﻿The birth of skyscrapers in the 1880s was a defining moment in the history of architecture,
engineering and construction. High rises grew in popularity because of mass migration to urban
areas. Urban city centers are appealing to live in because of accessibility to transportation,
restaurants and shops. Although skyscrapers were first used as office spaces,
they have become a popular housing option. High rises can increase the density of cities
by providing more housing in a given area. They can also define a city’s skyline and become the
nucleus of an entire tourism industry. What I find even more exciting than the
appearance of skyscrapers is the engineering behind it. These buildings allow humans to
push the limits of materials. Buildings that were impossible just a few decades ago, no longer are.
The term “skyscraper” is used pretty loosely, but it technically defines a structure
that is over 492ft or 150m tall. At least 50% of its height must be habitable.
Every high rise and skyscraper around the world is built with concrete and steel;
two of the most versatile and valuable building materials. However, they are energy intensive
materials with massive carbon footprints. They can also make the interiors feel cold,
harsh and uninviting. In the search for more environmentally friendly skyscrapers, designers
have turned to good old-fashioned wood. The Stadthaus in London, which was built in 2009,
was one of the first high rises made of wood. It has 9 storeys and stands 99ft or 30m tall.
Brock Commons in Canada, which was built in 2017, broke records as the
tallest contemporary wood building. It has 18 storeys and stands 190ft or 58m tall.
Mjostarnet in Norway, which was built in 2019, is now the tallest timber building in the world.
It has 18 storeys and stands 280ft or 85m tall. As the timber skyscraper momentum grows,
we’re starting to see some outlandish proposals including a mixed use tower in Tokyo, Japan
that will contain retail, office, hotel and residential facilities.
Another unconventional proposal is the Oakwood Timber Tower in London.
This lightweight tower will have 80 storeys and stand 985ft or 300m tall.
The invention and mass production of steel and concrete made skyscrapers possible in the 1800s.
They worked together to hold tall buildings upright and battle strong winds. Similarly,
a very important human invention makes all these wood high rises and skyscrapers now possible:
mass timber or engineered wood. Traditional lumber is strong against forces parallel to the wood's
fiber growth but it is vulnerable to perpendicular forces. Wood also lacks steel’s tensile strength,
which is the ability to withstand pulling or tensile forces. Wood also lack’s concrete’s
compressive strength which is the ability to withstand compression or pushing forces.
To improve the properties of wood and make it even stronger than steel and concrete,
moisture resistant glues are added in between layers of wood to make engineered
mass timber products. Some examples are: Glulam or glued laminated timber which
consists of several layers of wood with the grain running in one direction.
Cross laminated timber or CLT consists of layers of wood in alternating directions.
Laminated veneer lumber or LVL consists of thin layers of wood
all stacked in the same direction. So, we have a basic understanding of
how wood high-rises and possible wood skyscrapers work but are they
really better than traditional steel and concrete construction? Are they going to save the planet
Help cool the planet. Transform construction.
Be a solution to climate change. Be the future of flat-pack cities.
If you’ve watched any of my previous videos, you already know the answer to those questions.
I wish I had a dollar for every time I’ve been told that a new product or technology is the
LEGO of construction. Let’s take a critical look at wood skyscraper construction and examine its
advantages and disadvantages. Mass timber structural members ilke
floor slabs and columns can be cheaper than steel and concrete, particularly in
volatile markets, like we’re experiencing right now. The lower weight of mass timber
also reduces the cost of other structural members and foundations. For example,
during the construction of a mass timber project called The Ascent, in Milwaukee, 100 support piles
had to be driven into the soil rather than 200 for a similar heavy concrete and steel building.
Even though we’re in the early stages of mass timber construction, structural engineers say
that mass timber projects are approximately 25% faster to construct than similar concrete and
steel projects. The Ascent tower, which we discussed, was built 4 months faster
than expected. I’m not sold on the increased speed of construction, because prefabricated
modular steel and concrete skyscrapers can be constructed in a matter of days.
Contrary to what many people think, sustainably harvested wood can be much more environmentally
friendly than concrete or steel. The manufacturing of mass timber produces much less carbon than
other materials and can sometimes be carbon neutral or carbon negative. During photosynthesis,
plants and trees take in carbon dioxide and give out oxygen. That carbon is locked into the
tree so long as it doesn't rot or burn. This can reduce the overall carbon footprint of buildings.
Wood for Good, a campaign by the timber industry, claims that producing a ton of bricks requires
four times the amount of energy as a ton of softwood, while concrete requires five times,
steel 24 times, and aluminum 126 times. It’s important to note that trees to make
mass timber are selectively cut rather than clear cut. New saplings are also planted for every tree
that’s cut down. Mass timber construction does not equate to deforestation. Be wary of misinformation
on wood harvesting and wood construction. Another surprising advantage of mass timber is its
superior fire resistance compared to steel. Wood will char on the outside, sealing the interior and
protecting it from damage. Charred wood can also retain 85-90% of its structural integrity.
Of course, mass timber isn’t a miracle material. It has some disadvantages that prevent its wide
adoption. Concrete and steel are able to withstand acids, alkalis and other corrosive substances
better than mass timber. Foundations, structural cores and piers are still made of concrete.
This sort of mass timber hybrid construction isn’t a bad thing. By merging these materials, we can
get the best of both worlds; stability and a lower carbon footprint. The decks on the upper floors of
the Mjorstarnet are made of concrete to stabilize the building and keep it from swaying.
Restrictive code requirements are another disadvantage. These wooden structures used to be
limited to 85 feet or 9 storeys, but you can now build up to 270 feet or 18 storeys. Unfortunately,
the International Building Code says that taller mass timber buildings must conceal all the timber
members because of fire safety concerns. There’s also a significant psychological barrier
to overcome. Investors may see mass timber high rises as a risky investment. The general
public might see them as flimsy buildings, prone to fires, earthquake damage and more.
Finally, we cannot be sure that the trees used for mass timber are sustainably harvested,
especially in countries that have looser restrictions on tree cutting.
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In conclusion, I am very excited about mass timber inventions
and hybrid timber explorations. We are witnessing the early stages of brand new building materials.
Mass timber will continue to improve and we will be able to push the limits of buildings yet again.
Of course, the material itself will not make high rises and skyscrapers magically energy
efficient and they will not be the LEGO of building, whatever the heck that means.
We need good design and planning to prevent these mass timber structures
from being energy guzzlers. Let me know what you think about mass timber in the comments below.
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