Curtain Glazing

CURTAIN
GLAZING
REPORT
CURTAIN WALLS ??
Curtain wall systemsare a non-structuralcladding
systems for the external walls of buildings. They are
generally associated with large, multi-storey
buildings.
Curtain walls separate the interior from the exterior,
but only support their own weight and the loads
imposed on them (such as wind loads, seismic loads
and so on) which they transfer back to the primary
structure of the building.
Typicallycurtain wall systemscomprise a lightweight
aluminium frame onto which glazed or opaque infill
panels can be fixed. These infill panels are often
described as glazing whether or not they are made
of glass.
Curtain wall systemscan be custom designed and
manufactured, but are often manufacturer's
proprietary systems that can be bought off the shelf.
Custom-designed systems are generally only cost
effective for larger buildings.
THE UNITIZED CURTAIN

WALL
A glass and aluminum curtain wall fabricated and

installed as a panel system is referred to as a unitized
curtain wall system. A unitized curtain wall will have the
same components as a stick built curtain wall system. It
will comprise aluminum mullions, an IGU and a spandrel
panel mounted in a prefabricated aluminum frame.
However, instead of assembling the glass and
aluminum curtain wall in the field, most of the system
components are assembled in a plant under controlled
working conditions.
This promotes quality assembly and allows for
fabrication lead-time and rapid closure of the building.
The unitized system is assembled on the building as
panels (see Fig. 4, page 4). The mullions and rails are
fabricated as half sections instead of tubular sections,
which mate at assembly time to form the curtain wall
system. The panels are installed in shingle fashion,
starting from the bottom of the building and going
around each floor and up the building.
While the unitized system offers many advantages with respect to

quality assembly and speed of on building closure, there is one
design concern with respect to installed performance and durability.
In a stick built system, there are two joints along every mullion and
rail. In a unitized system, there are three joints along every mullion
and rail. These include the two glass to aluminum joints and a third
joint at the junction between the half mullions and half rails.
Three joints instead of two increases the potential air and water
leaks by 50% over a stick built system. Should an air or water leak
develop at the third joint, there is usually no practical method of
accessing the in-between panel joint for repair (see Fig. 5) unless
the manufacturer has provided a serviceable joint system design.
In a unitized system, the manufacturer must rely on qualified
installers to ensure that the air seals are properly installed between
the split mullions.
Nevertheless, the unitized system is now as popular as the stick
system according to one manufacturer and it has performed
satisfactorily when installed correctly.
STICK BUILT SYSTEM

Curtain wallscan adopt a stick
system, or can be unitised:
Stick systems are installed piece by piece on site,
with the glazing inserted into the frame from the
inside or the outside depending on access conditions.
Unitised systems are pre-fabricated in modules offsite and delivered in panels. Unitised systems are
better able to exploit the benefits of factory condition
manufacturing andquality controland require lower
installation time on site.
There are a wide range of possible infill panels
forcurtain wall systems, including:
Vision glass (which may be double or triple glazed,
may include low-e coatings, reflective coatings and so
on).
Spandrel (non-vision) glass.
Aluminium or other metals.
Stone veneer.
Fibre-reinforced plastic (FRP).
Louvres or vents.
Panels are often composites, with the facing
Glass Systems
Structural Glass Systems Structural Glass
Systems, often called Spider Systems or
Bolted Systems, have been used on many
high profile buildings. Holes are typically drilled
in each corner of each glass pane and the
glass is attached mechanically with stainless
steel spiders. These systems are not
structural glazing although they have a similar
appearance from the exterior. In certain
designs, the spider only attaches to the
internal pane of an insulating glass unit. In
such designs, the insulating glass sealant will
have a structural function. In all types of
Structural Glass Systems, silicone sealants
play an important role in maintaining a
watertight weatherseal and in the performance
of the insulating glass units.
Toughened glass
Toughened or tempered glass is glass that
has undergone processes of controlled
thermal treatment to increase its strength.
Toughened glass is made from annealed glass

that has been heated to approximately 650C
and then rapidly cooled. Due to the increased
heat treatment and rapid cooling of the glass,
especially between the surface and the inside
of the glass, the treatment produces different
physical properties. This results in
compressive stress on the surface and
improved bending strength of glass.
Before toughening, the glass must be cut to

size or pressed to shape. This is because once
it is toughened, it cannot be re-worked on.
Toughened glass is widely used in a number
of applications
Laminated glass
is a kind ofsafety
glaSSthat is commonly used for automobile
windshields. It consists of two layers of glass with
a layer of film, called the interlayer, in between
them. The glass is designed this way in order to
prevent it from shattering into sharp pieces when
struck by an object or when the car is in an crash.
The interlayer in the glass is a film of a tough, yet
pliable material known asPOLY VYNIL (PVB). In
the event that the glass breaks, the two layers
are held together by the PVB, allowing the sheet
as a whole to bend and absorb the impact. This
characteristic is especially important for car
windshields since, ideally, the film will keep
objects from penetrating through the glass and
possibly injuring the cars occupants. Laminated
glass is also used in prisons, jewelry stores,
hospitals, and other places where safety or
security are paramount.
SPIDER FITTINGS
SINGLE ARM SPIDER
2 WAY SPIDER
4 WAY SPIDER FITTING
Frame and panel designs are very

complex, as they need to perform
multiple functions:
Transferring loads back to the primary
structure of the building.
Providingthermal insulationand avoiding cold
bridging andcondensation.
Providing fire, smoke and acoustic separation.
This is particularly difficult at joints between
the curtain wallsystem and interior walls and
floors.
Creating a barrier to water penetration.
Accommodating differential movement and
deflection.
Preventing panels from falling out of the
frame.
Allowing for opening windows.
Preventing the accumulation of dirt.
On tall buildings, access systems must be
provided to allow regularinspection,
Systems used to prevent the passage of water through joints

(driven by pressure differences between the inside and outside)
include; face-sealed, water-managed and pressure-equalised (PE
or rainscreen) systems.
Pressure-equalised systems create a rebate between the internal and
external gasket that is ventilated to the outside so that there is no
pressure difference between the outside and the rebate.
As a result, water is not driven into the rebate by a pressure difference
that would otherwise build up across the outer gasket. Any rain that
penetrates the outer seal can be drained to the outside through the
vents, or weep holes. This is considered to be more reliable than facesealed systems that attempt to create a perfect seal which inevitably
fails due to pressure-driven moisture.
Water-managed systems are similar to pressure-equalised systems,
but there is no attempt to prevent water penetrating the outer seal, and
so the primary function of weep holes or drains is to drain water rather
than to allow pressure equalisation.

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CURTAIN

THE UNITIZED CURTAIN

A glass and aluminum curtain wall fabricated and

While the unitized system offers many advantages with respect to

STICK BUILT SYSTEM

Toughened glass is made from annealed glass

Before toughening, the glass must be cut to

SINGLE ARM SPIDER

4 WAY SPIDER FITTING

Frame and panel designs are very

Systems used to prevent the passage of water through joints

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