Mass timber construction is mainstream in the code and increasingly mainstream in the supply chain. It is not yet mainstream in the pro forma. For a four to twelve story office, multifamily, or education project within trucking distance of a fabricator, it is now a normal option that a normal owner will consider. For a speculative developer in a market with no local supplier and a lender who has never financed one, it is still a conversation you have to win.
The code argument, at least, is over. That happened in 2021 and most architects have not fully absorbed it.
What counts as mass timber construction?
Mass timber means structural wood in large solid sections rather than dimensional framing. The workhorses are cross-laminated timber (CLT, layers of lumber stacked in alternating directions and glued into panels), glue-laminated timber (glulam, laminations bonded into beams and columns), nail-laminated and dowel-laminated timber, mass plywood panels, and laminated veneer lumber.
The distinction that matters on a job site is not the acronym. It is that these are panelized products, cut to a shop drawing, delivered on a truck in a sequence, and set with a crane. You are specifying a fabricated assembly, closer to structural steel than to a stick-framed apartment building.
APA, the Engineered Wood Association, publishes the product standards behind most of it, and ANSI/APA PRG 320 is the one you will cite for CLT. Structural design provisions live in the American Wood Council’s National Design Specification for Wood Construction, the NDS, 2024 edition.
What changed in the building code?
Heavy timber, now Type IV-HT, has been in the building code for a century. What the 2021 International Building Code (IBC, the model code most U.S. jurisdictions adopt with amendments) added were three new construction types built for tall mass timber, and they were carried into the 2024 IBC:
- Type IV-A: up to 18 stories and 270 feet, with all mass timber covered by noncombustible protection.
- Type IV-B: up to 12 stories and 180 feet, with a limited amount of timber left exposed.
- Type IV-C: up to 9 stories and 85 feet, with timber exposed throughout and lower height limits as the trade.
Read that as a menu of three trades between exposed wood and height. The design conversation on a mass timber project is largely about which of those you can afford and how much of the structure the client wants to see.
Fire performance is calculated, not assumed. Wood chars at a predictable rate and the char layer protects the section underneath, which is why the NDS gives a nominal char rate of 1.5 inches per hour for sizing exposed members to an hourly rating. Assemblies still get tested to ASTM E119 or UL 263 like anything else. Your plan checker will ask for the listing, not for the theory.
One caution on timing. The ICC runs a three-year cycle, the 2024 I-Codes are current, and the 2027 edition is in development. Adoption is state by state and city by city, so confirm which edition your authority having jurisdiction (AHJ, the building department that will actually review your set) has adopted before you promise anyone nine stories.
Does mass timber pencil yet?
Sometimes, and the honest answer is that you cannot know without a fabricator budget in schematic design.
The structural package usually costs more than concrete or steel on a line-item comparison. Where the money comes back is elsewhere: a shorter erection schedule and fewer trades on site, lighter structure and therefore smaller foundations, and the ceiling. On a project where exposed timber is the finish, you delete the acoustical ceiling, the drywall, and the paint from most of the floor plate. If the client was going to spend money on a warm interior anyway, that is a real offset. If the client was going to leave the deck exposed and unfinished, it is not.
Two variables move faster than anything in a textbook. Supplier distance drives freight, and a job 1,400 miles from the nearest plant carries a different number than one 90 miles away. And tariff policy on wood products has been moving: a 10% Section 232 duty on softwood lumber, with higher rates on cabinets, vanities, and upholstered furniture, took effect in October 2025, which is enough to make a spring 2026 budget stale by fall.
The carbon case is stronger and more stable than the cost case. Architecture 2030 puts the embodied carbon of building materials and construction at roughly 11% of global energy-related emissions, within buildings’ overall share of roughly 37% to 39%. Structure is the largest single slice of most projects’ embodied carbon, which is why a structural swap moves the number more than any finish decision. That argument is worth making to institutional clients with published climate commitments, and it lands better when you bring an actual embodied carbon comparison rather than an adjective.
What does it change about your drawing set and your fee?
More than most firms budget for, which is the single most common way a first mass timber project goes sideways.
The fabricator has to be on board early, and their shop drawings are on the critical path in a way that steel shop drawings usually are not. Panel layout, connection design, and the fabricator’s tolerances feed back into your plans during design development, not after.
Then there is the coordination that comes with a structure you intend to look at. Every mechanical, electrical, and plumbing penetration through a CLT panel is a coordinated hole in a shop drawing, not a hole a subcontractor cuts in the field. Acoustics between residential units usually needs a topping slab or a resilient assembly, so the floor buildup you sketched in schematic design will change. Moisture protection during erection needs a written plan, since a panel that sits in three weeks of rain will show it forever.
Price the coordination. A firm that quotes its usual construction documents fee on a first mass timber project will absorb the difference, and the traditional fee split (schematic design 15%, design development 20%, construction documents 40%, bidding and negotiation 5%, and construction administration 20% per the American Institute of Architects (AIA) Handbook of Professional Practice, 15th ed.) will not survive contact with a fabricator submittal cycle nobody budgeted.
Where mass timber still falls down
Insurance and lending are the quiet obstacles. Builder’s risk pricing for combustible construction during erection, and a lender who has never underwritten one, will sink a project long before a plan checker does.
Regional supply is uneven. So is contractor experience: a general contractor pricing their first mass timber job will add contingency, and they are right to. Some AHJs are still working through their first tall timber submittal and will ask for more substantiation than the code strictly requires. And exposed structure is unforgiving of sloppy work, which means the trades who follow you need to be told, in writing, that the ceiling is the finish.
None of that is a reason to avoid the material. It is a reason to treat your first one as a project with a learning curve, priced accordingly, rather than as a normal building made of a different material. That is the same lesson every genuinely new delivery method teaches, which is why it shows up again in modular construction and across the trends worth tracking into 2027.
AECPulse Project Manager tracks hours by phase against budget on your first mass timber project, so the coordination time you spent this round becomes the fee you propose on the next one.