Mass Timber Construction: What Every Contractor Needs to Know About CLT, Glulam, and NLT

If you have been in commercial construction for more than a few years, you have probably noticed mass timber showing up on more and more bid invitations. What used to be a niche product for architects chasing sustainability awards has become a legitimate structural system that owners and developers are choosing for cost, speed, and aesthetics.

But here is the thing: most contractors who have spent their careers pouring concrete and erecting steel are not sure what to make of mass timber. The questions are reasonable. Is it really strong enough? What about fire? How do I bid something I have never built?

This guide breaks down everything you need to know about mass timber construction, from the different product types to fire performance, cost considerations, and practical tips for contractors taking on their first mass timber project.

What Is Mass Timber, Exactly?

Mass timber is a category of engineered wood products that are large enough and strong enough to serve as primary structural elements. We are not talking about stick framing or heavy timber post-and-beam. These are factory-manufactured panels and beams that can replace concrete slabs and steel beams in mid-rise and tall buildings.

The most common mass timber products include:

Cross-Laminated Timber (CLT)

CLT is the flagship product. It consists of layers of dimensional lumber stacked at right angles and bonded with structural adhesive. A typical CLT panel is 3, 5, or 7 layers thick, ranging from about 4 inches to over 12 inches in total thickness.

CLT panels can serve as floors, walls, and roofs. They arrive on site pre-cut to exact dimensions, often with window and door openings already machined. Think of it like a massive, structural version of plywood.

Glue-Laminated Timber (Glulam)

Glulam has actually been around for decades. It consists of dimensional lumber laminated together with the grain running in the same direction, creating beams and columns. If you have ever worked on a building with exposed wood arches or large timber beams, you have probably seen glulam.

In mass timber construction, glulam typically serves as the beam and column system that supports CLT floor and roof panels. It is the skeleton that holds everything up.

Nail-Laminated Timber (NLT)

NLT is the simplest mass timber product. It consists of dimensional lumber (usually 2x4, 2x6, or 2x8) stacked on edge and nailed together. The result is a solid wood panel that works well for floors, walls, and roof decks.

NLT is popular for renovations and adaptive reuse projects because it can be fabricated locally without specialized manufacturing equipment. Any competent framing crew can build NLT panels on site if needed.

Dowel-Laminated Timber (DLT)

DLT is similar to NLT but uses hardwood dowels instead of nails to hold the laminations together. This creates a product with no metal fasteners, which appeals to architects who want a clean, all-wood aesthetic on exposed ceilings. It also makes the panels easier to modify on site since there are no hidden nails to hit with a saw.

Why Owners and Developers Are Choosing Mass Timber

Before you invest time learning a new construction method, you need to understand why this market is growing. Here are the drivers:

Speed of Construction

Mass timber buildings go up fast. Really fast. Because panels arrive pre-cut and pre-drilled from the factory, erection is closer to structural steel than cast-in-place concrete. A typical mid-rise mass timber floor can be erected in days, not weeks.

One widely cited example: the 8-story Carbon12 building in Portland, Oregon erected its mass timber superstructure in just 9 weeks. Comparable concrete buildings take months. That speed translates directly to reduced general conditions, earlier occupancy, and faster return on investment for the owner.

Lighter Weight

Mass timber weighs roughly one-fifth as much as an equivalent concrete structure. That means smaller foundations, reduced seismic loads, and the ability to build on sites with challenging soil conditions where a heavy concrete building would require expensive deep foundations.

For contractors, lighter weight also means smaller cranes and less complex rigging. A CLT panel that a tower crane swings into place in minutes would require significantly more effort as a concrete pour.

Carbon and Sustainability

Mass timber stores carbon rather than emitting it. Trees absorb CO2 as they grow, and that carbon stays locked in the wood for the life of the building. By contrast, cement production alone accounts for roughly 8 percent of global CO2 emissions.

Owners pursuing LEED certification, carbon-neutral goals, or ESG commitments find mass timber attractive because it dramatically reduces the embodied carbon of a building. This is not just a feel-good story. Many institutional and corporate clients now require carbon accounting on their projects.

Aesthetics

Exposed mass timber ceilings and walls look stunning. There is no way around it. Architects and owners love the warmth and texture of exposed wood, and studies suggest that occupants in mass timber buildings report higher satisfaction and well-being. For commercial office, hospitality, and multifamily projects, this aesthetic premium can translate into higher rents and faster lease-up.

Fire Performance: Addressing the Elephant in the Room

Every contractor asks the same question: “What happens when it catches fire?”

