More Green Building News
It’s only been a year since the City of Milwaukee officially unveiled the Ascent, the 25-story high-rise apartment building that earned the distinction of world’s tallest mass timber building, comprising a composite of cross-laminated timber (CLT) and glulam. It was also certified by the Council on Tall Buildings and Urban Habitat (CTUBH), in July 2022, as the world’s tallest timber-concrete hybrid building, owing to the Ascent’s six-story concrete podium. But who’s counting?
It turns out, everyone. And when it comes to employing mass timber materials for luxury high-rises in one global city after the next, developers aren’t just fixated on one-upping one another, but themselves too. When Milwaukee city officials approved plans for the Ascent, in 2018, the building was slated to be 21 stories. Upon opening, at 25, it surpassed the previous record holder, the 18-story, mixed-use Mjøstårnet, in Brumunddal, Norway.
Today, The Neutral Project, a sustainability-focused real estate developer with offices in Madison and Milwaukee, is building The Edison, a 32-story luxury apartment building that—you guessed it—will become the world’s tallest mass timber structure. (In January 2022, the Edison was planned for 15 stories, with a three-story concrete base and 12 floors of mass timber; as of last February, plans indicated 28 stories, with an unspecified breakdown of concrete vs. timber.) Not to make too fine a point, but assuming the Edison remains steady at 32 stories, it will soon be eclipsed, in 2026, by Atlassian Central in Sydney, Australia, a mass timber high-rise that’s planned to be 42 stories and 599 feet tall. (It was 39 stories just a few months ago.)
What’s it really mean—broad scope?
For better or for worse, mass timber’s race to the sky isn’t ending any time soon. If anything, the intervals between world record holders in this building category are growing shorter and, consequently, directing the public’s attention away from what really matters, which is the environmental impacts and broader significance of using mass timber to build high-rises in urban centers.
When the Ascent got certified, Daniel Safarik, CTBUH’s director of research and thought leadership, stated publicly that the building “is helping advance the conversation about how we build more sustainable and healthy cities, especially in the face of mass urbanization and the increasing effects of climate change.” Although well intended, this is a questionable assertion.
The benefits of building with mass timber are well documented, chief among them being long-term carbon sequestration. But success in this arena is contingent on several factors, namely, responsible forest management. If the pine forestlands of the U.S.—those that are prime regional sources for lumber used for structural timber materials—are not responsibly maintained, then harvesting all that lumber becomes a zero-sum game. At that point, even if that virgin lumber eventually becomes a building, clear-cutting entire hectares of young conifers hardly constitutes an offset for another building made of steel and concrete that emits several thousand metric tons of CO2. And to the mass timber evangelists who are fond of proffering how a timber building is the carbon inverse of a concrete one, your math is funky.
As for Safarik’s take on building “more sustainable and healthy cities,” he’s definitely onto something. But are buildings like the Ascent and the Edison part of that solution? It’s doubtful.
According to Patrick Doss-Smith, a structural technician with design and engineering firm HGA, “Of course we need more density in our cities. But in terms of scale, how do you justify the sustainability [of these projects] with the knowledge we currently have about our limited resources and constrictions in the market?” Doss-Smith adds, “At that height, you lose all your benefits from fire codes because the actual timber has to be covered up. So, you lose that lifecycle analysis benefit.”
Height matters (and other considerations)
To be fair, the Edison has some sustainability bona fides worth celebrating. The building’s HVAC design features a high-efficiency variable refrigerant flow (VRF) system, an energy recovery ventilator, and a mix of low- and no-VOC finishings. A representative from the Neutral Project confirmed that they “plan on meeting all criteria necessary to achieve Passive House Certification.” Taken as a whole, that’s not nothing. Whether the building itself is contributing to greater density and sustainable urbanization, the fact that it’s a luxury residential property going up in Milwaukee’s already commercially and culturally thriving Deer District makes the whole thing feel much less impactful.
“Taller isn’t better. It certainly doesn’t make the project more sustainable from a material standpoint,” says Jacob Mans, associate professor of architecture at the University of Minnesota and founding partner of Decentralized Design Lab. “If we as architects aren’t digging into the ecology of the things we’re building and looking at the details of those details, then we’re avoiding the important questions—the ones that are more difficult to answer than what can be measured with a ruler.”
