Can you build skyscrapers or other massive structures with wood? Mass timber buildings are changing skylines and changing the way engineers and architects think about building big with wood. They go up faster than steel and concrete. They cost less. They’re made from sustainable resources, and they’re getting taller and taller.

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Iain Macdonald (left) and Andre Barbosa (right) Iain Macdonald (left), director of the Tallwood Design Institute, and Andre Barbosa, assistant professor of structural engineering at Oregon State University, at the construction site for the Oregon Forest Science Complex, a mass timber building.

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[SOUND EFFECT: Pine beetle eating, used with permission under a Creative Commons License]

STEVE FRANDZEL: Can you hear that? Wait, let me turn it up. That is the sound of a mountain pine beetle larvae chomping away inside a tree. It’s no bigger than a grain of rice. Beetles just like it, untold hordes of them, have decimated vast stretches of forests in the U.S. and Canada.

[SOUND EFFECT: Construction Site, used with permission under a Creative Commons Attribution License]

Now this one’s much easier. That’s a construction site where a rare breed of building is going up: a high-rise made mostly out of wood or, more precisely, mass timber. I’m Steve Frandzel, and in this episode of Engineering Out Loud we’ll find out why there’s so much buzz about mass timber, why the number of mass timber buildings is growing, and how hungry insects created a new urgency for building with wood in North America.

[MUSIC: The Ether Bunny, by Eyes Closed Audio, used with permission under a Creative Commons Attribution License]

NARRATOR: From the College of Engineering at Oregon State University, this is Engineering Out Loud.

ANDRE BARBOSA: There’s a lot of tall buildings out of steel, there’s a lot of tall buildings out of concrete, but we can take advantage of mass timber to make our buildings lighter. Because buildings are lighter, our foundations are lighter, our foundations are cheaper, so we can actually make a cheaper building, and that’s where it’s competitive. There is experience in Europe, 25 years worth of experience of building with mass timber and cross-laminated timber, but that’s an opportunity there that we’re exploring in the U.S.

STEVE FRANDZEL: That’s Andre Barbosa, an assistant professor of structural engineering at Oregon State. He’ll be back with a couple of his colleagues to enlighten us about mass timber and why we should care. But first I think it’s a good idea to run through a crash course. Let’s call it Mass Timber 101. No quizzes, no essays, an easy A. OK.

[SOUND EFFECT: Chalk writing on board, used with permission under a Creative Commons Attribution License]

[MUSIC: Drum Solo, by Jed Irvine, used with permission of the artist]

In a mass timber building, wood replaces many of the elements that are usually made from concrete or steel. They’re really hybrid buildings where wood predominates, but they still need some concrete and steel in them. What makes mass timber possible are really big pieces of laminated wood, like cross-laminated timber, or CLT, and glue-laminated timber, or glulam. Cross-laminated timber is made by bonding together several layers of solid wood planks at right angles to each other. Think plywood on steroids. Same idea, but the outcome can be massive multi-story wall panels or 40-foot sections of flooring that are half a foot thick. The largest CLT panels in the world are 65 feet – that’s six and a half stories – tall, 20 feet wide and 20 inches thick. Each panel is transported whole to the construction site.  Glulam is more linear. It’s made from standard lumber stock – two by fours, two by sixes, four by fours – you know, that kind of thing, that are glued side by side to create beams and columns.

[SOUND EFFECT: School Bell, used with permission under a Creative Commons License]

OK, class dismissed, let’s move on. Here’s Iain Macdonald, director of the Tallwood Design Institute, a partnership between the Oregon State Colleges of Forestry and Engineering and the University of Oregon’s College of Design. The institute will soon move to its new home in the Oregon Forest Science Complex, a mass timber building, naturally, that’s under construction on the west side of the OSU campus. Among the institute’s objectives: advance the science and commerce of mass timber.

[MUSIC, Bumba Crossing, by Kevin MacLeod, used with permission under a Creative Commons Attribution License]

IAIN MACDONALD: I think CLT has become a little bit of a game changer in that it allows you to replace what used to be done with formed, reinforced concrete with wood panels, which are lighter and more able to be prefabricated, for example. Glulam beams and columns have been around for a long time, but when you put those in combination with these mass timber panels, then you have this kind of powerful Lego kit of wooden components to build from.

BARBOSA: Some of the benefits of mass timber, and using glulams, using CLT, is really that you have very good strength to weight ratio. From a structural engineering perspective, that’s one of the most exciting things. I would even dare to say that it’s better than concrete.

