August 2022 Lessons in Firestop: Understanding Mass Timber Construction

Lessons in Firestop by Sharron HalpertWelcome back to our Lessons in Firestop. In our last lesson we talked about how the codes change every three years and how important it is to stay on top of the changes that impact your scope of work. I promised to tell you about a few changes to the 2021 International Building Code (IBC) so you are aware of how it will impact your work when you work in a jurisdiction that has adopted it.

Before delving into this month’s lesson, you should refresh your memory of that discussion, but as a quick recap, firestop special inspection is going to be required when you have a high-rise building as well as a risk category III or IV project.

The Two Major Changes

When considering the 2021 IBC, we will address two changes in this lesson. The first is related to the special inspection. Risk category III includes group R with occupancy over 250—think hotels and apartment buildings and join us for our next lesson, where we will point out some things that are done wrong on this occupancy type when it’s Type V wood-framed construction.

The other change you will see in the 2021 IBC concerns building codes that allow for mass timber construction up to 18 stories. Let’s be very clear here: There is a tremendous difference between wood-framed construction and mass timber.

Wood-Framed Construction vs. Mass Timber

Let me give you a quick rundown so you can see the difference. Regarding wood framed (and we will dig into firestop issues in the next section), the WoodWorks website explains it as follows: “Cost-effective, efficient, and accessible, light wood-frame construction is commonly used in Type III and V buildings up to six stories and podium projects with up to six stories of wood over another construction type (typically Type I-A concrete).”

Nail-laminated timber (NLT). Source: WoodWorks

Regarding mass timber, we are talking about something altogether different—you will hear terms like CLT, NLT, DLT, and glulam. Let me explain the middle ones first.

WoodWorks describes nail-laminated timber (NLT or nail-lam) as “a century-old construction material that is undergoing a design renaissance. Its structural performance and design elegance come together to create inspiring spaces in many historical buildings as well as modern new projects of all sizes.”

Dowel-laminated timber (DLT). Source: WoodWorks

Dowel-laminated timber (DLT) is common in Europe and is gaining traction in the United States for its ease of use with computer-controlled (CNC) machinery—such as lathes, routers, and mills—and its all-wood composition. DLT is similar to nail-laminated timber, but instead of nails or screws, DLT uses wood dowels to join laminations.

Then we come to glulam (glue-laminated timber). Imagine taking 10 pieces of lumber that are 2×12 inches and standing them on the 2-inch face and glueing the 12-inch faces together to make one big beam that would be 15×12 inches. (Remember that 2×12 pieces of timber are nominally 1½ inches by 11½ inches, so the beam would be roughly 10 × 1.5 = 15 inches wide.) They can make glulam beams as well as glulam floor slabs.

Glue-laminated timber (glulam). Source: WoodWorks

Glulam is a structural engineered wood product commonly used for beams and columns in residential and commercial applications. It is a highly visible form of mass timber, with long spans framing designs left exposed to take advantage of the wood’s natural aesthetic.

The one remaining type to explain is CLT, or cross-laminate timber. I want you to imagine two by fours that are finger cut at the ends and then glued together. There are short lengths and long lengths. The long lengths run north and south on the first layer, or lamella, the second lamella runs east and west. Then the next layer runs north and south again. This combination allows for the panel to have the strength of the wood running in both directions.

Cross-laminate timber (CLT). Source: WoodWorks

Historically, the use of mass timber has been strong in Europe, and now, due to several factors, interest in the U.S. is growing as companies such as Adidas, Google, Walmart, Under Armor, and a dozen other major brand names are looking toward sustainability as they build. Groups such as WoodWorks are looking to help project teams ensure that projects “pencil out,” or generate the desired returns. They are a free resource available to anyone who seeks support. Other groups such as Sister City are really pushing boundaries because historically it has been believed that you can’t make low-income housing pencil out, or you can’t make projects pencil out unless they are six stories or taller. Sister City and other developers are building projects that are four-story low-income housing projects that are financially feasible.

What Does This Mean for Plumbing Engineers and Field Crews?

Well, a lot of that will depend on the developer and the level of planning. Some projects buy the floor slabs and all the openings are coordinated onsite, similar to how you would work with prefabricated concrete slabs. Other projects have a great deal more upfront coordination, which means that some of your openings will be coordinated in the factory and they will arrive onsite with the openings already made. From what I hear, that is typical for openings larger than 4 inches. That means you will need to have the proper tools to make holes in wood for openings 4 inches and smaller. If you are doing hot works, then it means the typical housekeeping measures will suddenly become even more important. If you have hot works, you might want to consider using a system like this wireless smoke and fire detector.

Working in mass timber means that you will have to find some unique solutions when it comes to firestop as well. Hilti has the lion’s share of solutions, but don’t discount STI and 3M because they might be able to help you with some unique solutions, as can companies like Provent who has a really unique product suited to mass timber.

If you are working on a mass timber project and have questions, don’t hesitate to reach out to me. I would be more than happy to support your project and make you aware of some unique solutions that could work in your favor.

Connect with Sharron

A former kindergarten teacher turned firestop expert, Sharron is President of Halpert Life Safety Consulting LLC, a leading provider of firestop-related life-safety and passive fire protection solutions.

If you like what you read here and want to know more, email [email protected] or connect with her on LinkedIn or Twitter to tell her what else you want her to cover in this column. You can also follow her on Instagram. If you find this information valuable, please like, share, comment, repost, retweet, and throw it on IG to help people build better.

The opinions expressed in this article are those of the author and not the American Society of Plumbing Engineers.

Want news delivered right to your inbox?

Sign up for our free newsletter, delivered every other Thursday.

Scroll to Top