Timber! The Promise of CLT

eight lessons learned to make the most of mass timber buildings

“Globally the number of mass timber buildings will double every two years. The result is that the North American timber industry will store more carbon than it emits by the year 2034.”
— North American Mass Timber Report: 2021 State of the Industry

Ten years ago, there were no Cross Laminated Timber (CLT) factories in the United States. Today, there are more than a dozen. In 2015 CLT was recognized as a structural product in the International Building Code (IBC) for buildings up to six stories. As of this year, the IBC allows the use of mass timber structural products (which include CLT panels and glulam columns and beams among others) in buildings up to 25 stories tall (Milwaukee multifamily tower).

While the benefits of mass timber use may not live up to its proponents’ inspiring predictions, the speed with which this renewable material has been taken up in an industry that is notoriously slow to change speaks to its promise: it is a strong, safe, beautiful, and low-carbon alternative (or complement) to concrete and steel —and its use also speeds construction.

CLT is still a relatively new material for building in New England, but it won’t be for long; CLT can be used as floor and roof slabs as well as shear and shaft walls. It is typically combined with a glulam, steel, or concrete superstructure of beams and columns. It is suitable in just about any midrise project that involves new construction, including additions and renovations. This last point is important, because using existing building stock is the first strategy in building green.

Anyone who works in the AEC industry is well aware of our sector’s contribution to greenhouse gas emissions; taken together, buildings (operation) and their construction account for 38% of all energy-related CO2, according to the UN 2020 Global Status Report for Building and Construction. The report notes that direct building CO2 emissions need to halve by 2030 to get on track for net zero carbon building stock by 2050 (which is a critical target for keeping the global temperature rise below 1.5°C). Mass timber can help us get there — mostly by reducing emissions associated with building construction, although it can also make contributions to energy performance.

More and more facilities in Massachusetts are being planned and built using CLT each day. Jones designed one of our state’s first handful of CLT buildings, the $28.1 million construction cost C. Gerald Lucey office building for the Commonwealth’s Department of Employment Assistance in Brockton, which will be occupied in June 2022.

The building, designed with a CLT and glulam beam and column structural system surrounding a steel core, presented a number of design opportunities — and not a few procurement hurdles, due chiefly to the project’s status as the Commonwealth’s first CLT building of this scale to use solely public funds. (Learn more about the project here, and about the procurement process here.)

Lessons Learned
For any owner or developer looking to reduce their carbon footprint and construction time while capitalizing on the material’s inspiring design, health and wellness possibilities, CLT deserves serious consideration. Here’s what you need to know before you press go.

1 – Buy-in starts at the top

Owners must recognize the added value of using cross laminated timber from a sustainability, schedule and experiential standpoint and be willing to incur new costs that may be associated with the learning curve for the design, procurement, and construction teams. While costs associated with mass timber can be more than the cost of concrete and steel, savings come in reduced finish materials (in particular ceilings) and advantages during construction, namely reduced installation timelines. The timber in the C. Gerald Lucey Building (which is two thirds of the structure) took about half the time to install as the steel. One estimate puts the average reduction in construction schedule at 25%. And then there are the less quantifiable, though no less valuable, aspects of wood’s visual appeal, which can provide advantages in areas like lease rates, worker productivity and student learning. CLT also provides LEED (or other green building rating systems) points for those institutions pursuing a sustainability certification.


2 – Early participation of supplier and installer required

Early and willing engagement with mass timber representatives by both the design team and construction manager is critical for determining the correct approach to documentation and bidding. In the case of public procurement an early timber bid package can provide the necessary hard bid and still allow the installer to join in the design process before construction documents are completed.


3 – Mass timber presents new design opportunities — and challenges

The obvious design opportunity associated with a mass timber structural system is its aesthetic qualities — wood has tremendous visual appeal. Its warmth and beauty has a comforting and uplifting effect on people, and that has documented effects on wellbeing in classrooms and in the office environments.

Because this means exposing at least parts of your building’s structure, design drawings need to be extremely detailed, for example to route conduit and ductwork and locate equipment in ways that are visually appealing, and to accurately account for the different tolerances between wood and steel. This adds to design costs.

Recognize that a simple building geometry works best for CLT. The more complex the shape of the building, the more challenging it is to design a timber structure to support it — not impossible, just more expensive. And if you have your heart set on a masonry façade, think hard about whether CLT is the right solution. CLT is much better suited for lightweight skin systems – wood or cement board panels for example — than masonry, which will need a robust secondary structure to carry it.


4 – Acoustic considerations are considerable

Anyone who’s lived in an old apartment building with wood floors understands the acoustic properties of wood. While it’s wonderful to use wood as a finish material, keep in mind that it is a hard surface — we’re all glad not to see acoustic ceiling tile, but wood does not take away sound. As such, we need to find ways to absorb and/or mask sound, through baffles and other strategies. For the C. Gerald Lucey Building, we used raised floors to run the majority of power and data required for the space, and then carpeted it. This build up effectively eliminates the concern of footfall noise from a space to the floor below.


5 – Coordination is key

We cannot overstate the amount of coordination that is needed between the design team and construction manager during design, and with subcontractors post bid. Close collaboration is critical to achieving the aesthetic goals inherent in the use of mass timber. For the C. Gerald Lucey Building project, we had eight months of weekly calls with the subs to ensure installation met design goals.

6 – Some designs may still require variances

For example, while CLT is more fire resistant than steel, many municipal codes still require protective cladding for wood framing. That said, the codes are evolving as the material becomes more mainstream. This is one of the many reasons that you should engage local authorities having jurisdiction early in the process to brief them on the fact that you are using a wood structural system.


