A global model of mass timber construction, Limberlost Place is a 10-storey, tall wood, net-zero carbon emission building that will soon be a part of George Brown College’s Waterfront campus in downtown Toronto, Ontario. From custom engineering to intricate mass timber installations, constructing a building of this caliber required PCL to put years of experience in the mass timber construction industry to work.
Hear from three PCL subject matter experts, Lori O’Malley, Mike Buckley and Stephen Montgomery, as they share insights into Limberlost Place’s innovative construction process and how it is pioneering the future of mass timber construction in Ontario and beyond.
With more than 25 years of experience in the industry, including 15 at PCL, Lori O’Malley is PCL’s in-house building envelope expert. Lori has contributed her building envelope knowledge to projects around the globe, providing technical support and mitigating risk throughout all phases of construction.
Involved from the preconstruction phase and throughout construction, O’Malley focuses on identifying potential constructability, continuity, material compatibility and adhesion issues with Limberlost Place’s building envelope to determine solutions before these problems have the chance to arise. She has worked alongside the day-to-day project management team to provide drawing, submittal and plan reviews to ensure that best practices are being used and envelope details unique to mass timber construction are being considered. O’Malley also helped the site team throughout the construction and performed regular site reviews.
A: All building projects want to install their building envelope as soon as possible to achieve a water-tight stable environment and commence the installation of materials and systems within the building. However, on mass timber projects, there also is the need to expedite this installation to minimize the exposure of the wood structure to exterior precipitation to reduce the potential for deterioration and staining. This requires selecting and using building envelope systems that can reduce this exposure time, and it requires developing a moisture management plan specific to each project to mitigate risks to the mass timber.
A: Timber requires a unique moisture management approach because timber’s moisture content is affected by the presence of water and the relative humidity and temperature of the air. Too much moisture can result in deterioration and staining of the wood. Too little moisture or too fast of drying can result in checking or cracking of the timber. Therefore, a moisture management plan is required to help mitigate these risks. Since water must be controlled in all three states of matter, planning is key for managing moisture as the envelope schedule must be balanced with the needs of the mass timber. There are broadly three phases to this plan:
- No building envelope is installed: Without the envelope being installed, the mass timber is exposed to precipitation (i.e. rain, snow and ice) and exterior moisture sources. Temporary measures may be required to preserve the structural integrity and appearance of the timber.
- Envelope installed and the building is watertight: The interior environment is controlled using temporary systems to allow the timber to dry and to ensure there are not any rapid changes to the moisture content of the wood.
- Permanent mechanical systems deployed: The timber can be slowly acclimatized to the design conditions and reach the stable point (i.e. equilibrium moisture content) that it will be at when the building is operational.
The moisture management strategy required on projects depends on the type of mass timber structure, shape or shedding potential of the structure, and the location of the project. The type of mass timber and the shape of the system impacts the wetting and drying potential. Similarly, the amount of precipitation experienced will vary depending upon the geographic location and climate of the project. For example, a flat cross-laminated timber (CLT) panel has a higher wetting potential than a sloped nail-laminated timber (NLT) panel since water will “sit” on top of the CLT while it will shed off or drain through the sloped NLT. Moreover, what is acceptable in Toronto will not be applicable in Vancouver due to the amount of precipitation Vancouver receives.
A: On the Limberlost Place project, the biggest takeaway is that the mass timber and the building envelope can significantly impact other construction activities. As always, it is key to determine potential areas for improvement early in the construction process so that these conditions can be flagged in the preconstruction phase and incorporated into the construction execution plan. I am very proud of how we have approached this on Limberlost Place as our highly skilled project team works quickly to consider and incorporate feedback, following PCL’s motto of “building it right, once!”
As a project director, Mike Buckley brings 36 years of design and value management experience to PCL. Responsible for managing project design processes, Buckley has a holistic knowledge of architectural, mechanical and electrical systems, as well as design and construction processes and methods needed for successful project implementation.
On Limberlost Place, Buckley acts as a sounding board for the project team to discuss means and methods of construction based on how things are unfolding on-site. With the possibility that the theoretical behaviour of the composite structural system differs from its actual behaviour in the field, he helps the team reconcile variations between results and expectations throughout the construction process.
A: At the highest level, there isn’t much of a difference in the way a mass timber building carries its load compared to traditional structural steel or cast-in-place concrete projects. The difference is in how much you have to push the envelope and composite systems to get the same floor spans and column spaces that rival traditional building structures. For mass timber projects, there are a different set of parameters to achieve the same kind of outcomes, such as load capacity.
