| Concrete
Slab-on-grade Floors
| An ever-increasing number of new houses
in New Zealand are being built on concrete ground floor
slabs, the result of builders and homeowners having discovered
the benefits of concrete ground floor slab construction.
The inherent qualities provided by concrete floors are
dependent on good design and construction practices. Concrete
is formed on site through a series of sequential steps.
Careful control must be maintained throughout to help
ensure maximum benefit from the material. |
©ccanz |
Concrete slab floors provide good resistance
to the lateral transmission of impact noise, which results
in a quieter home. Concrete floors also perform well under
seismic loads, as the earthquake forces are distributed over
a greater area of ground, thus reducing the risk of foundation
movement.
When building on a flat site, a concrete
slab is generally less expensive to construct than a suspended
timber floor. On flat and gently sloping sites (up to 15°),
the speed of construction of a slab-on-grade is also competitive
with that of a timber floor.
The high thermal mass of concrete allows
floors to be used as part of a passive solar heating system.
Another advantage of a concrete floor is that a heat supply
can be cast directly into the slab, in the form of electric
cables or piped hot water. Embedded heating systems reduce
the occurrence of cold air draughts at floor level and reduce
the risk of humidity and mildew, without taking up any room
space.
Methods of finishing a concrete floor are
almost endless, ranging from steel trowelled to ground or
polished finishes, to stained or pigmented concrete. Other
finishes include exposed aggregates, imprinting in a variety
of patterns and layouts, and a range of inlaid materials,
including metal strips, timber, glass and even plastic. While
there is an initial capital cost of finishing a concrete floor,
a well-finished and attractive floor slab means that the cost
of applied floor finishes can be avoided.
Instead of a surface treatment, the concrete
slab can also be covered in a common flooring material such
as linoleum or vinyl tile, or hardwood flooring. However,
these types of materials reduce the effectiveness of the use
of the floor mass in controlling internal temperatures. Materials
such as slate, concrete or ceramic tile, terrazzo enable the
floor mass to be fully utilized to improve thermal comfort.
Typical Recommendations:
(General)
Slab Thickness: 100mm
Concrete Strength: 17.5 MPa - generally 20MPa - garage
or workshops or where harder wearing surface is required.
Reinforcement: 665 Mesh or equivalent
Shrinkage control joints: Maximum spacing 6m depth
not less than ¼ of slab thickness
Damp Proof Membrane: Typically polyethylene sheet.
Minimum thickness of 0.25mm
A minimum of 150 mm of compacted hard fill
or granular fill should be placed under all concrete floor
slabs except where subsoil is rock. Final levels can be achieved
through compacted layer of blinding sand 5mm to 25mm thick.
For more information:
|
