Commercial and multi-family residential construction represents a growth area for the Canadian wood products industry. To capitalize on this opportunity, a thorough understanding of the necessary products and system attributes will be essential. Adequate levels of noise/sound control in multi-family buildings are mandatory requirements of building codes in Canada, the United States, Europe, and most developed Asian countries. In many jurisdictions, these requirements are as strictly enforced as those for structural sufficiency and fire safety. Much effort has been spent on evaluation of sound transmission class (STC) and impact sound insulation class (IIC) of floor and wall assemblies and on studies of flanking transmission in multi-family dwellings in Canada. However, continuing occupant complaints of poor acoustic performance in wood-frame buildings that appear to have been built according to wall and floor construction practices recommended in building codes suggest the existence of gaps in current noise control techniques.
Forintek initiated this project to investigate the relative importance of noise transmission in wood-frame residential buildings in comparison with other building serviceability issues, and to conduct a pilot study to examine construction designs of wood-frame buildings that exhibit unsatisfactory and satisfactory noise control and to identify existing gaps in current noise control techniques.
A literature review and survey of 123 occupants of wood-framed multi- and single-family residential buildings was conducted to determine the relative importance of noise transmission in comparison with other building serviceability attributes. Case studies were conducted on construction details and designs of six new wood-frame condominiums and one single family-house that were built according to code requirements and recommendations for controlling noise transmission.
We found that the general public had high expectations regarding adequate acoustic privacy. Even single- family house builders considered low sound transmission important. The multi-family building occupants ranked “sound insulation” the most “important” serviceability attribute, while single-family occupants were most concerned with “water penetration and condensation”. The lowest level of “satisfaction” was given by all respondents to “noise transmission” for their current residences, including single-family occupants, who had ranked it as not being so “important”. The case studies revealed that, current construction practices were much more effective in controlling airborne sound transmission than impact noise. The footfall noise transmission from stairs through the walls is still an unresolved issue that is not considered in the current Canadian Building Code. The low frequency footfall noise transmission between vertically-stacked units was the common complaint in some of these buildings. With no requirement for impact sound insulation in the current National Building Code of Canada, and with our existing knowledge gap concerning low frequency footfall noise transmission problems and solutions to control them, builders, acoustics consultants and design engineers have simply tended to blame wood building materials for noise-related complaints.
We concluded that if we are to satisfy the occupants of both single-and multi-family wood-frame buildings and to provide confidence for builders and design engineers in wood-frame construction with satisfactory acoustic performance, a much greater effort is needed to improve sound insulation including development of better sound insulated wood-frame systems and building materials as well as retrofitting techniques. Acoustic performance will be a critical factor for the wood products industry in gaining a greater share of the multi-family construction market and in competing with other building materials.
This report addresses serviceability issues of tall wood buildings focusing on vibration and sound insulation performance. The sound insulation and vibration performance may not affect building's safety, but affects occupants' comfort and proper operation of the buildings and the funciton of sensitive equipment, consequently the acceptance of midrise and tall wood buildings in market place. Lack of data, knowledge and experience of sound and vibration performance of tall wood buildings is one of the issues related to design and construction of tall wood buildings.
This report addresses serviceability issues of tall wood buildings focusing on their vibration and sound insulation performance. The sound insulation and vibration performance may not affect the building’s safety, but affects the occupants’ comfort and the proper operation of the buildings and the function of sensitive equipment, consequently the acceptance of the midrise and tall wood buildings in market place. Lack of data, knowledge and experience of sound and vibration performance of tall wood buildings is one of the issues related to design and construction of tall wood buildings.
The measured and estimated values should also be correlated with actual experiences of the occupants in the building if such information is obtained, for example, through a survey.
Serviceability performance studied covers three different performance attributes of a building. These attributes are 1) vibration of the whole building structure, 2) vibration of the floor system, typically in regards to motions in a localized area within the entire floor plate, and 3) sound insulation performance of the wall and floor assemblies. Serviceability performance of a building is important as it affects the comfort of its occupants and the functionality of sensitive equipment as well. Many physical factors influence these performances. Designers use various parameters to account for them in their designs and different criteria to manage these performances. Lack of data, knowledge and experience of sound and vibration performance of tall wood buildings is one of the issues related to design and construction of tall wood buildings.
For wood floor systems, their vibration performance is significantly dependent on the conditions of their supports, specifically the rigidity of the support. Detrimental effects could result if the floor supports do not have sufficient rigidity. This is special ture for floor supporting beams. The problem of vibrating floor due to flexible supporting beams can be solved through proper design of the supporting beams. However, there is currently no criterion set for the minimum requirement for floor supporting beam stiffness to ensure the beam is rigid enough. Designers’ current practice is to use the uniform load deflection criteria specified in the code for designing the supporting beams. This criterion is based on certain ratios of the floor span (e.g. L/360, L/480 etc.). The disadvantage of this approach is that it allows larger deflections for longer-span beams than for shorter beams. This means that engineers have to use their experience and judgement to select a proper ratio, particularly for the long-span beams. Therefore, a better vibration-controlled design criterion for supporting beams is needed.
