Modular x Mass Timber: How Manufacturers & Developers Can Get Going with CLT w/ Sterling Structural

A modular schedule can collapse over one thing: late decisions. That’s why cross-laminated timber (CLT) and modular construction fit together so well and why they can also magnify each other’s coordination mistakes if you treat them like conventional builds. Sidney Filippis, Director of Design at Sterling Structural, details what it really takes to bring mass timber into a factory-driven workflow without surprises. 

Sidney explains how modular teams should think about CLT, whether as a substitute for familiar assemblies or as a structural system that changes how loads, tolerances, and interfaces behave. Sidney also shares the first design assumptions to revisit when moving from steel to mass timber, including lighter weight impacts and the reality that wood, steel, and concrete each bring different tolerance expectations. Additionally, Sidney discusses costs: CLT can be more expensive up front, so the smarter comparison is total project cost, where exposed wood finishes can reduce drywall, paint, and labor while faster installs cut schedule risk. 

From there, Sidney details aspects that can make or break projects: MEP penetrations, connection engineering, acoustics planning, and moisture protection on site, and more.

If you’re considering a first step, Sidney explains why a plant tour and a pilot project can de-risk adoption, plus what success could look like for mass timber and commercial modular construction in the coming years.

Transcript

Welcome To Inside Modular

SPEAKER_01 0:00

Hello and welcome to Inside Modular, the podcast of commercial modular construction, brought to you by the Modular Building Institute. Welcome everyone. My name is John McMullen. I'm the marketing director here at MBI. Today I'm joined by Sydney Philippus, Director of Design at Sterling Structural. Sydney is here to talk about how cross-laminated timber can be used in modular building projects and the potential it offers the industry at large. Sydney, welcome.

SPEAKER_00 0:29

Hi, everyone. Thanks for having me.

SPEAKER_01 0:31

My pleasure. Thank you for being here.

Sydney’s Mass Timber Origin Story

SPEAKER_01 0:33

Tell me about yourself, Sydney. What's your background and what got you interested in mass timber?

SPEAKER_00 0:38

Yeah, so my background is I come from the architecture industry. So I was working as a traditional architect for a little over a decade on a mix of buildings. So breweries, casinos, residential. But the most recent project was a multifamily Mass Timber housing project. And while working through that, I had the pleasure of meeting one of my now coworkers, Michaela Harms, the vice president of Mass Timber at Sterling. And I learned that they were growing their design department and looking for a director of design. And it seems like the right fit, the right culture fit. So I've been with Sterling for about two and a half years now, running our design department and really working with the operations and the sales teams, making buildings come to life.

Why CLT And Modular Match

SPEAKER_01 1:32

Very good. It sounds like you've had experience designing all my very favorite structures. So mass timber and modular construction both depend on precision, repetition, and a lot of upfront coordination. From your perspective, especially from your architectural background, why do these two approaches seem to fit together so naturally?

SPEAKER_00 1:56

It's a really uh good kind of point here that mass timber and modular are very similar because the upfront coordination is not typical for all architecture projects, right? Sometimes things are just figured out in the field. Um, but with mass timber and modular, the the two things that I think you listed too that are so critical is the precision precision and the repetition. Um, so when you're manufacturing anything, uh the more times you can repeat whatever that part is, um, the faster it becomes from a manufacturing perspective, and the more precise it becomes because you get really good at uh making it using the right tools and checking that everything is uh directly related to the way it was modeled and drawn. So mass timber and modular really uh work well together and fit together naturally because mass timber has to be manufactured uh off site. So there's these massive pieces of equipment that are pressing either it's the CLT panels and in my area of work or the GLULAN members. And then a lot of the connections are also prefabricated and coordinated. So that really lends itself to the modular world and the way that that has been operating, um, even without mass timber as a component.

SPEAKER_01 3:27

Should

CLT As Product Or System

SPEAKER_01 3:28

modular builders think of mass timber as a as a product, as a structural system, or something else entirely?

