The Human Response to Wood

Originally published in the June 2013 issue of Architectural Record

Measures of performance for building occupants

Sponsored by reThink Wood, American Wood Council, and US WoodWorks

By Layne Evans

Use the following learning objectives to focus your study while reading this month’s Continuing Education article.

Learning Objectives - After reading this article, you will be able to:

1.  Define the relationship between a building’s sustainability and the health and performance of the building’s occupants.

2.  Explore how wood was used to enhance the experience of building occupants in projects from around the country.

3.  Recognize how wood used as a structural and finish material contributes to key elements of occupant environment including indoor air quality, acoustic performance, and physical health.

4.  Examine evidence confirming the positive human response to wood for its aesthetic qualities and connection to nature.

The objectives of sustainable design are broader than just environmental effects, having come to embrace issues of human health and performance. As sedentary and service-related work becomes more prevalent in our society, the amount of time people spend inside buildings increases—the average North American spends 90 percent of his or her time indoors, another 5 percent in cars and only 5 percent outside. This not only makes the design of building interiors ever more important, but calls for the buildings themselves to provide a connection to nature that will only get harder to come by.

Many factors influence whether a building has a positive or negative impact on its occupants. This course highlights remarkable buildings where the use of wood as a structural or finish material has made a unique contribution, with a focus on indoor air quality, acoustics, physical health, and a natural, positive human response to wood that has always been intuitive, but is increasingly being proven by research and experience.

“This is one of the most overlooked aspects of sustainability. It's not about the points. It's about designing places where people want to be,” says Marc L'Italien of EHDD, discussing the David and Lucile Packard Foundation Headquarters, one of the innovative projects featured in this course (see the online version of this article). Wood has been extensively researched and shown to be sustainable by measures that include renewability, embodied energy, air and water pollution, and carbon footprint. But it also performs well in areas that are essential to occupant comfort and performance, resulting in spaces where people feel good and do well over long periods of time.

Indoor Air Quality

For example, indoor air quality is a basic requirement for humans in any space. Wood itself is considered to be hypoallergenic; its smooth surfaces are easy to clean and prevent the buildup of particles that are common in soft finishes like carpet. Solid wood products, particularly flooring, are often specified in environments where the occupants are known to have allergies to dust or other particulates. Glues and adhesives, which were once based on formaldehyde, have been reformulated in many certified products and now contain urethane-type resins without measurable off-gassing.

The use of wood products can also improve indoor air quality by moderating humidity. Acting like a sponge, the wood absorbs or releases moisture in order to maintain equilibrium with the adjacent air. This has the effect of raising humidity when the air is dry, and lowering it when the air is moist—the humidity equivalent of the thermal flywheel effect.

A wooden “bird’s nest” created in the bent glulam wood trusses supports the library’s roof structure, bringing the forest into the heart of Trillium Creek Primary School in West Linn, Oregon.
Photo by Parallel Photography, courtesy of Dull Olson Weekes-IBI Group Architects Inc.

Sound of Wood

For centuries, wood has been the material of choice for architects and designers intent on delivering the highest quality acoustic performance. From a violin to a concert hall, wood plays a role in delivering memorable acoustic experiences. Wood produces sound by direct striking and it amplifies or absorbs sound waves that originate from other bodies. For these reasons, wood is an ideal material for musical instruments and other acoustic applications, including architectural ones.

Wood is not as “acoustically lively” (translation: noisy) as other surfaces. Post-occupancy evaluations of buildings have revealed that poor acoustic performance is a common problem in buildings with large areas of hard, acoustically reflective surfaces. Ironically, such surfaces are frequently found in buildings designed to be sustainable, where the use of absorbent materials is minimized due to indoor air quality concerns.

In large buildings with hundreds or even thousands of occupants—for example, apartment buildings, condominiums, hotels or dormitories—every acoustic detail has a positive or negative effect on the quality of daily life. Wood-frame construction is efficient in buildings where sound insulation is required. In particular, wood doesn't present the impact noise transmission issues commonly associated with concrete construction.

