
As Mass Timber Takes Off, How Green Is This New Building Material? - aaronbrethorst
https://e360.yale.edu/features/as-mass-timber-takes-off-how-green-is-this-new-building-material
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paulsutter
The correct term is CLT (cross laminated timber). A big chunk of Katerra’s
recent big financing is to pay for CLT factories.

The cool thing about CLT is that it can be “printed” in arbitrary shapes and
sizes in a factory setting and shipped to construction sites for rapid
assembly. Structurally it can replace steel/concrete in a certain range of
structures.

The potential for automation and mass customization is absent from the article
and the most exciting aspect of CLT.

Factory prefabrication may also be a way to reduce construction costs and
schedules in expensive areas like SF.

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benj111
Came here to say this, I've heard it called 'glue lam' also.

Who the hell thought up the mass timber name though?! That just says to me a
solid (mass) of unengineered wood.

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masklinn
I guess they mean the main structural mass is timber-based? It's really odd
terminology but might simply crop up from details of the field's lingo which
makes no sense to outsider.

Apparently CLT and gluelam are different methods of engineering wood: in CLT
the boards are laminated in cross-frames (so one layer is laid north-south and
the next is east-west) to improve structural resistance across non-
longitudinal orientations; while for gluelam all layers have the same
orientation so the end-result is closer in behaviour to regular sold timber.

~~~
benj111
Yes, I would guess constructions like this make use of both gluelam and CLT.

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mjevans
I would like to know more about the long term stability of the glues involved
and how the entire structure as a whole decays / fails over what timeframes
under what exposures.

Most other building materials in use today, the actual core structural
elements, have withstood the test of centuries of use and are well proven and
stable technologies.

~~~
benj111
Centuries? Reinforced concrete is 150 years old, steel frame construction a
little less so.

~~~
barrkel
Sure, but we have concrete buildings still standing from Roman times - most
famously, the Pantheon.

I grew up in a cottage a couple of hundred years old, with thick walls built
from stone and mortar. It's not unusual to live in a house that's over a
century old in Europe.

I've also lived in a wooden house - more of a three room + toilet chalet,
really. Biggest irritations were all the noises from thermal expansion in the
summer, and the fact rats could eat their way in. I think it's a bit more
effort to actively maintain wood and be sure it's in good condition than brick
and concrete construction.

That cottage, btw - the roof had a wood frame, but it wasn't the original -
that had burned down along with the thatch at least once, and been replaced
some time before we moved in.

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willyt
Roman concrete doesn’t have the same chemistry as modern concrete.

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jabl
And, Roman concrete doesn't have steel rebar which rusts and cracks the
concrete.

~~~
dsfyu404ed
Eh, properly done reinforced concrete should last hundreds of years.

Of course it's possible to use the wrong concrete formula for the job (the
concrete for your driveway is not the same as the concrete for a boat ramp)
but if done right it should last.

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myspy
Funny that this topic is coming up, we're currently in the execution of
building a house made of this material. We did choose the CLT because of the
spruce interior look. But not all walls are like that. Most part will be
covered by clay plaster. This should also help with soundproofing.

As for the glue. We asked the producer and they use a glue which has no
negative side effect when finished hardening but is not that nice to breath
while being in production.

Apparently there are no better glues. Another option would be to use only
wood, but this is not CLT, it has another name, but the same result. The
difference is that the interior has to be covered by something because the
wall looks rough. And it costs a little more.

Termites are no problem in Europe and leaking water is a problem in every type
of house, but it won't go undetected for long.

As we live in areas with houses made of wood around 300 to 500 years ago and
those houses still standing and being ok, I plan our home to be here for the
same amount of time :)

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proee
Termites are going to love this ;-)

Even with termite treated lumber, they will still need annual inspections to
look for damage. If they do find out the structure is laden with termites, it
would most likely require a complete evacuation of the building and "tenting"
to gas them out - which might be tricky if it's in an urban area.

Also, any undetected leaks in the structure could cause slow rotting of the
wood.

~~~
WalterBright
Concrete rots away if it is not protected properly from water. It soaks up
water, the rebar rusts, expands, and splits the concrete.