SPEAKER_00 3:36

It really depends on how that modular builder is intending to use it. So sometimes it could be thought of as a substitute for CLR concrete. So we're seeing CLT shaft walls work really well with modular multifamily building. So the modular building would be typically using either CMU or maybe precast concrete in that application. And CLT is actually a really great alternative for the way that they're already working and the equipment that they already have. So that's one case where I think they could think of it as a substitute. But they also could think of it as I would say more of a structural system uh rather than an entirely different delivery model. It still is very similar to maybe they're familiar with panelized wall systems or, like I mentioned, precast. So it has a lot of similarities to other materials in the industry. It has its own unique properties in the sense that it is a wood product. And so where maybe, you know, glass, I was just working with someone on a curtain wall system. Glass is really hard to modify in the field. CLT, you don't want to modify it in the field, but it still can be modified in the field. So it's it's a little bit more flexible in the sense that it is a wood product.

Lighter Structures And Tight Tolerances

SPEAKER_01 5:02

So for modular manufacturers who are used to dealing with you know steel frames or precast, what are the first design assumptions that they need to rethink when they begin incorporating CLT or other mass timber components?

SPEAKER_00 5:20

We work with a lot of different um partners that are kind of making this switch. So I can think of a couple good examples. Um, one in particular, they're used to working with steel uh for these modules, and they're looking to switch it over to CLT. And one of the early design assumptions that helped them switch their brain a little bit was uh how much lighter the material is. So they're used to the weight and thickness of steel plates and steel members, and then using the CLT, it is a lot lighter. So that then impacts, right? The foundations, it impacts other systems that are tying into it. Uh, another thing that I think is really important when they are starting to incorporate it with maybe other materials, it could be like a hybrid structure, is thinking about the tolerances as things come together. So modular manufacturers are already set up so well to understand tolerance because they have materials coming together in a controlled environment. But just thinking through wood is gonna move different than steel and concrete, and those things have their own tolerance. So making sure that you're accommodating for wood, we typically say is like anywhere from an eighth to a sixteenth of an inch for precision. That's a lot closer than concrete. So making sure they have that in their design assumptions as they're putting things together.

Pricing CLT Beyond Material Cost

SPEAKER_01 6:52

As I understand it, the CLT is very similar to modular construction in that it can cost more upfront, but you know, like modular, the benefits come through faster schedules, less labor, fewer change orders. Assuming that's true, what should uh developers and modular manufacturers look at when comparing the true total cost rather than just you know material cost? Are there even greater benefits when using CLT and modular construction?

SPEAKER_00 7:19

When it comes to cost, I you know, I'd love to sit here and say, yeah, it's cheaper, but it's it's not. Um using CLT just like modular is going to be upfront more expensive. And sometimes that's a little scary uh for the building owner and or the developer. But a couple things that often aren't considered, and you know, my team really likes to remind the designers and maybe the GCs or whoever is kind of managing that full budget to think about when using CLT is that there are a lot of trades that are impacted by maybe swapping a modular material for CLT that then save costs in other places. So, like an example would be if the CLT is going to be the final finish, uh, you don't have drywallers coming back and installing drywall. So that's not only a labor, but also a material. They're not coming back and then taping those walls and painting those walls. So when you're looking at, or like a ceiling, for example, I could see um we have a project right now that we're working on that is using CLT in the corridor for the floor system, and they're not going to have the same amount of labor as it relates to all of their MAP penetrations running down that corridor. So it's really hard to say, okay, this material does cost more, but you have to really look at the big picture when you're comparing costs. It's not really just a true material cost to compare.

SPEAKER_01 8:55

You mentioned

Penetrations And MEP Timing Choices

SPEAKER_01 8:56

uh the penetration aspect just a second ago, and I wanted to ask uh about the thought and the work that goes in before fabrication begins. So, what issues need to be resolved, you know, before fabrication starts up? You said you mentioned penetrations, but there's also MEP coordination and connections and you know, fire systems and that kind of thing. What happens when a team waits too long to answer those kinds of questions?

