The number of occupant complaints received about annoying low-frequency footstep impact sound transmission through wood floor-ceiling assemblies has been increasing in proportion with the increase in the number of multi-family wood buildings built. Little work has been conducted to develop solutions to control the low-frequency footstep impact sound transmission. There are no code provisions or sound solutions in the codes. Current construction practices are based on a trial and error approach. This two-years project was conducted to remove this barrier and to successfully expand the use of wood in the multi-family and mid- to high-rise building markets. The key objective was to build a framework for the development of thorough solutions to control low-frequency footstep sound transmission through wood floor-ceiling assemblies.
Field acoustic tests and case studies were conducted in collaboration with acoustics researchers, builders, developers, architects, design engineers and producers of wood building components.
The field study found that:
1. With proper design of the base wood-joisted floors and sound details of the ceiling:
With no topping on the floor, the floor-ceiling assembly did not provide sufficient impact sound insulation for low- to high-frequency sound components ;
Use of a 13-mm thick wood composite topping along with the ceiling did not ensure satisfactory impact sound insulation;
Even if there was the ceiling, use of a 38-mm thick concrete topping without a proper insulation layer to float the topping did not ensure satisfactory impact sound insulation ;
A topping system having a mass over 20 kg/m2 and composed of composite panels and an insulation layer with proper thickness achieved satisfactory impact sound insulation.
2. The proper design of the base wood-joisted floors was achieved by the correct combination of floor mass and stiffness. The heaviest wood-joisted floors did not necessarily ensure satisfactory impact insulation.
3. Proper sound ceiling details were found to be achieved through:
Use of two layers of gypsum board;
Use of sound absorption materials filling at least 50% of the cavity ;
Installation of resilient channels to the bottom of the joists through anchoring acoustic system resulted in improved impact sound insulation than directly attaching the resilient channels to the bottom of the joists.
A four-task research plan was developed to thoroughly address the issue of poor low-frequency footstep impact insulation of current lightweight wood floor-ceiling assemblies and to correct prejudice against wood. The tasks include: 1) fundamental work to develop code provisions; 2) expansion of FPInnovations’ material testing laboratory to include tests to characterize the acoustic properties of materials; 3) development of control strategies; and 4) implementation.
The laboratory acoustic research facility built includes a mock-up field floor-ceiling assembly with adjustable span and room height, a testing system and a building acoustic simulation software.
The preliminary study on the effects of flooring, topping and underlayment on FIIC of the mock-up of the filed floor-ceiling assembly in FPInnovations’ acoustic chamber confirmed some findings from the field study. The laboratory study found that:
A topping was necessary to ensure the satisfactory impact sound insulation;
The topping should be floated on proper underlayment;
Topping mass affects impact sound insulation of wood framed floors;
A floating flooring enhanced the impact sound insulation of wood framed floors along with the floating topping.
It is concluded that:
1. even if the studies only touched the tip of the iceberg of the footstep impact sound insulation of lightweight wood-joisted floor systems, the proposed solutions are promising but still need verification ;
2. with proper design of the base wood floor structure, the proper combination of flooring, and sound ceiling details along with proper installation, the lightweight wood floor-ceiling assembly can achieve satisfactory impact sound insulation ;
3. this study establishes a framework for thoroughly solving low-frequency footstep impact sound insulation problem in lightweight wood-joisted floor systems.
Solutions will be developed in the next phase of this study as planned and the study will be conducted under NRCan Transformative Technology program with a project dedicated to “Serviceability of next generation wood building systems”.