Project1_Layout 1 07/05/2013 THE PITCH
I am therefore suggesting that architects perhaps
ought to consider the limitations in working
practices of roofi ng contractors when they are
designing the roof shape. For example, it is diffi cult,
if not impossible, to install a hip system without
standing on laid roof tiles. I am not suggesting
hips be designed out of the roof (although there is
something to be said for that), but perhaps some
form of access could be designed into the roof, such
as steps. This is common practice in Europe.
• Ensure fascias are set at the correct height
and, in the case of plastic fascias, provision is
provided to fi x the tails of the eave course tiles
• Provide adequate provision for securing
eave course dry verge units, whether they be
individual (i.e. one unit per tile course) or
continuous verge systems
• If using dry verge against pitched-faced walling,
make provision to close any resulting gaps if the
verge units are set away from the wall
• Take care to coordinate the installation of
cavity trays with the tile fl ashings at abutments
• Consider roof access and the working
practices of roofers in the roof design
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articles from John Mercer
What does thermal performance really mean?
In the second of a six-part series on the technical factors to consider when choosing a roof window, Lee Griffi ths, technical sales manager GBI at
TDakea, looks at the thermal performance of windows, why it’s important and what features will minimise heat loss he rising cost of heating coupled with
government pressure to reduce carbon
emissions has led to a growing focus
on the energy-effi ciency of buildings.
Homeowners are much more savvy when
it comes to making their house energy-effi cient,
thanks to initiatives like the London Boiler
Cashback scheme and grants for wall and loft
insulation. Therefore, trade professionals offering
added value help and advice, will be better placed
to ensure a superior service for their customers.
For a newbuild property or a refurbishment
project, one of the main design considerations is
to maximise the amount of natural light, and the
careful placement of windows – in particular roof
windows – can make all the difference.
This however, does create a potential source of
heat loss if the windows are not chosen correctly.
When the warm air inside meets the surface of the
window, the heat can be transferred to the glass
and lost to the surrounding environment. This
means that the heating has to work harder to keep
the home warm, resulting in higher energy bills.
A U-value is used to measure the thermal
effi ciency of a building component, and indicates
the rate at which heat is transferred through the
material to the outside world. The U-value of
a product or structure is expressed in watts per
090 MAY 2018 RCIMAG.COM
The construction of a Dakea U ltima roof window
square metre kelvin (W/m²K). The more insulated
the product is, the lower the U-value will be.
Typically, a lower U-value is achieved by
separating the internal and external surfaces of
the window (double glazing) and ensuring that the
construction does not allow heat to be transferred
between them – this is known as thermal bridging.
Other features may be included in the window
to improve performance further. For example,
the Dakea Ultima roof window includes two low
emission coatings that contribute to retaining
heat. During the manufacture of the window, a
transparent metallic coating is applied on the
surface of the glass, and when installed, this
refl ects the heat back into the room. Furthermore,
the glazing unit is fi lled with krypton gas, which
conducts 46% less heat than the more commonly
used argon. The design of Ultima means it has a
low U-value of just 1.2 W/m²K.
Understanding what needs to be considered
when selecting a roof window for a customer will
really help homeowners make the right decision,
bringing them both long-term benefi ts in the
form of lower heating bills, not to mention a more
comfortable home. What’s more, providing the
best possible customer service is great for your
business as a satisfi ed customer is more likely to
recommend your services to others.
“The Dakea Ultima
includes two low
that contribute to
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