~~~
zihotki
There are different kinds of concrete and there are some that are specially
made to be used in such conditions. Best example will be concrete bridge
supports which are constantly in the water.

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rjf72
Would this not be just another form of kicking the can? In particular once
these buildings are demolished and replaced with new ones, I don't imagine
that the old wood would (or even could) be reused. Instead it'd be sent to a
landfill and decay at which point its stored carbon would be released.

In favor of this regardless. Wood is so much more pleasant on the eyes, and
creating an incentive for huge sustainable forests is an awesome thing any way
you look at it. But unless I'm missing something, framing this as something
that could effectively mitigate against increasing emissions seems to be
misleading.

~~~
perfunctory
> Instead it'd be sent to a landfill and decay at which point its stored
> carbon would be released.

Even then it's still carbon neutral. Or am I missing something?

Or, since carbon is gonna be released anyway, we could burn it and make some
energy as a bonus.

~~~
kaybe
Apart from the energy used in harvesting, transport and construction (if not
carbon-neutral), yes.

However, what you actually do is add a new carbon sink, with a flux in and a
flux out, just like the eco-system, the ocean, the atmosphere etc. As long as
you keep the outflow lower or equal than the inflow it's a net win.

Edit: Another point - we might not be in a position to think about this at the
moment, but we should not store all available carbon in rock form (some of the
carbon sequestration ideas lead to rockform carbon basically) because our
descendents may really need it one day.

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diveanon
I read this as "Mass Tinder" and it gave me an idea for a group dating app
that helps organize strangers into meeting up as a group for "activities".

~~~
bufferoverflow
That's meetup.com

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orbifold
I think the gp had different „activities“ in mind.

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dgacmu
That's Groupon? ;)

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willyt
Once you have more than about 150mm (6”) of insulation a typical building will
be losing more energy through air leakage than through conduction. CLT in
particular is excellent for airtightness because it is pretty airtight in of
itself and it comes in big accurately machined panels which minimises the
number of joints that need to be sealed up.

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Quequau
Do anyone know of any project to genetically engineer trees for producing
better timber?

~~~
perfunctory
Not genetic engineering but Acetylation technology can increase wood
durability [0]. The company mentioned on the wikipedia page is [1]

[0]
[https://en.wikipedia.org/wiki/Acetylation#Acetylation_of_Woo...](https://en.wikipedia.org/wiki/Acetylation#Acetylation_of_Wood)

[1] [https://www.accsysplc.com/](https://www.accsysplc.com/)

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baybal2
Bigger question, how fire inspection ever cleared a wooden highrise?

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Tharkun
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.

~~~
srfilipek
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.

~~~
lorenb
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.

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faissaloo
Won't we just end up worsening deforestation?

~~~
alkonaut
Funny, where timber is produced (e.g. Scandinavia) we are always complaining
that the forests are taking over. People can basically be subsidized to keep
animals to "keep the landscape open" when forests would otherwise take over
old farm land. We have 7000 trees per person. We plant more than we cut down.
Just buy our timber. "Deforestation" is a problem in various parts of the
world because of ecosystems, erosion, desert spread. It's not an issue
everywhere.

From a CO2 perspective, cutting down a tree and making a house of is
excellent. The CO2 is bound in the timber and a new tree can be planted in its
place.

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ilaksh
I will just say the obvious thing. I thought we were supposed to be planting
more trees. Doesn't cutting more of them down go in the opposite direction?

I like the idea of engineered wood for construction. I am just suspicious that
a lot of this hype is coming from the logging industry and the CO2 stuff is
just a marketing coup.

~~~
WalterBright
There's a great deal of land that could be covered with planted trees, which
pull CO2 out of the air. When they are mature, then they can be used as
building material, and a new tree planted.

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eeZah7Ux
> planted trees, which pull CO2 out of the air

When an old building is torn down and the wood is burnt all the CO2 goes back
into the environment.

Unless we start burying old wood into sealed underground chambers (like
depleted oil wells) all the CO2 stays around.

~~~
imtringued
Concrete isn't carbon neutral therefore mass timber can still be better for
the environment.

