Wood Scores A+ for Schools & Student Housing

Natural building material takes top honors for cost, aesthetics, and performance
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LPA's Rogers notes that speed of construction was important in the firm's work for the cash-strapped Lake Tahoe Unified School District in building South Tahoe High School. Rogers says both time and money were saved by using wood-frame construction. “Specifically, we benefitted from rapid erection and minimized labor required for assembling wall-to-roof connections.”

PAt El Dorado High School in Arkansas, switching to wood framing from the original design saved $2.7 million.

At El Dorado High School in Arkansas, switching to wood framing from the original design saved $2.7 million.

Photos courtesy of W.I. Bell (under construction); Dennis Ivy

Also from a cost-saving perspective, wood's relative light weight reduces the need for foundation capacity and associated costs. “Wood-frame walls can be used as load-bearing walls, eliminating the need for additional beams,” says Lockyear, who also reports growing interest from architects in wood roofs. “Utilizing a sloped wooden roof system which can house mechanical systems in a conditioned space can also reduce HVAC requirements as compared to flat roof systems with mechanical units exposed on the roof. In terms of aesthetics, cost, and design flexibility, the use of wood in school construction offers significant value.”

In Arkansas, wood framing proved to be the most cost-effective structural system for the El Dorado High School. “Originally, the project was designed in steel and masonry, which is common for a building this size,” says J. Richard Brown, PE, principal engineer with Engineering Consultants, Inc. in Little Rock. “But the budget was too high. So our response was to look at other framing types. That's where we found considerable savings.” During the early pre-construction stages, structural steel, pre-cast concrete, and wood were evaluated against steel framing. “Ultimately we made the decision to maximize the use of wood framing throughout the project. By just changing the framing, we were able to save about $2.7 million.”

School Safety

Regardless of whether they're built in wood, steel, or concrete, schools must be safe. Protection from fire, seismic, and wind events is a concern in schools across the country.

Fire protection. While no building is completely fireproof, construction materials and systems can make a building fire safe. Fire-resistive construction allows time to discover a fire, suppress it before it spreads, and evacuate if necessary. Ordinary wood-frame construction with plywood or oriented strand board (OSB) sheathing provides ample fire safety and easily meets requirements of the International Building Code (IBC). For larger wood-frame schools, protected construction, heavy timber construction, or fire-retardant-treated construction on exterior walls may be required. Per IBC 903.2.3, sprinklers are required in areas larger than 12,000 square feet in Occupancy Group E building types. Most schools fall into this category. In addition, local building code amendments typically require sprinkler systems and other fire control measures in school construction, regardless of size or material used.

Another advantage of wood, and particularly heavy timber, is its unique charring properties. When exposed to fire, surface char insulates the member so it can continue to support its load, increasing the amount of time before the member fails.

“At South Tahoe High School, there were only a few areas that required additional fire protection and they were met using fire-treated dimensional wood,” says Rogers. “Where portions of a glued laminated (glulam) member needed to be protected, the member itself met the criteria for heavy timber.”

Seismic performance. In some parts of the country, seismic safety is particularly important. In California, for example, one of the most highly regulated states in the U.S. in terms of seismic requirements, wood-frame schools are common. “Wood has historically performed well during an earthquake,” says Lockyear. “Wood is lightweight relative to other construction materials, and light weight correlates directly to lower seismic forces and better performance during seismic events.” In addition, wood-frame structures, which have numerous nailed joints, are inherently more ductile than those with rigid connections, making them more flexible and allowing them to dissipate energy when subjected to the sudden loads of an earthquake. The fact that wood structures have numerous load paths also helps avoid collapse should some connections fail.

Performance in high winds. All buildings are at risk during high wind events and each structure, with its own unique set of characteristics such as stiffness and strength, reacts differently to wind loads. However, wood buildings can be effectively designed to resist high winds. When designing a wood-frame building to resist high winds and other lateral loads, design engineers use sheathing products such as wood structural panels, structural fiberboard, particleboard, and board sheathing to create diaphragms and shear walls that transfer the loads into the foundation. When structural wood panels such as plywood and OSB are properly attached to lumber framing members, they form some of the most solid and stable roof, floor, and wall systems available. These materials are also used to form the diaphragms and shear walls necessary to resist high wind loads. Alternatively, designers can use rigid-frame construction to transfer the lateral loads. Wood is able to resist higher stresses when the load is applied for a short time, a feature that enhances its performance in high wind events, which are typically of short duration. 


In designing the K-12 Polytechnic School (see cover image) as a podium structure with two stories of wood-frame construction over a concrete parking garage, Kyle Peterson, LEED AP BD+C of HMC Architects in Los Angeles, took an ingenious approach to meeting California's seismic criteria. “We have a fairly high floor-to-floor dimension, thus the design team needed to be creative in order to get the required shear values and maintain the large window openings that were desired,” he says. As part of the project, two relocated historic wood-frame buildings were also upgraded to meet shear and seismic requirements. “Since there were no requirements for shear in the early 20th century, there was very little available space to add shear walls. The use of prefabricated shear panels was the best solution in order to maintain the beautiful, large window openings and provide the required shear values. The buildings were gutted, and the interior framing was upgraded to achieve all these requirements.”

Mid-Rise Wood-Frame Housing Makes the Grade
Wood Scores A+ for Schools & Student Housing

Rendering courtesy of Lord, Aeck & Sargent Architecture

The academic and social benefits of having students live on campus are widely recognized. However, with a record number of students attending colleges and universities, educational institutions are looking for creative ways to cost-effectively expand their housing capabilities. They also want developments that help to attract and retain students by meeting the same quality and environmental objectives as other campus buildings. For many, mid-rise wood construction is an obvious choice.

At the University of North Carolina at Greensboro, for example, wood saved $15 a square foot on one student housing project, Spartan Village Phase I, compared to a metal and concrete alternative. Designed by Lord, Aeck & Sargent Architecture, the 385,000-square-foot project provides 800 new student beds while creating a new neighborhood that sets the tone for future mixed-use developments.

Where student housing is being added to existing neighborhoods, wood offers several advantages. Multi-story wood structures meet residential code requirements and adhere to required safety and structural performance guidelines for urban infill buildings. Plus, infill real estate often carries a premium price, so the economic advantage gained by building multiple stories of wood over a podium-type structure may be the only way a project can work financially. At the same time, educational institutions are increasingly using mixed-use projects to add vital businesses to surrounding neighborhoods.

At the University of Washington, Mahlum Architects made the most of the urban location for a five-building project known as West Campus Student Housing – Phase 1, designing each building with five stories of wood-frame construction over a two-story concrete podium. Constructed for $177 per square foot, the award-winning development includes ground-floor amenities such as a grocery store, conference center, and fitness center, which project architect Anne Schopf calls, “part of a growing trend to make urban campuses more student-friendly.”

 

 

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Originally published in Architectural Record
Originally published in January 2014

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