Historically, most tall buildings have been built out of concrete, steel, and glass.
These materials are strong, widely available, and easy to work with; especially concrete which will take the shape of any mold you pour it into. Buildings have also been growing taller since the early 1900s thanks to new methods that improved the strength of steel and concrete, but this added strength and convenience has come with a cost.
Concrete and steel production are responsible for a combined 16% of global greenhouse gas emissions. Most of these emissions are released during material processing; during which raw materials must be heated to thousands of degrees Fahrenheit in order to produce steel and Portland cement (an important ingredient in concrete).
With aggressive national climate goals on the horizon, there’s plenty of opportunity for positive change in the building industry. A lot of attention has been given to energy efficiency (and rightfully so), but we also need to focus on emissions released from the production and transportation of building materials themselves. This category of emissions, called embodied carbon, accounts for 28% of total building emissions.
A Million-Year-Old Solution
Luckily, there is a material out there that can help us with this issue. The material is low cost, easy to transport, and doesn’t require multi-thousand-degree blast furnaces to produce. In fact, it even sucks in carbon and stores it during the “production” process. You’ve probably encountered this material before. It’s in your house, it’s on your street, and it has been used to build things for thousands of years.
This low-carbon material is wood.
Wood used to be the building material of choice for many cities around the world, but concerns over flammability and the emergence of new materials caused builders and architects to phase it out.
Wood is making a comeback though. Growing trees is much less energy intensive than producing steel and concrete, and wood can even have a negative carbon footprint when you consider the amount of carbon it absorbs and stores.
According to Circular Ecology’s Embodied Carbon Footprint Database, producing a kilogram of wood generates one third the emissions of the equivalent amount of steel or glass, and one half the emissions of an equivalent amount of concrete. Many timber products also actually end up being carbon negative, as they absorb more C02 when they grow than is released during processing and transportation.
But There Are Some Concerns…
It’s well established that wood has less embodied carbon than concrete and steel, but before we crown wood the building material of the future we must address some of the concerns that caused wood to fall out of mainstream building in the first place.
The biggest concern about wood is flammability. Wood is very flammable, and before concrete and steel became standard, many cities around the world were faced with catastrophic fires (notably the great Chicago fire of 1871 that killed close to 300 people and caused over $200 million in damage) that ravaged their wooden buildings, destroying homes and workplaces.
There are also concerns about stability. Yes, wood is great from an embodied carbon standpoint, but for much of history, wood hasn’t been strong enough to support buildings of more than a few stories.
Enter a new building material called mass timber.
Mass timber (short for massive timber) was developed in the heavily wooded country of Austria in the 1990’s by Gerhard Schickhofer. Schickhofer wanted to find a way to use the country’s plentiful and renewable resource to build taller buildings, so he developed a product that consisted of multiple beams of wood glued together in a crosshatch pattern.
This material, called cross laminated timber (or CLT), achieved all of Schickhofer’s goals. It also pioneered the Mass Timber industry which now consists of CLT, Nail Laminated Timber, Dowel Laminated Timber, and Glue Laminated Timber (or Glulam) among other emerging materials.
Other Mass Timber Benefits
CLT and other types of mass timber also offer many other advantages. They make the building process much faster and easier as they allow slabs and beams to be built to very specific sizes and lengths off site. According to reThink Woodopens PDF file , mass timber buildings are roughly “25% faster to construct than a similar project in concrete” and require “90% less construction traffic.”
This efficient building process along with lower material costs make mass timber structures cost competitive, and even cheaper than traditional steel and concrete construction. A comparative analysisopens PDF file conducted by WoodWorks in 2015, found that “wood offices are 20-30% less expensive per square foot than non-wood offices.”
Mass timber materials also empower architects and designers to create aesthetically appealing buildings that bring more natural elements into our artificial metropolises. The look and feel of exposed wood—and other biophilic design principals that building with wood encourages—reduces stress and improves wellbeing according to a recent studyopens PDF file by Forest and Wood Products Australia.
The major caveat here is that the wood for mass timber panels and beams that are used in construction needs to be sustainably sourced. Forest degradation and deforestation are always a threat, and if harvesting timber for CLT degrades and ruins forests, the environmental benefits may not outweigh the drawbacks.
Fortunately, this isn’t much of an issue, as most builders and architects who use CLT and other mass timber products have sustainability in mind. Mass timber manufacturers can also depend on nonprofit organizations like the Forest Stewardship Council (FSC) to independently audit forests and certify that they are being managed responsibly.
Many builders and architects are also using timber from local sources.
Despite recent progress, there are still a number of obstacles that stand in the way of mass timber becoming a more widely accepted and used building material.
Building codes that were established in the era of concrete and steel have been slow to change, as have many builders and architects who have been building with concrete and steel for their whole careers.
Availability of the material is also an issue as the large-scale processing plants needed to make mass timber a more viable option have only just begun to be built.
Nevertheless, builders, architects, and green building certification organizations are beginning to take notice and incorporate mass timber and other low-embodied-carbon materials into their certifications. A prime example of this is LEED certification.
The LEED certification program promotes the use of these materials by including “materials and resources” as one of its main credit categories. Building with mass timber can help achieve this competency through the “responsible sourcing of raw materials” credit.
Inclusion in LEED and other certification programs can go a long way towards incorporating these materials into homes and smaller office buildings.
On the skyscraper front, taller and taller mass timber buildings are continuing to pop up all over the world. The world’s tallest timber building, the 85.4-meter Mjøstårnet by Voll Arkitekter in Brumunddal, Norway, was recently completed, and is set to be surpassed by the 25 story Ascent building in Milwaukee, Wisconsin in 2022.
Mass timber products are quickly gaining popularity worldwide as builders and architects work to design and build the eco-friendly buildings of the future.
If you are interested in incorporating mass timber or other low-embodied-carbon building materials into a LEED certified or other green building project (like Passive House or ENERGY STAR), contact our high performance building team!
Learn more about the future of the high performance and green building industry at our upcoming virtual panel event!