It is commonplace in several structures to incorporate beam and block systems. These consist of a combination of pre-stressed beams made from concrete and fill in blocks. Conventionally, such blocks are also constructed from concrete. Yet, more and more, these are being replaced by polystyrene substitutes. So configured, this method avoids the need for insulation on top of suspended flooring. The happy result is more cost-effective and more easily installed.
Types of Precast Flooring System
In the construction of houses, there are three predominant kinds of precast concrete floors:
• Beam and block
• Lattice girder
These elements have been designed in a range of sizes that work with the most significant spans for domestic applications at all floor levels.
Beam and block
These elements cater for depths to a maximum of 225mm. They are used alongside standard blocks to facilitate quick fitting at a reasonable price. Suitable for all levels.
Ground floors may be thermally insulated by combining pre-stressed beams and expanded polystyrene blocks. This approach meets the expectations of Building Regulations (Document L), reducing running costs, and improving comfort levels.
Insulated ribbed floor
This composite unit approach is another means to achieve thermal insulation on ground floors.
This is another combination of materials, where permanent concrete structures are employed with a topping of composite concrete to provide an exposed concrete finish.
Next, we consider the actual thermal performance of beam and block flooring. Such floors contribute to the overall thermal mass of a building and so help control inside temperatures.
Beam-and-block floors contribute to the thermal mass of a building, helping to improve its thermal performance and regulate internal temperatures. Even better performances can be achieved when polystyrene blocks are used to replace concrete infill blocks.
Several studies have revealed a shortfall of up to 30% between energy conservation calculations when comparing new homes with predicted conservation calculations derived during the design phase.
Changes were made to SAP calculations to enhance build quality as a means to close the gap:
• The standard for air-tightness was lowered. Higher thresholds result in more significant air leakage, which in turn causes increased heat loss.
• A shift in focus to improved thermally efficient bridging at junctions
• More effective central heating
Other Design Considerations
In the main, flooring systems require certification by a certification body (BBA or BDA, for example.) This is a useful form of quality assurance as, in practice, flooring may be constructed according to the National House Building Council (NHBC) standards.
Beam and block flooring may exhibit a range of fire resistance depending on beam type and the chosen finish. It depends on the section’s size, but you can expect around 1 hour’s resistance per individual beam.
Final floor specifications determine the sound resistance of flooring. Depending on the particular specification, beam and block flooring may be acceptable as intermediate flooring in housing or separating floors in residential accommodation with multiple occupancies.
Concrete beams which have been pre-stressed show an upward camber, dependent on the span and designed pre-stress.
On masonry, end bearings need to be 100mm (75mm if steel). In most cases, end bearings don’t get bedded to the supporting wall—they sit on a damp-proof course to protect the steel.
It is possible for floor-beams to be notched to rest in steel on upper levels. However, this requires manufacturer consent on a design by design basis. If using blocks for infill on a load-bearing wall, the strength of both infill blocks and wall blocks must be equal.
Suspended floors sit atop a void, which requires ventilation conforming to should current Building Regulations. Varying site conditions will give rise to a range of values. It is also possible to include radon barriers within the design, although this requires input from a qualified building designer to vouchsafed the barrier’s continuity.
Insulation units can be constructed to form an unbroken strip of beneath T-beams, thereby removing thermal bridges.
On occasions, such systems prove unsuitable to stakeholders. Another way to achieve the same end is to place a top sheet onto the T-beams and put on a concrete topping.
To achieve the best heat performance may be combined, resulting in both systems, minimal heat loss at critical junctions. Insulation is available to clients in a variety of thermal grades. On the one hand, higher thermal grades can be made thinner. The downside is that higher thermal grades cost more.
Environmentally, there is considerable good news. EPS is judged a low global warming risk and has the potential to be used to pose no depletion to the ozone layer.
Furthermore, EPS rates A+ in the BRE Green Guide to Specification. The raw materials are also fully recyclable. Several manufacturers have pledged to offer schemes for the high-quality re-cycling of scrap material, where the quality of end products matches the quality of the original material.