Issue 44 winter 24 - Journal - Page 30
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.
To avoid any ambiguity it is 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,
for example in a barn conversion. 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.
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.
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Conservation & Heritage Journal
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