Mans’s research focuses on the manufacturing processes and practical applications of mass timber, among other things. He’s a staunch advocate for using the technology to build smaller and at scales other than straight up. He also believes that the design community, despite excelling time and again at the height question, has been very slow to innovate when it comes understanding the ecological impacts and long-term carbon performance of the things getting built. To get to that point, Mans makes the case for including forestry and land management experts in integrated design teams to complement the usual makeup of architects, GC’s, MEP engineers, structural engineers, and other subconsultants. “It’s great to be sequestering carbon long term in these tall wood buildings,” he says. “But these forest ecosystems and habitats, and the communities that live in them, that’s a huge part of carbon sequestration as well.”
The engineered timber industry has done nothing but innovate within the last decade. Building heights have grown exponentially not because of some endemic desire to stroke one’s ego, or at least not solely because of that. It’s occurred due to continued advancements in seismic resistance, fire suppression, and structural integrity. But to Mans’s point, technological advancements in mass timber have not occurred in tandem with like-minded advancements in forest management practices. If the former continues to move forward without the latter, then we can pretty much do away with all our eco-conscious arithmetic about mass timber construction constituting one big carbon sink.
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Justin R. Wolf is a Maine-based writer who covers green building trends and energy policy.
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14 Comments
I'm a bit perplexed by what this article is trying to convey. It asserts there is an issue with the height of mass timber buildings increasing, but the reason for this issue is not made clear. Interspered with the discussion of height and building use (luxury apartments) is the notion that we must improve forest management practices. These may all be great points with enough context, but I'm confused if there is some sort of implied connection between the height of the building and forest management? What is 'building ecology' and why is more building height bad for it? Why does covering wood undo the life cycle analysis benefit?
I'm sure much of this is apparent with a certain baseline of assumptions, but I'm not sure what those are.
Point taken. If things got a little convoluted between the lines, well, that's on me. Here's my attempt to clarify some things.
Mass timber construction continues to grow in popularity, evidenced by all the high rises, and the architects and developers behind it love touting its sustainability bona fides. But to date, there isn't *enough* of a correlation between advances in mass timber construction and forest management practices. We've just become content with wood = good. But it's not that simple.
Building heights are an issue for several reasons: these buildings are not contributing to greater density or sustainable development in any meaningful way; they're indicative of a construction practice that's convinced itself it's more sustainable than the alternative regardless of context/use/sourcing; and at a certain heights mass timber buildings require cladding systems (glass and metal), which can compromise mass timber's fire resistance appeal.
I'm a fan of mass timber, but we shouldn't just focus on the end product of this tech. We shouldn't delude ourselves that it's sustainable just because these things are made from wood. The whole point of it should be in support of circular economies and sustainable forestry practices, and sustainable/smart urban growth. The obsession over height is a big distraction and a poor use of an otherwise innovative use of bio-based building materials.
Again, if all those points and more didn't come together properly in the article, that's on me. I appreciate your comment.
Thanks for the additional summary-- that does help to bring things together for me.
"We shouldn't delude ourselves that it's sustainable just because these things are made from wood." Dead on. Andrew Waugh who knows more about wood buildings than anyone on earth, notes in Dezeen:
Waugh is skeptical of the growing trend for timber high-rises and proposals to build tall skyscrapers out of wood, questioning whether they make best use of the material.
"Architecture practices all over the world are coming out with these CGIs of supertall buildings, coloured in brown with an arrow that says timber," he said.
"It's bullshit, because if you're going to build a tall building in timber, you still have to fill it full of concrete to make sure it doesn't wave around."
I think the technology shows enormous potential, and may well turn out to be an integral part of how we should build in the future, but the mass timber advocates are on a giddy high, and if they keep going in the same direction something bad is almost inevitably to happen.
The push for height, as though that somehow validates mass timber as an approach, and architect's increasing desire to express the large timbers by placing them on the exterior where they are vulnerable to the elements, are both bad ideas. There is a real Tower of Babel feel to a lot of the renderings I see coming off the drawing boards of architect's offices right now.
