
The Case for Wooden Skyscrapers - oli5679
http://www.economist.com/news/science-and-technology/21706492-case-wooden-skyscrapers-not-barking-top-tree
======
vlehto
It's often surprising how much of building codes are about fire safety.
Occasional hazards practically define your day to day environment.

The most fire sensitive part of a high building is the staircase. You want
long burn time in fire but also have very little "fire load". (Amount of
energy released from material that can burn in typical fire. Typically
MJ/sqm.)

Steel staircase gets you 0 fire load but relatively short "burn time". Because
steel gets soft at relatively low temperature and more importantly conducts
heat very well.

Pure concrete stair case is better, but you get cracking that shortens the
burn time.

Wood is surprizingly good for burn time, but you greatly increase the
likelihood that the fire will start form the staircase. Which is really big
no-no. Sometimes even burning a complete house (starting from somewhere else)
is lot better than just burning the emergency exit.

The only really good option is reinforced concrete. The concrete insulates the
steel, which provides ductility to the whole structure. With reinforced
concrete staircase and stairwell, it's questionable how much you benefit from
wooden load bearing structure.

I think it can be done. And it can be done really well too. But you may need
to step away from typical architecture and step into something more modular.

~~~
Spooky23
There's a reason for that. My father in law was a fireman who retired as chief
after 45 years.

Fires are rare today -- but were incredibly common during the 60s and 70s. He
was at an _average_ of two a week in those days. It was common enough that
insurance companies had "protectives" who were firemen to go in and pull out
your furniture.

Fire is rare because of those codes today.

~~~
vlehto
Even 60's were safe compared to earlier centuries. It used to be common for
whole cities to burn down. And again we can thank the codes.

~~~
ddeck
The development of pressurized water systems and thus the ability to quickly
extinguish fires likely had a pretty significant impact.

The first Steam-pump fire engines only came into (very limited) use in the
1850s and ICE pumpers in the early 1900s.

~~~
vlehto
Fire codes at the time required wide paved streets to act as fire barriers.
You get double benefit when you can get your fire engine to the desired
location by that new fat street.

And then again reinforced concrete also became available around 1900.

So yes, the code is only small part of all that. But I'd claim it's
significant part.

------
mhomde
There's a really interested building material called CLT (cross-laminated
timber) that's exceptionally strong and durable, and has good fire resistant
properties. In Sweden some have started building houses out of them since
their load bearing qualities enables open floor plans. It's like plywood on
steroids and you use giant cutters to assemble buildings in a few large pieces

Here's an article, I think there's a few variant of similar materials, not
sure which is "best"

[http://www.popsci.com/article/technology/world%E2%80%99s-mos...](http://www.popsci.com/article/technology/world%E2%80%99s-most-
advanced-building-material-wood)

~~~
arjie
There's a building in Portland that's going to be twelve stories tall and
built with CLT. My uncle works with one of the companies involved in its
construction which is how I heard of it:
[http://www.structurecraft.com/projects/framework](http://www.structurecraft.com/projects/framework)

~~~
mhomde
Nice building, looks very Scandinavian/danish to me for some reason :)

------
wimagguc
Previous discussion on the same topic (different article but might be based on
the same press release, the 3D renders are suspiciously similar):
[https://news.ycombinator.com/item?id=12190537](https://news.ycombinator.com/item?id=12190537)

Safety was the first to pop in mind there too -- I guess it won't be easy
selling those flats.

------
fpoling
A highest wooden house is in Bergen, Norway -
[http://journalofcommerce.com/Projects/News/2016/1/Norwegian-...](http://journalofcommerce.com/Projects/News/2016/1/Norwegian-
project-breaks-tall-wood-building-record-1013064W/)

It is 14 floor apartment building and owners had no problems to sell the
apartments there. Personally it looks rather ugly especially when looking from
near bridge. But then a lot of modern architecture is ugly for my taste...

~~~
jeff_petersen
> Personally it looks rather ugly especially when looking from near bridge.
> But then a lot of modern architecture is ugly for my taste...

I agree with you 100% there. That is a particularly ugly building.

------
twelvechairs
There's a lifecycle issue which isn't accounted for here. Steel and concrete
last almost forever once built - how long do you trust your glue-laminated,
termite-sprayed, fire-sprayed timber floor? Especially after a couple of cases
of water or impact damage over time...

Reconstructing towers (particularity residential towers) in-use is an
incredibly problematic process.

