A New England Forestry Foundation Program


A fir tree in Downeast Maine. This is one of the trees approved for use in structural cross-laminated timber. Photo by Lauren Owens Lambert.

Mass Timber

Mass Timber

Mass timber is a term that refers to any construction technique that relies on massive pieces of wood. This includes post- and beam-framed homes and barns, as well as traditional mill buildings in New England that rely on massive wood beams to hold them up. Many of these buildings have stood in New England for centuries.

Today, mass timber also describes construction using large engineered wood structures, and these new techniques are transforming the way we construct tall buildings around the world. Formed by gluing or otherwise attaching smaller pieces of wood to form larger components, modern mass timber has the aesthetic appeal of natural wood patterns. And when sourced from sustainably managed forests mass timber contributes much less greenhouse gas pollution to the atmosphere than other structural building materials. Explore the sections below to learn more about mass timber and its benefits.

What is mass timber and how is it made?

Mass timber products are large building components, often made today by fusing smaller pieces of lumber together with nails, dowels, or structural, emission-free glues. Modern mass timber products are a type of “engineered wood.” As a result of combining multiple smaller wood components, mass timber products are capable of bearing much heavier loads than traditional wooden beams, and can be formed into shapes that exceed what can be derived from a single tree. For example, mass timber beams can (and do) arch over the entire width of an Olympic hockey stadium, while mass timber walls, floors and roofs may be made from wooden panels a foot or more thick, 12 feet high and 60 feet long. And making these large wood objects does not require harvest of mature or special trees like ancient Giant Sequoias. To date, softwood species such as New England’s red spruce and balsam fir and are used to make modern mass timber products.

Mass Timber Types and Common Uses

Mass timber products are used in a variety of building applications, such as walls, floors, structural spans, and roofing. They can substitute for concrete and steel in these roles. Because of the versatility and strength of mass timber products, it is possible to build tall buildings, currently up to 18 stories, out of wood.

  • Cross-laminated timber, or CLT, is a type of mass timber product that is formed by gluing lumber together edge to edge, and then alternating the directions of successive layers, to create sandwiched structure of perpendicular layers, with tremendous structural strength. CLT is the product at the forefront of contemporary tall wood building trends, with wide use in Europe and growing popularity in North America.
  • Glued-laminated timber, or Glulam, is made of parallel wooden laminations that are bonded together with adhesives. In a by-weight comparison, glulam is stronger than steel and can easily be formed into either straight or curved forms. It is commonly used for beams and arching roof supports, with striking visual and aesthetic appeal.
  • Nail-laminated timber, NLT, is comprised of lumber pieces bonded together with nails or screws. It is a wood construction technology that has existed since the 1800s, but has been updated with modern fabrication techniques. It is commonly used in flooring, decking, walls, roofing, and shafts.

Mass timber safety and strength

Mass timber products have proven time and again to be strong and safe building materials. As with any advance in construction, a new building material’s safety must be rigorously demonstrated and understood before people are living in residences made from it. Here in the United States, government agencies including the Department of Defense and the Bureau of Alcohol, Tobacco and Firearms have tested mass timber by blowing it up, subjecting it to conflagration at temperatures that would melt steel, and peppering it with shrapnel. After analyzing these tests and others conducted by engineers testing pioneering wood buildings and by the insurance industry, mass timber buildings of up to 18 stories now are included as a standard technique under the newest iteration of the International Building Code, which will be adopted by jurisdictions in the United States. These code provisions ensure the safety of mass timber in catastrophic events.

A common concern of many people learning about mass timber for the first time is fire safety. As confirmed by the International Building Code, mass timber buildings meet the highest standards of fire safety. Tests have shown that mass timber forms an outer layer of char when set on fire, which then self-extinguishes and preserves the structural integrity of the wood underneath. While steel beams may melt and fail in fires, similar strength mass timber elements, to the surprise of many, remain structurally sound. For this reason, mass timber buildings sometimes can be repaired after a fire that would condemn buildings constructed with steel, concrete or typical wood stud construction. Fireproofing treatments, such as covering wood surfaces with fireproof plasterboard, are sometimes included in mass timber buildings to add another layer of safety.

Barriers to mass timber construction

There are certain obstacles preventing wider use of mass timber. One of these roadblocks, particularly for tall wooden buildings, comes from outdated building codes. Older building codes do not have the same specifications and permissions for tall wood construction as the 2021 International Building Code, making it more difficult for builders to undertake projects in the high-rise range. Using the latest building code can significantly help to streamline the process of constructing cutting-edge wood buildings.

Another challenge for mass timber is a lack of in-depth knowledge and understanding of the material among architects, builders, and other stakeholders involved in its implementation. In order to overcome, for example, resistance to designing buildings with mass timber in mind or to taking on construction projects involving the material, stakeholders need to have a clear and up-to-date understanding of its safety and properties. Raising the level of familiarity with mass timber across the value chain will be crucial to accelerating its uptake, and organizations like WoodWorks have provided great technical support and education to building professionals to help overcome these barriers.

What we are doing to help bring mass timber to New England

NEFF’s Build It With Wood program aims to bring about a revolution in sustainable, climate-friendly, innovative wood construction for New England. NEFF’s expert staff produce evidence-based research and life cycle analyses to inform decision making around mass timber projects. With their expertise, NEFF staff advise policymakers and other stakeholders to facilitate mass timber construction and to raise its profile.

And through the Forest-to-Cities Climate Challenge, we are engaging directly with forest landowners, manufacturers, architects, builders, and housing advocates to take action for mass timber construction. The Forest-to-Cities Climate Challenge includes direct outreach and assistance for parties interested in mass timber, as well as forums aimed at fostering the connections, shared knowledge, and enthusiasm for the material from the standing trees to the finished buildings, creating the world’s first carbon value chain in service of climate mitigation. With work well underway in these areas, NEFF is helping to move its partners to action, bringing sustainable, locally-produced mass timber to New England.