DECEMBER 2019 | 33
Products
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which ultimately means
40% less light entering a
building.
One of the easiest ways
to lower a U-value on a
window or rooflight is
to increase the thickness
of the glazing. A decent
double glazed unit will
give a centre pane value
of 1.0W/m²K and a triple
around 0.5W/m²K. Then of
course there are some that
offer quad glazing, which
reduces this figure further.
However, it should also
be noted that by reducing
the U-value in this way,
you will be significantly in-
creasing the weight of the
product, the cost and also
the depth of the rooflight
profile.
If you are working on
a Listed Building or in a
Conservation area then you
will require a conservation
rooflight design, which
should sit completely flush
with your roofline. If you
are looking to use quad
glazing or modern bulky
rooflights to improve ther-
mal performance then this
will most certainly be to
the detriment of the build-
ings aesthetics.
There are a few excep-
tions relating to the ther-
mal requirements in certain
buildings and it is always a
good idea to take profes-
sional advice should your
project fall into one of the
following categories:
i. Where the replace-
ment roof windows
are unable to meet the
requirements because
of the need to maintain
the external appear-
ance of the façade or
the character of the
building, replacement
windows should meet
a centre pane U-value
of 1.2 W/m2K.
ii. Buildings which are;
Listed in accordance
with section 1 of the
Planning (Listed Build-
ings and Conservation
Areas) Act 1990; In
a conservation area
designated in accord-
ance with section 69 of
that Act; or Included in
the schedule of mon-
uments maintained
under section 1 of the
Ancient Monuments
and Archaeological
Areas Act 1979; Car-
ports.
iii. Buildings which are;
Listed in accordance
with section 1 of the
Planning (Listed Build-
ings and Conservation
Areas) Act 1990; In a
conservation area des-
ignated in accordance
with section 69 of that
Act; or Included in the
schedule of monuments
maintained under
section 1 of the Ancient
Monuments and Ar-
chaeological Areas Act
1979; Used primarily or
solely used as places of
worship; Stand-alone
buildings with floor
area less than 50m2;
Carports; Temporary
building with a planned
time of use less than
two years.
a U-value figure is very important when
‘ both
choosing products and in the overall
construction of your property. The lower
the figure the more thermally efficient a
product or building is and this can contribute
to reducing heating costs and ultimately
helps in the fight against global warming
’
In conclusion, despite
the fact that the testing
methods for obtaining a
rooflight’s thermal perfor-
mance could do with an
overhaul, a U-value figure
is very important when
both choosing products
and in the overall con-
struction of your property.
The lower the figure the
more thermally efficient
a product or building is
and this can contribute
to reducing heating costs
and ultimately helps in
the fight against global
warming.
It is also important that
the figures provided are
genuine and it is advisa-
ble to request proof that
U-values being quoted are
not only correct but are
applicable for the appli-
cation that you are using
that product. Nowhere is
this more important than
rooflights because of the
current way in which
these products are tested.
If you have any questions
or require further
technical information
concerning the use of
rooflights in your own
project, please contact
one of the Stella Rooflight
team on 01794 745445 or
visit www.stellarooflight.
co.uk