[peterwwillis]

Large solid timber beams actually burn incredibly slowly: partly because they're so dense, and because wood is a good insulator. For a similar thickness beam, wood takes much longer to fail than steel when superheated. At 1100F, steel starts turning into spaghetti. But on wood, the layer of carbon created by the char becomes an insulating barrier that reduces heat on the non-charred side by up to 90%.

A bigger concern to me is the wood rotting from exposure to water or chemicals. Although reinforced concrete also "rots", but in different ways. Wood at least tends to sag before failing from rotting, unlike concrete.

I'm kind of surprised they don't utilize things like steel torsion boxes for the foundations instead of concrete, but perhaps there's cost considerations. They could do a lot of fancy things to extend the size of wooden buildings using steel if they don't mind losing those fire retardant properties.

Also, it should be mentioned that wood-based buildings can re-ignite after an initial fire, which doesn't happen with steel or concrete. While you may escape the fire and the fire gets put out, the structure may still not be safe. We may need new fire codes if these buildings become commonplace.

[brudgers]

Timbers burn more slowly than intuition might suggest because the fire first chars the flame exposed surfaces and the charred surfaces no longer contain much fuel to feed further combustion. The likelihood of charring rather than combustion is increased by chamferring the corners of the members.

The problem with incorporating steel into wooden buildings is the difference in coefficients of expansion. Not just thermal but expansion when exposed to bulk water or merely humidity as well. The reason reinforced concrete works is the similar thermal expansion of concrete and steel and their negligible expansion from moisture and humidity.

The development of better engineering methods to deal with wood's expansion in the past two decades or so is one of the reasons tall wood buildings meeting contemporary construction requirements have become more practical and widespread.

[chrishacken]

"A bigger concern to me is the wood rotting from exposure to water or chemicals. Although reinforced concrete also "rots", but in different ways. Wood at least tends to sag before failing from rotting, unlike concrete."

This. We just moved our office into a 100+ year old wood building. We're doing the renovating ourselves. Most of the wood in the building is rotting or uneven. I've spent a week so far leveling the floors. Every old (70+ years old) building I've ever been in is like this; some worse than others.

We have our datacenter in a stone/concrete building that was built in 1912. While it has also deteriorated, it's not nearly as bad as the wooden buildings. The floors have cracks in them, but they're still level for the most part, or easily repairable. The building will easily be standing for another 200+ years. I can't say the same for the wood building.

[flavor8]

That is not a modern wooden building, however, i.e. not an apples to apples comparison to the subject of tfa. Cross laminated timber has a high resin (plastic?) content, which makes it a very different material from construction lumber in terms of how it interacts with moisture.

[peterwwillis]

You really don't know that about concrete buildings without inspection, and possibly core sampling of the concrete. You don't know what the true grade of the concrete is or whether it's thick enough depending on loading. And you need to look for signs of common failure modes such as carbonation, chloride penetration, freeze/thaw cycles, alkali-aggregate reactions, etc. Most concrete failures can penetrate the entire slab before showing outward signs. And concrete slabs have 'exploded' from as little as 200C of heat due to trapped water vapor. This assumes it's earthquake-code concrete construction.

A mostly-stone building will be perfectly fine, though :)