One of the many innovative uses of wood on the exterior and interior of new student housing at the University of Washington in Seattle.
Photo by Benjamin Benschneider, courtesy of Mahlum Architects

University of Washington

In 2012, the University of Washington in Seattle added nearly 1,700 student housing beds by constructing three residential halls and two apartment buildings, all of which include five stories of wood-frame construction over two stories of concrete. Designed by Mahlum Architects and winner of a recent WoodWorks Wood Design Award, the 668,800-square-foot project is the first of four phases planned to add much-needed student housing to the urban campus.

“Acoustics are important for any multifamily housing project, but especially for student housing,” says Anne Schopf, FAIA, a design partner with Mahlum. “Mitigation measures must be weighed against budget, which is why we brought in experts from Seattle-based SSA Acoustics for the design of this project.”

Because they knew single stud walls would not provide adequate performance, SSA recommended staggered stud walls between residential units. Since there is no rigid connection between the gypsum board on each side (except at the plate), a staggered stud wall performs better than a single stud wall. Double stud walls perform better than a staggered stud design because plates are separated by an air space, so they used double stud walls between residential units and common spaces (e.g., lounges, staircases, and elevators) and service areas.

In the floor/ceiling assembly, they paid careful attention to the installation of resilient channels, which are often one of the main causes of failed floor/ceiling assemblies from an acoustical standpoint. In fact, there is a difference of 8 to 10 IIC and STC points between assemblies with resilient channels versus those without. Channel installation has fairly straightforward requirements; for example, screws for the gypsum board should never touch the framing behind the resilient channel.

“We used enhanced acoustical walls between rooms in the same unit,” says Mohamed Ait Allaoua, managing partner of SSA Acoustics. “Although not a typical approach in multifamily buildings, this is important in student housing projects where people within a relatively small space have different needs—if one student wants to watch TV in the living room, for example, while another is studying in the bedroom.”

Bechtel Conference Center at the Public Policy Institute of California (PPIC)

Architect Marcy Wong articulates the connection between acoustics and sustainability in the Bechtel Conference Center at the Public Policy Institute of California (PPIC) in San Francisco this way: “In addition to the usual sustainable advantages of wood—renewability, nontoxic, carbon storing—this project had an additional sustainable aspect, that being acoustics. Sustainability is more than being responsible about the impact of a project on the earth's resources and climate, but also on the quality of environment for the users. The client's programmatic brief for this conference center space is best met by a round room, which happens to be the shape most difficult to acoustically resolve.”

Pearson Theater at Meyer Sound Laboratories

In some projects, acoustical performance is not only a contributor to the building's mission, it is at the heart of its purpose. The Pearson Theater at Meyer Sound Laboratories in Berkeley, California, for example, was designed to showcase the products of a renowned company that develops and manufactures state-of-the-art sound system and integrative technologies including hardware, software, and audio analysis tools. Clients range from opera houses and concert halls, to London and Broadway productions, to rock and roll bands around the world. The theater, also designed by Marcy Wong Donn Logan Architects, needed to deliver the clearest sense possible of how the equipment would perform in a client's own specific context. Thus the design had to feature extreme flexibility in order to configure it for different sound systems in all parts of the theater, which is also used for other purposes including seminars, in-house training, and film screenings.

The design team, which benefited from the considerable acoustical expertise and resources of Meyer Sound, faced the fundamental issue of sound isolation, particularly from truck traffic on the busy street adjacent to the theater's wall. The solution was the creation of a floating room-within-a-room where the interior structure has no contact with the outer shell.

The seating riser central to the Pearson Theater at Meyer Sound Laboratories rests on a 1-inch subfloor of 12-ply birch. The design of the riser and floor are among many acoustic innovations.
Photo by Sharon Risedorph, courtesy of Marcy Wong Donn Logan Architects, Inc.

