“Mass timber is a sustainable, engineered wood construction material made by laminating layers of lumber or veneer, offering a strong, fire-resistant alternative to steel and concrete. It is available in Upper Michigan, with projects like the DNR Newberry Customer Service Center utilizing it, and researchers actively exploring local, hardwood-based production.”
What is Mass Timber?
Definition: Engineered wood panels, posts, or beams (e.g., Cross-Laminated Timber, Glue-laminated timber) glued or nailed together.
Benefits: It is strong, lightweight, and often prefabricated as a “kit of parts,” allowing for faster construction.
Sustainability: It has a lower carbon footprint and stores carbon, unlike concrete and steel.
Availability and Use in Upper Michigan (U.P.)
Projects: The DNR Newberry Customer Service Center in the U.P. is a prime example of a Michigan-sourced mass timber project.
Production & Research: Michigan Technological University (MTU) in the U.P. is actively researching the use of regional hardwoods (like red maple) and cross-laminated timber technology for local mass timber production.
Statewide Growth: The State of Michigan is actively promoting mass timber, with over 65 projects identified across Michigan by 2026, says Mass Timber at MSU.
The market is rapidly expanding, with new building codes in 2025 further enabling its use in Michigan, says Michigan State University.
Mass Timber in More Detail
Safety in mass timber construction demands you understand predictable charring, applicable codes, and tested CLT (Cross-Laminated Timber) assemblies so you can design for required fire-resistance ratings, manage construction-phase fire risks, and ensure your adhesive, encapsulation, and sprinkler strategies meet permit and firefighting needs.
Understanding Mass Timber
Types of Mass Timber
You’ll encounter engineered products like glulam, cross-laminated timber (CLT), nail-laminated timber (NLT), mass plywood panels (MPP), and laminated veneer lumber or dowel-laminated timber (LVL/DLT); sections are often 12 inches (300 mm) or more. CLT panels have been fire tested to ASTM E119, demonstrating two-hour FRR for many suppliers, and projects such as the 18‑storey Brock Commons (UBC, 2017) show how these systems scale into taller buildings.
Glulam
Glued Laminated Beams/Columns for long spans and heavy loads; commonly used for primary frames and exposed architectural elements.
CLT
Cross‑Laminated Timber panels (typically 3-7 plies) for floors and walls; predictable charring behavior and ASTM E119 two‑hour FRR test records.
NLT
Nail‑Laminated Timber built from stacked sawn lumber fastened with nails-cost‑effective for floor platforms and retrofits.
MPP
Mass Plywood Panels offering dimensional stability and high strength-to-weight, are used where plywood properties are advantageous over solid-sawn plies.
LVL / DLT
Laminated Veneer Lumber for beams/joists and dowel‑laminated timber for assembly without adhesives; both support long spans and predictable performance.
- Glulam excels where you need exposed beams and high bending capacity.
- CLT is often chosen for rapid panelized floor and wall construction in mid‑rise projects.
- NLT and MPP can reduce material cost while retaining mass timber benefits in renovations.
- Recognizing adhesives and connection details drives fire and structural behavior, so you must verify manufacturer test data and standards compliance.
Advantages of Mass Timber Construction
You gain lighter structural weights compared with concrete, often reducing foundation size, and you benefit from off-site prefabrication that shortens onsite schedules; mass timber also affords quieter construction, smaller crews, and inherent fire performance via predictable charring rather than reliance on drywall encapsulation.
Digging deeper, your project can leverage the two‑hour FRR (Fire Resistance Rating) test heritage for CLT and design methods in the NDS/CLT Handbook to meet code requirements; this allows you to engineer members to survive applied loads even during fire exposure. You can also improve sustainability goals since engineered wood stores biogenic carbon during the building life, while standardized panel sizes and factory tolerances cut onsite labor and trade coordination-examples like Brock Commons (18 stories) illustrate how engineered timber supports taller, high‑quality construction when you align material selection, connection detailing, and supplier test reports early in design.
Fire Safety Considerations
When assessing fire safety for mass timber, you focus on both the material’s predictable charring behavior and the engineered systems that supplement it; CLT and glulam can provide rated structural performance while active systems and detailing manage fire growth, spread, and occupant safety. You should incorporate validated FRR (Fire Resistance Rating) data, tested assemblies, and construction‑phase safeguards (NFPA 241) into design and operations to meet code obligations for mid‑ and high‑rise buildings.
Fire Resistance Ratings of CLT
For CLT, you rely on either ASTM E119/UL 263 fire tests or calculation methods in the CLT Handbook and NDS to establish FRRs; North American suppliers have E119 reports demonstrating two‑hour ratings for many panel configurations. You must account for ply thickness, number of plys and adhesive type (ANSI‑APA PRG‑320 updated in 2021) when sizing members and predicting char depth for fire design.
