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.
###
|
TIMECODE |
LOWER
THIRD |
1 |
1:32 |
TIM GOKHMAN NEW LAND ENTERPRISES |
2 |
1:35 |
[COURTESY] THORNTON TOMASETTI |
3 |
1:43 |
[COURTESY] THORNTON TOMASETTI |
4 |
2:25 |
[COURTESY] STRUCTURLAM |
5 |
2:33 |
[COURTESY] STRUCTURLAM |
6 |
3:23 |
DAVID CORR NORTHWESTERN UNIVERSITY |
7 |
4:23 |
KIRIN KENNEDY SIERRA CLUB |
8 |
5:23 |
[COURTESY] HOHO VIENNA/DERFRITZ |
9 |
5:26 |
[COURTESY] Mjøstårnet/Anti Hamar/Moelven |
10 |
5:29 |
[COURTESY] CARBON12/ANDREW POGUE |
11 |
5:33 |
[COURTESY] INTRO/HPA |
12 |
5:57 |
[COURTESY] USDA FOREST PRODUCTS LABORATORY |
13 |
6:05 |
TIM GOKHMAN NEW LAND ENTERPRISES |
14 |
6:09 |
[COURTESY] USDA FOREST PRODUCTS LABORATORY |
15 |
6:25 |
JASON KORB KORB + ASSOCIATES ARCHITECTS |
16 |
8:21 |
CHRIS JOHANSEN C.D. SMITH CONSTRUCTION |
17 |
8:38 |
[COURTESY] STRUCTURLAM |
18 |
8:48 |
[COURTESY] WALMART/ARTIST RENDERING |