March 2018

Roof Windows
ROOF WINDOW INSTALLATION:
GET IT RIGHT FIRST TIME
If not selected and installed correctly, a roof window can be a potential point of leaks and
affect the thermal performance of the building. Lee Griffiths, Technical Sales Manager GBI at
Dakea, discusses the factors to consider when selecting a roof window, and provides a stepby-step
guide on how to install a roof window and get it right first time.
Establishing the customer’s exact
requirements from the outset sounds
obvious but most definitely avoids
disappointment further down the line.
Consider the size and number
of roof windows
A good starting point is establishing the size of
the roof window and the number of windows
required. Bigger windows, of course, admit more
daylight, but it is also worth considering a number
of smaller windows instead, as a better overall
effect can sometimes be achieved.
Other factors worth discussing
with your client
If thermal performance is a
priority there are roof
windows that keep houses
warm in the winter and
prevent heat build-up in
the summer. Systems that
feature double-pane
window glazing units filled
with krypton and covered in a
double low emission coating will
achieve this.
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Reviewing how the room will be used can also
throw up questions when it comes to noise
protection. At Dakea we have introduced our
Noise Block technology - a 6mm thick, toughened
outer pane, flashing system and inner pane with
two layers of noise-reducing film. This means
external noise is reduced 50% more effectively
than comparable windows on the market.
Installing correctly first time
There are also a few challenges to combat when
installing a roof window and it depends on the
particular situation. This step-by-step guide
focuses on an outside-in sequence for the Ultima
window.
Firstly, remove the battens to the
extent of the framed area.
The aperture on the roof
must be at least 6cm
wider and 12.5cm (for tile
roofing) higher than the
outer size of the window.
Cut out the roofing underlay
and fix it with staples, cutting
away the excess.
Determine the correct height of the window
“An un-insulated gap
between the rafter and
back of the window
frame means water and
air can pass through”
installation (for tile roofing only) and fasten a
batten to support the frame – level and position
8cm above the tiles.
It is essential to repair the roofing membrane. An
un-insulated gap between the rafter and back of
the window frame means water and air can pass
through. Exposed gaps can cause interior surface
damage and colder room temperatures,
compromising energy efficiency and a resulting
rise in heating costs.
Meeting various regulation requirements is also
important. Filling the un-insulated gap between
the rafters and the roof window will ensure it is
compliant with Part L1B of the Building
Regulations.
Many installers choose to use rigid foam cut to fit
from larger, premium priced sheets. While this leads
to a secure and tight fit around the frame, it
The impact to which the window will be exposed
is also worth considering. With increasingly
extreme UK weather conditions, options that offer
storm resistance and glass protection against
impact from both the exterior and the interior are
advisable – some include a lifetime guarantee
against hail damage for the pane.
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36 TC MARCH 2018