Acoustically optimised floor system made of hardwood

The project focused on the development and investigation of a new timber floor system with improved acoustic control properties in the low-frequency range below 200 hertz (Hz). In addition to meeting various technical criteria, the new system was required to be no thicker than existing timber floor assemblies.

A solution to the complex research question was achieved through a combination of experimental investigations and finite-element modelling of dynamic behaviour. The result offers an interesting alternative to standard concrete floor constructions. The project has also unlocked new potential for the use of Swiss beech.

One of the goals of Swiss governmental policy on wood is to increase the use of hardwood in the building sector. Among the challenges to be met is the acoustic insulation of wooden buildings, particularly in the low-frequency range below 200 Hz. Sound at these frequencies is generated by walking and jumping or, for example, by the use of home cinemas in apartments. Although noise of this kind is not covered by Switzerland's acoustic control standard and thus raises no legal issues, it can often be a nuisance for neighbours. To achieve a level of sound insulation comparable to that of concrete structures, multi-storey wooden buildings currently require special floor constructions with complicated designs and large thicknesses. As a result, wooden buildings often cannot compete with concrete buildings.

The aim of the project was to develop a multi-functional floor system made from Swiss hardwood that offers at least 10 dB better impact sound insulation in the low-frequency range than the other timber floor systems currently used for multi-storey buildings. The envisaged timber floor system was required to have a similar thickness to standard concrete floor constructions. Through its lower environmental impact, it was also expected to score better in terms of the environmental life cycle impact.

A further goal was to open up new perspectives for the use of hardwood, primarily beech. Thanks to its high apparent density and hence its favourable acoustic performance – and despite its marked deformation properties – beech is well-suited for use as a structural timber. At present, beech is mainly used in the manufacture of furniture and veneer boards.

The project achieved its main aim, namely the development of a prototype timber floor system made from beech with improved impact sound insulation in the low-frequency range. The dowelled-joist timber floor meets the requirements of Swiss standard SIA 181:2006 on sound control in buildings. It also responds to the latest trends and requirements regarding sustainability, multifunctionality and aesthetic design.

Other project deliverables included a detailed acoustic control analysis, the design of a wooden dowel connection plus details of the impact of this connection on sound transmission.

The experimental investigations and the subsequently validated finite-element model for dynamic behaviour showed dowelled wood assemblies with floating screeds to exhibit similar impact sound insulation properties in the low-frequency range to standard concrete constructions. The use of suitably sized elastic layers reduces flanking transmission and thereby cuts the cost of impact sound control.

The project analyses and product design specifications have paved the way for commercial use of the dowelled-joist timber floor made from beech.

The use of acoustically optimised timber floor systems would appear to be particularly worthwhile in apartment blocks and multi-storey office buildings. Such applications may further raise the profile of wooden buildings in the urban environment and make them a realistic alternative to concrete structures. This would help to make hardwood more competitive, in line with Swiss governmental policy on natural resources.

Competitive wooden floor system

Multi-objective optimisation based on acoustics improvement