May. 14, 2020 by Gary Pitts, AIA, DLR Group

An Introduction to Mass Timber

Can a construction material used for thousands of years be reborn to rival current modern construction methodologies? Is it possible to have both a safe and environmentally friendly building product that is truly sustainable and long-lasting? Is there a domestically produced framing material that can eliminate tariffs and reduce lead times?

The answer to all of these questions is a resounding YES. It’s mass timber, and it’s an important topic for The Real Estate Council and Dallas community.

Several of our members are pursuing mass timber projects and would like to build taller/larger mass timber structures in their developments. To that end, TREC has connected with WoodWorks and the American Wood Council and will soon be meeting with the City of Dallas and North Central Texas Council of Governments (NCTCOG) to advocate for early ratification of the 2021 IBC pursuant to those new mass timber allowances.

First, a quick look at how the use of mass timber has grown in popularity:

  • In the 1970s, European and Canadian architects and researchers began to experiment with glue-laminated floor panels. The first legitimate breakthroughs occurred in the 1990s at the Federal Institute of Technology at Lausanne, Switzerland. These flooring panels were simple wood 2x material “cross-laminated” to specific thicknesses and lengths to support typical floor loads with spans up to 30 feet in length.
  • Fast forward to 2015, when British Columbia published local code amendments allowing 12 stories of mass timber (twice their current height limit) and increased that limit to 18 stories later that year when research was provided to allow more lenient code proposals. These efforts are also mirrored by the recent International Code Council’s 2021 Code Proposals (for adoption by the International Building Code [IBC]) allowing for up to 18 stories/270 feet, 972,000 square feet (54,000 square feet per floor average).
  • In the U.S., several states and municipalities have already ratified these 2021 codes by writing their own code amendments based on the ICC Code Proposals. The list includes Oregon, Washington, the City and County of Denver, Colorado; and the City of Milwaukee, Wisconsin (which has increased the allowable height to 23 stories).

Mass Timber: Frequently Asked Questions

Q: How can cutting down more trees be good for the environment?
A: Two major barriers to mass timber use in North America are bark beetle infestations and the risk of forest fires. Bark beetles kill thousands of acres of trees each year, and these infestations increase dramatically due to rising temperatures from global warming. Clearing the forest floor and thinning out existing trees would reduce bark beetle travel from tree to tree. Adding firebreaks to areas of our forests where there is a lack of combustible material would slow or stop the spread of brushfire or wildfire. The mass timber revolution has actually reduced carbon in two ways. First, by improving our growing forest lands, and secondly by harvesting trees for construction as this sequesters the carbon within the buildings that they produce. If trees die in the forest, by fire or disease, all of the carbon they have taken in throughout their lives is released back into the atmosphere. Therefore, the most efficient way to improve the environment is to continue to grow and maintain our forests while harvesting a small percentage of trees for construction to sequester the carbon they capture.

Q: Doesn’t it take 50 years to grow a tree large enough to make it worth harvesting?
A: Trees that are harvested for mass timber construction are in the 8-inch to 9-inch diameter range and grow very quickly, making their stock more accessible. Forestation managers plant 2.5 trees for every mass timber tree harvested. Older trees are actually too large for the equipment used, so they are not considered for harvesting.

Q: Even if managing the forests is helpful, all the energy required to harvest the trees – cutting the lumber, producing the engineered mass timber, and transporting it to the construction site – must be very costly.
A: We call this energy that is necessary to produce a building material and transporting it to the construction site, as its “embodied energy.” Mass timber actually has the lowest embodied energy among the three construction framing materials in use today:

  • Engineered Wood (mass timber) embodied energy value: 78
  • Concrete embodied energy value: 380
  • Steel embodied energy value: 513

Q: Understanding that wood burns, does mass timber require fire-proofing or is there a special type of fire sprinkler system that has to be installed to keep the timber building standing?
A: No, mass timber has its own fire proofing, of sorts. When wood is exposed to fire, it chars, and if the thickness of the material is sufficient the char acts as an oxygen barrier, not allowing the flame to get past the char. It is this simple and natural process that allows mass timber products of the specified thicknesses to pass stringent fire testing, which ultimately earns the U.L. Ratings necessary to be considered for a construction framing material.

Q: Are mass timber products long-lasting?  Are they affected by moisture-related decay?
A: Yes, if installed within a well-detailed building to minimize water intrusion, wood can last centuries. In fact, there is an ancient wood pagoda in Japan that has endured for 1,400 years. But if there is a roof leak that goes unnoticed for an extended period of time and a column or beam is affected, they can easily be replaced with other mass timber components.

Q: How do the construction costs and schedule durations of a mass timber building compare to similar buildings of concrete and/or steel?
A: Mass timber buildings can be equal to or less than the costs for concrete and steel buildings, depending on their size and location. A taller mass timber building typically has a much shorter construction duration which can be very significant to the bottom line. That is because the entire mass timber frame is prefabricated, and with just-in-time delivery a small crew can quickly erect the components. For example, in 2018 the University of British Columbia in Vancouver built an 18-story dormitory building with mass timber. That frame was erected in 66 days with no more than nine crew members, including the truck driver and crane operator. Another factor to consider is the project’s location. Texas has a vast forest of South Yellow Pine trees that extends from East Texas to the Atlantic that is perfectly suitable for mass timber construction.

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