Rooflights ~ the useful penetration of daylight through the
windows in external walls of buildings is from 6„000 to 9„000
depending on the height and size of the window. In buildings with
spans over 18„000 side wall daylighting needs to be supplemented
by artificial lighting or in the case of top floors or single storey
buildings by rooflights. The total maximum area of wall window
openings and rooflights for the various purpose groups is set out
in the Building Regulations with allowances for increased areas if
double or triple glazing is used. In pitched roofs such as northlight
and monitor roofs the rooflights are usually in the form of patent
glazing (see Long Span Roofs on pages 570 and 571). In flat roof
construction natural daylighting can be provided by one or more
of the following methods:-- Lantern lights † see page 592.
- Lens lights † see page 592.
- Dome, pyramid and similar rooflights † see page 593.
Patent Glazing ~ these are systems of steel or aluminium alloy
glazing bars which span the distance to be glazed whilst giving
continuous edge support to the glass. They can be used in the roof
forms noted above as well as in pitched roofs with profiled
coverings where the patent glazing bars are fixed above and below
the profiled sheets † see page 591.Rooflights