283757893275

238 Barry’s Advanced Construction of Buildings
Profiled coated steel roof cladding sheet
Mastic sealing strip between steel and
translucent sheets
Translucent sheets to
match profile of steel sheets
Self-tapping screws
with PVC washers and caps
End lap
150
Zed
purlin
Profiled polyethylene
filler piece
60 glass fibre insulation
laid over rigid boards fixed over purlins
A double skin of two profiled
translucent sheets spaced 50
apart to provide a rooflight
to profiled coated steel roof
covering
Zed
purlin
Filler piece
Figure 4.74 Rooflights: translucent sheets in profiled steel-covered pitched roof.
Translucent PVC (uPVC) sheets are produced in a range of profiles to match most metal
and fibre cement sheeting. For roof pitches of 15° or less, the side and end laps should be
sealed with sealing strips and all laps between uPVC sheets should be sealed. Fixing holes
should be 3 mm larger in diameter than the fixing to allow for thermal expansion of the
material. Fasteners similar to those used for fixing roofing sheets are used. Double skin
rooflights are formed in a similar manner to that shown in Figure 4.74.
Flat cellular sheets of PC are supported by aluminium glazing bars fixed to purlins as
illustrated in Figure 4.75 to form a rooflight to a north-facing roof slope. The capping of
the glazing bars compresses a Neoprene gasket to the sheets to make a watertight seal.
Patent glazing
The traditional method of fixing glass in the slopes of roofs to create a rooflight is by means
of wood or metal glazing bars that provide support for the glass and form weather flashings,
or cappings, to exclude water. The word ‘patent’ refers to the patents taken out by the original
makers of glazing bars. Timber, iron and steel glazing bars have largely been replaced
by aluminium and lead or plastic-coated steel bars. Likewise, single glazing has been
replaced by double glazed units and wired glass. Patent glazing is relatively labour intensive
due to the provision and fixing of the glazing bars at relatively close centres; however, the
result can be an attractive, durable rooflight with good light transmission.
The most commonly used glazing bars are of extruded aluminium with seatings for glass,
condensation channels and a deep web top flange for strength and stiffness in supporting