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Cladding and Curtain Wall Construction 471
of the glass by means of end stops or horizontal transoms and cills, and to make a weathertight
seal at horizontal joints. The traditional metal roof glazing bar generally took the
form of an inverted T-section, with the tail of the T vertical for strength in carrying loads
between points of support with the two wings of the T supporting glass. For use in vertical
wall glazing, it was usual practice to fix the glazing bars with the tail of the T, inside with
a compression seal and on the outside holding the glass in place, as illustrated in Figure 7.49.
The usual section of metal glazing bar, which is well suited to roof glazing, did not
provide a simple, positive fixing for the horizontal transoms and cills necessary for vertical
glazing systems. The solution was to use continuous horizontal flashings on to which the
upper bays of glass bore and up to which the lower bays were fitted, as illustrated in Figure
7.49. Patent roof glazing techniques, adapted for use as vertical glazing, are still in use but
have by and large been superseded by extruded hollow box section mullion systems.
Hollow box section mullions were designed specifically for glass curtain walling. These
mullion sections provided the strong vertical emphasis to the framing of curtain walling
Aluminium
glazing bar
Neoprene gaskets
Screw on
clamp
Cover to
joint
Snap on cover
to glazing bar
Butyl
strip
Aluminium
frame
Figure 7.49 Aluminium glazing but used for vertical glazing.