Refurb Projects September 2018

INSULATION
Flat Out performance
by Adrian Pargeter, Head of Technical and Product Development, Kingspan Insulation Limited
As we head into the wetter
winter months, the nation’s
roofs are once again set to be
put to the test. This can
prove to be a particularly challenging
time for buildings with flat roofs, with
water ponding occurring either
because the existing surface has
become damaged or an insufficient
fall was introduced when the building
was first constructed. When
refurbishing these surfaces,
contractors should not only look to
address drainage issues but also to
consider whether improvements can
be made to the thermal performance
of the element. One of the simplest
ways to achieve both of these aims is
by installing a tapered insulation
system. The latest systems now
incorporate phenolic insulation,
allowing the desired U-value to be
met with a slimmer build-up.
Refurbishment Requirements
Flat roofs are defined in BS 6229:
2003 as “having a pitch less than 10o
to the horizontal”, although some
within the industry extend this
definition to pitches of up to 15o.
The British Standard recommends
that flat roofs should have a design
fall of 1:40 and a minimum “as-built”
fall of 1:80. These falls are crucial as
failure to effectively channel
rainwater run-off can result in water
ponding. If untreated, this can lead to
a number of further issues including
alkaline formation and mould growth.
The additional roof loading can cause
further deflection, aggravating the
issue and potentially reducing the
design life of the roof.
Poorly insulated flat roofs can also
act as a significant source of heat loss
from a property, so it makes sense to
raise the thermal performance of
these surfaces as part of any work.
Typically, this can
either be 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 50mm between
the insulation and
the deck.
Recently, a
trend has emerged
where installers fit
a hybrid solution
with a thin layer
of insulation above
the deck and the
rest below. Whilst
in principle this may seem like a
sensible way to reduce the above-deck
construction depth whilst eliminating
the need for a below deck ventilation
gap, it can lead to significant longterm
issues.
In a warm roof, condensation is
prevented by keeping the deck at a
warm temperature, therefore there is
no cold surface for the condensation
to form on. In a cold roof,
condensation is prevented as the
ventilation current takes away the
moisture 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 and as the
ventilation void is absent there is no
way to remove the moisture before it
forms condensation. This construction
should only be considered if a full
condensation risk analysis is carried
out and even then, it will rely on an
almost perfect level of workmanship.
Kingspan Thermataper TT44-K and TT47-K incorporate phenolic
packer boards, allowing the desired drainage and thermal
performance to be achieved with a reduced system thickness
compared with PIR only solutions.
Tapered insulation systems can
provide a better
alternative,
delivering
excellent drainage
and thermal
performance in a
single solution.
Insulated Fall
Tapered
systems typically
comprise sloped
tapered boards, hip
and valley boards
and flat packer
boards. They can
be installed above
concrete and
metal decks either
with standard waterproofing or as
part of a green roof system.
The systems offer a number of
practical benefits for contractors.
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
such as EPS (expanded polystyrene),
XPS (extruded polystyrene) or
Polyisocyanurate (PIR). For enhanced
thermal performance, systems are
now available which combine PIR
sloped, hip and valley boards with
Phenolic insulation packer boards 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.
Kingspan Insulation provide a tapered roofing design
service to ensure the most cost-effective solution is
identified.
Some suppliers also provide a
tapered roofing design service to
support installers. The system boards
are provided with a clear layout
tailored to the specific design of the
roof. This allows a simple installation
and ensures the desired level of
rainwater run-off and insulation
performance to be achieved with a
minimal construction depth. Some
also include a full condensation risk
analysis as part of this process.
Designed to Last
As with any refurbishment work,
improvements to flat roofs should
provide a lasting resolution to the
underlying issue, not a quick patch
which allow it to reoccur at a later
date. Combined PIR and Phenolic
tapered insulation systems can be
quickly and easily installed whilst also
delivering lasting improvements to
roof drainage and the overall energy
performance of the building.
Kingspan Thermataper systems combine insulation and drainage in a
single, lightweight solution allowing simple, fast-track installations.
For further information and technical
support, please contact:
Tel: +44 (0) 1544 387 384
Fax: +44 (0) 1544 387 484
e.mail: info@kingspaninsulation.co.uk
www.kingspaninsulation.co.uk/tapered
18 SEPTEMBER 2018, REFURBISHMENT PROJECTS