There are two methods of protecting a building. When it's tall, we need to separate a building horizontally and vertically with what's called a two-hour fire separation. There are two ways we can do that with wood.
One is we take our wood and cover it up with two layers of fire-rated gypsum products, meaning drywall. That's what we did in Brock Commons. That's really heavy and it hides the wood, but it creates a traditional fire barrier to protect the wood.
The other method, which is really based on the way we've done things for 100 years—it's not new—is that we overbuild the size of the wood by a certain dimension. If it needs to be this wide structurally, we build it this much wider. That extra width is basically what would be allowed to burn in a big fire. It burns away very slowly—it actually burns at 0.6 millimetres per minute—so we can calculate exactly how much burn there will be. Over two hours, we lose a certain amount of material, but the remaining material still has the structural soundness to support the weight of the building plus the weights of the occupants and the firefighters who need to fight the fire. That's the principle involved.
The reality is that in all of the fire testing we're seeing for CLT products, it's very difficult to sustain a fire. Again, this is a public perception issue. The analogy I give is that it's like taking a big log and a lighter and trying to make a fire. You can't do it. You need little sticks, and you need to build up your kindling before you can put the big log on. These products are so robust that they do not catch fire very easily because they have this massive thickness.
As I said, we've designed wood buildings like this, and our codes have accepted wood buildings like this for the last century, since the beginning of building codes. We build heavy timber buildings with these big wood beams that are allowed to char naturally in a fire, but that protect the core structure. We've been doing it, but we just haven't shifted from thinking about it at certain heights to allow it to go to bigger heights. That's really the obstacle, and it's really, again, just an emotional shift that has to happen to embrace the science we already know. I think we're getting there, but it's going a little bit too slowly to really advance it.