~~~
vlehto
Reinforced concrete suffers from carbonation. The concrete is base, but slowly
get's neutralized by carbon dioxide. Once this has been done, the concrete no
longer chemically protects the rebar inside. Then if we take into account that
most concrete is porous and has moisture content, that rebar is going to rust
relatively quickly. When it rusts, it expands breaking away the covering
cement.

Typically reinforced concrete has lifespan ranging from 60 to 150 years. Wood
in colder climates often has similar lifespan.

[https://en.wikipedia.org/wiki/Concrete_cover](https://en.wikipedia.org/wiki/Concrete_cover)

~~~
brudgers
Ordinary buildings are considered to have a lifespan of thirty years. That
doesn't mean that they won't be around longer, but that there is often a point
of diminishing economic returns in designing for a longer life cycle because
maintenance tends to become a primary factor...for example thirty years is a
long life for a roof system or the sealant joints upon which modern buildings
rely.

~~~
dredmorbius
Would you happen to have a reference for that 30 year lifespan?

Is that residential, commercial, industrial, all, other?

~~~
vlehto
I'd like to know that too. Never heard anything shorter than 60 years. But my
sources are vague. Stuff heard at civil engineering class and my dad who is
construction engineer.

------
thr0waway1239
If you are reading this thread, you will probably also find the comment thread
on the Economist article somewhat informative. (They seem to be moderating it
quite well too)

------
snthd
What about lightning and seismic zones?

~~~
praptak
Lightning is dealt with by lighting rods. Seismic zones are very non-obvious
as factors like eigenfrequency of the building comes into play, not just bare
static resistance to stress.

------
drivingmenuts
The one major issue not addressed is: deforestation. Yes, we can make
skyscrapers out of wood, but should we? Where do we get the trees from and
will they be replaced quickly enough to provide a sustainable future?

~~~
DrPhish
You can replace (replant) trees faster than you log them. How are you
replacing the steel you're pulling out of the ground? You can recycle steel,
but there is a limited supply and extracting it is energy intensive. We can
grow an almost unlimited number of trees, and each one is a carbon sink to
boot

~~~
Tempest1981
Does the soil eventually need to be replenished, and are there any limits on
that?

------
codesterling
No thanks. Steel and concrete don't get termites or burn. So the risk is more,
but the benefit is negligible.

~~~
Normal_gaussian
You may have missed them but it is worth pointing out these two tiny sections
of the article:

> In general, a large mass of wood, such as a CLT floor, is difficult to burn
> without a sustained heat source—for the same reason that it is hard to light
> a camp fire when all you have is logs. Once the outside of the timber chars
> it can prevent the wood inside from igniting. The big urban fires of the
> past, such as the Great Fire of London, which occurred 350 years ago this
> month, were mostly fuelled by smaller sections of timber acting as kindling.
> Prospective tenants would doubtless need lots of reassurance. But with other
> fire-resistant layers and modern sprinkler systems, tall wooden buildings
> can exceed existing fire standards

> What about woodworm and rot? “If you don’t look after it, steel and concrete
> will fail just as quickly as timber,” says Michael Ramage, head of the
> Centre for Natural Material Innovation at the University of Cambridge in
> Britain.

~~~
unholythree
I read the article and I still don't buy it.

In New Orleans 1972 a concrete and steel building called the Rault Center had
it's top two floors gutted by fire, likely arson. The building has been vacant
since then, much of it in an almost skeletal state and yet a renovation
started last year.

If the Rault Center had sprinklers tragedy could have averted, but I don't
believe a wood building could have contained the fire. A wood building
certainly couldn't have stood neglected for decades after and still been of
any use.
[http://www.theadvocate.com/new_orleans/news/article_9ca3a457...](http://www.theadvocate.com/new_orleans/news/article_9ca3a457-d492-57a2-80c7-d61fd9ad7375.html)

~~~
brudgers
Many contemporary building codes require sprinklers for any building over four
stories. To me, the neglect is a sign of economic conditions effecting
development more than other factors. For example, if the location was highly
desirable and the market for new space strong, redevelopment would make sense.

