A Timber Tower design for a 42-story wood tower, the tallest yet envisioned, has been published in a report by Skidmore Owings & Merrill (SOM), world renowned architects. Its carbon footprint is smaller than a steel tower.

The building would be constructed using “Mass Timber Products,” says SOM, including CLT or Cross Laminated Timber, and mixes of species in the mass timbers.

“The proposed structural system can be designed with mass timber products built up using different species and grades of wood. Potential species include: Douglas Fir – Larch (DF – L), Hemlock – Fir (HR), Spruce – Pine – Fir (SPF), and Southern Yellow Pine (SYP).

“The grade chosen is related to the desired performance for the different elements in the structural system such as the floors and the columns. In that respect, it is more useful to categorize the wood material chosen in terms of desired strength and stiffness similar to a machine stress rated (MSR) lumber,” says SOM.

Funding for the Timber Tower Research Project was provided by the Softwood Lumber Board, an industry funded research, promotion and information program for softwood lumber.

The 72-page report details materials and engineering involved in construction of a wood building. moving a step beyond theoretical wood skyscraper, SOM has devloped engineering and design approaches that would make the construction practical.

In fact, SOM has used an existing concrete apartment building that it designed in 1965 as the basis for the Timber Tower. The 395-foot-tall, 42-story Dewitt-Chestnnut Apartments used an advanced cantilivered approach to its construction.

“The goal of the Timber Tower Research Project was to develop a structural system for tall buildings that uses mass timber as the main structural material and minimizes the embodied carbon footprint of the building,” says SOM in its report. “SOM’s solution to the tall wooden building problem is the ‘Concrete Jointed Timber Frame.'”

SOM explains that its system relies primarily on mass timber for the main structural elements, with supplementary reinforced concrete at the highly stressed locations of the structure: the connecting joints.

“This system plays to the strengths of both materials and allows the engineer to apply sound tall building engineering fundamentals. The result is believed to be an efficient structure that could compete with reinforced concrete and steel while reducing the carbon footprint by 60 to 75%,” says the report.

SOM says because wood “is arguably the most sustainable structural material, the system is to consist primarily of wood. Technological advances in wood technology have made this possible with products referred to as ‘mass timber,'” which use softwood products built up using adhesives.

“The resulting structural elements behave similar to heavy timber. The advantage is that the material can scale to larger sizes necessary to support the required loads as well as behave like heavy timber in a fire by charring rather than burning,” says the report from SOM.