34 | FEBRUARY 2018
Window Technology
BEST GLASS TYPES FOR
OVERHEAD GLAZING
With the myriad of glass types available now, it is often confusing what to choose in terms of safety, thermal and
solar performance and balancing cost with the benefits on offer. Richard Burgess, Managing Director of patent
glazing and roof light manufacturer Lonsdale Metal Company Ltd shares his experience of 30 years in the industry.
Safety
Above all, safety is the critical factor in overhead glazing
and the table below summarises what type of glass com-
plies with current Building Regulations at time of writing:
Glazing Height
above floor
level Suitable types for
Single Glazing Suitable types for
Double Glazing
Upto 5 Metres Toughened,
Laminated or Wired
Glass The inner pane
must be Toughened
or Laminated. The
upper pane should
be Toughened in
either instance.
5 to 13 Metres Toughened glass
not more than 6mm
thick and panes
not larger than
3sq/m. Laminated
or Wired Glass The inner pane
must be Toughened
or Laminated. The
upper pane should
Toughened in either
instance.
Above 13
Metres Laminated or Wired
Glass The lower pane
must be Laminated
From time to time, it is desirable to use Wired Glass in
double glazed combinations. However, there is a high risk
of breakage due to thermal stress and advice should be sort
from the sealed unit manufacturer.
It is not recommended to use toughened glass in single
glazing or to the inner pane of double glazed units over
swimming pools, food & beverage preparation units or any
areas where the small broken pieces characteristic to this
glass type, could cause subsequent injury due to contami-
nation. In these situations laminated glass or polycarbonate
would be the best choices.
Triple Glazing
All of the above glass type can be combined in a triple
glazed units achieving both improved sound insulation and
U-values as low as 0.60W/m2.K Consideration however,
must be given to the additional weight and handling during
installation.
Double Glazing
More or less without exception, the outer pane of a
double glazed unit should be toughened glass. The inner
pane may be toughened or laminated depending upon
location and height above ground. Generally two sheets of
toughened glass provide the most economical solution for
domestic projects where the roof light is no more than 5m
above floor level. If the height exceeds this, then laminated
glass should be used for the inner pane.
When it comes to performance, the following are features
to consider:
Low-e coating – offers improved thermal efficiency re-
taining more heat within the building.
There are two types available standard ‘hard’ coat finish
or the more popular ‘soft’ coat which offers a typical centre
pane uvalue of 1.2W/m2 when combined with an argon
filled cavity.
Large Pane Rooflights
Tinted anti-sun glass – body tinted toughened glass can
be used as the outer pane combined with a laminated low-e
softcoat glass to give the added benefit of reducing solar
heat gain in the summer months at reasonable cost. This is
most commonly used in blue, but green, grey and bronze
colours are also available. Typically this provides a 50%
reduction in solar transfer and 50% light transmission.
Neutral solar control glass – has a special coating that
provided improved solar control and appear more neutral
in colour albeit with a slight grey/green tint. This is often
described as 70/30 meaning it offers a 70% light transmis-
sion, but only 30% of the sun’s heat enters the building.
The most economic glass tends to be 4-6mm thick which
rarely can be installed wider than 1000mm, hence most
domestic roof lantern and conservatory installation featur-
ing glazing bars every 600 to 900mm. However, with the
current trend for flat rooflights, single pane rooflights can
be installed up to 3m x 6m in one pane of glass. This calls
for specialist manufacturing and installation by experienced
companies with the necessary handling equipment and
expertise. Much thicker toughened & laminated glass is
required so as not to deflect and care must be taken to en-
sure compliance with building regulations and local, design
wind & snow loads.
For readers wanting to learn more about Lonsdale’s
products and services, visit www.lonsdalemetal.co.uk