Mass Timber High-Rise

PBS NewsHour Weekend | 9min

Postproduction Script

Megan Thompson: In downtown Milwaukee, Wisconsin, a new luxury apartment building is rising in the upscale East Town neighborhood. The project is called Ascent. And to most passing by, it probably looks like a typical high-rise construction site. Turns out, it’s anything but.

Chris Johansen: To say it's very unusual is a massive understatement. 

Megan Thompson: Tall buildings like this are usually built out of steel and concrete. But this one? It's being built mostly out of wood.

Megan Thompson: How unique is this project here in the United States? 

Tim Gokhman: Oh, it's unprecedented. From an approvals standpoint, from a fire testing standpoint, from a design and engineering standpoint, there was so much innovation in this project.

Megan Thompson: Tim Gokhman is the managing director of New Land Enterprises, the development company behind Ascent. Building it out of timber was his idea. 

Megan Thompson: Constructing with wood isn’t new.  We’ve been doing it for eons. But this uses a new technology called “massive timber” or mass timber for short. Mass timber, which is surprisingly fire resistant, has made it possible to construct wood buildings that are larger and taller than ever before. In fact, when the 25-floor Ascent building is completed next summer, it will be the tallest structure of its kind in the world.  

Megan Thompson: What made you say, ‘I want to build a high rise out of timber?’ 

Tim Gokhman: Once you go into a building that has exposed wood, you understand right away. It's beautiful and you feel great in it. ​​It is fast, it is precise, it is light, it is clean. 

Megan Thompson: The first six floors, which will house a parking garage and a pool, are built from steel and concrete. So are the elevator shaft, stairwell and foundation. But the nineteen upper floors are constructed from gigantic mass timber beams, columns and boards.  

David Corr: This is relatively new, especially in the United States. It's more common in some parts of Europe, especially Scandinavia.

Megan Thompson: David Corr is a civil engineer and director of Architectural Engineering and Design Studies at Northwestern University. He’s currently studying the structural properties of mass timber.

Megan Thompson: So when we're talking about mass timber or tall timber, what's new here?

David Corr: This would be a two by four, this would be a familiar piece of timber. If you tear down the walls of your house, you would find small pieces of wood like that behind the walls, and that's what carries all the load in your house. This is an example of mass timber, and it's important for people to understand that this is a very small part of something that would be very large. So there'd be a single layer on the bottom and then a layer of glue and then another layer, layer of glue. It's kind of like making a cake out of wood, where the glue is the frosting.

Megan Thompson: This material is called “cross laminated timber,” because each layer is glued crosswise, which makes the material stronger.

Megan Thompson: So it's kind of like plywood on steroids.

David Corr: That's exactly right. It's structural scale plywood, plywood on steroids. 

Megan Thompson: These huge slabs can carry massive loads. But, inch for inch, timber’s not quite as strong as steel and concrete, Corr says. So it’s not great for wide, open floor plans with no supporting columns. And there won’t be a wood skyscraper as tall as the Empire State Building any time soon. Mass timber was first pioneered in Austria in the nineties...and is gaining popularity in the United States.  In 2013, the U.S. had 26 mass timber buildings.  Today there are 576 built or under construction. And several hundred more are in the works.

David Corr: There's a lot of appealing attributes to mass timber. One of them is the sustainability aspect. So one of the downsides of the materials that we commonly build large scale structures with throughout the world, those being concrete and steel, is they have a lot of what's known as embodied carbon. 

Megan Thompson: Meaning, production of steel and cement is very polluting, contributing somewhere around 15% of global carbon dioxide emissions. On the other hand, trees are what’s known as a “carbon sink.” They suck in carbon dioxide and lock it in. And studies have shown, replacing steel and concrete with timber can lower a building’s global warming potential. But cutting down too many trees can contribute to global warming, and some environmental groups are wary of an increased demand for wood.

Kirin Kennedy: There's still a lot of questions and the jury is still out on whether or not it can be achieved sustainably. 

Megan Thompson: Kirin Kennedy directs People and Nature Policy for the Sierra Club. She worries that a logging boom could lead to the loss of a critical tool for fighting climate change. Because once they’re cut down, trees stop actively sucking in carbon, and lose a portion of the carbon they stored.

Kirin Kennedy: The question that we and other folks are wondering is, is there enough forested area to both be able to sustain mass building and protect our forests or, are our forests better left intact as a natural carbon sink? 

