More and More School Districts Specify Wood to Save Dollars & Time
Doing more with less is a central credo for many public school systems today. When it comes to new school construction, how that belief manifests itself is taking many U.S. school districts in interesting new directions.
That helps explain the rising emergence of wood construction in school building, especially panelized products such as cross-laminated timber (CLT) and prefabrication. This growing trend means code officials should have even greater familiarity with building code-compliant wood-frame elementary, middle school, and high schools.
The chief drivers behind the trend are, of course, construction cost and speed.
The cost of materials and wider availability of skilled labor usually favors wood construction vs. steel-frame construction.
Similarly, construction speed often favors wood. For example, a recent 14,000 square foot high school addition in New Haven, Conn. required just a five-person assembly crew to install the primary structure and enclosure in just four weeks using a combination of CLT and glulam. The idea of completing a major construction project while school is out is appealing to school boards and administrators.
Many other reasons favor a transition to wood-frame construction. Among those frequently cited:
- Design flexibility. Architects can span a wide range of open spaces, including large auditoriums and gyms.
- Structural versatility. Wood framing is easy to modify without the likelihood of demolition or costly retrofitting.
- Acoustics. Wood is naturally sound damping, offering excellent sound control.
- Insurance. Lower-cost structures result in lower insurance premiums. In effect, a continuous savings annuity for the school district.
By 2024, less than 10 years from now, it’s estimated U.S. schools will be required to support an additional 2.8 million students1. It’s a safe assumption school construction, and with it, wood-base school construction, will be a regular feature of code enforcement for many code officials.
Building Size Considerations
Is it possible to deliver an average-size school, say 80,000 to 155,000 square feet, as a Type III or V wood building? Absolutely. To achieve larger sizes, designers can utilize a variety of space multipliers to achieve nearly any school size requirement. Here are several methods:
Sprinklers. Sprinkler use is determined by occupancy group, occupant load, size of the fire area, and other occupant-specific criteria. Per IBC Section 903.2, an NFPA 13 sprinkler system is required throughout all educational and assembly occupancies where the fire area exceeds 12,000 square feet – virtually all school design. The NFPA 13 sprinkler system allows designers to:
- Add one story and 20 feet to the base stories and heights in IBC Table 503 (per IBC Section 504.2)
- Add 200-300 percent to the base floor areas in IBC Table 503. For a multi-story building, the base area can be multiplied by three. For a single-story, the base area can be multiplied by four.
- Story and height increases are permitted to be used concurrently with the area increase per IBC Sections 504.2 and 506.3.
Open Frontage. Allowing ample open space around a school allows improved firefighting access. The IBC offers designers several formulas to increase structure space through frontage allowances. For example, if more than 25 percent of the building’s perimeter is open for a minimum of 20 feet, IBC Section 506.2 permits an increase of up to 75 percent of the base floor area as specified in Table 503.
Unlimited Area. Per IBC Section 507.3 and Section 507.10, a wood-frame school may qualify for unlimited space. The IBC lists an assortment of conditions, including a minimum of 60 feet of open frontage around the perimeter and, in the case of Type III or IV Construction, one-story fully-sprinklered, and classified as Assembly Group occupancy (A-4), will meet the unlimited standard.
Fire Walls. Because of their construction rigor, a fire wall allows an area within a building to be considered as a separate building for the purpose of calculating height and area, further multiplying space allowances.
Fire and Seismic Considerations
Sprinklers, as mentioned, are a mandatory in virtually all school design. Passive features, such as the charring properties of heavy and mass timber, help wood to meet or exceed fire-rated code requirements, no different than any fire-rated building material.
Today more than 40 percent of California public schools are constructed with wood2. West Coast school boards routinely approve wood construction because of wood’s long history of superior performance during earthquakes. Wood is light weight, highly ductible, and presents redundant load paths, helping preserve structural integrity and safeguarding lives.
Lower cost, speedy construction, sustainable material, safe, durable, and attractive are all factors that continue to prompt many school districts to rethink traditional construction assumptions and specify wood.
1. National Center for Education Statistics, Projections of Education Statistics to 2024, http://nces.ed.gov/pubs2016/2016013.pdf
2. “Wood-Framed Schools,” by Scott Lockyear, P.E., 2/19/14, civil + structural ENGINEER magazine, February 19, 2014, http://csengineermag.com/article/wood-framed-schools/
The views and opinions expressed in this article are those of the sponsor and do not necessarily reflect those of the International Code Council, or Hanley Wood.
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