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IGU’s
consist of two or more panels of glass separated by an
airspace and an aluminium or other type of spacer around
the edges, sealed to the perimeter in controlled conditions.
The spacer contains a desiccant (drying agent) which
eliminates moisture vapour in the cavity. The combination
of the two panels of glass and the trapped air is what
makes IGU’s a superior energy efficient method of
glazing.
IGU’s are not to be confused with double glass windows or secondary
sashes/windows, where the two panes have not been hermitically sealed.
The above mentioned can perform a thermal and noise insulating function.
An IGU depending on the type of glazing used is generally glazed into an
aluminium, timber or PVC window frame.
FEATURES
AND APPLICATIONS
 reduction
of heat build up in summer;
reduction
of winter heat loss and condensation;
lower
air conditioning and heating costs;
lower
noise penetration;
lower
UV transmission;
increased
windload strength;
increased
security;
greater
spandrel and vision panel matching for commercial applications.
Refer Spandrel and Fritted Glass.
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GLAZING
IGU’S
90% of double glazed units fail because of improper glazing techniques.
Failure is most commonly characterised by the appearance of moisture in
the cavity suggesting seal and/or dessicant failure. The glazing system
must be designed to drain out all water in the rebate and a void must exist
under the unit so that moisture is not trapped against the edge of the
glass. Setting blocks should be centred at the bottom quarter points of
the unit (two per unit) and should always be an equal distance from the
centre of the glass. Blocks must be neoprene or rubber of 80 - 90 shore
hardness and allow no water to gather on the unit.
Generally units should be glazed with a minimum 3mm clearance between the
glass face to rebate, a minimum 3 - 6mm clearance under the unit in the
rebate (size of block) and a minimum 12mm cover or bite in the rebate.
Compatible sealants must be used.
Dry glazing of units is always recommended but if units are to be glazed
or bedded into compounds or sealants it is imperative that compatible sealants
are used or edge failure may result. Linseed oil, acid cure silicones and
small joint sealants must be avoided.
Some soft coat low-E glass must be edge deleted prior to unit assembly
for maximum sealant bonding.
The
sun’s energy with its damaging UV radiation
will have a detrimental effect on IGU seals. To prevent
failure of the unit, it is critical to have all the
edges protected from the sun. Exposed edges should
be fully over flashed with an aluminium strip or
similar using an adhesive such as neutral cure silicone.
Do not use setting blocks which expose the spacer
to sunlight.
For structurally glazed IGU’s where the edges are exposed, the minimum
requirement for the secondary seal is structural silicone, due to its
high resistance to UV radiation.
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