooflight discusses the practicalities involved in specifying large rooflights
» AS A BESPOKE ROOFLIGHT manufacturer we often see grand plans with expansive areas of roof glazing , as architects continue to seek innovative ways in which to exploit natural daylight . As much as bespoke rooflights can certainly help bring these designs to life , there are some important factors that need to be considered when the glazing is turned from drawing to reality .
In recent years we have noticed a trend towards larger rooflights , with sizes regularly exceeding 2500mm in width , height or both . While Stella can certainly accommodate these , one has to appreciate the practicalities of weight , transportation and cost .
It stands to reason that the larger the rooflight , the thicker the glass will need to be , therefore as rooflight sizes get bigger their weight can increase exponentially . In context , our double glazed units comprising of 4mm thick glass weigh 20kgs per square metre and those using 6mm are 30kgs per square metre . Triple glazed units are 30kgs and 45kgs respectively . Add the stainless steel frames and hardwood liners into the equation and you can start to see how even a modest sized rooflight can weigh something akin to a small elephant ! Indeed it ’ s not uncommon for us to produce rooflights weighing in excess of 200kg .
The reality is that when you scale things up even the simplest plans can start to become complex - a truth that should be all too familiar to architects . But before drawing that large rectangle on a roof plan , it is important to consider how the rooflight is going to be lifted from the ground to roof level and what the weight implications might be for the structure . Stella can weld stainless eyelets to the rooflight frame to aid the lifting process and we would suggest doing this on frames which weigh in excess of 100kg , which is the point where we expect a crane might be required . However , does the site have suitable access for any specialist lifting equipment , and has this additional cost been budgeted for ?
The weight of an opening rooflight will also
determine whether it is manually operated or requires electric actuation . We would suggest that our largest manually operated rooflight be around 1000mm wide or 1400mm high . Anything over this size will generally require electric actuation to lift the weight and in the case of wider casements , to provide a tight seal . Manual operating casements are less expensive than electric so there is a cost element that also needs to be considered when specifying larger opening rooflights . There is no maximum size in terms of what is possible to manufacture , although it is worth keeping in mind that a single piece of glass with an area over 5m2 becomes significantly more expensive .
Fortunately there are alternatives to using large expensive single panes of glazing , such as introducing glazing bars to reduce the unit sizes , linking frames , and having more than one casement . This not only makes the rooflights easier to transport , lift and install , but can also reduce the price .
If a large , single rooflight is the only option for your project then you must also make sure that it is safe to install . While rooflight manufacturers will be able to provide advice on a suitable specification for the job in terms
of materials , glazing thickness , functionality and installation , it is ultimately the responsibility of a structural engineer to ensure that the product being specified is fit ( and safe ) for the building that it is fitted into .
To avoid any ambiguity it is fairly essential that the architect , structural engineer and rooflight manufacturer discuss large rooflight installations , likely weights , load bearings , site access , and lifting capacity at an early stage to avoid any problems down the line . It is not advisable to leave this for the builder to deal with at the last minute .
Another area for consideration should be the safety of large areas of glazing situated high up in a roof structure . Again , much like an elephant , there is a lot of grey area here !
Regardless of size your rooflight should meet the BS 5516-2 : 2004 patent glazing and sloping glazing for buildings standard . This code of practice for sloping glazing defines that inner panes must always be laminated wherever rooflights are more than 5 metres above floor level ( increased to 13 metres for panes less than 3 square metres ) or are located over water ( e . g . swimming pools ). The Standard permits the use of toughened inner panes in other applications ( for example where rooflights are less than 5 metres from floor level ), but only where a stringent risk assessment for the particular application has been completed and has concluded that the use of toughened glass does not give any additional risk to those below the rooflight .
50 » DEC 2020 » CLEARVIEW-UK . COM