Are Cities Ready for Renewable Skyscrapers?

Every so often a product comes along that presents itself as a “sustainable” innovation, yet has compelling appeal even if sustainability isn’t someone’s top priority. Of course, sustainability has become something of an overused buzzword, but it generally refers to a production process that doesn’t deplete natural resources or damage the environment.

So called “mass timber” is an example of such an innovation. Able to replace reinforced concrete as a building material, it is economically competitive and aesthetically superior. It is perhaps the most profound innovation in building materials since the invention of reinforced concrete over 150 years ago – and it has the power to transform urban development.

By every measure of sustainability, mass timber beats concrete. As a forest product, it is genuinely renewable. Since smaller trees can be used for mass timber than for conventional lumber, more comprehensive forest thinning and fire prevention operations are commercially viable and larger trees can remain untouched.

For those who prioritize these variables, it is also an excellent way to permanently sequester carbon. Manufacturing concrete, by contrast, is a far more energy intensive process, and each year utilizes millions of tons of sand which is – surprisingly – a dwindling and non-renewable resource.

Laminated veneer, commonly known as plywood, has been around for decades. Mass timber (also referred to by the more descriptive term “cross laminated timber”) is where strips of wood are pressed together into large beams and panels, with each layer of grain running perpendicular to the layer above and below it. It has only been around since the 1990s.

The products available today are amazing: structural pillars with cross sections 60 inches on a side; lateral beams; floor panels eight inches thick, 10 feet wide, and 40 feet long.

The specifications defining cross-laminated timber should silence the skeptics. They weigh about one-fifth as much as similar sized structural materials made of reinforced concrete, while offering the same strength. They are not combustible. In hot structure fires, only the outer skin of the beams are charred. They are aesthetically pleasing and, unlike concrete, do not require surface treatments to soften their appearance.

This characteristic allows, for example, the floor panel in a high-rise unit to constitute the ceiling panel for the unit underneath. They have better thermal characteristics than concrete, meaning less additional insulation is required. And they can be manufactured to precise sizes and delivered ready for assembly, a tremendous time saver.

The construction industry changes slowly, but after a slow start, the use of mass timber is taking off around the world. Last July, what is currently the tallest mass-timber tower in the world opened in Milwaukee, Wis. Technically speaking, this is a “hybrid” building, with reinforced concrete used for the first six floors, plus for the staircases and elevator shafts. But at 25 stories, most of the superstructure of this building makes exclusive use of wood.

Tim Gokhman, the managing director of New Land Enterprises, the development company behind the Milwaukee tower, explained the appeal of mass timber: “There’s a reason it’s taking off. It’s lighter and faster and more precise and takes a smaller labor force to install. It can be economically equivalent and in some areas better, and it is a way more beautiful product and it is sustainable. It is in many cases a superior technology which is why it’s going to be transformational.”

Milwaukee’s mass-timber tower will not hold the world record for long. Taking shape over the skyline in Sydney is a 40-story hybrid timber building that will become the new headquarters of the Australian software company Atlassian. The building is a designed to be a showcase of sustainable technologies, with natural ventilation, large planted terraces, a photovoltaic skin and a veritable forest of vegetation on the roof.

While expensive statements such as the development in Sydney may offer valuable visibility to the phenomenon, mass timber has experienced hockey stick growth because it offers an economic advantage to builders. The renewable nature of mass timber gives it additional appeal.

You can’t research the product without having to wade through endless computations of how much carbon mass timber will sequester, or horror stories about the amount of carbon emissions caused by the manufacture of concrete. But is mass timber renewable at scale? Could it replace reinforced concrete? The short answer is yes.

In the United States in 2020, about 370 million cubic yards of concrete were produced. About 40 percent of that went for commercial real estate construction. If we assume half of that can be replaced by mass timber, that would mean our forests would need to replace 74 million cubic yards of concrete, which equates to 24 billion board feet of timber. That sounds like a lot, but compared to the annual timber harvest in the United States, it’s not.

According to the U.S. Forest Service, there are 12 trillion board feet of timber volume in the United States and about 186 billion board feet were harvested in 2018. That is, the U.S. timber harvest each year represents about 2 percent of the U.S. timber by volume. In the United States, forest growth has outpaced harvesting for many decades. For mass timber to replace half the concrete used in commercial construction, the nation’s forest harvest would only have to increase by 13 percent.

Increasing the timber harvest would certainly make sense in California, where the timber industry has been reduced from annual harvests of up to 6 billion board feet as recently as the 1990s to only 1.5 billion board feet in recent years. The result has been overcrowding, with dense stands of unhealthy trees. In dry years, these trees drink up most of California’s precipitation before it can percolate or runoff, exacerbating the state’s water shortage.

And the main reason for catastrophic forest fires in California is the combination of fire suppression, unreasonable restrictions on controlled burns or mechanical thinning, combined with the near destruction of the timber industry. So mass timber offers a public safety advantage, too.

Despite some official resistance to increasing the harvest and manufacture of mass timber in state, these products are catching on as a building material. Last month, California building codes were updated to allow for construction of mass timber buildings up to 18 stories tall. Mid-rise buildings using mass timber are opening or under construction in Los AngelesSan JoseSan FranciscoSacramento and elsewhere across California.

It’s not always easy to know which technologies will gain the imprimatur of today’s green clerisy, as even advanced hybrid vehicles that provide versatility and economy are on the outs as environmentalists promote purely electric vehicles. But advancements in mass timber should tick everyone’s boxes – and it might soon transform our cities’ skylines.

This article was originally published by the Pacific Research Institute.

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