As Mass Timber Takes Off, How Green Is This New Building Material? • Hacker News Board

Re: As Mass Timber Takes Off, How Green Is This New Building Material?

#81

Post by lucas_membrane » Sat, Jun 01, 2019, 1:16 AM UTC

paulsutter wrote: post #2

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 absen…

Now in the US, building codes are allowing construction of buildings of 6 stories with only the first being concrete and iron, and the upper 5 wood frame with neither concrete nor iron structure, and such buildings are proliferating. Is this CLT a part of the rationale that such structures are acceptably durable?

Re: As Mass Timber Takes Off, How Green Is This New Building Material?

#82

Post by rstuart4133 » Sun, Jun 02, 2019, 5:55 AM UTC

faissaloo wrote: post #57

Won't we just end up worsening deforestation?

> Won't we just end up worsening deforestation?

Probably the reverse. Structural timer beams used to be made out of a single length of timber, which of course could only come from a old, large tree. Now houses in Australia now use wooden I-Beams made out of this laminated wood. It's made from young trees (read: plantation timber), which are small and thinner than the I-Breams themselves, but that means the I-Breams made out of them can be any length. In fact their rise seem to be driven by the change from using old-growth timber to plantation timber.

I was surprised when I first saw it, because the manufactured timer I'm used to such as chipboard and fibreboard are really at the bottom of the barrel. They are heavy, rapidly destroyed by moisture, and weak. These glued laminates seem to be reverse of that - stronger by weight than the original wood (largely because you can shape them, eg into a I shape), and of course that makes lighter than solid beam of wood, and they are just as waterproof.

As a consequence anything much ticker than a wall stud is made out of the stuff now - large long beams of a single piece of timer seem to be a thing of the past.

Re: As Mass Timber Takes Off, How Green Is This New Building Material?

#83

Post by jbay808 » Tue, Jun 04, 2019, 3:09 AM UTC

lsc wrote: post #79

jbay808 wrote: post #77

Earlier quoted context omitted.

As far as I know, the romans had better cement. We're still trying to reverse engineer it.

this is my understanding as well... but I wonder how much of that is that they just had more variable cement, and the stuff that wasn't incredibly great turned to dust long ago? Certainly, our modern processes are more repeatable and produce a narrower range of results. What if the existent buildings are outliers of the roman process?

Attributing the accomplishments of the past to survivor bias is a popular line of thought these days, but...

It's unlikely. They used a completely different chemical formula than we do. If you have two processes X and Y, and you observe consistently that Y >> X, and you know that Y and X are produced by different processes so you don't have a strong prior on the mean of Y being similar to the mean of X, then you should conclude it's very likely that the mean of Y is greater than the mean of X. Even if you know for certain that you only have the best samples of Y.

But more importantly, we don't really care if the romans also built a bunch of bad buildings using counterfeit cement with a botched formula, that failed to last until today. What matters is that we don't have the technology today that can match their best work. That's what makes it worthy of study.