Regular readers will know I’m a big fan of manufactured lumber, a.k.a cross-laminated timber (CLT) or engineered wood. It’s basically a way to glue together smaller pieces of timber to create wooden beams which can replace a lot of steel and even concrete in mid-rise construction, locking away the carbon and replacing carbon-producing industries. Building multi-story buildings with wood is generally seen as one of the important ways we can reduce future climate change.
Turns out, however, that’s not the only way to make sure of the Northeast’s trees that are too young and small to become standard lumber. You can use it as “structural round timber”.
We know them as logs.
Yes, creating modern buildings (not cabins) with logs is a thing, and a Maine town wants to create a factory to take advantage of it. Mainebiz has a story, right here, and you should check it out.
Engineered or manufactured lumber is dangerous for firefighters. It burns more quickly and the loss of structural support can be sudden.
CLT and other engineered lumber is not inherently more dangerous for firefighters – it burns much *less* quickly than traditional wood framing – but just like any new construction technology, it does have some different characteristics that fire departments must factor in as they attack any fire.
David is correct. The code has been updated in 2015 and 2021 to reflect the performance of heavy timber, glulam, clt, etc. The ICC and NFPA do not approve systems without significant testing and research. The idea that “wood burns” doesn’t apply the way people think it does. Sure, a toothpick will burn quickly. Try lighting a 20″ diameter log on fire with a lighter, I’ll wait. In fact, steel is far more subject to structural fire than the comparable heavy timber elements, which is why it must be encapsulated with intumescent coating or drywall, while wood can be exposed.
Depending on the diameter, round timber can have a one to five-hour fire rating. That is because round timber, unlike milled lumber, creates a “char” layer that protects the internal structure. Milled lumber and other engineered wood products do not behave in the same fashion.
While steel does not start to melt until it reaches over 2,500°F, it softens at temperatures as low as 1,000°F, and can result in steel beams giving way long before a round timber would.