SPEAKER_00 9:24

Yeah, sometimes it's a little bit like pulling teeth to get these questions answered. So there's a couple different paths that you can go, and it really just depends on the availability and maybe accuracy of information that the design team and the construction team is given and has the ability to support. So, for example, it is preferred, just like with modular, that all of the electrical and mechanical and plumbing penetrations would be pre-coordinated. Uh, that way they could be prefabricated in a controlled environment. And then when they get installed on site, the trades can basically come back in and they have all of their holes and they know where their things need to go. That isn't always the case. And the the kind of difference between modular and mass timber is some of those can be done in the field, and it really is just a conversation with your construction team. So, what what does that skilled labor look like? Um, and some of them, maybe it's better for the overall timeline of the project to do them in the field. Now I know that sounds like a little bit scary, but the time that it might take to coordinate with your architect and engineer of record exactly where all the penetrations are might be actually, you know, adding too much time because we're waiting for those answers to get that into fabrication. So while there are definitely issues in making sure that we have all of that precise, um, one way would be maybe you're, you know, putting off any penetration that's smaller than two inches to be done in the field. So you could set like a size tolerance. Um, and then another way could maybe just be that you're working through all of the, you know, large mechanical openings, for example. So there's a there's a couple different ways that you could resolve the MEP because that is, you know, one of the greatest hurdles that you'll have to get

Smart First Uses Plus Hybrid Lessons

SPEAKER_00 11:24

over.

SPEAKER_01 11:24

In your experience, and I'm thinking about factories here, modular factories, what are the most practical ways that they can start incorporating mass timber? We've talked about structural elements, we've talked about some interior sort of facade uh applications, but where do you see really uh the the best ways and the most practical ways for factories to start incorporating mass timber now?

SPEAKER_00 11:48

I would see if it was in more of the structural systems to start. So maybe they've historically been working on like a panelized volumetric module and it's made out of uh it could be, you know, cold form metal steel or some panelized wall system. I could see where you're swapping out um some or part of the walls for mass timber, and that would add to your like shear capacity of the building. So thinking from a structural perspective. And then also the floor and ceiling assemblies make a lot of sense. What I always like to say is like that use needs to do more than one thing. It can't just be a floor for the aesthetic of the underside of the ceiling, it has to be maybe it's part of your structural system. Like I said, it's helping with your diaphragm, or um it's adding a shear wall to the building. So, how can you have this material do more than one thing?

SPEAKER_01 12:55

I was looking at uh Sterling Structural's website to prepare for this. I came upon um the 500 Emma project, which is a housing project, uses uh CLT floors and roof decks uh with a stick frame, uh load-bearing walls. And I think uh there were some prefab bathroom pods in there as well. What does that kind of hybrid approach teach uh teach you or and teach other modular manufacturers about where mass timber delivers the most value in modular structures and in other forms of you know repeatable housing buildings?

SPEAKER_00 13:30

That was a really good find on your part because that is it's one of our favorite projects because of how smart they were in a variety of ways using hybrid structures, but also using prefab modular construction. So for using CLT for the floor and roof decks, they're really optimizing that repetition, kind of getting back to what's important in prefabrication with mass timber. So the floor system and the roof system, there was a lot of uh repeated parts, making it really fast to manufacture on our side and then fast for them to install. They also did something super smart, the design team did with uh looking at where the bathroom pods were going to go and understanding there was gonna be a drop ceiling. We were able to utilize uh, so there's typically three ply, five ply, seven ply in CLT. And for fire rating, if you're gonna leave it exposed, you typically see it be a five ply. But because they knew those bath pods were in certain areas, they were actually able to utilize three ply in some of the very repeated parts and save on their material cost there. So by using really smart design, some parts of it prefabricated off-site, some of it coordinated on-site, they were able to make this uh housing a really, really phenomenal project.

Connections Codes Moisture Acoustics

SPEAKER_01 14:59

So for manufacturers who are considering CLT, how should they think about the connections between the mass timber CLT components and traditional modular systems, you know, especially where uh the CLT product interfaces with a pre-existing, you know, steel chassis or a light frame wall or a concrete foundation, something like that?

SPEAKER_00 15:21

Yeah, one thing that's super critical is in all modular manufacturers will have either they have engineers on staff or they have preferred engineers that they're working with. But working with an engineer that has is familiar with Mass Timber is really critical to make those connections with Mass Timber. What we've seen is when someone takes on this scope for their first time, there there are some more questions and adds more time, and maybe they start to delegate some of that to the mass timber supplier. And it doesn't necessarily have to be delegated to the mass timber supplier. And when that is the process, that usually adds time and cost. So if the engineer that you are using could feel confident and comfortable engineering both the modular traditional modular systems and how it connects to the CLT, that's where it's gonna really pay off in the long run. So making sure they understand how to design for the connections, how to design for maybe it's in a seismic zone. Um, do we have to kind of change the ratio of the panels? Is there more hold downs? You know, there's a lot of things that go into the full system. And then I think understanding how it interfaces with light frame walls and concrete foundations, what are those tolerances? And how can we build smart details around those tolerances so that when the concrete is off by a quarter or a half an inch, what are we going to do? Um, and so we have a couple backups on the solution.

