Mass timber has moved from a niche idea to a mainstream structural system, and the newest member of the family starts with the smallest logs. Multi laminated timber, or MLT, builds small-diameter pieces into beams large enough for floors, roofs, and mid-rise frames. The approach follows the same logic that runs through structural timber engineering, where sawn lumber, glulam, and cross-laminated timber each convert raw logs into predictable engineered products with published design values.
This article explains how MLT is made, why salvage timber feeds it, how it is certified, and where it fits alongside CLT and glulam in the building market.
How Multi Laminated Timber Is Made
MLT production starts with timber too small for conventional framing, often 2×2 and 4×4 pieces that would otherwise go to pulp or firewood. The pieces are cleaned, dried, and built up through three joining steps into solid laminated beams. Because the process uses small fiber, it does not need the mature, large-diameter logs that sawmills compete for.
Three Joining Steps, One Beam
- Fingerjointing: small pieces are end-jointed with interlocking fingers and adhesive to make long, continuous stock.
- Edge-gluing: the long stock is glued side to side to reach the beam’s finished width.
- Face lamination: the wide boards are stacked and bonded face to face to build beam depth.
Feedstock Other Mills Reject
Much of the feedstock comes from stands devastated by forest fires and pine beetles. The trees are dead but structurally sound, and their fiber remains usable for years after the kill. MLT belongs to a family of advanced construction materials that stretch the usable fiber supply beyond what conventional sawmills accept, and it gives forest managers a market for timber that once had no buyer.
Fire-Killed and Beetle-Killed Fiber
Fire-killed and beetle-killed trees lose moisture and surface quality, but their core strength holds for a limited window. Salvage logging inside that window captures usable fiber; leaving it standing means the value goes to decay. MLT’s laminating process tolerates the shorter pieces and variable grade that such stands produce.
Kiln schedules for salvage fiber run longer than for green lumber, because dead wood absorbs and releases moisture unevenly. Producers account for that in drying time and in the moisture checks between lamination steps, and the extra handling is part of why MLT carries a structural price rather than a pulp price.
Why Salvage Timber Matters
Beetle epidemics and wildfire leave millions of acres of standing dead timber. Conventional mills skip it because small, dead logs cost more to handle than they return in lumber. Laminating turns the economics around by using the fiber in a product that commands structural prices, so a stand that looked like a liability becomes a feedstock source.
The Scale of the Resource
In western North America alone, pine beetle outbreaks have affected tens of millions of acres since the late 1990s. Even a fraction of that standing fiber, converted to beams, represents years of manufacturing capacity, and the volume grows every fire season. The resource is large enough that product developers keep looking for ways to use it at structural grade.
Salvage logging runs on a clock. Dead timber loses grade as decay advances, so operators harvest beetle-killed stands within a few years of the kill and fire-killed stands as soon as access allows. The recovered logs feed sorting lines that separate mill-grade material from salvage-grade material, and MLT plants take the shorter, smaller pieces that dimensional mills reject.
Code and Policy Momentum
Building codes and state policies have opened the door for engineered timber, and the pace of acceptance varies by region. Washington has been the proving ground for tall wood buildings, and the lessons learned there show the way for mass timber construction in other states, from code officials to fire departments to engineering review boards.
State Leadership
Early adopters funded demonstration projects, trained inspectors, and published guidance that other jurisdictions now copy. That institutional memory matters more than the products themselves, because a contractor cannot build in mass timber where no one will review the drawings.
