From a carbon footprint perspective, wood continues to store carbon absorbed during the tree's growing cycle, keeping it out of the atmosphere for the lifetime of the building—or longer if the wood is reclaimed at the end of the building's service life and reused or manufactured into other products. The manufacturing of wood products also results in less greenhouse gas emissions than other materials.² For example, according to the online Wood Carbon Calculator for Buildings,³ the new Crescent Terminus development, which includes three buildings, each with five stories of wood-frame construction over a concrete podium, has a carbon benefit equivalent to 13,523 metric tons of CO₂. This includes 4,327 metric tons of CO₂ stored in the wood products and 9,196 metric tons of avoided CO₂ emissions.

According to the U.S. Environmental Protection Agency's Greenhouse Gas Equivalencies Calculator, this equates to emissions from 2,583 cars in a year, or from the energy to operate an average home for 1,149 years.⁴

“Wood is also versatile and adaptable,” says Kam-Biron. “Modifications on the jobsite tend to be straightforward and are easily made.”

When asked how building with wood fits into Crescent Communities' quality mission, Ford cites both sustainability and design flexibility. “With concrete, you can't easily design to have the building pop in and out to create the architectural reveals the way you can with a wood-frame building. We can do a lot more design-wise with wood that we couldn't do with other products. So both our environmental goals and our design goals provided the motivation for [Crescent Terminus] to be a wood-frame building.”

A survey of 227 buildings demolished in Minneapolis/St. Paul found that buildings are often torn down within 50 years, regardless of material, because of changing needs and increasing land values as opposed to performance issues.⁵ Overall, wood buildings in the study had the longest life spans, showing that wood structural systems are fully capable of meeting a building's longevity expectations. However, when you consider the embodied energy in demolished buildings and the implications of material disposal, the fact that wood is adaptable—either through renovation or deconstruction and reuse (with minimal additional processing)—is a significant advantage.

Mastering Wood Construction Design

As with any type of construction, mastering the technical details of wood-frame construction is critical to creating cost-effective buildings that are safe and durable. Building codes require all building systems to perform to the same level of safety, regardless of material used, and wood-frame structures can be designed to meet or exceed standards for (among other things) fire protection, seismic performance and resistance to high winds.

FIVE STORIES OF WOOD OVER A CONCRETE PODIUM

Photo: Lincoln Barbour

Project: University House Arena District
Location: Eugene, Oregon
Architect: Mahlum Architects
Structural engineer: Froelich Engineers
Owner: Inland American Communities
Developer: Gerding Edlen
Size: 109,600 square feet, 65 units
Type of construction: Type IIIB wood-frame construction over Type IA concrete podium
Year of completion: 2013

Built to accommodate recent growth at the University of Oregon, the University House Arena District student housing project includes five stories of wood-frame construction over a concrete podium. (Not shown in the photo, the podium is akin to a ‘daylighted basement’ at the rear of the building.)

The use of wood framing over concrete helped the design team achieve an aggressive budget of $128/square foot while ensuring a modern design aesthetic. The team also underwent an Alternate Materials and Methods Review with the City of Eugene to allow wood wrapped in fire-retardant gypsum board for exterior walls. Previously accepted as an alternate method by the City of Portland, this design approach was used instead of the fire retardant-treated wood required for exterior walls as an alternate to non-combustible construction in Type III buildings under the IBC.

“The project is a showcase of smart design that leverages tested assemblies for fire protection as well as innovative materials to express the culture of Eugene,” says Kurt Haapala, principal in charge of the project at Mahlum Architects. Just a five-minute walk to the university, it contributes to the City’s ‘Envision Eugene’ program, which encourages compact development in the city’s core.

Among its sustainability features, the LEED Gold-certified project includes wood studs spaced at 24 inches on center to allow more insulation within the wall cavity, as well as a rooftop solar hot water system and energy-efficient LED lighting throughout. Based on actual utility data analyzed against the energy model, the building is operating approximately 50 percent more efficiently than originally anticipated.