We’ve several of these wood high rises here in Norway now, and our building code is pretty strict.

A friend of mine lives in one of these (Treet in Bergen, built using glu-lam), from what I remember it’s covered in fire-retardant coating, and has lots of sensors and sprinklers. And pretty strict rules (no BBQ of any kind on the roof terrace, etc).

Edit: have a look here, google translated (sorry) https://translate.googleusercontent.com/translate_c?depth=1&...

> - When glulam structures begin to burn, a layer of coal is formed on the outside of the wood and the fire goes out. All wood surfaces are painted with fire paint and there are outlets for extinguishing water on each floor. There is sprinkling in apartments, in corridors, on balconies, over the ceiling and in the garage facility. The apartments are also approved in fire class EI90, says Kleppe.

This question comes up every single time anything related to wood construction is talked about. The keyword in mass timber is mass. It's quite hard to set a big mass of wood on fire. It burns slowly and relatively predictably -- meaning you have more time to evacuate. And because of its mass, an outer layer can char, burn out and leave the building standing.

Also sprinklers.

The problem is the glue. When the glue melts (which it does at a much lower temperature than wood burns), the structural integrity is lost.

Firefighters do not enter new construction homes in the US because they often use these as floor joists. The time until failure has been greatly reduced compared to older homes. Things may have gotten better in the last few decades, but I'd like to see the data.

You’re thinking of I-joists, which are a kind of engineered lumber, not a kind of mass timber. And those do light up like kindling. The glue used in glulams and the like chars at the same rate as the wood, and it’s pretty easy to achieve known fire ratings simply by making the members a little chunkier than they need to be since the char rate is known.

There are various ways of joining large amounts of wood together. CLT uses glue. Brettstapel uses wooden dowels (using two kinds of wood with a different hardness, so the dowels stay in place). I'm sure there are other variants as well.

Wooden houses catch fire relatively easily because they're made of many small pieces of wood. Larger, monolithic pieces of wood are considerably less flammable. (Imagine trying to start a campfire with a single log.)

This. If a log house or similar construction burns, the walls are often left standing afterwards. Solid logs are really slow burners.

These structures are actually pretty fire resistant and does not loose structural integrity at high temperatures. Only the outer layer will burn to charcoal which then functions as an insulating layer protecting the inner layers.

Probably a lot better than what happens to modern concrete buildings which are then wrapped in plastic:

https://en.wikipedia.org/wiki/Grenfell_Tower_fire

Timber doesn't burn as fast as that, especially in a city as wet as London.

Mass timber is more fire resistant than steel.

Edit: In building applications. Steel softens and loses its strength in the presence of heat.