SPEAKER_01 17:01

What are some of the other aspects of CLT and mass timber that that maybe uh module manufacturers wouldn't know as much about at the outset? If they're considering using CLT, what should they be thinking about in terms of you know codes and moisture protection and acoustics? And you mentioned, you know, seismic zones a second ago. What about you know the vibration of the wall itself when when it comes to different different zones? What um what are what are some of these things that they should be thinking about?

SPEAKER_00 17:31

One thing that um I've heard is like a little bit of a misconception in the industry is that Mass Timber is really good with acoustics. It's not. Uh so one thing I would plan on is having a plan for how you're going to resolve the separation, whether that's from like unit to unit or floor to floor, because wood does transfer that sound. So having a having a good consultant or having a good rep for whether that's like a acoustic mat that's gonna go in between the floor systems. I also think the moisture mitigation that you that you mentioned, this is something a lot of people don't really consider. And so this has to be a meeting with all of the parties involved. And you want to talk through how are we keeping water off the material while it's on site, while other trades are going through it. Uh, and you really want to talk through what's the process of like drying in the building, because that's really, you know, wood is a natural material, it can get wet. Um, but it's more of a concern when people basically turn on their HVAC system and try to dry the building out really fast. That's when you're gonna get problems with your with your wood finish. Um, so having that plan, talking to, you know, woodworks is a great resource, asking the questions, you know, what have you seen in this climate, in this area, so that you have that plan together.

SPEAKER_01 19:06

Speaking of plans, um, what does a good digital workflow look like? You know, uh before we get to fabrication, before we're putting anything together, what what's the digital workflow look like through the concept and design uh phases of a CLT modular project? You know, shop drawings and fabrication files, logistics, that kind of thing. Um, what's your experience there and where do you think projects most often you know lose information between steps?

SPEAKER_00 19:37

Yeah, so Sterling is operating um on all of our shop drawings. We use Revit, which is pretty industry norm now for most architecture and engineering uh companies. So everyone is familiar with it. The cool thing about it is we're using that workflow from receiving models from our external team, coordinating amongst the trades, generating a 3D file that then is translated to our CNC machine. Uh so it's it's really one continuous software system that's managing design from architect, where maybe you're at like a level, you know, 300 of detail to we have to get to an LOD5. So the best ways to communicate always are sharing both 3D and drawings. Uh, you know, drawings are really where you can the models, we don't you can't always trust everyone's model. Um you can maybe trust your own, but that's about it. And so you want to make sure you have good drawings to look at. So whether that's, you know, architect of record or engineer of records drawings, and then also our shop drawings to compare and make sure that the design intent is really met. And take the time to walk your teams through those drawings so that maybe this is everyone's first time reviewing the shop drawings for a Mass Timber project and they don't really know what they need to be looking at and what really matters. And so I think it's really critical for the teams that are generating those high level of detailed drawings to explain to the entire team, you know, this one-eighth of an inch tolerance is really critical, and we need to talk about this. And so, where do projects often lose information is they're I think they're moving a little bit too fast, they're not really looking at the details, and there's always that um, you know, that Spider Man meme with everyone pointing at one another, and it's like refer to architecture, refer to mechanical. Um, and so making sure that something isn't like kind of lost in someone else's scope is another thing that always comes up. So with connections and the CNC fabrication in particular.

SPEAKER_01 22:00

Oh, it's a great visual. It's one of my favorite movies.

SPEAKER_00 22:03

I always think of it, yeah.

First Steps Risk And Future Outlook

SPEAKER_01 22:05

So, uh, what is a modular manufacturer who wants to start using mass timber? What is what should they do first? We've talked a lot about the different phases of construction, design, uh, pre-construction. What is the first thing they need to do when they begin a project and they want to use cross-laminated timber?