Megan Thompson: She also notes, our forests are important wildlife habitats and natural buffers against flooding and erosion. So Kennedy and some other environmentalists are hesitant to embrace mass timber just yet.

Jason Korb: This is European white spruce. So this is sustainably farmed.

Megan Thompson: Jason Korb is the architect of the Ascent building. He says the team was careful to source their wood from sustainably managed forests.

Megan Thompson: Had you ever designed a timber building before? 

Jason Korb: Never, once. So we went big. 

Megan Thompson: What was that like?

Jason Korb: I think we knew about five percent of what we needed to know when we started in March of 2018. And I liken it to going to graduate school for two years 

Megan Thompson: Part of what Korb had to figure out was how to get the City of Milwaukee to approve his plans. The tallest mass timber buildings right now are in Europe, including the very tallest, an 18-story tower in Norway. But the tallest buildings in the U.S. are between 7 and 10 stories. In part because American building codes have been slow to catch up. Architect Jason Korb spent more than two years proving his twenty-five story building would be safe. Including answering the question often on people’s minds: how will the structure hold up in a fire? The Ascent team worked with the U.S. Forest Service to do extensive fire testing, the first of their kind ever conducted. Nine wood columns were burned in a furnace for three hours straight, at temperatures reaching more than 2000 degrees. 

Tim Gokhman: So mass timber doesn't burn. It's very different from your standard two by four. It chars. 

Megan Thompson: That charring layer actually acts as insulation, protecting the rest of the wood. The Ascent columns charred, and held up. The columns were designed a few inches wider to allow for this fire-proofing layer. It was just one of many new things architect Jason Korb had to do.

Jason Korb: The amount of pre-construction work that needs to be done in a tall timber building is pretty much like nothing we've ever seen, especially in a residential building. 

Megan Thompson: That's because, in traditional construction, all the holes for things like plumbing, wiring and ductwork are drilled in the steel or formed in the concrete as the building is going up. But in timber, all of that is cut beforehand. So Korb and his team had to create a precise digital model.

Jason Korb: The building was modeled down to the last screw. Those files are then fed to the manufacturer. And they are laser drilled to a tolerance of about three millimeters. 

Megan Thompson: Korb says, at the time, it cost less to import the wood from Austria than if he bought from a North American supplier. So the 3700 precisely cut pieces have been shipped to Milwaukee, where the construction team is now putting them all together.

Chris Johansen: We're currently installing the columns from level 19 to 20...

Megan Thompson: Chris Johansen is the project manager for C.D. Smith, the construction company building Ascent.  Each enormous column is hoisted by a crane. Special glue is pumped into the hole. Then the column is carefully put into place.

Chris Johansen: There's not one column, there's not one beam, one floor panel that is interchangeable. So we have detailed plans, a lot of color coding and a lot of communication to ensure that we're installing things in the right place. 

Megan Thompson: All the wood is treated with a waterproof coating and the building’s glass facade will protect the timber structure inside, where about 50 percent of the wood will remain exposed. Any wood outside is protected by sheeting, a water-resistant sealant and insulation. Assembling the structure is comparatively quick, at least four months faster than if this was all steel and concrete. And johansen needs less labor for this part - about a quarter of the workers. He says the work is also much less strenuous and dirty.

Chris Johansen: One of the guys told me that, you know, his wife is questioning if he's going to work because he's not coming home covered in concrete. 

Megan Thompson: Fewer workers and a faster job mean big savings on construction costs. But the wood itself isn’t cheap. Architect Jason Korb estimates it’s about 10% more than what you’d pay for concrete in Milwaukee. But that price might start coming down as the supply in the U.S. grows. The Canada-based company Structurlam opened its first U.S. plant this summer in Arkansas, a few hours from Walmart's headquarters.  That's because Walmart is building its new corporate campus out of - you guessed it - mass timber.  2.4 million square feet of office space.  

Tim Gokhman: It's not just my hope but my prediction is that it's a matter of time until the United States overtakes the rest of the world in production and assembly and in the use of buildings like this.

Megan Thompson: From the avalanche of interest Tim Gokhman says he’s gotten in ascent, he could be right.  He’s already rented nearly 10% of the units.  Normally he wouldn’t have even started leasing yet.  Ascent is slated to open next July.

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