Are we better off just building significantly more energy efficient buildings out of concrete?
I can see how nothing should be seen as a panacea, but it seems like something that is marginally better is still better than something that is marginally worse. Taking new growth tree farms and converting them into long lived structures (thereby locking the carbon up for the near term at least) seems like a net positive.
Its a tough proposition. Even if most of the benefit is just that it gives rich people who fancy themselves climate conscious a place to live, if we assume that they're going to live SOMEWHERE, why not in a mass timber highrise?
thedman07,
My fear is proponents will push the limits of the technology until there is a failure, which will set things back for a long time.
Architects seem to forget that with good design, form should follow function. Function is about more than just tasks and traffic flow; if a material is at high risk of failure when exposed, but safe and effective when covered, then no matter how pretty it is, maybe it should be covered.
Mass timber/CLT/Glulam are not without issues. I had some glulam beams installed for my roof support and experienced checking that caused a potential structural issues. This is supposedly not uncommon with laminated lumber. Moisture content in the wood, storage, transportation, weather elements, heat, sun, rain, during construction, all play roles in how the laminated lumber reacts. Wood dries, swells, expands, contracts, during the install and construction process and mass timber can split and even de-laminate. Especially if it gets wet a lot and dries out during construction. I've seen mass timber de-laminate as the beam got wet and then froze during construction and the glue failed.
While it has its place, mass timber is not the panacea for high rise structures. If a fire sprinkler valve opens (which happens a lot in high rises), the amount of water damage on a wood structure is great. While concrete really doesn't care if it gets wet, wood is different.
We all know money talks and the timber industry is pushing buildings like this. As that means more profits for the timber industry.
Great to see the clarification of intent of the article: There's not a perfect answer, but mass timber shouldn't be discounted (and these are elements to consider)
To some of the comments:
Wholeheartedly agree that the rush to be the tallest mass timber building will lead to unintended consequences. Fire sealing (penetrations) methods probably need more testing, but impressive fire tests out of Canada for general structural impacts should address some general concerns about survivability. CLT up through 10-12 stories has now had enough "proof of concept to reach mainstream. Sustainably harvested timber is critical to the sustainability/carbon impact consideration; but pointing to poor timber practices as the norm is a poor argument. Mass timber can use fire recovery and insect-kill lumber (something we can expect to increase); If ANY product can be installed on the site unleashing less hydrocarbon than other construction materials, it's a win: but in 20 years there will be a replacement tree (especially in the case of dead/dying/forest health removal), while in 20 years, the hole in the ground won't magically refill with sand (critical shortage), iron ore, etc. CLT can be so stiff that engineers have to build in flexibility into even mid-rise structures for seismic; not all mass timber needs a concrete core.
oregonbed,
One thing we haven't touched on it the whole aesthetic of mass time structures. I find some of them very beautiful.
Thanks for the terrific article. And agreed about the architectural side rushing to champion something it knows little about. As someone who switched from architecture to weatherization, I have some experience with this. Firms focusing on LEED credits for bike racks, recycled carpeting and LED lighting, rather than orienting buildings for passive heating and lighting. Or covering buildings with three-pane, low E, argon/krypton filled windows rather than focusing on the fundamentals of air leakage, insulation and smart window placement. Not that wood structures or other energy-saving items are bad, but you can’t cherry pick items just to make your designs sexy . . . it all has to work together as a system.
shtrum2,
Bang on.
This was a bizarre sentence to read in this forum, "And to the mass timber evangelists who are fond of proffering how a timber building is the carbon inverse of a concrete one, your math is funky." As they say on Wikipedia, [citation needed].
The clarification in the comments is helpful, I suppose, but the article should stand on its own.
If the point is to bring to the discussion of highrises the recent controversies on the upfront carbon impact of wood harvesting practices, then actually do that in the article. With links. Ideally, that means using high and low estimates to show the credible range of upfront carbon impacts that could result from this project. Then compare them to a similar building constructed without mass timber. Or renovation of whatever structure was previously occupying the location (or a nearby location).
If doing that analysis is not available, then commission it. Or at least tell us why it isn't available. Turn the piece from FUD into a call for improved modeling, or whatever is needed that would actually advance the discussion.
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