Tanya Luthi is a timber expert and a Vice President in our New York City office. She is also a member of the NYC structural code committee, which advises the Department of Buildings on revisions to the city’s building code.
Recently, we sat down with Tanya to understand how timber might be better integrated as a building material in New York City, talking about the code and the challenges and benefits of timber.
What are the current code and regulations for timber as a building material?
In terms of height, the building code in New York City allows combustible construction (which includes timber) for certain occupancies up to 7 stories and 85 feet above grade, provided that the exterior walls are noncombustible and the building is fully sprinklered.
Although all wood is combustible, there’s an important distinction between the fire behavior of unprotected light-frame construction and mass timber structures. When exposed to a fire, large timber cross-sections form a char layer that insulates the wood in the center, which allows the interior of the section to retain its load-carrying capacity. This char behavior results in a much more fire-resistant structure than one built with small pieces of dimension lumber.
The New York City code acknowledges this behavior indirectly through its heavy timber provisions (Type IV construction), which specifies minimum timber dimensions for the interior structural elements in lieu of a calculated fire-resistance rating. These provisions are based on historic timber-frame construction that was common in the late 19th and early 20th centuries. We have some wonderful surviving examples of these structures scattered throughout the city, such as the historic brick-and-timber lofts in DUMBO.
However, these historic code provisions are not always well suited for modern mass timber construction. For example, we have a whole new range of engineered mass timber products available to us today, some of which are not yet acknowledged in the New York City code. Cross-laminated timber (CLT) is the most prominent example. Adding CLT provisions to the code was an important effort in this most recent code revision, which we hope will be adopted by the City Council later this year. We’re a bit behind other jurisdictions since our current code is based on the 2009 version of the International Building Code (IBC), but CLT was incorporated into IBC in 2015.
What about other code changes that might be in store down the line?
The 2021 version of IBC is introducing new mass timber construction types and revised height and area limits, permitting timber buildings up to 18 stories (though at that height they need to be fully encapsulated in non-combustible finishes such as drywall). The new New York City code which is soon to come out will be based on a combination of the 2015 and 2018 versions of IBC, so these proposed height limit changes will not come under consideration for New York City until the next code cycle.
Given your experience with the code revision process, have you seen challenges that are specific to timber?
Modern mass timber is at a disadvantage because it is “coming of age” at a time when we have very prescriptive building codes. Steel and reinforced concrete are mature industries, and most people in the world of buildings (designers, contractors, developers, code officials) are familiar and comfortable with them. Going even further back, think of the Gothic cathedrals all over Europe built with unreinforced masonry. There were no building codes back then; people figured out what to do by trial and error. That’s obviously not acceptable today, because an error can cause catastrophic loss of life. However, we do still need a way to allow people to (safely) do something that’s never been done before, otherwise, we’ll never innovate. We already know how difficult it can be to innovate in this industry: labor productivity in construction has actually declined since the late 1960s.
We keep hearing that timber is on the rise and getting trendy in NYC. What are some current projects?
The developer Flank recently completed two mixed-use mass timber projects in Williamsburg, Brooklyn: 320 and 360 Wythe. There are two residential projects at or near completion that I know of and others that are in various stages of the permitting process.
In addition to the projects that are being built, there have been numerous others on the drawing boards that either have not gone forward or are currently on hold but demonstrate the way timber is capturing the imagination of the design community. The most well-known is probably SHoP Architects’ proposal for a 10-story building at 475 West 18th Street, one of the winners of the USDA’s 2015 tall wood building competition. I also loved the MGA study envisioning how to build the Empire State Building in mass timber. Our building envelope group is involved with a development in Red Hook which is currently on hold in the design phase but has been designed as mass timber, so we’re hoping that project comes back online.
It’s clear from some of these early projects that timber is becoming a preferred building material. What are some of the reasons for this?
There’s not a single reason; timber’s appeal is different depending on where you sit.
The term “sustainability” is everywhere now, and, as with many words that are commonly used, it’s also sometimes abused. But you don’t need to squint or stretch the truth to make the case that timber is a truly sustainable building material.
In the past, when we talked about carbon footprint, our industry was mainly focused on operational carbon. We’ve made huge strides, and now it’s time to think about embodied carbon in an equally serious way. That’s especially true when you consider that the benefits of reducing embodied carbon are realized right away, not spread over decades like operational carbon. As climate science has shown us, we need to make an impact now, before the damage is irreversible.
Trees sequester carbon from the atmosphere, and we can keep that carbon locked away for decades or even centuries by using timber in our buildings. That’s particularly true if we are using timber to replace more carbon-intensive materials like concrete, either as a wholesale replacement or a partial one through the use of hybrid and composite systems. Sustainable forestry practices are key here, and we know how to manage healthy forests while harvesting selectively so that we can also have a thriving timber products industry.
In New York City specifically, we’re still more focused on operational energy (think Local Law 97, which is a seminal piece of legislation but still doesn’t address embodied carbon). With the lack of leadership at the federal level, cities and states are in the best position to light the way.
