Cross Laminated Timber: The New Frontier in Parking Construction
The State of Parking Structures in 2018
Building a parking facility is expensive. Not only the land, the permits, and the technology you have to incorporate into the facility… but also the material and construction costs. Plus, there is a huge push from many directions to be more environmentally conscious in our endeavours – things like LEED certification, Parksmart certification, and sustainability, to name a few.
So, we recognize that we need to make a change in building new parking structures. But what?
A buzzword we’ve heard a lot lately is “future-proofing”. Under this buzz-brella, a couple of the key trends the parking industry has seen for new parking facilities are:
Mixed use developments; parking, commercial, residential, or some combination under one roof
Convertibility; meaning that at the end of their parking lifespan, structures can be repurposed
So, how can we plan for the future of parking infrastructure while making it cost less, be more environmentally friendly, and evolve to meet future users’ needs?
Enter Cross Laminated Timber
Cross laminated timber (CLT; also known as mass timber) is an engineered wood product made by gluing planks together to form layers, and gluing layers together (perpendicularly) to form panels. The panels are used in construction for walls, floors, and framing, either exclusively using CLT or in conjunction with other building materials (steel, concrete, etc.)[i].
Why Use CLT?
The most common benefits of CLT are its light weight, fast construction time, environmental impact, and cost savings during construction and installation.
Weight: Mass timber materials weight significantly less than traditional building materials like concrete. Less weight means less demands on the foundation, and the ability to build tall structures as the base can support a higher volume of materials. It’s also less dense, which means it does not transmit as much noise.
Speed: CLT is a prefabricated material, so panels that meet exact sizes and specifications can be made in advance. This reduces construction time, especially since it’s produced in North America.
Environment: Mass timber is a renewable resource, in that trees used to make the panels come from sustainably managed forests which are planted and regrown. Trees are CO2 negative, and each cubic meter of wood saves 2 tonnes of emissions, resulting in a savings of 50,000 tonnes for a 40 story building[ii]. Best of all, it’s made primarily from trees infected with mountain pine beetle that would have had to be removed and destroyed[iii].
Cost: Foundation requirements are reduced significantly when CLT is used for building due to decreased weight. Labour requirements are also reduced as specialists aren’t required[iv], and construction can be completed sooner meaning the building can open and start generating revenue faster.
Can CLT Be Used for Parking Structures?
My answer (after much research and interviewing John Nairn, a Professor of Mechanical Engineering at Oregon State University, and an avid researcher of CLT[v]) is a definite yes… with some considerations.
The first thing to think about is climate. Wood components of CLT are ideally dried to within 1-3% moisture, and then remain at the same moisture content. That being said, rainy climates like Vancouver and Seattle are some of the most prominent (North American) pioneers when it comes to building projects using mass timber. Issues occur when there is a change in the environment – the resulting residual shrinkage and expansion causes problems, not any given environment itself.
The second thing to think about is maintaining a consistent temperature. Cross laminated timber cracks the least when it’s kept at a relatively consistent temperature. So, if you’re in a climate (like I am here in Calgary) that varies drastically between seasons, it would be prudent to keep the material temperature controlled.
The third consideration is the quality of the CLT panels. A CLT panel with thinner but more layers is better resistant to fire, cracking, can handle more weight, and is generally better prepared to handle other issues. However, these quality concerns often come at a higher price, and it may also be more difficult to find a production facility willing to accommodate.
In addition to ongoing monitoring and a thorough preventative maintenance plan, the following challenges also need to be addressed before they develop further.
Cracking: This isn’t necessarily a problem. Panels can lose up to 50% of their strength and weight bearing ability once cracked, but if you build to only ever use the panels up to 50% of their rated capacity, you won’t have an issue with cracks. A durability analysis is a good step to figuring out the rate at which cracks are likely to occur[vi], and planning occupancy and use around the results will mitigate any issues.
Consistent temperature: If you live in a moderate climate, you’re set. If you don’t, consider using mass timber inside a structure – for walls, floors, and ceilings. In parking, a heated or temperature controlled garage is an ideal use case. Mass timber products works great in conjunction with other materials. So, you could build a concrete foundation and exterior walls, and use CLT for the elevator shafts, stairwells, ceilings, and other indoor components.
Here are some examples from Canada and the US of successful construction projects.
Wayne Gretzky Sports Centre: Located in Brantford, ON, this project used CLT in expansion of the pre-existing facility for ceilings, outdoor shelters, indoor panels, design elements[vii].
Albina Yard: A four-story office building in Portland, Oregon, which was the first U.S. building to use a domestically made CLT structural system[viii].
Riverfront Square: 2 million square feet of offices, 2000 residential units, a hotel, public space and cultural facilities comprise the 3-building project[ix].
More research is definitely on the agenda. Organizations such as the Softwood Lumber Board, United States Department of Agriculture, and Natural Resources Canada are supporting considerable research around the use of CLT and other mass timber systems[x]. Things like lifespan, load bearing, and durability all need to be carefully researched and conditions for proper use documented.
Expanded mass timber production is also on the horizon. New production facilities are opening on a monthly basis around North America, especially in the Eastern US. They produce CLT for projects across North America and are supplying materials to all sorts of projects across Canada and the US[xi].
Urban design is constantly evolving, and aesthetics are a current focal point. CLT can be left visible in building interiors, offering what’s currently a desirable visual element. Components like exposed wall sections, open concept mass timber stairs, and mass timber ceilings with beams and other details can increase the value of buildings and potential to convert into mixed use dwellings.
Overall, cross laminated timber is a promising new application of wood as a safe and efficient building material – for residential, commercial, recreational, and parking buildings. It lowers the cost of the project, speeds up construction time, and is environmentally friendly.
You can dip your toes and experiment with mass timber by combining it with other building materials to get the best of both worlds. For example, you could use composite timber floors and ceilings with a concrete foundation system; or structural steel frames with timber for stairwells and elevator shafts. Or, you can add in concrete or steel joints or other components as needed to a primarily CLT project.
By incorporating mass timber in this way, we meet a lot of needs in parking: we stay relevant and innovative for our customers; we meet environmental regulations; and we implement new overhead cost reduction options. When it comes down to it, who wouldn’t like to be on the forefront of bringing these benefits to the parking industry?
[ii] CORE: https://core.ac.uk/download/pdf/82228698.pdf
[v] Personal interview with John Nairn, Professor of Mechanical Engineering and Chair in Wood Science & Engineering at Oregon State University; he can be reached here: http://www.cof.orst.edu/cof/wse/faculty/Nairn/
[xi] List of Structurlam projects: http://www.structurlam.com/portfolio/all-projects/