STRUCTURES + BUILDINGS
Breaking convention with wood offices Wood framing creates inspirational work environments that are code-compliant, cost effective, and sustainable. Great solutions often lie beyond convention. Consider that most of- fices in the U.S. could be built with a wood structure, yet very few are. Many designers assume they’re limited to concrete and steel for workplace environments — because that’s the common default — but in fact, wood systems can accommodate the space and performance needs of office occupancies while providing advantages such as cost savings, versatility, ease and speed of construction, and a lighter carbon footprint. This excerpt of a WoodWorks case study examines common consid- erations for office design in the context of wood structural solutions permitted under the 2015 International Building Code (IBC). Read the full case study at www.woodworks.org/wood-offices. The commercial real estate industry classifies office space based on quality, location, amenities, age, and other factors. Classifications allow realtors to compare spaces for potential tenants; Class A build- ings are most desirable, often garnering higher lease rates and more culture-conscious tenants than Class B spaces. Classifications are not directly related to the structural material; they are driven by building performance and quality of space. Wood buildings can be designed to meet all performance levels, often with cost savings over concrete and steel (see Tables 1, 2, and 3 on page 32). Design considerations: Construction types, heights, and areas Building codes allow wood structure in a variety of construction types, all of which can be used to build attractive, functional, and affordable offices. Type III construction is often associated with multi-family light-frame buildings; however, the heights and areas afforded by this construction type can also accommodate other large light-frame or post-and-beam structures. For business occupancies, Type IIIA buildings are permit- ted to have as many as six stories of wood construction for office use and total building areas in excess of 250,000 square feet. The height and area allowance assume NFPA 13 sprinklers throughout and three or more stories in height. While fire retardant-treated wood (FRTW) or non-combustible framing is required for exterior walls, interior building elements may be of any material allowed by code, including light-frame, heavy or mass timber, and mixed-wood systems. FRTW is permitted in place of non-combustible exterior wall framing when the fire rating requirement is 2 hours or less.
Washington Fruit & Produce Company’s headquarters won a 2018WoodWorksWood Design Award. Architect: Graham Baba Architects; Structural engineer: M.A.Wright, LLC. Photo: Kevin Scott
Type IV construction , also known as heavy timber, may include the use of solid or laminated wood members such as glulam and wood decking — provided minimum sizes and restrictions on concealed spaces are met. Concealed cavities are only permitted in partitions; they may be of solid wood or 1-hour fire-resistant construction, which would allow rated wall construction with a cavity to house mechani- cal, plumbing, or electrical systems. Similar to Type III construction, FRTW can be used to frame exterior walls with fire ratings of 2 hours or less, although in many cases non-combustible curtain walls or glaz- ing systems are wrapped around the timber post-and-beam frame. Mass timber is permitted in floors, roofs, and walls, including exterior walls when protected by a non-combustible material on the outside face; however, mass timber is not limited to this construction type. Type V construction may use untreated wood throughout. Exposed light-frame construction, often Type VB, is becoming increasingly popular as a cost-effective way to create a modern industrial aesthetic for office buildings up to three stories with more than 27,000 square feet per floor (with an NFPA 13-compliant sprinkler system). There are several options for using wood to more affordably achieve the scale of a Type IIA or IIB building (see table, Multi-Story Business Occupancy: Allowable Business Sizes). For example, Types IIIB and VA can be used to achieve the same height and number of stories as Type IIB, with a slightly smaller per-story area. Similarly, Type IIIA or Type IV structures allow heights, stories, and per-story area that are comparable with Type IIA. With these alternatives, architects ac- customed to designing Type II structures can increase their options to include cost-effective wood structure and the aesthetics of exposed wood.
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csengineermag.com
august 2018
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