Innovation and increased investment
in labour and resources has enabled precast concrete
panels to be specified for a wide range of new
building projects. Stephen Maddalena explains what
advantages this method of construction can bring
to local authorities, especially in social housing
developments on brownfield sites.
Off-site prefabrication in construction is not
a new concept. Architectural precast concrete panels
have been produced off-site for many decades and
are increasingly being specified to clad a wide
range of new buildings.
Despite this trend, there are many building projects
that fail to benefit because the advantages of
precast cladding construction are not fully considered
early enough. The direct and incidental advantages
of precast cladding construction help enhance quality
and safety, improve efficiency and productivity
and provide programme and price certainty.
Innovation in production methods and investment
in labour and plant resources enable architectural
precast concrete panels to be provided in an increasing
range of finishes and facings, shapes and sizes
to suit the requirements of individual projects.
In addition to a wide range of applications, we
are witnessing an upsurge in the use of this versatile
product in the housing sector, particularly for
multi-storey residential developments on brownfield
sites.
As a general guide, the economics of precast cladding
are optimised through the use of large storey-height
panels as they are relatively less time consuming
to manufacture than the correspondingly greater
number of smaller units.
Moreover, the larger the panel the greater the
area clad in one crane lift and consequently the
shorter the construction programme.
For example, consider a storey height panel spanning
between grids, say 4.2m high by 6.0m long. With
six or more such panels being erected daily by
one 5-man team of installers with shared use of
craneage facilities, the building's structural
frame would be enclosed at the rapid rate of at
least 150m2 per day, irrespective of wet or cold
weather conditions or any local labour constraints.
Panels are produced by skilled craftsmen in purpose-built
factory environment using specialist equipment.
Each stage of manufacture is subject to inspection
in accordance with an independently-certified quality
system, and finish and dimensional accuracy are
checked before delivery.
Precast panel construction produces negligible
waste, just enough concrete being batched to fill
available moulds. And at the end of the economic
life of a building, the precast panels may be refurbished
for re-use or crushed as hardcore.
Precast concrete cladding produced in accordance
with BS CP 8297:2000 has a life expectancy of 60+
years and is generally maintenance-free. Dense
concrete is air and water-tight, giving superior
weathering performance and corrosion resistance.
The thermal mass of concrete serves to reduce peak
heating and cooling loads.
Insulation can readily be incorporated
either as a lining to the internal face of a panel
or as a core between two concrete layers, achieving
U-values of 0.35W/m2K and better.
Precast cladding panels are erected on site by
specialist teams trained in safe handling and fixing,
typically without the need for an external scaffold.
Panels are delivered on a just-in-time basis, allowing
large areas of the frame to be rapidly enclosed
to give an early start to weather-sensitive following
trades. Window apertures within the panels can
be framed, glazed and sealed before delivery.
Off-site
prefabrication and increased on-site productivity
facilitate optimum value. Similarly, decreasing
the dependence on site-based activities helps stabilise
the total construction cost and shortens construction
periods, at the same time reducing financing costs.
The secret in every case is to involve the precaster
as early as possible in the design.
Stephen Maddalena
is Chairman of the Architectural Cladding Association
and joint Managing Director of The Marble Mosaic
Co.
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