Ten best practices
Best practices derived from the qualitative results of this study were wide-ranging.
1. Design to the product
Solid timber products come in set dimensions. For example, CLT panels start at 3 x 12 m (10 x 40 ft), up to 27 m (90 ft) long. Walls, floors, and roofs should be designed to maximize the yield of the standard dimensions the fabricator uses. Designers need to be educated on fabrication machine capabilities, methods, and limits.
2. Complete the design
It is difficult to make changes to a solid panel onsite, given the ‘finished’ nature of the product. The location of electrical chases and penetrations in the panel need to be designed before fabrication. This means all the designs and drawings must be complete before they are sent to fabrication.
This front loads the design process, but quickly speeds up construction.
3. Start small and scale up
A large number of the case studies surveyed were pilot projects or were using solid timber in an innovative way for the first time. Using the project as a testing ground, some stakeholders then took knowledge gained and created additional projects.
4. Talk to local AHJ early
Authorities having jurisdiction (AHJs) need to know early on in the design process the plan to build using solid timber. Additional documentation/approval may be needed. This can also help to expedite inspections and permit approval.
5. Design in 3-D
Designing in 3-D software or with building information modeling (BIM) tools provides clash detection and identifies possible problems before fabrication. This also speeds up the process for fabrication; providing a single model to all subcontractors increases consistency.
6. Remember not all trades are as accurate as CNC machinery
Some trades only come within 12 to 6-mm (½ to a ¼-in.) tolerances, while computer numerically controlled (CNC) machines have tolerances within millimeters. Connections between CNC-cut panels and onsite fabricated materials can become complicated with different tolerances. One must allow room for proper tolerances in design and fabrication.
7. Consider the finish of the timber
There are different types and grades of solid timber panels, and some even come with certain sealers or finishes from the fabricator. Understanding how panels will be exposed is critical in the design process.
8. Collaborate early
All project stakeholders (e.g. owner, architect, fabricator, manufacturer, and contractor) should be working together from the beginning. This collaboration can help speed up the project schedule considerably, and help avoid mistakes.
It is very beneficial to involve fabricators early to help with design, scope, and limitation of materials on the project. They can also assist the architect with designs and terminology of solid timber.
9. Keep logistics in mind
Transportation of panels can require additional permits and even weight requirements, depending on the travel route. One must evaluate the restrictions of shipping containers/trucks that will be enforced along the transportation route from the fabricator to the jobsite. Also, shipping wood panels between states may not be allowed due to possible introduction of invasive species or bringing foreign material into that jurisdiction.
10. Be aware of software interoperability
Coordination with fabricators prior to design regarding the applications they use to fabricate solid timber is critical. As such, architects should design to communicate with fabricator software as seamlessly as possible. Some of the most common export extensions are .SAT and .IFC file types.
There is seemingly a cost advantage and more certainly a schedule advantage to solid timber construction. Additionally, the material’s use demonstrates a manageable number of change orders and is seen as a safe construction delivery method. During interviews, stakeholder respondents substantiated schedule and safety benefits. Additionally, they indicated timber promotes a reduction in weight compared to steel and concrete construction, requiring less material in foundations.
The disadvantages expressed by those interviewed indicate knowledge and labor skill to handle solid timber continue to be obstacles. Additionally, much early-design-stage planning needs to occur with project stakeholders and code officials to ensure a more streamlined design phase execution. The most important best practice recommendation is early engagement of key personnel—especially the mass timber product manufacturer. This has the potential to be coordinated through a digital modeling platform using .IFC-compliant file types.
There is a market for timber, and from the project study the most efficient building types are housing, commercial/retail, or office spaces three to four stories tall or higher. Further, markets that can benefit from fast construction times, where owners can start collecting rental/lease income sooner, have a greater chance of realizing the material’s extrinsic benefits. Timber also lends itself to panelized and repetitive construction.
Ryan E. Smith is an associate professor and director of the Integrated Technology in Architecture Center (ITAC) at the University of Utah. He chairs the National Institute of Building Sciences (NIBS) Offsite Construction Council, and publishes or presents on offsite design and manufacturing. Smith is author of Prefab Architecture (Wiley, 2010) and co-author of Building Systems (Routledge, 2012). He is a senior research fellow in the Centre for Offsite Construction + Innovative Structures (COCIS) at Edinburgh Napier University in Scotland. Smith can be reached via e-mail at email@example.com.