The answer is more reassuring than you might expect. Mass timber does not behave like dimensional lumber in a fire. Here is why:

Charring Behavior

When mass timber is exposed to fire, the outer surface chars at a predictable rate, roughly 1.5 inches per hour for most species. That char layer acts as insulation, protecting the structural core from heat. A 7-layer CLT panel can burn on one side for over two hours and still maintain its structural capacity.

This predictable charring behavior is actually an advantage over unprotected steel. Steel does not burn, but it loses roughly half its strength at 1,100 degrees Fahrenheit. In a fully developed fire, unprotected steel beams can fail within 15 to 20 minutes. Mass timber, by contrast, degrades slowly and predictably.

Code Requirements

The 2021 IBC introduced three new construction types for mass timber:

• Type IV-A: Up to 18 stories, requires noncombustible protection (like gypsum board) on all mass timber surfaces
• Type IV-B: Up to 12 stories, allows some exposed mass timber with noncombustible protection on certain elements
• Type IV-C: Up to 9 stories, allows exposed mass timber throughout (this is the “all-wood” look that architects love)

Each type has specific requirements for fire-resistance ratings, allowable area, sprinkler systems, and shaft enclosures. The key takeaway: mass timber buildings are heavily regulated and thoroughly tested. This is not cowboy engineering.

Construction Phase Fire Risk

The real fire risk with mass timber is during construction, before the building is enclosed and fire protection systems are installed. Exposed wood on an active construction site is more vulnerable than in a finished building.

Best practices include:

• Hot work permits and fire watch protocols
• Temporary sprinkler coverage on completed floors
• On-site fire suppression equipment (extinguishers, standpipes)
• Limiting exposed wood area by installing gypsum protection as floors are completed
• Security to prevent arson and unauthorized access

Your builder’s risk insurer will likely have specific requirements. Address these during preconstruction, not after you have panels on site.

Cost Considerations: Does Mass Timber Make Financial Sense?

This is where the conversation gets practical. Contractors need to know if mass timber pencils out.

Material Costs

CLT panels typically cost more per square foot than a concrete slab or steel deck. Depending on the market and project, you might see a 5 to 15 percent premium on structural materials alone. Glulam beams and columns are generally competitive with structural steel on a per-member basis.

However, material cost is only one piece of the puzzle.

Installation Speed

Mass timber erection is fast, and speed saves money across the board. Fewer weeks of crane rental, general conditions, temporary facilities, and supervision add up quickly. On a 6-story building, shaving 8 to 12 weeks off the schedule can save hundreds of thousands of dollars.

Foundation Savings

Because mass timber weighs so much less than concrete, foundation requirements shrink. On projects with good soil conditions, you might go from deep foundations to spread footings. On projects with poor soils, you might reduce pile counts by 30 to 50 percent. These savings can be substantial.

Reduced On-Site Trades

A mass timber erection crew is small compared to the army of formwork carpenters, rebar installers, and concrete finishers needed for a cast-in-place structure. Fewer trades on site means less coordination, fewer conflicts, and simpler logistics.

The Bottom Line

For the right project, mass timber can be cost-competitive with concrete and steel, and sometimes cheaper when you factor in schedule savings and foundation reductions. The best candidates are mid-rise buildings (4 to 12 stories) with repetitive floor plates, like multifamily housing, office buildings, and hotels.

The worst candidates are one-off, complex geometries where the factory prefabrication advantage is limited, or very tall buildings where concrete and steel still dominate.

How to Bid Your First Mass Timber Project

If you are a GC or CM looking at your first mass timber opportunity, here is how to approach it:

1. Find an Experienced Mass Timber Erector

Unless you plan to self-perform the erection, you need a subcontractor who has done this before. Mass timber erection is not complicated, but it requires understanding panel sequencing, connection details, and crane planning specific to large wood panels. Ask manufacturers like Structurlam, Sterling, Kalesnikoff, or Nordic Structures for referrals to erection crews in your region.

2. Engage the Manufacturer Early

Mass timber manufacturers are not commodity suppliers. They are design-assist partners who engineer the panel layouts, connection details, and fabrication drawings. Engage them during preconstruction, ideally during design development or early construction documents. Their input on panel sizes, connection types, and erection sequences will shape your bid.

3. Understand Lead Times

CLT and glulam are manufactured to order. Lead times range from 12 to 20 weeks depending on the manufacturer and market conditions. If you are building a schedule, account for this and coordinate with the design team to finalize structural drawings early enough to feed the factory.

