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 being recently built. Little work has been done to develop solutions to control low-frequency footstep impact sound transmission. There are no code provisions nor are there any sound solutions in the codes. Current construction practices are based on a trial and error approach. This two-year project was conducted to remove this barrier and 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, and producers of wood building components.
This 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 did not ensure satisfactory impact sound insulation;
use of a 38-mm thick concrete topping without a proper insulation layer to float the topping did not ensure satisfactory impact sound insulation;
use of 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. 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 an acoustic anchoring system; this resulted in a much better 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 included: 1) fundamental work to develop code provisions; 2) expansion of FPInnovations’ material testing laboratory to include tests that 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 building acoustic-simulation software.
It is concluded that with proper design of the base wood floor structure and the use of the right topping and sound ceiling details, a lightweight wood floor-ceiling assembly can achieve satisfactory impact sound insulation. As planned, solutions will be developed in the next phase of this project.