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Residential Precast Concrete Systems
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The use of precast
panel systems for the walls of a concrete home offers
the homebuyer the opportunity to control the quality
of the end product to a very high degree, as precast
panels are usually supplied from specialist precasting
factories. Casting multiple panels from the same mould
can also help reduce building costs.
A variety of attractive surface finishes are possible
using precast panels, some of which eliminate the need
for any ongoing coatings or other decorative finishes.
Savings in construction costs are also possible if the
surfaces of the precast panels can be left unpainted
or unlined. Precast construction is often chosen by
designers and/or builders seeking to achieve a particular
look as it provides limitless flexibility of shape and
size. Consideration given to the placement and treatment
of panel joints can also reduce costs. |
©CCANZ
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Precasting offside can also improve the speed of construction.
While the panels are being prepared, workers can spend time
preparing the site. Once the floor slab or foundation is made
ready to accept the system and the panels are delivered, it
is often possible to erect all of the walls within a day,
and have the house closed in and secured shortly thereafter.
Another option is to precast the panels
on site (variously referred to as 'site precasting' or 'tilt-up
construction'). Tilt up panels will save money on transportation
costs to site, particularly if the site is remote. They are
also an option when there is little room for cranage on the
site. The panels can be cast in position and once cured, erected
with the use of a lifting frame. The size of the precast panels
is limited by the area of flat surface on which to cast and
by the lifting equipment.
The quality of on-site precast panels is dependent on the
experience of the on-site personnel and on the site conditions.
Absolute and expert control of the preparation, casting and
curing of panels, and the creation of particular special surface
finishes, may only be possible from a dedicated precasting
factory.
Precast panel systems can be manufactured with higher insulation
values by the use of various insulating mediums. Most common
is the use of polystyrene sheeting attached to either the
interior or exterior face of the panel. The polystyrene can
also be located within the panel (referred to as 'sandwich
panel construction'). Insulating plaster renders can also
be applied to the panel surface. Another option is to strap
and line from the inside, with insulation (usually a fibre
system such as glass or wool) in the cavity.
As with some forms of masonry construction, panels insulated
on the internal face of the wall isolate the mass of the wall
from internally reflected and radiated heat. This can reduce
some of the benefits of the high mass system. One system involves
casting the concrete panel onto a layer of polystyrene with
splayed ribs. These ribs help the concrete key to the insulation.
These walls can then be clad using conventional wallboard
systems.
Panels insulated on the external face of the wall only will
provide thermal mass to the interior, and require an external
plaster coating to protect the insulation from possible damage.
Precast systems with insulation in the middle of the panels
mean that the thermal mass is available to contribute to the
comfortable living environment in the home and the exterior
is a robust concrete surface. Some manufacturers produce these
panels to a regular modular size, using window and door openings
to break up the wall for architectural relief, while others
cast panels to a range of sizes and shapes.
Precast panels can also be constructed of lightweight concrete.
These panels are usually reinforced with fibres rather than
conventional steel reinforcing and can have a variety of finishes
applied or cast integrally on the surface. One system uses
a material that is only 33% of the weight of conventional
concrete. Services can be run easily through the void formed
by the permanent steel frames on the inside face of the panel,
which can then be lined with traditional materials. Lighter
panels mean that smaller cranes can be used to lift and place
the panels with consequential cost savings. Using lightweight
panels is a good option when building on softy unsteady soil
and could also result in lower costs for the foundations due
to the lower mass of the panels. These panels have a higher
insulation value but lower thermal mass capacity than conventional
concrete panels.
For more information:
For New Zealand residents only: The CCANZ has an information
pack that we can send you, please email admin@cca.org.nz
for a pack.
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