4. Plan Your Crane Strategy

Mass timber panels are large but relatively light. A typical CLT floor panel might be 8 feet wide, 40 feet long, and weigh 8,000 to 12,000 pounds. That is well within the capacity of most mobile and tower cranes, but panel size affects rigging, laydown area, and sequencing. Work with your erector and crane operator to develop a detailed lift plan.

5. Coordinate MEP Early

One of the trickiest aspects of mass timber is MEP coordination. Unlike concrete, you cannot easily core-drill CLT panels after installation. Penetrations for plumbing, electrical, and HVAC need to be planned during the shop drawing phase and machined at the factory. Any missed penetration means field cutting, which is slower, messier, and can compromise fire ratings.

This is where your project management software earns its keep. Tracking RFIs, shop drawing approvals, and MEP coordination across multiple trades and the manufacturer requires serious organizational discipline.

6. Develop a Construction Fire Protection Plan

As mentioned earlier, fire protection during construction is critical. Develop a written plan that addresses hot work, temporary suppression, security, and insurance requirements. Share it with your insurer, the fire marshal, and your entire project team.

Common Mistakes Contractors Make on Mass Timber Projects

Learning from other people’s mistakes is cheaper than making your own. Here are the most common pitfalls:

Treating It Like Concrete Construction

Mass timber has a different rhythm than concrete. You cannot adjust panel sizes on the fly. You cannot pour a little extra to fix a dimensional error. Everything is manufactured to precise tolerances, and the panels arrive ready to install. Embrace the prefabrication mindset: invest in preconstruction, and the field work becomes almost easy.

Ignoring Moisture Protection

Wood and water do not get along. CLT and glulam are kiln-dried to specific moisture content during manufacturing, and keeping them dry on site is critical. This means covered storage, tarps during erection, and a plan for drying out panels that get wet during rain events.

Most manufacturers provide moisture management guidelines. Follow them. Panels that absorb too much moisture can swell, cup, or develop mold, and remediation is expensive and time-consuming.

Skipping the Mockup

On your first mass timber project, build a mockup of a typical connection or panel assembly. This lets your crew practice the installation sequence, test connection hardware, and identify issues before you are 6 stories up with a crane running at $500 per hour. A few thousand dollars on a mockup can save tens of thousands in the field.

Underestimating Connection Complexity

Mass timber connections are engineered assemblies that use a combination of steel plates, screws, bolts, and bearing surfaces. They are not complicated individually, but there can be dozens of unique connection types on a single project. Make sure your erection crew has reviewed every connection detail in the shop drawings and has the correct hardware on site before erection begins.

The Mass Timber Market in 2026

The mass timber market has grown significantly over the past five years. Here is where things stand:

• Over 1,700 mass timber buildings have been completed or are under construction in the United States
• Manufacturing capacity has expanded with new plants in Arkansas, Alabama, Washington, and Montana
• Several buildings over 20 stories are in design or under construction worldwide
• Insurance companies are becoming more comfortable with mass timber, and premiums are normalizing
• Universities including Oregon State, Virginia Tech, and Georgia Tech have active research programs advancing the science

For contractors, this growth means more opportunities and more competition. The firms that invest in mass timber experience now will have a significant advantage as the market continues to expand.

How Project Management Software Supports Mass Timber Construction

Mass timber projects demand tight coordination between design teams, manufacturers, erection crews, and finishing trades. The prefabrication workflow means that decisions made (or missed) during preconstruction have amplified consequences in the field.

Construction project management software like Projul helps contractors:

• Track manufacturing lead times alongside the project schedule so panels arrive on time
• Manage RFIs and submittals between the design team and manufacturer with clear approval workflows
• Coordinate MEP penetrations through centralized document management so nothing gets missed
• Log daily progress with photos that document panel placement, connections, and moisture protection
• Communicate with the full team including subs, suppliers, and the owner through a single platform

When you are building with a material that arrives fully manufactured, staying organized is not optional. It is the difference between a smooth erection sequence and a project that stalls waiting for answers.

Getting Started

Mass timber construction is not a fad. It is a structural system with real advantages in speed, sustainability, and aesthetics. The contractors who learn this building method now will be positioned to capture a growing share of the commercial construction market.

If you are considering your first mass timber project, start by visiting a completed building to see the product firsthand. Talk to manufacturers about design-assist partnerships. Find an experienced erection crew. And make sure your project management systems can handle the coordination demands that come with prefabricated construction.

The learning curve is real but manageable. And once your crew has one mass timber project under their belt, they will wonder why everything is not built this way.