It is recommended to further verify the ruggedness of the proposed stiffness criterion for floor supporting beams using new field supporting beam data whenever they become available.
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.
It is not surprising to see a rapid growth in the demand for mid- to high-rise buildings. Traditionally, these types of buildings have been dominated by steel and concrete. This trend creates a great opportunity for wood to expand its traditional single and low-rise multi-family building market to the growing mid- to high-rise building market. The significance and importance of wood construction to environmental conservation and the Canadian economy has been recognized by governments, the building industry, architects, design engineers, builders, and clients. It is expected that more and more tall wood frame buildings of 6- to 8-storeys (or taller) will be constructed in Canada. Before we can push for use of wood in such applications, however, several barriers to wood’s success in its traditional and potential market places have to be removed. Lack of knowledge of the dynamic properties of mid- to high-rise wood and hybrid wood buildings and their responses to wind, and absence of current guidelines for wind vibration design of mid- to high-rise wood and hybrid wood buildings are examples of such barriers.
This pilot study was conducted to build a framework for the development of design and construction solutions for controlling wind-induced vibration of mid- to high-rise wood and hybrid wood frame buildings, to ensure satisfactory vibration performance during high winds.
A literature review and ambient vibration tests (AVT) on existing two- to six-storey wood frame buildings were conducted to establish a database of the vibration properties of wood frame buildings. Monitoring the vibration response to wind of a six-storey wood frame building was initiated. Collaboration with McGill University was also established to verify the AVT results. The measured fundamental natural frequencies of the wood-frame building were used to verify the NBCC equations to estimate the building’s fundamental natural frequencies. Collaboration with Tongji University was established to explore the potential use of the finite element commercial software Ansys, for simulation of vibration performance of wood frame buildings.
It is concluded that this project achieved its objectives, i.e. built a framework for the development of a design guide for controlling wind-induced vibrations of mid- to high-rise wood frame buildings. The framework includes the AVT system, software and protocol, a building vibration monitoring system and protocol, computer simulation tool, a database of natural frequencies and damping ratios of wood frame buildings, and the expertise for conducting AVT, building monitoring, and computer simulation. Pilot study results confirmed that AVT and computer simulation are useful, and appropriate tools for the development of techniques and a design guide for controlling wood frame building vibrations in wind.
It is recommended that current NBCC equations using building height as a variable to estimate the building’s fundamental natural frequency be used to predict the fundamental natural frequencies of wood-frame buildings, until a better calculation methodology is developed. More field data of the fundamental natural frequencies measured on mid- to high-rise wood frame or hybrid wood buildings are needed to further verify the NBCC equations, or to develop more suitable equations for wood buildings.
“Conservatively, there are an estimated 10 million houses in North America with springy floors or other structural problems” http://www.ridgwaystructuralsystems.com. We have found that the springy floors were caused by improper design or construction practices. The improper design is specially true for engineered wood floors because of lack of proper design method and knowledge.
This report is focused on the development of a new design guide to demonstrate that floor vibration problems can be solved through proper design and construction practices. The design guide is aimed at assisting those who are involved in wood-framed floor design, construction, and product development, in better controlling feelable vibrations and in achieving optimum value engineered (OVE) floor systems.
The scope of this design guide is limited to: wood-framed floors, or light-weight floors with a fundamental natural frequency above 10 Hz; controlling feelable vibrations, but not “drum effect” vibrations induced by normal walking; ensuring human comfort.
The design guide first explains the fundamental physics behind the vibrations induced in wood-framed floors by normal walking and the human response to vibrations. The general theory of vibrations relevant to the vibrations induced in wood-framed floors by normal walking is included in Appendix I. Then a mechanics-based new design method and its verifications are presented. Working examples are provided along with the design tool, i.e. an ”Excel spread sheet” that incorporated the design method and the working examples to assist readers in using the new design method effectively. Various remedy techniques are provided along with a case analysis of unsatisfied floors. Finally, the design guide includes a systems analysis of the effects of various construction practices on floor multi-performance attributes, ease of installation and cost effectiveness. This assists the user in adopting a systems approach for designing an optimum value floor system when developing practices for controlling floor vibrations.
The knowledge, experience and understanding of floor vibration control compiled in this design guide is based on over ten years of research, with contributions from various floor researchers, practitioners, product manufacturers and home owners that Forintek has encountered in the course of conducting various floor studies.
This design guide is not the end of the process. Rather, it is considered to be part of an ongoing process to provide practitioners and researchers with state-of-the-art information to control floor vibration, as our knowledge of floor vibration and noise control, floor construction products and techniques evolve over time.