7 – Anticipate capital costs coming down as demand increases

Costs vary by region. In New England right now, higher costs for mass timber center around the fact that our region lacks a robust field of contractors that have experience installing CLT. That’s quickly changing, and costs will adjust as supply and demand stabilize. Ultimately, mass timber will likely be close to equal to or even less than the cost of concrete and steel, especially if the vision for revitalizing the Northeast’s forestry industry is realized.

8 – There are so many good reasons to use wood

We love its design possibilities, its effects on health and wellbeing, and most of all, that mass timber is a renewable material with the power to reduce the building sector’s contribution to global climate change, and the potential to breathe new life into an industry that has been vital to our regional economy. It’s not a silver bullet, but it is a game changer, and Jones Architecture is thrilled to be playing. 

WOOD (CLT AND GLULAM)  


C. Gerald Lucey Building

Mass timber structural elements for the C. Gerald Lucey Building included CLT floor and roof panels, glulam beams and glulam columns. CLT wall panels were eliminated due to fire code requirement of cladding, and glulam diagonal braces were eliminated to forego variance process.

  • Volume of wood products used: 333 cubic meters (11,763 cubic feet)
  • According to the Woodworks Calculator, U.S. and Canadian forests grow this much wood in: 1 minute
  • Total potential carbon benefit: 362 metric tons
    • Carbon stored in the wood: 261 Metric Tons.
    • Avoided greenhouse gas emissions: 101 Metric Tons.

Quote:
“The work of Jones Architecture at the Department of Unemployment Assistance in Brockton exemplifies a profoundly humane and increasingly important approach to sustainability. The planning of spaces, material choices, and connections to place, daylight and even the canopy of the trees on the terrace are centered on human comfort and wellbeing. This humane form of sustainability is critical for the design of workplaces where people spend so much of their lives, sometimes in stressful jobs. The smart organization of structure and systems is evidence that there is beauty in simplicity and adaptability."

 — Michelle Laboy, Assistant Professor, School of Architecture, Northeastern University

Aren’t we supposed to be saving trees?
Yes. The whole calculation of embodied energy and sequestration relative to mass timber — which some scientists question — depends on preserving old growth forests and responsible forest management. It is critical that designers specify only salvaged wood or wood certified by the Forest Stewardship Council (FSC) in mass timber projects. This means the products come from forests that are managed to reduce habitat destruction and optimize growing period, then sustainably harvested and replanted as part of a larger strategy of carbon sequestration.  

The most important aspect of sustainability in terms of mass timber is its embodied energy. According to Wood for Good, an organization that advocates for sustainable wood construction, concrete requires five times the amount of energy to go from raw material to finished product, while steel requires 24 times the amount of energy. Then there’s the fact that wood sequesters carbon, unlike its concrete and steel counterparts, which introduce more carbon into the atmosphere. And, because wood is a good insulator, less energy is needed to heat and cool wood buildings.

MORE RESOURCES:

“Cross Laminated Timber and Public Procurement,” Marc Perras with Jeff Freitas (Project Engineer, DCAMM), Jennifer McClain (Principal, RSE Associates), and Dave Capaldo (Director of Public Construction, BOND) presented in December 2020 at the Architecture Boston Expo (ABX) Virtual Tradeshow.

“Mass Timber Construction in the Northeast,” Marc Perras presented in May 2021 at the Building Energy Boston NESEA (Northeast Sustainable Energy Association) Conference.

2022 CMAA Award! BOND Building Construction, our partner on the C. Gerald Lucey Building constructed with cross-laminated timber for DCAMM’s Department of Unemployment Assistance offices in Brockton, MA was recognized by the CMAA/Construction Management Association of America with a New England Chapter Project Achievement Award.

On season 2, episode 13 of the High Profile Build Better podcast, "Achieving Sustainability Goals with CLT Building Project," Anastasia Barnes talks with Marc Perras, associate principal at Jones Architecture and Jon Rossini, project manager at Bond Building Construction, about the new C. Gerald Lucey building project for the DUA. As the Commonwealth’s first CLT project of this scale using only public funds, Perras and Rossini talk about the sustainable design elements of the DUA building, and how cross-laminated timber can be used to achieve sustainability goals in a variety of construction projects.

MORE RESOURCES:

Marc Perras Speaker Interview: Advancing Mass Timber Construction 2022.

Marc Perras provided a presentation, Lessons Learned Designing a Mass Timber Building in a Public Procurement Environment and tour of the C. Gerald Lucey Building for the Advancing Mass Timber Construction Conference.

2023 ENR Best Project Award-Office/Retail/Mixed-Use Category. 2022 CMAA Project Achievement Award. Sustainable Construction Innovation, 2022 Award Recipient. Awarded by Built Environment Plus (BE+) and convened practitioner community at the Green Building Showcase for our CLT (Cross Laminated Timber) project: Mass Timber for Mass Workers, The C. Gerald Lucey Building in Brockton, MA.

Marc Perras and South County Post & Beam's Ethan Biederman collaborated on an article for High Profile's December 2022 Green Supplement Issue highlighting the sustainable and economic benefits of utilizing mass timber. The Promise of CLT: Top 6 Reasons for Using Mass Timber.

Marc Perras and Sarah Tarbet of Jones Architecture are featured speakers at the North Shore Technology Council Presentation, Building Sustainably: Trends in Green Architecture in April 2024.