{"id":78100,"date":"2018-12-28T15:15:35","date_gmt":"2018-12-28T20:15:35","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=78100"},"modified":"2018-12-28T15:15:35","modified_gmt":"2018-12-28T20:15:35","slug":"timber-towers-the-future-of-tall-wood-design","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/timber-towers-the-future-of-tall-wood-design\/","title":{"rendered":"Timber towers: The future of tall wood design"},"content":{"rendered":"

by Sean McTaggart, AIA<\/strong><\/p>\n

\"All<\/a>
All images courtesy Hickok Cole and Arup<\/span><\/em><\/figcaption><\/figure>\n

Advocates for mass timber construction, a relatively new technology, boast of faster construction times, lower labor costs, and environmental benefits. However, some building professionals are still skeptical. Did we not learn our lesson from the great fires of Chicago and San Francisco? how can we afford to cut even more trees down when deforestation is a huge global problem? Despite this heated debate, wood office buildings as tall as eight stories are popping up across the United States, and architects are dreaming up timber towers as tall as 80 stories.<\/p>\n

Hickok Cole, a design firm in the nation\u2019s capital, has partnered with industry experts to carry out various pricing exercises, research grants, and client feasibility studies. Building on this experience, the firm has designed Timber Towers<\/a>, a conceptual 60-story mass timber skyscraper in Philadelphia, to showcase what is possible with wood.<\/p>\n

\"Design<\/a>
Design firm Hickok Cole designed Timber Towers, a conceptual 60-story mass timber skyscraper in Philadelphia, to showcase what is possible with wood.<\/span><\/figcaption><\/figure>\n

Inspired by the various mass timber projects demonstrating alternative means of construction at Timber City, a 2017 exhibition at the National Building Museum in Washington, D.C., a small Hickok Cole team partnered with DPR Construction and Arup to develop an apples-to-apples comparison between mass timber, concrete, and steel. The goal was to understand not only the cost premiums but also the design implications of bringing a code-compliant mass timber building to the D.C. market. Along with several pure wood and composite structure solutions, the pricing exercise concluded mass timber costs roughly $8 more per square foot than concrete, a material dominating construction in the nation\u2019s capital.<\/p>\n

With this newfound knowledge, the next logical step was for Hickok Cole and Arup to push the limit of tall wood construction, but not in a city with a 40-m (130-ft) height limit. The closest market supporting a true \u2018skyscraper\u2019 is Philadelphia that unlike Washington, D.C., has no prohibitive building height limit. The vehicle for this exploration was \u2018Timber Towers,\u2019 their submission for the Skyhive Skyscraper Challenge. The competition asks participants to rethink construction materials and technologies in a future of rapid urbanization and depleting resources.<\/p>\n

<\/p>\n

Understanding mass timber<\/strong><\/p>\n

\"Mass<\/a>
Mass timber buildings usually have exposed wood ceilings, beams, and columns, allowing occupants to be much more connected with natural elements. This can have a positive impact on their overall well-being.<\/span><\/figcaption><\/figure>\n

Before talking about tall wood buildings, it is important to first clarify some misconceptions about mass timber, particularly with regard to fire safety and building codes. David Barber, principal at Arup, explains mass timber quickly forms a protective char layer<\/a> in the event of a fire, and actually holds up longer than unprotected steel in some fire tests.\u00a0The beauty of mass timber is it can serve as a finish material while providing the required fire-resistance rating. Wood also burns much more predictably than concrete, and the required thickness (generally 19 mm [\u00be in.] for each hour of fire rating) can easily be engineered.<\/p>\n

\u2018Mass timber\u2019 should not be confused with \u2018stick-built\u2019 or \u2018light-framed\u2019 wood construction, commonly employed for single-family residential homes. Mass timber is an engineered, solid-wood system, technically falling under Type IV heavy timber construction. The current height limit for this category is 26 m (85 ft) tall, if one were to build a concrete podium with mass timber above, which likely allows for five or six stories. The 2021 International Building Code<\/em><\/a> (IBC<\/em>) will soon split this into three categories:<\/p>\n