Beam Sizes, Ratings, and Certification
MLT beams range from 4×4 posts to members as large as 12x20x20, and they are ANSI certified by the Timber Products Inspection agency. The certification gives engineers published design values they can use without additional testing, which removes a barrier that stops new products at the specification stage.
| Product | Build-up | Typical span | Best applications |
|---|---|---|---|
| MLT | Small timber fingerjointed, edge-glued, face-laminated | Short to medium | Beams, headers, mid-rise framing |
| Glulam | Dried lumber laminations | Long | Roof beams, arches, long spans |
| CLT | Boards laminated in alternating directions | Two-way panels | Walls, floors, tall buildings |
| NLT | Dimension lumber nailed on edge | Medium | Floors, roofs, industrial decks |
Certification and Design Values
ANSI certification means the product meets published standards for strength, stiffness, and dimensional stability, and TPI accreditation backs the grading. The documentation trail mirrors the one that made cross-laminated timber in tall buildings credible, where material properties had to be proven before codes accepted them.
What the Tests Cover
Certified beams are tested for bending, compression, shear, and fastener performance. The same test data supports the fire, earthquake, and wind resistance ratings that engineers use in design, so a specifier can compare MLT with steel and concrete on published numbers rather than promises.
Structural Performance Under Fire, Earthquake, and Wind
MLT meets traditional building standards for fire resistance, earthquake resistance, and wind resistance. The behavior is not identical to steel or concrete, so engineers design with timber-specific assumptions about char, connection stiffness, and mass.
Fire Behavior of Laminated Timber
Large timber members char at a predictable rate, and the char layer insulates the unburned core. A 12-inch beam retains most of its section for the duration of a standard fire test, which is why heavy timber assemblies earn long ratings even without sprinklers in some occupancies.
Seismic and Wind Performance
Timber systems resist lateral loads through connections, not through monolithic behavior, so detailing decides performance in an earthquake or windstorm. Scalable timber engineering with LVL and CLT has already shown how engineered wood systems perform in mixed-use buildings, and MLT follows the same detailing rules for hold-downs, shear transfer, and diaphragm connections.
Connections Carry the Load
A beam is only as strong as the bracket that ties it to the column. MLT projects spec galvanized or concealed connectors sized to the member, and engineers check both the timber bearing and the fastener group at every transfer point.
Design values from the ANSI program let engineers size members directly from tables, the same way they use steel section properties. A 12×20 MLT beam, for example, can carry substantial floor loads over a clear span, and the published values remove the guesswork from preliminary sizing.
Where MLT Fits in the Building Market
MLT suits single-family, multi-family, and mid-rise office buildings. Its beams work as headers, girders, and floor supports, and its small-log feedstock keeps cost competitive when large timbers are scarce or priced for export.
Applications by Building Type
- Single-family: floor girders, ridge beams, and window headers over wide openings.
- Multi-family: floor and roof framing, party-wall headers, and balcony supports.
- Mid-rise offices: columns and beams in hybrid frames with concrete cores or steel moment frames.
The Relationship With CLT
MLT does not replace cross-laminated timber so much as complement it. The structural innovations shaping modern mass timber construction include both products, and designers choose between them based on span, loading, and panelization, with MLT carrying line loads and CLT carrying area loads.
Choosing by Span and Load
Where a floor must span two ways or a wall must carry distributed load, CLT panels win. Where the demand is a point load on a beam, MLT and glulam are simpler and cheaper to detail, and the decision usually comes down to framing economy.
Sourcing Questions for MLT Buyers
MLT’s selling point is that it uses fiber other products reject, but buyers should verify where the fiber actually comes from and how it was graded. A beam is only as good as its feedstock history, and salvage timber varies more than plantation-grown stock.
The Environmental Case
Sourcing from fire-killed and beetle-killed stands keeps carbon in the building instead of releasing it in a burn pile, but the math works only when the forest is managed responsibly. Buyers weighing MLT should examine the same evidence that goes into evaluating the environmental case for mass timber in any form, from harvesting methods to transportation distances to end-of-life options.
Questions to Ask a Supplier
- What species and moisture content are in the beam, and how are they controlled?
- Where did the fiber come from, and is the forest source third-party certified?
- What grade and design values does the ANSI certification cover?
- How are end joints tested for structural continuity in production?
Answers to those four questions separate a product engineered for the long term from one assembled from whatever logs were cheapest that month, and the distinction shows up in the first decade of service.