The introduction of new engineered wood projects, such as Cross Laminated Timber, offer fire resistive properties and a high strength-to-weight ratio which allows for its use in taller mid-rise structures. Structural wood products like CLT provide a number of advantages. It has a lighter environmental footprint than concrete or steel due to its ability to sequester carbon, lower embodied energy and excellent thermal performance.

Building with mass timber requires a customized approach and a shift in mindset. The considerations that should be accounted for when building mass timber structures are outlined below.

Including the contractor before design documents are completed provides an opportunity to optimize the design and reduce the cost of the mass timber structure. Place an emphasis on competitive early procurement of the CLT supplier during schematic design to take advantage of the design-assist services suppliers can offer. CLT is not a commodity material and optimization of the structural grid, panel layout and overall volume of wood fiber can only be done when accounting for the CLT supplier’s panel fabrication capacity and structural properties of the selected wood species.

The duration to top-out mass timber post and beam structures can be up to 50% shorter than similar concrete or structural steel structures, and even faster if CLT panels are used in lieu of concrete core walls. Foundations are typically smaller, and successor activities such as overhead mechanical, electrical and plumbing rough-in can start sooner since re-shores are not required below the active floor. Shorter construction schedules result in reduced general conditions and an overall reduction in cost.

Take a comprehensive approach to pricing mass timber projects and understand where complementary cost savings can be realized beyond the structure. Confidently accounting for smaller foundations, reduced ceiling finishes and shorter construction durations at the early stages of design allow mass timber to be cost-competitive when compared to other structure types.

Proper planning of the mass timber erection sequence defines the fabrication sequence, may influence CLT panel and connection details and ensures just-in-time product delivery to the site. Without this upfront planning, a large laydown area is required to stage and sort CLT panels prior to installation, extending the erection duration. 

Mass timber buildings require a greater degree of coordination/BIM modeling due to the concealed engineered connections, CLT fabrication process and exposed timber throughout the structure. Early engagement of the CLT fabricator and erector, mechanical and electrical trade contractors in the design process allows the project team to develop a strong schematic design and construction plan/schedule that captures the critical details and time necessary to model the structure and coordinate services. 

Many mass timber structures still require an interface with concrete foundations, structural steel or concrete core walls. The interface between different materials requires extra attention due to the differences in allowable construction tolerances. The contractor needs to with the design team to ensure built-in flexibility in the base plate and core wall connection details and to build concrete or steel structures to as tight a tolerance as possible.

Wood is sensitive to changes in levels of humidity over periods of time. This is especially critical if humidity levels vary between the source of production and project location. Continually monitor humidity levels during construction, protect the wood from standing precipitation and snow and specify an air barrier with a high drying capacity to allow the wood to continue releasing moisture even after the building is enclosed.

The wood finish can become stained during construction, either from precipitation or ‘rust bleed’ from exposed steel or metal connections, or extended UV exposure. Be diligent about protecting the wood during transit and throughout construction, provide a protective coating or primer on all steel connections and apply protective sealers to all wood products.

As building with mass timber is still a newer construction method, strong coordination and collaboration between the owner, designer, CLT supplier, construction manager and all trades from preconstruction to project completion is a key requirement for project success. Taking these best practices into account at the start of your next mass timber project will assist your team in delivering a sustainable project while realizing schedule and cost savings.