Wood Works Fire Safety Acoustics

Mass Timber Building Design: Fire Safety and Acoustics

Foreword by Ian Thompson, Editor

Mass Timber Building Design: Fire Safety and Acoustics

Mass Timber Building Design: Fire Safety and Acoustics

Unveil the innovative world of Mass Timber Building Design in our latest video post hosted by Wood Works. We focus on the design and construction of the Junction Lofts project, highlighting the use of mass timber – an innovative, sustainable, and durable material.

Our journey through the mass timber building design introduces you to the critical aspects of fire safety and sound insulation. We delve into how mass timber constructions ensure the safety and comfort of their inhabitants, addressing common concerns about fire hazards and noise transmission in such structures.

We talk about the rigorous fire assembly ratings, the thickness of the floor planks, and the dimensions of the beams and columns, all contributing to the fire safety of the building. We also discuss the innovative solutions used to minimize sound transmission between floors and units, vital for maintaining the tranquility within these spaces.

Using resources like the WoodWorks website, we’ve gathered valuable information about the performance of mass timber, particularly during fire events. This video post serves as a comprehensive guide not only for architects, developers, and construction engineers but also for anyone interested in sustainable building practices.

Join us as we explore the beauty, strength, and versatility of mass timber and its pivotal role in modern building design. Discover the meticulous planning, in-depth research, and attention to detail that goes into creating safe, soundproof, and environmentally friendly mass timber buildings.

Video Transcript

You know if you look around at this building, it’s concrete floors, there’s a little bit of drywall on the walls, and the rest of it is wood. We’re standing here in the Junction Lofts project. It was completed at the end of December 2022. It’s located within the Valley Junction neighborhood of West Des Moines.

The building has approximately a 4,000 square foot footprint. That’s three stories, with retail on the first floor, and then we have 11 apartments and two small offices on levels two and three. We were drawn to mass timber in the design of this Junction Lofts project, and for the Star Lofts project. Mass timber comes with a number of environmental benefits.

Of course, mass timber is made from wood, which is a sustainable resource. It has significant durability benefits.

When you see the exposed wood in a mass timber building, it’s natural to be concerned about fire. One of the bigger challenges with a building of this type is ensuring the safety of the folks that use the building. In this case, the fire assembly ratings required were to provide 1-hour protection on the floors between levels, as well as some of the structure that holds up those floors.

So that affected our design in terms of the thickness of the floor plank, the thickness of the concrete we put on top of the plank, as well as the dimension of the beams and columns that were required to be rated as well.

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In terms of the overall safety, I mean, we have the same fire separations as any traditional building would have of this type. The interesting thing about the actual timbers is they oversize them an inch and a half in all directions to allow them to burn for up to an hour before they actually begin to become structurally compromised.

We have found that the city code officials have been very open to this building type, but they’re excited about it and they’ve been very open and available to us to make sure that our life safety strategies align with what they are comfortable with.

Yeah, I mean, I think we just shared the same material with them that we were reviewing as we tried to understand how mass timber performs in a fire event, because we had kind of a mix of commercial office and residential. The lines where those ratings weren’t as obvious as if maybe one or two of those different elements had been left out.

I did spend a lot of time on the WoodWorks website. I did have a few conversations with some folks from that organization to help us understand. Our structural engineer did a lot of research as well, specifically around the columns and beams, and how to design those to the right size to, you know, achieve the structural strength that we needed to support the building, but then to accommodate the charring should there be a fire.

We used them just with some of their historical data, some of their white papers and things like that, some of their precedent projects of how previous projects had been, you know, designed, procured, put through the regulatory agencies and things like that. So we just used some of their online resources, the white papers, and some of their design guides.

I would say really a lot of those challenges end up being solved through education. There’s a lot of data out there on, and actually on how well mass timber projects perform in the event of a fire. The other thing we had to consider, because this is a multifamily as well as a commercial mixed-use project, is the way that we deal with sound transmitting from space to space.

As you can see in the exposed columns, beams and decking behind me, the beauty that it brings, it’s a double-edged sword because it also means that you’re not taking advantage of the plenum space and that air gap that would be in a more traditionally constructed building.

There’s two kinds of sound transmittance that we were dealing with: one is like just the voice noise in the atmosphere to transmit through the elements of the structure, the other one is called impact insulated class, which is, say you’re in your kitchen and you drop a pan and that vibrates the floor.

On the Junction Lofts project and the Star Lofts project, we have decking that’s approximately 4 inches thick. That decking mass does provide some sound insulation, but additional insulation is definitely needed. So I mean, a sound barrier is extremely important in a mixed-use building, in particular because there’s apartments above us and this is going to be a restaurant/bar.

So we have a layer in the floor that is helping us to reduce the sound transmission from floor to floor. Additionally, we have some measures in place from unit to unit. Nobody wants to hear their neighbor flushing the toilet, so in this building we have a Maxon acousta mat is what we used. That is in between the mass plywood panel and the concrete floor. It essentially holds the concrete about 3/4 of an inch above the plywood so that it prevents the vibration from transferring through the floor system, you know, from one floor to the next.

So we have to have acoustic tests just to pass code, you know, to prove to the city that the building is going to be what we say it is. But then also, that’s very helpful for us to have a good understanding of how the building will perform. So the testing is more limited than on other building types, just mass timber is newer.

The resources that really helped us the most were the WoodWorks testing index, various white papers both from WoodWorks and manufacturers, just to get a good general understanding of the performance of mass timber. And then we had a few consultants that we were pointed to that gave us a good understanding of the overall systems as well as pointed us to some specific tests.

We had very few issues on this project in particular when it actually showed up on the job site. The sequence of events is not terribly challenging. I think the biggest thing is making sure that your planning is done appropriately on the front end. Essentially, what you’re trying to do is get a building that fits together like Lincoln Logs, so it shows up on the job site and you can tilt panels up, put columns and beams together, everything fits right into place.

If somebody were to come to me and tell me they want to build a mass timber building, and wanted my advice, I would say the first step is to make sure that your design is super dialed. If your design is dialed and your shop drawings are accurate, it’ll fit together easily, you know, fits together just like Lincoln Logs.

Overall, we found mass timber to be more approachable, I think, than we potentially expected or at least feared. There truly is a community, I think, when it comes to designing and building mass timber structures. WoodWorks, Think Wood, other organizations as well, provided so much support along the way. We’ve been able to spread the message about mass timber to people seeking to learn more about the building.

For instance, several of the development corporations in Des Moines and across the Midwest have sought out tours of the building, in addition to construction companies in the area. Our goal is really to use this building to help share information about mass timber and encourage other developers, construction engineers, architects and everyone in between to look into mass timber and take the risk. It’s worth it.

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