B
olt-on cantilevered steel balconies
are an architectural feature that is
becoming increasingly popular both in
new build apartments and the housing
market more widely, as they provide visual
interest and signify a quality development to
prospective buyers. Balconies offer
homeowners an outdoor living space and are
seen as a desirable addition to a dwelling.
From a structural perspective the
difficulty with balconies (and for that
matter any architectural feature located
outside of the building’s insulation
envelope), is how to support the balcony
while avoiding a thermal bridge between
the internal building structure and the
balcony steel frame in order to comply with
the Building Regulations Approved
Documents and meeting the requirements
of the thermal modelling calculations for
limiting thermal bridging. Thermal bridging
occurs when conductive materials, such as
steel or concrete, provide a path for heat
energy to flow across a building’s thermally
insulated layer, resulting in heat loss and the
potential for condensation to form.
One solution to this problem is to design
the balcony with support posts on concrete
foundations and bolt the balcony steel
frame to the outer masonry leaf. This
approach is likely to avoid the thermal
bridging issue and is generally the only
viable option on existing properties.
However the dwelling outer leaf may not be
load-bearing, for instance lightweight
cladding materials, and support posts are
widely considered to be detrimental to the
appearance of new build dwellings.
Fortunately for architects the
construction industry has addressed
these issues with companies specialising
in bolt-on cantilever steel balconies
ffering complete balcony packages which
are practical and excellent value for
money, and comprise the balcony and
structural thermally broken building
connection systems.
Typically these balcony packages are
installed as a first fix and then a second fix
item. The first fix installation commences
with the building connection plate which,
depending upon the floor construction, is
either bolted to solid timber joists or a
concrete floor slab. The essential structural
thermal break component is bolted to the
connection plate and is ideally located
within the building insulation layer, thereby
minimising or eliminating the thermal
bridge. A steel stub is bolted to the
structural thermal break, which is designed
to project beyond the face of the external
envelope and position the balcony steel
frame at the correct floor level. After the
first fix is installed, the contractor continues
with the wall construction so that when
completed the stub faceplates are left
exposed for the second fix balconies.
The installation of the balconies usually
takes place towards the end of the build
programme on site and is simply a matter
of offering the balcony steel frame up to the
stub face plates with lifting equipment and
bolting them on, after which the balcony
glass balustrade or metal railing balustrade
and balcony decking are installed.
Balcony rainwater drainage is frequently
raised as a concern, but here again
companies specialising in bolt-on cantilever
steel balconies provide a solution with a
controlled rainwater drainage system which
eliminates the need for unsightly external
rainwater pipes and avoid taking rainwater
pipes into the building, which could have
the potential to leak and cause damage to
the building fabric and interior. The
principle of controlled rainwater drainage is
very simple with rainwater being allowed to
flow into the balcony, and prevented from
draining through the balcony with a soffit
panel to the underside of the balcony.Balconies can enhance residential developments and provide the amenity of outdoor
living space for residents. Lee Barber of Balcony Life explains how bolt-on cantilevered
steel systems can avoid structural issues and problems with thermal bridging
The practicalities of providing
an outdoor living space
EXTERNAL ENVELOPE 55ADF JUNE 2019 WWW.ARCHITECTSDATAFILE.CO.UK