MASS TIMBER CONSTRUCTION
WHAT IS MASS TIMBER?
Mass timber is an innovative group of wood-based products that may well transform the way we construct buildings. There are many advantages to utilizing cross-laminated timber (CLT) and glulam as structural components in designs, a key direct result is a reduction in construction schedules from mass timber being prefabricated off-site and delivered sequentially to the job site.. Shifting manual labor-intensive work off-site makes construction sites safer, minimizes local disturbances, and reduces material waste. CNC precision cutting during prefab makes extremely low tolerances achievable. Mass timber can be used to construct tight building envelopes in high-performance buildings.
Increasing the use of mass timber in lieu of concrete or steel will significantly reduce the embodied emissions of a building. Mass timber requires marginal processing compared to its carbon-intensive counterparts and is one material solution to decarbonize the built environment.
IDENTIFYING MAIN CHALLENGES
Harbor Bay Real Estate Advisors are the project owners and developers of INTRO in Cleveland, OH. This landmark project is the first mass timber building in the city and at the time of approval, the largest mass timber building in the country. Harbor Bay consulted on this project as a collaborating partner and they shared their knowledge and insight. The results of primary research interviews indicate the most arduous challenges in a new mass timber project are the people and frameworks (building codes) that require the most attention. The consensus was technical challenges were easier to overcome.
Based on these results, the subject of the survey focused heavily on gathering input from key stakeholders who are gatekeepers responsible for enforcing state and local building codes during the permit approval process.
Photo credit: Harbor Bay Real Estate Advisors INTRO Cleveland, OH
Ishikawa diagram identifying the root causes of challenges for new mass timber construction.
BENCHMARKING STUDY
The focus of the benchmarking study was to further investigate the "soft costs" associated with the permit review process and working with local building officials. The aim of the study was not to criticize building officials but to compare the environment of those who have embraced mass timber in their city as early adopters. Mass timber was first introduced into the International Building Code in 2015, as more performance-based tests are completed, the code has changed to allow for taller, larger wood buildings. Historically mass timber buildings were limited to 6 stories but new provisions recommended by the ICC Tall Wood Committee went into effect in 2021 allowing up to 18 stories.
A survey was distributed to each city's representative, and the answers to questions in the survey were used to assign a City Timber Score- a composite score based on past achievements with wood construction, expertise with mass timber, and code framework of a given jurisdiction. The score attempts to measure a city’s planning department's willingness and preparedness to approve a tall wood building and is intended to match like-minded stakeholders investing in new mass timber projects as the supply chains grow.
City Timber Score
Category
Objective
Example
Questions
Past Achievements
weight = 50%
What mass timber projects have been built or approved?
Approximately how many permits have been approved in your jurisdiction for Type IV-A, IV-B, IV-V construction?
Has your jurisdiction issued a permit for Type IV-A, IV-B, or IV-C construction where mass timber was used for the primary or secondary structural components?
Expertise
weight = 25%
How familiar with mas timber are stakeholders at the city level?
Have you or any staff members in your department received any ICC Continuing Education credits for mass timber construction?
Has the Authority Having Jurisdiction ever engaged in supportive discussions about mass timber with the Fire Marshal?
Framework
weight = 25%
What are the available pathways for mass timber project approval?
Would mass timber designs conforming to construction subtypes IV-A, IV-B, IV-C follow a prescriptive code path in your jurisdiction?
Is your jurisdiction willing to proactively adopt future code changes for mass timber as they are approved by the ICC?
FINDINGS
The cities that had issued permits for tall timber (construction subtype IV-A, IV-B) scored the highest. The local building officials were maintaining their knowledge base the timber industry and their state likely has a presprictive pathway for tall timber which streamlines project approval, the alternative to a variance or special buidlling permit. Some cities scored lower because they have not issued permits for any tall timber structures but have proliferic experience with timber in light frame Type III or Type IV construction.