FRANDZEL: And the modular nature of mass timber completely changes the dynamics of the construction process itself. When CLT and glulam components arrive at the building site, workers can tilt them up or hoist them into position and fasten them into place very quickly.

MACDONALD: Typically, the panels are prefabricated in a factory and they use computer controlled equipment to cut out channels for electrical and mechanical, cut out openings for doors and windows and other things that normally would be done on the construction site.

[MUSIC: Onward, by Poddington Bear, used with permission under a Creative Commons Attribution NonCommercial License]

So when you get those prefabricated elements to the construction site, the building can go up rapidly, and you can save a lot on the construction schedule. So the building can be moved into faster, you have less need for some of the equipment that you have on site for long periods, like scaffolding, and cranes and so on. You can often install the building, install the timber elements in the building with less people. Typically, if you’re installing these buildings in large urban areas, disrupting traffic patterns and so on is a problem. Noise pollution if you’re in a residential neighborhood. So typically you have far less deliveries required, you have far less disruption to traffic patterns and noise. Jobsites are quieter.

FRANDZEL: The impact of prefabrication can be seen at the construction site of Brock Commons building in Vancouver. At 174 feet tall, the dormitory at the University of British Columbia is the tallest mass timber building in the world, though I guarantee you that title won’t last long. The building went up in just 66 days. That’s two stories a week, which is about half the time it takes to put up a traditional concrete and steel design. It could have gone up even faster.

MACDONALD: I think in North America, sometimes there’s a bit of a problem when the timber industry will put out a claim about how quickly the timber elements can go up, and follow-on trades don’t believe you.

FRANDZEL: Follow-on trades are framing crews, electricians, plumbers. That sort of thing.

MACDONALD: And I know that with the Brock Commons Building for example, the timber guys finished three months ahead of schedule, but the building as a whole only finished one month ahead of schedule, because the follow-on trades were not ready to come in in the numbers required to really take advantage of that time savings that had been acquired on the timber install, if you see what I mean.

FRANDZEL: When you get a chance, take a look at a snappy little time-lapse video of the Brock Commons construction site. There’s a link in the show notes for this episode on our website. Keep your eye on how fast the wood floors and columns are set into place, and you start to understand how mass timber buildings can go up so fast. You also get a good view of the building’s hybrid nature.

BARBOSA: The walls, all the way up and down, those are concrete. The elevator cores, the staircases, those are made out of concrete, and then the floor systems and the columns – so what we call our gravity system – that’s all made out of mass timber. That’s where I’d see opportunities. It’s a limitation because you can’t use wood all the way up, it just probably wouldn’t be feasible, but it’s also an opportunity, because you can mix different materials and take advantage of the best of both materials.  

[MUSIC: Onward, by Poddington Bear, used with permission under a Creative Commons Attribution NonCommercial License]

MACDONALD: It’s also hybrid in the sense that there’s a concrete topping on top of the timber floors, and what that does is it reduces the vibration that would be felt through the floor and it improves acoustic insulation between floors. As well, it provides some fire protection.

BARBOSA: Not fire itself, but it allows you across the floors to create a barrier for smoke.

FRANDZEL: Notice that Andre emphasized smoke, not fire. That’s because builders are very confident about fire safety in mass timber buildings. One of first questions many people ask about mass timber is What about fire? What if I’m on the tenth floor when a fire breaks out in the lobby? That’s fair to ask. Wood burns, and there’s a long and tragic history of entire cities destroyed by flames. So how could a wood building possibly be fire safe, especially a high-rise? To answer that, I’ll turn to Judith Sheine, a professor of architecture at the University of Oregon and director of design for the Tallwood Design Institute. We spoke by phone.

JUDITH SHEINE: There’s been a bunch of fire tests now in this country, in the US, that show that CLT does very well under fire, because like all heavy timber it will burn to a certain degree, what's known as a char layer, and then that protects the rest of the wood from burning. In fact, there’s wooden bridges that have been around for hundreds of years and they do often much better in fires than steel or concrete, because the steel will melt and the concrete cracks, and then the steel inside the concrete melts. But heavy timber bridges, if you just put enough wood on them to account for the char layer, it will burn up to a little bit through the surface and then will stop. So structurally it will remain intact and allow people who are in buildings or on bridges to survive.

FRANDZEL: It’s kind of like throwing a huge log onto a campfire. It turns black on the outside but it doesn’t catch very easily. Earthquakes are another concern, one that’s of particular interest to Andre, whose primary research focus is earthquake engineering.