SPEAKER_00 22:26

I would recommend getting a tour of a mass timber manufacturing plant. Uh, there's always so much to be learned when you see kind of how the sausage is made. And people are really happy to, you know, get you in and show you how it how they work and where their bottlenecks are and where their challenges are. And I think they would learn a lot about how they could integrate together and work more as partners instead of like a supplier, right? And then a pilot project is always another great example. So whether that's starting, maybe you're a modular manufacturer and you typically work on really massive projects, but you know of you know a smaller infill housing, and that could be a really good one because it's, you know, less of an upfront risk. And so you're working through something at a smaller scale. Um, I see a lot of times meetings we've had with people who work on modular where we do talk through, okay, these are our typical details, and then that's how that would work in with their typical details, or in the reverse, you know, they're like, we've been doing this for 15 years like this. Is this something you guys could take on? So then then bringing that to my operations team and saying, hey guys, I know we usually do this like, you know, with four inches. Could we do three and a half as a typical? Just having a lot of conversations, I think being really communicative and asking questions is pretty critical.

SPEAKER_01 23:57

You mentioned the word risk in in your response, and it and it makes me think of a modular manufacturer who may be thinking, you know, things are great for me now. I'm using all the materials I know, uh, things are going very well. In your experience, having designed uh CLT structures, why should modular manufacturers be considering that product for their buildings?

SPEAKER_00 24:21

There's a couple different reasons I would be drawn to it. One being it is a domestic material. So you can get it from, let's say you're all your projects are in the Midwest or you know, in the US in particular. Um, it's not something where the logistics supply chain is coming from overseas. And so that's definitely going to de-risk your project. Uh, another, another reason I would say it's worth looking at is a lot of large companies are starting to look at how they can better support a sustainable future, right? If they're coming in and building a project, people want to know how are you making my community better? And if you can say not only that you're supporting a sustainable material that supports, you know, rural economies, if you think of the forest industry, and that it's also, you know, storing carbon. And so then it's lowering that project's carbon footprint. Um, that's what we're seeing as like a lot of drivers for why people are starting to look at it and maybe changing from a material that they've historic, exactly, they're like, it's working, why would I change it? And then the last thing I've seen most recently is with the volatility of the steel market. People are looking to diversify their options uh with lead times and cost.

SPEAKER_01 25:51

So looking ahead uh, you know, five to 10 years, what uh from your vantage point, what does success look like uh for the relationship between mass timber and modular construction?

SPEAKER_00 26:04

You know, five to ten years from now, I think the world is going to look very different as it relates to mass timber. As I mentioned, I've only been with Sterling for two and a half years. And in that time, I've seen it go from a material, and it still isn't mainstream, right? It's we are such a small part of the larger construction industry. And if you were to walk down the street and ask anyone about modular construction, I'd say most people understand a little bit about that. We're getting there. Yeah, you guys are you're doing the work. Um, but if you were to ask a random person on the street what is mass timber, your chances of someone knowing really what it is are much lower. And so I think what do I see a successful relationship looking like with Mass Timber and Modular is that they are working together more. I think right now we have a handful of partners that I would say are working in modular construction and incorporating Mass Timber. And we have a lot of inquiry, right? We have a lot of people say, I really want to use this. I just haven't found the right, the right instance or the right project. Um, and so seeing those get off the ground more, like how you pointed to the 500 Emma project, having projects that we can point to and say, you know, we worked with a modular partner on this, super successful. And this is how it was successful, like this is how we were measuring it, whether it was, you know, time from release for shop drawings to delivery, or it was time for erection, or whatever, whatever that metric is for how we're deciding what is success. I'd love to see more examples of it in the built world instead of in this design phase where everyone's thinking about how they can make this happen.

SPEAKER_01 27:55

Sydney, thank you so much for your time today. It was great to talk with you. I know five to 10 years was a long time to look forward, but hopefully it's less than that. Uh either way, I look forward to seeing more mass timber projects uh in the near future.

SPEAKER_00 28:11

Me too. I really, you know, the opportunity is there. And if anyone has ever been into a mass timber building, it feels great.

SPEAKER_01 28:19

They absolutely are. Um, thank you again. I really appreciate your time.

SPEAKER_00 28:23

No, thank you so much for having me.

SPEAKER_01 28:25

My name is John McMullen. This has been another episode of Inside Modular, the podcast of commercial modular construction. Until next time.