Steve Broadhurst, Technical and NPD Manager at Jablite, explains the requirements of suspended beam and block floor construction.
Suspended beam and block floor construction has been an increasingly popular option for housebuilders since the 1970s – and this structural option now has a market share of approximately 40 per cent. The basic design of the structure has remained unchanged: T-shaped precast concrete beams are laid in rows suspended on the inner leaf of the main walls. The gaps between the beams are then infilled with blocks. In the earliest iterations of this system, the block material was usually concrete. Now, increasingly, architects and construction companies are specifying materials with more attractive insulating properties – and which are also easier to install.
Specifying insulating materials for block infill is a win-win option. Structural integrity isn’t compromised, but thermal performance is vastly improved. Additionally, many insulating materials are, by definition, light in weight. This means they can be speedily and easily installed by trained workers – and are safer to handle.
Thermal performance can be improved even further by placing a separate insulating sheet between the beam tops and the floor screed or topping. In summary, insulating block infill materials offer:
- Enhanced thermal performance
- Increased speed of installation
- Reduced Health & Safety risk for the installer
Until relatively recently infill blocks would be designed to lie flush with the tops of the concrete beams, with the volume of the insulating panel beneath the beam. However, improvements in design mean that increasingly, we’re seeing insulating layers being designed to lie between-and over the concrete beams.
Self-bearing & non-self-bearing
In a self-bearing structure the concrete beams alone provide the final strength of the floor independently of infill blocks and the structural topping. In a non-selfbearing structure, load is shared with the concrete topping cast directly over the tops of the suspended concrete beams.
Specifications for suspended Beam and Block floor systems are covered by the harmonised European Standard BS EN 15037 which is published in parts 1 to 5.
In addition to the beam and block/infill specification, consideration must also be given to the floor finish. This will largely be dependent on the type of substrate, the beam and infill system used and whether that system is deemed to be selfbearing or non-self-bearing as defined in BS EN 15037-1.
Pre-stressed concrete beams are designed to span the required suspended floor distances and be capable of withstanding the applied loads as a selfbearing specification. Suspended floor system providers will design the beam layouts to suit each specific application to ensure the system performs structurally.
Suspended concrete beams provide two specific support or bearing points. Floor system designs and the products specification used will transfer loads to the beams in different ways. The final beam layout will play an important part in the U-Value assessment of each design. An assessor will look at the beam centre ratio – and will use this to calculate the design’s percentage of concrete versus insulation.