BARBOSA: I would say we can make any building, any structural system, perform well. The advantages are, again, that you can have a lighter building. If you have a lighter building you have less forces.

FRANDZEL: In the summer of 2017, Andre and a bunch of his colleagues from several institutions gathered at the University of California in San Diego, the home of the world’s largest outdoor shake table. They built a full-size model of a two-story mass timber building on the table, then subjected the structure to the equivalent of 30 intense earthquakes. Here’s how that sounded.

[SOUND EFFECT: Shake Table Test, the University of California San Diego Earthquake Simulation Facility]

BARBOSA: The results were amazing. After a very big earthquake, we didn’t test all the systems, but we would expect that within two weeks to a month, people would be able to go back into their building, and this is after a very very major earthquake, and it’s assuming you’re water systems had some damage, because the building itself, structurally, had little to no damage. We were also excited to see that the building in general performed like we had thought it would, so our design methods made sense, and we were confident – after we did those big tests – we were confident that we can go and design other buildings now, because the tests show that our design methods were working well. It’s a self-centering system that allows the building to rock back and forth, but it centers after the earthquake, self centers after the earthquake.

FRANDZEL: Many of the findings from those tests will be incorporated into the 12-story Framework building in Portland, a mass timber structure that will start construction early in 2018.

[MUSIC: Elements – II The Rain, by Aitua, used with permission under a Creative Commons Attribution NonCommercial-Share Alike License]

So we’ve established that mass timber construction is strong, safe, and economically viable. It’s also a sustainable practice that relies on an abundant renewable resource.

MACDONALD: So a tree grows, it uses largely solar energy, you harvest it, that requires a little bit of energy, and then it goes through a sawmilling process or some kind of remanufacturing process and it gets to where you can use it in a building. If you’re talking about steel or concrete, that can be between five and 25 times as energy intensive as the wood products. The reality is that it sequesters a lot of carbon, and the embodied                                energy required to produce the materials that go in the building is significantly less than if this was a reinforced concrete building for example. 

FRANDZEL: By some estimates, making cement, the main ingredient in concrete, produces 5 percent of manmade carbon in the world, while steel accounts for another 3 to 5 percent. And wood, unlike concrete, is easily salvaged and reused at the end of a building’s life.

SHEINE: Sustainable design is increasingly important to architects all around the country. The building codes are changing to recognize it, and it’s also possible to expose it in the interior quite often, which architects like, because it looks really good. So we have reasons to use it because of sustainable principles, but we also have esthetic reasons where we think it's just appropriate and looks much better.

FRANDZEL: In 2015, representatives from the city of Springfield, Eugene’s neighbor, asked Judith if she’d lead a design studio at the University of Oregon.

[MUSIC: Kombucha Drone, by Unicorn Heads, used with permission of the artist]

The assignment was to design, of all things, a mass timber, multi-story parking deck that would become part of a multimillion dollar community revitalization on the Eugene-Springfield boundary. The idea to use wood came from Springfield’s mayor, Christine Lundberg, who thought it would showcase timber’s historical prominence in the region and possibly spur more mass timber construction.  

SHEINE: They asked me about doing this project, it sounded exciting and interesting, but we could only find one other mass timber parking garage in the world.

FRANDZEL: Which was in Sweden. The fact that wood parking decks are almost nonexistent was not a big selling point.

SHEINE: Honestly, the only person who was really convinced at the beginning that this was a great idea apparently was the mayor.

FRANDZEL: But the stunning plans that the students came up with turned the tide of opinion. In fact, the architecture firm hired to design the deck incorporated many of their ideas.

SHEINE: They essentially mushed together five of the projects. – actually called me to ask how they should credit the students, since they were using so many of the ideas that came out of the studio. So w e were actually extremely influential in the design, which is great, and for the students it was really an amazing experience.

FRANDZEL: Judith hopes the deck gets built by 2019, but it’s hard to say. In the meantime, she’s moved on to other mass timber projects.

SHEINE: I think that we're just beginning to explore really all the esthetic potential of mass timber. I mean it's been around Europe for 20, 25 years, but that's still considered a relatively new material. And it's certainly new to the U.S. One of the best and the most exciting things about mass timber as opposed to concrete and steel is that you can not only make the panels in a kind of very advanced processing way, but you can use digital files to cut them up in the factory in any way you want – to cut in doors and windows and notches and even cut them into funny shapes of all kinds. So you can actually make really interesting buildings out of them. The design possibilities are really limitless, and I think architects are really excited about that.

