Page 6 - MCRMA Metal Matters Oct 2022

Cavity Barriers and Fire Stopping
by Chris Hall, external affairs director, Siderise Insulation Limited
Most modern buildings contain a multitude of
concealed cavities and voids within or passing
through walls, floors, ceilings and roofs.
Effective fire stopping and cavity barriers are
essential elements of fire protection to restrict
the spread of smoke or flames, and to maintain
compartmentation.
The Metal Cladding and Roofing Manufacturers
Association (MCRMA) has published a guidance
document, supported by an online CPD module,
titled GD36 Cavity barriers for ventilated rainscreen
facades which considers the key questions
about cavity barriers and offers guidance for their
correct specification. The document explains the
difference between a fire stop and a cavity barrier;
the types of cavity barriers used in ventilated
rainscreen facades and examines the regulations
that apply to the different countries of the for the
various parts of the UK.
The role of fire stops and cavity barriers in building
construction is often confused. For fire stopping,
Approved Document B defines a fire stop as “a seal
provided to close an imperfection of fit or design
tolerance between elements or components, to
restrict the spread of fire and smoke.”
Fire stopping needs to attain the same fire
resistance performance as the structural
elements and seal the junction of compartment
walls and floors to maintain the integrity of the
compartment. Fire stopping also seals around
penetrations and services and is fundamental to
compartmentation.
Cavity barriers are defined in Approved Document
B as “a construction within a concealed cavity
other than a smoke curtain, to perform either
of the following functions: to close a cavity to
stop smoke or flame entering or to restrict the
movement of smoke or flame within a cavity.
Image showing
closed state
vertical cavity
barriers on
the jamb of an
opening and
horizontal open
state on the
head and cill.
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By their function, ventilated rainscreen systems
create a concealed space (cavity) that can, in the
event of a fire, provide a route for the passage for
flames, hot gases, and smoke to move, unseen,
between separate compartments of a building.
The accepted method of inhibiting the fire spread
within such a concealed cavity is the use of cavity
barriers. These will be positioned on the line of
any compartment wall or floor so that they sub-
divide the building both horizontally and vertically
into specific compartments in line with Building
Regulations, the fire strategy plan for the building,
or specific requirements of warranty providers
or insurers. Cavity barriers will also close off
penetrations through the façade such as windows,
doors, and openings.
It must be noted that the minimum requirements
for the performance of cavity barriers can vary
depending on which part of the UK they are
being used. In addition to the guidance set out by
the various country-specific technical guidance
documents, warranty providers will have additional
requirements regarding the performance and
placement of the cavity barriers. However, it is
accepted that fire stopping products should meet
the same requirements of resistance as the adjacent
compartment elements, wherever practicable.
There are two types of cavity barriers which are
typically used in ventilated rainscreen facades:
vertical closed state cavity barriers and horizontal
open state cavity barriers.
Vertical closed state cavity barriers are cavity
barriers that fully fill the void from the outer
surface of the inner leaf to the inner surface of
the outer leaf. They are typically used to provide
vertical compartmentation of the external facade
cavity in a ventilated rainscreen and are installed
prior to the installation of a horizontal open state
cavity barrier.
Image showing
the vertical
closed state
cavity barrier
extending to
the full width of
the cavity with
the horizontal
open state set
back to allow
for ventilation
of the cavity.
Explore the
Horizontal open state cavity barriers
are delivered to site pre-cut to
size to suit the width of the cavity
less the air gap size. They have an
intumescent front face which allows
an air gap to be maintained (when in
the open state) to facilitate airflow for
ventilation.
Open state cavity barriers are
supplied with a continuously factory
bonded reactive intumescent strip
on the leading edge and will normally
come with a weather resistant
coating. An intumescent strip is a
material that is designed to activate
at a critical temperature and expand
to close off the purposely designed
air gap to slow the fire propagating
for a specified length of time,
normally 30, 60, 90, or 120 minutes,
depending on the specified product’s
integrity and insulation performance.
MCRMA member companies provide
a wide range of building envelope
solutions for metal-based roofing and
cladding products and services, and
they can advise on the suitability and
performance of materials, systems,
and assemblies.
Both the CPD and guidance
document are available at
www.mcrma.co.uk
Image showing the horizontal open state
cavity barrier installed tight to the backing
wall prior to the thermal insulation with the
horizontal open state set back to allow for
ventilation of the cavity.
Knowledge Base
MCRMA has produced four CPDs based on its
guidance document GD39 Sustainability and durability
of metal roofing and cladding systems.
▶ The introduction and overview CPD looks at how
metal roofing and cladding systems and their
associated components can significantly contribute
to achieving a sustainable building envelope
solution to meet both current and future needs and
requirements. and systems.
▶ Durability of metal roofing and cladding systems
- the aim of current UK government policy is to
achieve net zero by 2050 and one way that can
assist in this is through having buildings built
for durability with long design lives and utilising
materials, products and systems to construct them
that can match the desired design life. This CPD
examines how Life Cycle Costing can be used to
consider all relevant costs to ensure value for money
over the life of a building.
▶ Metals: steel and aluminium. This CPD looks in
detail at the two most common metals used for
manufacturing profiled roofing and cladding sheets
and how they and their associated components can
significantly contribute to achieving a sustainable
building envelope solution to meet both current
and future needs and requirements, thanks to their
low maintenance, durability, high recycled content,
recyclability and energy efficiency.
▶ Components. This CPD looks at the total
sustainable building design solutions which are
available thanks to a range of complementary
components and systems including sustainable
high performance thermal and acoustic insulation
products; high durability fixings, fillers, sealants
and membranes; daylight options, flexible solar PV
options and fastening systems; and ‘green’ and
‘brown’ roof options.
The modules represent
an anticipated 60 - 120
minutes of professional
development, and
following successful
completion of the CPD,
a certificate is available
for immediate download.
All modules have been
accredited by the CPD
Certification Service.
More information about the online CPD courses is
available at www.mcrma.co.uk/online-cpds/