A: Limberlost Place has unique three-storey CLT columns that create a beautiful, large open atrium space. Additionally, Limberlost Place uses a composite floor system composed of CLT and concrete that is thinner than the beams typically used in mass timber projects. This allows for increased ceiling height and leaves more space for mechanical and electrical components. Initially, there were challenges associated with implementing the composite floor systems, as temporary shoring would have been required throughout the full height of the building while concrete was being poured. This would have created schedule challenges since other construction activities could not continue while the shoring was in the way. To reduce schedule impacts, the project team developed an innovative solution to pre-top the CLT with concrete offsite to reduce the amount of shoring required.
A: There is a common misconception that mass timber buildings are more flammable or pose inherent acoustic issues. There are plenty of methods that can enhance mass timber’s fire-resistant properties and improve acoustic and vibration performance. Limberlost Place’s CLT panels are topped with concrete and acoustic mats to reduce vibrations and control sound passage. The build includes a standpipe system that provides reliable firehose connections throughout the building. Additionally, CLT panels contribute to fire safety due to their layered composition. In the event of a fire, the outside layer would char and serve as a protective barrier, preventing the fire from spreading to the inner layers for a prolonged period.
One of the first LEED certified engineers when the program launched in Canada in 2003, Stephen Montgomery brings over 23 years of experience in the construction industry. As PCL Toronto’s sustainability specialist and mechanical and electrical pursuits manager, Montgomery leverages his extensive experience in design and construction with his passion for sustainability to prioritize health and environmental outcomes in the built environment.
On Limberlost Place, Montgomery was involved in determining how to incorporate sustainable design aspects into the construction plan. He ensures that these solutions, such as Limberlost Place’s passive ventilation system, are accurately integrated into the day-to-day work plans and that they continue to meet schedule and budget requirements.
A: Limberlost Place incorporates sustainably sourced mass timber and prioritizes natural light access with an impressive window-to-wall ratio. The building will feature a natural ventilation system that includes two solar chimneys designed to draw air through the building from automatic and manually operable windows. The building will be able to operate in several different modes depending on the weather conditions detected via the rooftop weather station, allowing for passive ventilation particularly during the spring and fall months. With a focus on reducing energy usage, water consumption and operating costs, Limberlost Place will also integrate Enwave’s Deep Lake Water Cooling system and smart daylight sensors and dimming controls.
A: Traditional building materials, such as cement and concrete, are very carbon-intensive to produce compared to timber, as the processes require a lot of fuel. Timber sequesters carbon, meaning it continues to store the carbon it absorbed from the atmosphere after it is incorporated into a structure, which contributes to the material’s improved carbon emissions.
Timber can also be sourced sustainably. The mass timber used for Limberlost Place was harvested from sustainably managed forests in Quebec, supplied by Nordic Structures. Like any building material, mass timber must be implemented and sourced appropriately for its environmental benefits to be realized.
A: Demonstrating the project’s commitment to sustainable design and performance, Limberlost Place is targeting Tier 4 of the Toronto Green Standard. This performance level was seldom awarded in the City under Version 3. Limberlost Place is also targeting LEED Gold certification, as the use of mass timber contributes to earning points for recycled content and sustainability sourced materials.
A: Limberlost Place has infused a bit of energy and excitement into our teams for what’s possible in mass timber construction. With codes continuing to be amended to facilitate the use of timber for tall structures, we hope Limberlost Place will help generate more demand for mass timber structures in the built environment. These are safe, low carbon spaces with warm, inviting, healthy interiors. George Brown College has shown us how to steward a better product, pioneering a building of this type that incorporates cutting-edge technology to contribute to the well-being of residents and the environment. Long term across the industry, quality assurance and quality control will be key in determining the future of mass timber construction, as these projects must be properly executed for all the benefits to be recognized.
With early engagement of PCL subject matter experts, we are able to anticipate and proactively address construction considerations that are unique to mass timber. Our team of experts can help develop creative solutions that will bring your project to life. Join us in the wood building revolution.
The project team includes:
- Owner: George Brown College
- Architect: Moriyama Teshima Architects in joint venture with Acton Ostry Architects
- Construction manager: PCL Constructors Canada Inc.
- Mass Timber: Nordic Structures
- Structural Engineer: Fast + Epp
- Mechanical and Electrical Engineer: Integral Group
- Structural Steel Design-Assist: Walters Group
- Building Envelope: Morrison Hershfield
- Sustainability Consultant: Transsolar
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