[MUSIC: Elements – II The Rain, by Aitua, used with permission under a Creative Commons Attribution NonCommercial-Share Alike License]

FRANDZEL: The mass timber movement also has expanded the market for less desirable lumber, as well as small, young trees.

MACDONALD: CLT actually originated as a way to use a byproduct of the sawmilling process in Europe. So the side lumber that falls off the edge of a board is usually smaller. It has some wane on it or something like that, so you end up with these small pieces. They’re not very useful for construction lumber or for the higher value grades of lumber. The Europeans were looking for a way to use this in some value-added product  , so they came up with the idea of putting it together into these larger panels. Here in the U.S., now we do have the ability, the potential, to use some small diameter timber and some less valuable, less utilized species in the middle layers of cross-laminated timber, for example, so that we can make use of what might otherwise be thrown away or chipped up for burning as biofuels or something like that.

[SOUND EFFECT: Pine beetle eating, used with permission under a Creative Commons License]

FRANDZEL: Here’s where that chomping beetle eats its way onto the scene. The catastrophic infestation – and we’re talking many millions of acres of brown, dead trees across North America, especially in the West – is linked to climate change. As winters turned milder and summers hotter, beetle populations exploded. But there is a little bright spot. It turns out that many of the trees retain commercial value if they’re cut down in time.  

[MUSIC: Cherry Blossom – Wonders, by Kevin MacLeod, used with permission under a Creative Commons Attribution License]

For a decade or so, there’s been a thriving niche market for beetle-kill pine as flooring, accent walls, and furniture, because the grain is shot through with striking veins of blues and grays that are caused by a fungus. It’s actually that fungus, released by the beetle, that kills the tree. But an oversupply of beetle-kill pine led to lower prices. And that made it very attractive as a raw material for cross-laminated timber and glulam.

BARBOSA: If you harvest a beetle-kill pine tree within three to five years, it does not lose any structural capacity. If you don’t harvest it within five years, it’s going to be in the forest and it would be potential fuel for fires, so you need to harvest it anyway. One of the big drivers for a lot of the push, first in Canada and then also in the U.S., was this idea “OK we have all this beetle-kill pine, what are we going to do about it?” And one of the processes and one of the uses was let’s add this value-added solution called cross-laminated timber.

FRANDZEL: Mass timber represents a tiny fraction of the construction market, but it’s boosted demand for products like CLT and glulam, and that’s started to inject some new life into the flagging timber industry.

BARBOSA: If we can add value-added solutions here in Oregon, here in the Northwest, value-added solutions means more jobs, it means that rural communities that typically they’ve seen the downsizing of their companies or even closure of some of their companies, they can have some livelihood again.

MACDONALD: When you build tall wood buildings, it captures people’s imagination, but also shows what is possible. We think there’s tremendous opportunity for increasing the use of wood and building more sustainably around the five to 12 story range, which might not be considered tall by some, but really that’s the majority of most buildings that are going up in cities today.

BARBOSA: It’s tall for wood.

MACDONALD: I would also say light industrial buildings and other structures, anywhere where we can use more wood in the proper context where it’s going to be safe and technically we have the means to do so, we’re replacing more energy intensive materials. That’s really the mission. I’ve seen such a tremendous buzz within the U.S. on this whole topic, and Canada has a lead right now, but in 2018, the U.S. is going to overtake Canada in the number of manufacturing facilities that are able to produce these products, and I think as we eliminate the barriers and do more research and testing, building codes are going to steadily evolve to incorporate more of these products into their core prescriptive guidelines. So I think it’s only going to snowball in the next few years.

[MUSIC: Dusty Road, by Jingle Punks, used with permission of the artist]

FRANDZEL: This episode was produced and hosted by me, Steve Frandzel, with additional audio editing by Brian Blythe. Thanks Brian. I also want to thank Larry the pine beetle who took a break from destroying our forests to join us in the recording studio. Our intro music is The Ether Bunny, by Eyes Closed Audio on SoundCloud and used with permission of a Creative Commons Attribution License. Other music and effects in this episode were also used with appropriate licenses. You can find the links on our website, as well as some great videos. For more episodes, visit, or subscribe by searching Engineering Out Loud on your favorite podcast app. Bye now.

[SOUND EFFECT: Chainsaw, used with permission under a Creative Commons License]

FRANDZEL: Larry, put that down. Put that down. Stop it! Stop it, now! Put it down, turn it off, now! Put it down, turn it off. Larry, we talked about this, weren’t you even listening? Larry?