Physically, the central feature of the room is the seating riser, which rests on a 1-inch subfloor of 12-ply birch (the same wood used to make the company's loudspeaker cabinets). Areas of the floor not covered by the riser are topped with a tough 1-inch-thick floor of end-grain Douglas-fir, bonded to the birch with fiberglass and urethane. The seating riser is constructed from wood rather than concrete, allowing it to couple with the wood floor and transmit structure-borne low frequencies to the seats from two stacks of four studio subwoofers positioned in the room's front corners. The result is a visceral experience of low-end sound achieved by transmitting bass through both the riser and the air.

To allow for meticulous acoustical adjustments throughout construction, a system of Douglas-fir slats and exposed black sound absorption insulation creates a wall pattern which can be manipulated to satisfy the acoustician's objectives. The theater also features an innovative sub-floor made by sandwiching sound absorption sheeting manufactured from recycled tire rubber between layers of plywood. In addition to providing excellent isolation from external noise, the system helps low-frequency sound couple into the wooden floor and bleacher structure so sounds can be felt as well as heard.

According to the client's artistic/technical director, “The completed theater is even more successful than we dreamed possible. The facility has drawn rave reviews from visiting artists, potential and current clients, and company staff for the aesthetic, acoustical, and technical experience.”

Sculptural wall fins fabricated from wood elements create an undulating 3D form while dispersing sound waves to enhance acoustic performance in the circular Bechtel Conference Center at the Public Policy Institute of California.
Photo by Billy Hustace; illustration by Justin Tang; both courtesy of Marcy Wong Donn Logan Architects, Inc.

One of the foremost policy organizations in the state, the PPIC is dedicated to impartial and nonpartisan research to inform public policy decisions; it was important that their new conference space communicate these ideals of openness and calm discussion, as well as presenting a forward-thinking image appropriate for an institution focused on issues of the future. To meet the acoustical challenge of the non-hierarchical circular plan, architects Wong, Donn Logan and Tai-Ran Tseng collaborated with acoustical engineer David Schwind of Charles M. Salter Associates to design a series of sculptural wall fins. Fabricated from wood elements, the fins disperse sound waves for enhanced acoustical distribution while creating the 3D undulating form that defines the architecture.

Wood best served this purpose for two basic reasons, says Wong: the molecular quality of the wood itself, and the ease with which complex geometric forms can be created.

The excellent machinability and edge appearance of the wood elements also proved essential to the project's feasibility and overall aesthetic impact. Virtually each of the CNC milled wood fins is unique in shape to augment the scattering of sound waves that would otherwise be unduly focused in the round room.

Health in Nature

The definition of sustainable building continues to deepen as we understand more about the impact of buildings on the environment and on people. One of the most promising areas of focus is “evidence-based design,” which involves using information gained from the rigorous analysis of past buildings to build better new ones. Healthcare architects have been at the forefront of this effort, exploring the physiological benefits of good design on patient recovery and the well-being of staff and visitors. Among the results, an increasing number of healthcare facilities are making use of natural daylight, views of nature, and exposed wood to create a warm, natural aesthetic that supports their healing objectives. These same techniques are also being used in schools and offices to improve performance, productivity, and occupant well-being.

Humans have a natural affinity for nature. Being in a natural environment—a forest, park or simply a garden—can make us feel more relaxed. The term “biophilia' has been coined to refer to this phenomenon. Although most of us understand the connection intuitively, the stress-reducing effects of outdoor nature are also well documented from a scientific perspective. Exposure to nature has been shown to lower blood pressure, heart rate, and aggression. Nature also increases the ability to focus attention and perform concentration and creative tasks. One landmark study of hospital patients recovering from abdominal surgery found that patients in rooms with a view to nature had shorter post-operative hospital stays and required fewer analgesics than patients with a view of another building from their window.1

But what about the “average North American” spending 90 percent of the time indoors? In addition to views of nature itself, there is growing evidence that a positive relationship exists between humans and natural materials.

For example, one study at the University of British Columbia and FPInnovations demonstrated that the presence of visual wood surfaces in a room lowered sympathetic nervous system (SNS) activation. The SNS is responsible for physiological stress responses in humans.