Prefabrication experiments - 154 - open building - 05 - Floor cassettes

Efficient industrialized building systems relate open building theory by means of their adaptability while being easily assembled and mitigating irritants associated with on-site construction. Irritants include time and labour intensive processes that are contingent to waste and climate unpredictability. Reducing these irritants involves spending less time on site and more time in a value adding climate and quality controlled environment. Further, modular subassemblies such as walls, floors, or service cores can reduce the on-site complexities associated with system coordination.

The floor (or roof) cassette is an assembly designed and manufactured to order using industrialized pieces. Part of the building industry for many years, a great number of cassette systems are on the market, however the systems which employ open web joists are of particular relevance to open building. The open web or hollow core facilitates system integration and the potential relocation of systems in two directions as a network of interstitial space is created. In systems other than stressed-skin systems, the open web joists are stabilised laterally by timber or steel bracing. Cassettes are packed flat and delivered and then easily combined to create floor plates both safely and efficiently.

Both unidirectional and two directional floor plates are possible as the cassettes sit on a major grid of structural beams. A German manufacturer Kielsteg has developed a particularly interesting system using a folded accordion-like core. Competing with mass timber floor panels the hollowed core is a more rational use of timber and makes the structure lighter.  The hollow core and the open web joists systems make the structure easier to transport. The cassettes thickness varies according to spans. Usually delivered as an under-floor and a ceiling framing most finish work is left to on-site workers. Many manufactures as is the case with the Colli system from Australia now offer a building information modeling service making mechanical systems an integral part of the cassette further simplifying the entanglement usually associated with floor construction. Less site-intensive than regular floor joist systems the cassettes are positioned in place simply using a crane. One of the great advantages over standard platform construction is the inbuilt stability of the cassettes once they are positioned in place.

Colli System (left) and Kielsteg system (right)