Fire Protection Methods for Mass Timber Buildings
You apply a mix of passive and active measures-encapsulation with gypsum or tested intumescent coatings, automatic sprinklers (designed per NFPA 13), compartmentation, firestopping at joints, and noncombustible exterior envelopes-to achieve target FRRs and limit smoke spread. Tested assemblies combining CLT and these systems are commonly used to secure permits and meet IBC (International Building Code) requirements for occupied heights.
In design detail, you specify sacrificial char allowances and use tested joint and penetration assemblies so mechanical, electrical, and plumbing services don’t void rated performance. You also validate sprinkler hydraulics and water supply per NFPA 13, require manufacturer test reports for coatings or claddings, and implement NFPA 241 controls during construction; this layered approach, tested materials, robust detection/suppression, and meticulous detailing, reduces uncertainty for approvals and for your building’s operational fire safety.
Building Codes and Regulations
Within the IBC, timber is permitted in Types III, IV, and V construction with prescriptive height/area limits, typically 85 feet (about seven stories) for Types III/IV. If your project crosses the 75‑foot high‑rise threshold, the IBC requires noncombustible primary structure and a minimum two‑hour FRR, plus enhanced fire protection and mandatory sprinklering. States and AHJs often adopt NFPA 101 or amend the IBC, so you should verify local amendments and consult AWC and WoodWorks guidance during design.
Compliance with IBC and NFPA Codes
You demonstrate compliance through tested assemblies, engineering calculations, and documented fire‑protection systems. Provide ASTM E119/UL 263 test reports or NDS/CLT Handbook calculations for member FRRs, show sprinkler and egress designs per IBC or NFPA 101, and specify PRG‑320-compliant adhesives (post‑2021) for CLT. Authorities typically accept manufacturer test data plus calculation paths, and mixed‑material façades may trigger NFPA 285 or equivalent wall assembly testing requirements.
The Role of Fire Testing in Approvals
Fire testing to ASTM E119 or UL 263 gives AHJs standardized evidence of FRR and is often the quickest route to permit approval; all North American CLT suppliers have E119 reports demonstrating two‑hour ratings for common panel constructions. You should submit full test reports, test configuration drawings, and witness statements so reviewers can confirm the tested assembly matches your as‑built design or accept calculated equivalencies endorsed by qualified engineers.
ASTM E119/UL 263 applies a time‑temperature curve to loaded elements to quantify FRR, while NFPA 285 assesses multi‑story combustible exterior wall spread; both are frequently requested by AHJs. You must account for adhesive influence on char behavior-ANSI‑APA PRG‑320 was updated in 2021 to require higher‑heat adhesives for CLT-and include specimen drawings, test witness records, and CLT Handbook/NDS calculations; some jurisdictions will still demand project‑specific assembly tests or mock‑ups to validate in‑place performance.
Construction Best Practices
You should prioritize sequencing, temporary fire protection, and tested details that preserve the inherent fire performance of mass timber. Because mass timber members are typically 12 inches (300 mm) or more, charring provides an FRR, but you must still control on‑site ignition sources, use NFPA 241 for construction safeguards, and coordinate temporary sprinklers, security, and hot‑work supervision to limit exposure during assembly and fit‑out.
Tips for Reducing Fire Risks During Construction
You can reduce fire risk by enforcing a hot‑work permit program, limiting on‑site cooking and combustible storage, providing 24/7 security, and installing temporary detection or sprinklers where the authority having jurisdiction requires them. Adopt NFPA 241 as your baseline for procedures and training so contractors and subcontractors follow a single standard.
- Implement a strict hot‑work permit and supervision system for welding, cutting, and grinding.
- Stage and segregate combustible materials off the main structure and clear sawdust daily.
- Provide temporary fire detection/sprinkler systems during the framing of floors and walls.
- Maintain locked, alarmed perimeters and nightly patrols to reduce vandalism and arson.
- After installing temporary protection, test systems daily and log inspections for the AHJ and owner.
Key Construction Details for Mass Timber
You must detail joints, edges, and penetrations to preserve calculated FRRs based on CLT ply counts and adhesive type; the CLT Handbook and NDS provide char‑rate calculation methods, and all North American CLT panels have ASTM E119 test data showing two‑hour FRRs for many assemblies. Coordinate with your supplier for PRG‑320 (2021) adhesive specifications and provide tested connection details to the building permit set.
You should use tested fire‑stop and joint systems at floor edges, stairs, and service shafts, specify sealed perimeter edges to prevent premature delamination, and protect temporary openings until permanent enclosures are in place. Work with the timber supplier to adopt their tested assembly drawings, ensure penetrations use rated collars or intumescent seals, and confirm sprinkler and detection tie‑ins are completed before leaving floors unattended.
Factors Impacting Fire Performance
You should assess variables such as ply thickness, number of plies, and adhesive chemistry, since char rate and residual section are directly affected; testing shows ASTM E119 two‑hour FRR is achievable with appropriate CLT layups. Connections, joint detailing, and sprinklers strongly influence overall performance, and construction sequencing often changes hazard exposure. Perceiving these variables helps you balance design, testing, and on‑site controls.
