Civil Engineering Reference
In-Depth Information
Window-to-wall joints
As with domestic scale windows, it is
the window-to-wall joint which is
crucial to performance. Since the
windows are normally larger than
domestic, and the area exposed to
sideways driven rain is
correspondingly larger, the extra
shelter to the window-to-wall joint to
be gained by setting the windows in
deep reveals is only marginal (Figure
4.23). Cornices, string courses, hood
and label moulds were the traditional
methods of providing more shelter.
●
laminated glass has considerable
impact resistance, depending on
thickness and number of
laminates, given that rebate depths
are also adequate. There may,
however, be implications
for means of escape in cases
of fire
●
bandit resistant glass, usually
laminated with a thick interlayer
●
bullet resistant glass, usually
heavy gauge laminated glass with
several glass sheets and
interlayers of a total thickness of
25 mm or more
Main performance
requirements and defects
Strength and stability
The larger the window, the more
likely it is to suffer deflection in
strong winds, though this ought to
have been taken into account at the
design stage.
The Building Regulations 1991,
Approved Document N, Glazing -
materials and protection
(186)
- now
requires BS 6206
(72)
'safe breakage'
or screen protection in critical
locations, which include glazing
between finished floor level and
800 mm above that level. Under these
regulations thick annealed glass not
complying with BS 6206
is restricted to a minimum of 8 mm
thickness, typically used in shop
fronts, showrooms etc. There are
limits on total areas relating to
thickness, with the larger windows
requiring 12 or 15 mm thickness.
The primary requirement for
windows is that glazing, if it breaks,
shall break in a safe manner and not
cause injury to building users (inside
or outside). This is governed by
BS 6262
(169)
for glazed panels beside
doors, glazed doors themselves, low-
level glazing (below 800 mm from
the floor), staircases, circulation
areas and buildings with special uses
(eg schools, pools and sports halls).
Glazing materials (whether glass or
plastics) are assessed according to
internationally agreed impact loading
tests which are set out in
BS 6206, and the main glazing Code
of practice, BS 6262.
The Workplace (Health, Safety
and Welfare) Regulations 1992
(187)
are retrospective, and now require all
glazing in relevant non-domestic
buildings which is at a vulnerable
height to either be protected or to be
in a safety glazing material.
Annealed glass may be suitable
provided it is thick enough.
plastics (eg polycarbonate sheet)
presents a formidable obstacle to
impact but is vulnerable to heat
and is marred by scratching in
service. Plastics is also much more
flexible, and needs much deeper
rebates than even laminated glass
for safe retention, more especially
so in large windows
●
Toughened glass can be easily
shattered with a centre punch, and is
not recommended for high risk areas.
If risks require it, and sometimes at
some cost in reduced light
transmission, additional protection
can be afforded by:
●
grilles or shutters (see
Chapter 5.3)
●
intruder detector systems
Figure 4.22
West window, Coventry Cathedral
Protection against unauthorised
entry
Shop windows and entrance doors
are increasingly prone to attack, and
special glazing should be considered
for replacements.
Special safety glazing includes:
Figure 4.23
Horizontally pivotted windows, the
Orangery, Margam Abbey
Figure 4.24
Early versions of louvred
windows sometimes leaked