Interesting. There’s certainly a case for how timber as a building material can create more sustainable environments. What about wellness?
That’s a great question. We’re starting to pay more attention to wellness and the impacts of biophilic design, which connects people and nature in the built environment. The science is still in the early stages, but we have evidence that exposure to natural materials like wood has a physical impact on us: reduced stress, better ability to concentrate, improved sleep.
I think New Yorkers, in particular, understand the value of green space – what would Manhattan be without Central Park? – but I find it ironic that we don’t always make the connection between outside and inside spaces. Parks are great, but the fact remains that we spend 80-90% of our time indoors. Why not bring some of that ethos to our building design as well as our landscapes?
Good point – we do spend a lot of time in buildings. Let’s take a look at the benefits of timber from more of a construction perspective. What benefits are there here?
If you’re approaching this from a more dollars-and-cents perspective, there are a whole other set of advantages that timber can offer. Any time you’re building on poor soils or adding stories to an existing building, timber’s lightweight can save on the costs of foundations and reinforcing existing structures.
Here in New York, where we have a huge inventory of existing buildings and most of the “good” land has already been developed, there’s a lot of opportunity. And, speaking of how tight on space we are here, the high level of prefabrication used in modern mass timber means that a lot of activity can be shifted from the job site to a plant, where it’s easier to control quality and provide safer conditions for workers. It also reduces construction time on-site, which means savings on general conditions for the contractor, as well as savings on financing costs for the owner.
And finally, for every New Yorker who has been driven to the brink of insanity by noise coming from a nearby construction site, mass timber builds are incredibly quiet: these jobs mean fewer trucks cycling through the area, and most of the installation happens with a crane and some hand-held power tools.
How can we advance the dial in terms of code to build more with timber and take advantage of some of the benefits you’ve outlined?
I think it’s incredibly important that we have a science- and evidence-based dialog with building and fire officials.
Many timber building designs are breaking new ground, which means they do not fit within the bounds of the prescriptive code. In New York City, we would need to exceed the current timber height limits to truly take advantage of mass timber’s “sweet spot,” which I think is in the 8- to 15-story range.
At Entuitive we believe strongly in engineering performance, and mass timber is no exception: we have to take a performance-based approach. This means quantifying what “performance” means, particularly in terms of life safety, and holding ourselves to consistent standards regardless of what material we’re building with. There’s a tendency to want to hold timber to a higher standard than steel or concrete because it’s unfamiliar, and that’s a flawed approach because every material comes with its own risks and advantages.
Is there anything we can learn from earlier recent efforts in terms of bringing timber online in New York?
Although we understand that mass timber behaves very differently from light-frame wood buildings, we do need to acknowledge that we are still dealing with combustible material. I think the early mass timber movement neglected to bring code and fire officials into the conversation, and that was a mistake.
What I see happening now, maybe as a result of that oversight, is that people are reacting to the idea of mass timber buildings in dense urban environments with a lot of emotion and not a lot of data. I do understand those emotions: if the safety of first responders isn’t worth getting emotional about, then I don’t know what is.
However, I’ve been thinking a lot about some advice I got recently from a friend. “First get the facts,” he told me. “Then you can get emotional.” And that’s really all I’m asking. Let’s make sure we’re dealing with the facts. We have a lot of data from research that’s been done all over the world: fire tests, durability tests, even blast tests. More research is still needed, but we have a solid foundation to work from if we’re willing to take a performance-based approach.
How do sustainability goals contribute to the conversation? Do the sustainable advantages of timber help to advance the timber agenda?
I would offer a qualified “yes”… qualified because much of our industry and our local codes and laws do not yet address embodied carbon in a meaningful way, and that’s where timber’s sustainability credentials truly make it stand out. Many mass timber projects don’t make it past the drawing boards because the cost estimates come back too high relative to steel or concrete alternatives. Part of the reason is that we don’t pay the true cost of materials with high embodied carbon content.
It’s often difficult to make a choice that’s better for the environment when the impact on our wallets is immediate but the impact on the planet is distant. It’s a little bit like buying organic food: you make the choice in a grocery store, where you might not be able to see any difference between a typical product and its organically grown counterpart, but you certainly see the difference in cost. You don’t necessarily understand what you’re getting for those extra dollars unless you are a highly educated consumer.
Tanya, thanks so much for your time and sharing your insight. Any parting thoughts or wisdom for our audience?
I’d hate to leave off on a note implying timber buildings are necessarily expensive, so I want to put my designer hat back on and say that if you have the right team and take the right approach, these buildings can be economical in addition to being beautiful and sustainable. We need to come at these designs from a “timber first” perspective. In other words, don’t just take your last concrete or steel design and try to morph it into a mass timber structure. Use the strengths (and limitations) of timber right from the start to make fundamental decisions about things like massing, column grids, floor-to-floor heights, lateral systems. Embrace the constraints instead of trying to fight them!