INSULATION
Falling for you
Adrian Pargeter, head of technical and product development at Kingspan Insulation, talks to RCI about
tapered insulation systems and the benefits they bring to flat roofs in terms of drainage and thermal
performance
We have now officially entered
the stormy season and roofs
across the country need
to be properly prepared
for the driving rain. For installers
dealing with large flat roofs, this can
be a particularly tricky task. Structural
falls, which must be carefully designed
for drainage, can take considerable
time to dry and require a separate layer
of insulation to effectively insulate
the roof. Tapered insulation systems
offer a proven alternative — delivering
drainage and thermal performance in
a single solution for faster installations.
Recent developments mean they are now
slimmer and lighter.
Right angles
BS 6229: 2003 recommends flat roofs
should have a design fall of 1:40 to
ensure they achieve a minimum actual
fall of 1:80. These falls are essential
to ensure rain run-off reaches drains,
otherwise water will pond on the roof.
Over time, this additional loading will
cause the surface to bow, aggravating
the issue. This can also lead to further
issues including alkaline formation and
mould growth.
Insulation
Contractors also need to keep a close
eye on the thermal performance of
the roof to ensure it meets the project
requirements.
Typically, this is either achieved with
a warm roof construction, where the
insulation layer is installed above the
deck, or a cold roof construction, where
insulation is installed between and
below the roof rafters with a minimum
air gap of 50 mm between the insulation
and the deck.
Recently, some installers have
switched to a hybrid method where a
thin layer of insulation is fitted above
the deck and the rest below. In theory,
this kills two birds with one stone,
reducing the above-deck construction
depth and eliminating the need for
a ventilation gap below the deck. In
practice, however, it can lead to some
significant issues.
In a warm roof, the insulation
prevents condensation from forming
by keeping the deck warm. In a cold
roof, the ventilation current takes
away vapour before it can form as
condensation.
With the hybrid solution, however,
the above-deck insulation layer often
offers insufficient performance to
keep the deck warm whilst the lack
of a ventilation void means moisture
is not removed before it forms as
condensation. This construction
should only be attempted with a full
condensation risk analysis and, even
then, installers should be aware that
workmanship will need to be almost
perfect to avoid the potential pitfalls.
Tapered insulation systems can
provide a better alternative, delivering
excellent drainage and thermal
performance in a single solution.
Tapered systems
Tapered systems typically comprise
wedge-angled boards, hip and valley
boards and flat packer boards. They can
be installed above a variety of decks
either with standard waterproofing or
as part of a green roof system.
Unlike screed to fall solutions,
tapered insulation systems can be fitted
with a dry installation process, meaning
no time is lost waiting for the surface to
dry. In many cases, these systems can
be fitted above the existing roof surface,
further streamlining project time scales.
They can also weigh as little as 1.5% that
of a screed to fall system – removing
structural loading concerns.
Tapered systems are typically
manufactured from rigid insulation.
Systems which combine PIR
Kingspan
Thermataper
systems
combine
insulation
and drainage
in a single,
lightweight
solution
allowing
simple,
fast-track
installations
(polyisocyanurate) sloped, hip and
valley boards with phenolic insulation
packer boards are now available,
with thermal conductivities as low as
0.018 W/m·K. This enhanced level of
thermal performance can allow desired
U-values to be met with thickness
savings of 20 – 40 mm, depending on
the individual scheme and build-up,
when compared with a full PIR system.
Some suppliers also provide a
tapered roofing design service to
support installers. A clear system layout
is provided, tailored to the specific
design of the roof. This ensures that the
desired level of rainwater run-off and
insulation performance can be achieved
with a minimal construction depth.
Some also include a full condensation
risk analysis as part of this process.
Peace of mind
The last thing any installer needs is to
have to deal with project over-runs or
to be forced to revisit a completed job to
fix issues. Tapered insulation systems,
backed with a specialist design service,
can take the hassle out of tackling
flat roofs, allowing a quick and easy
installation and ensuring the finished
surface will meet the expectations of
installers and clients alike.
w www.kingspan.com
46 www.rcimag.co.uk November 2018
/www.kingspan.com
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