- Ply thickness and ply count (affects char depth and residual strength)
- Adhesive type and ANSI‑APA PRG‑320 compliance (post‑2021 requirement)
- Member size and CLT Handbook/NDS char‑depth calculations
- Connection detailing, tested connectors, and load‑path redundancy
- Active systems: sprinkler reliability, detection, and compartmentation
- Construction‑phase controls per NFPA 241 and site security
The Influence of Adhesives and Manufacturing Standards
You must factor in that adhesive chemistry, phenol-resorcinol, and PUR systems behave differently under heat, and ANSI‑APA PRG‑320 was updated in 2021 to mandate adhesives with improved heat resistance. Fire tests in Europe, Canada, and North America show heat‑resistant adhesives delay delamination and preserve predictable char progression, supporting calculated FRRs under ASTM E119; when you specify CLT, request supplier test reports and documented PRG‑320 compliance.
Importance of Structural Design in Fire Safety
You need to design connections and load paths so that, if a charred depth reduces the section, the structure redistributes loads without progressive collapse; NDS and the CLT Handbook provide calculation methods for effective char depths to meet two‑hour FRRs. Include redundant ties, protected steel inserts, and tested connection details, and ensure your design accounts for reduced section capacity over time, as seen in tall timber projects.
You should verify connection fire tests (assembly or component) because an untested connector can drive unexpected failures; specify tested fasteners, mechanical anchors, and continuity details, and require post‑char structural analyses in your submittals. Engineers commonly model time‑to‑failure and residual capacity using calibrated case studies from North America and Europe, so insist on validated modeling and conservative safety factors for your project.
Pros and Cons of Mass Timber
Pros: Lower embodied carbon-timber stores CO2 and can improve life‑cycle emissions.
Cons: Perceived combustibility and prescriptive code limits (commonly ~85 ft in many jurisdictions).
Pros: Off-site prefabrication enables precise production and faster on‑site assembly.
Cons: Limited manufacturing capacity and variable lead times for large CLT panels.
Pros: Erection is often 20-50% faster than cast‑in‑place concrete, speeding ROI.
Cons: Upfront material cost variability and regional price fluctuations.
Pros: Lighter structures can reduce foundation size and cost.
Cons: Moisture exposure during transport/erection requires rigorous detailing and protection.
Pros: Predictable charring behavior yields fire resistance; many CLT panels meet ASTM E119 two‑hour FRR.
Cons: Fire performance can vary with adhesive type-standards were tightened in ANSI‑APA PRG‑320 (2021).
Pros: Strong market and aesthetic appeal-tenant and developer interest is high.
Cons: Acoustic and vibration control often need additional assemblies or damping solutions.
Pros: Quieter, safer sites with smaller crews and less hot‑work exposure.
Cons: Insurance and inspection practices can be inconsistent; some carriers apply higher premiums.
Pros: Renewable resource with potential for FSC/PEFC certification and sustainability credits.
Cons: Higher scrutiny for tall wood projects; additional engineered fire protection may be required above 75 ft.
Benefits of Using Mass Timber for Construction
You gain tangible schedule and sustainability benefits: offsite prefabrication can cut erection time by 20-50%, CLT and glulam reduce foundation loads, and mass timber stores carbon, improving your building’s embodied‑carbon footprint. Tested CLT panels have demonstrated two‑hour FRRs under ASTM E119, enabling exposed timber aesthetics while meeting fire‑safety requirements. You also benefit from quieter, cleaner sites and marketable design features that can boost leasing and developer returns.
Challenges and Limitations to Consider
You must navigate code limits, insurer unfamiliarity, and detailing demands: many jurisdictions cap mass timber heights near 85 feet, and authorities often request supplier ASTM E119 reports or FRR calculations. Moisture management, acoustic mitigation, and supply‑chain lead times require tight coordination, and adhesive performance variations prior to the 2021 PRG‑320 update still influence reviewer expectations.
To address these constraints, you should specify fire‑resistance calculations from the CLT Handbook or NDS and obtain manufacturer test reports for permit submittals. Implement NFPA 241 controls during construction-hot‑work supervision, site security, and temporary suppression, and coordinate early with acoustical and waterproofing consultants. Expect longer procurement timelines from specialty mills, and factor adhesive‑specific fire behavior, insurance requirements, and local code interpretations into your schedule and risk assessments.
Summing up
On the whole, you can view CLT and mass timber as a defensible structural choice when you design and build to tested fire‑resistance methods, leveraging predictable charring, using supplier test reports and recent adhesive standards; on your construction site you must mitigate ignition risks and follow NFPA 241 and code guidance; as codes and education progress, you should expect greater acceptance and capacity to safely deliver mid‑ and high‑rise timber projects.