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SEPTEMBER 2013 PRO INSTALLER
PRO NEWS
www.proinstaller.co.uk
THE BEST MATERIAL
FOR SASH WINDOWS
Last month Alan Burgess, MD at Masterframe Windows Ltd, wrote how expectations of conservation officers had
changed since the early days of UPVC in the 1970’s. This month he explores materials in a little more detail as
they relate to sash windows and the progress the industry has made towards protecting our heritage assets…
“Wood has been used
to make sash windows
for centuries. Solid
oak timbers for ship
building and house
construction have
endured for years, however being a natural
product, the wood
itself slowly decays so
paint, varnish or oils
are used to slow this
process. Ultra slender
bars from the Georgian
period cannot be replicated in anything other
than timber.
Today, because well-seasoned timbers are expensive and hard to come by,
engineered timbers or laminated wood is very popular.
As the name suggests, the
profile is made up from
a mixture of woods, the
expensive timbers used on
the external surfaces and
cheaper infills are used in
the centre.
Whilst these wooden
windows normally required
site glazing with putty or
beads, priming and then
painting, mass production
of metal framed windows
meant they soon became
popular during the early
part of the last century.
Steel windows via family
companies like Crittalls
from Braintree and Hopes
from Smethwick, dominated the window production
through the inter war years,
each making millions of
standard metal windows
(SMW’s) for social house
building projects, factories
and public buildings. Galvanising was an optional
extra as was weather stripping right up to the early
1970’s.
Whilst Crittall used alu-
‘a quality PVCu
sash window is
“indistinguishable
from a timber
original”’
minium for sash windows
they also dabbled a little
with Trocal and Mipolam
for the commercial sector
for casement windows,
it was Anglian and Everest who were the early
adopters of aluminium for
the domestic sector. Solid
slender aluminium sections
were ideal for secondary glazing (horizontal
or vertically sliding) and
gradually incorporated into
full replacement windows
particularly near airports
and for properties adjacent
to road building projects.
Aluminium, thermally
broken or solid has been
used since the 1960’s
but they often required a
subframe. Because mill fin-
‘Planners today expect the
detail, design and appearance
issues to have been sorted’
ished aluminium required
protection, factory applied
anodised, acrylic or powder
coatings provided great colour choices for architects
and specifiers, without the
expense of site painting. In
addition, commercial buildings, schools and hospitals,
soon appreciated the safety
benefits of windows that
didn’t open outwards and
the health benefits from
excellent ventilation.
Early users of sash windows understood rapid
ventilation is provided when
high and low openers are
used and because sashes do
not protrude from the face
of the window (they stay
vertical), children cannot
run into opening lights,
which were left ajar.
As for PVCu, it wasn’t
until the mid 80’s that PVCu
sash window profiles were
introduced, prior to that
lightweight, vinyl imports
from the states have been
trialled but Rehau introduced the UK’s first PVCu
sash window at the Alexander Palace in 1986 having
spent 18 months discussing
various requirements with
the former GLC.
While welded, grooved,
shiny white PVCu with
square edges, face drainage
slots, unequal glazing and
artificial glazing between
the units now seems a
pretty poor effort, back then
it was cutting edge technology and should be seen as
the first real step towards
producing fenestration that
retained the general character of heritage assets.
Up to that point, sash
windows were being ripped
out and aluminium or PVC
casement inserts were being
installed into the existing
timber box frames, destroying any character the property may possess. Every part
of the country has examples
of this destruction.
Planners today expect the
detail, design and appearance issues to have been
sorted.
Today wood foil, white or
coloured, raised plant on
Georgian bars, equal sightlines, with traditional butt
jointed sashes, run through
horns with “real” furniture
are all prerequisites for
good sash windows, which
in addition to building reg
compliance, A rated and
enhanced security, make
PVCu an excellent choice.
Putty line sashes, chamfered
astragal bars and extrusions
with staff bead all add to
the authenticity.
Being fitted behind the
outer skin of brickwork
with cement fillets, insulation and period architraves
will ensure they take proposals for new PVCu sash
windows seriously.
It isn’t about material, yes
wood is good, however
certain buildings require the
special aesthetics that only
aluminium can offer but for
me in domestic installations,
a quality PVCu sash window
is “indistinguishable from a
timber original”. Done well,
conservation officers cannot
tell when sash windows
have been changed.