As Mass Timber Takes Off, How Green Is This New Building Material?
e360.yale.edu
e360.yale.edu
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.
>Katerra's mass timber product line will include cross laminated timber (CLT) and glue-laminated timber (glulam) at both architectural and industrial appearance grades.
https://www.katerra.com/en/what-we-do/products/mass-timber-p...
> Explore the supply chain for cross-laminated timber (CLT), nail-laminated timber, glulam beams and panels, mass plywood panels, dowel-laminated timber, and laminated veneer lumber; and the opportunities and obstacles for mass timber in global manufacturing and construction.
CLT is the engineered product taking taking most of the limelight right now. It is only differentiated from glulam (glue laminated timber) by the layering. In CLT layers are perpendicular where glulam they are parallel. Glulam has been around a little longer and is more suited to posts and beams due to its linear nature where CLT is used for structural panels also.
There are also plenty of other less glamorous engineered timber products that have had a major impact in construction including timber I beams and OSB (Oriented Strand Board) panels.
If anyone is really interested in timber from forestry to bulding products I recommend looking at the Gifu Academy of Forest Science and Culture which is the only institution i know of that runs the gamut of forestry, environmental education, craft and furniture making, and wooden architecture
Who the hell thought up the mass timber name though?! That just says to me a solid (mass) of unengineered wood.
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.
So Gluelam beams are used as an alternative to steel beams.
This more recent tech is cross-laminated-timber (CLT) where flat pieces of timber and sheathing is glued together to form large construction elements (walls, floor sections) CLT is used as an alternative to building modules. E.g. CLT can form a floor slab between storeys of a highrise, or a wall section where you would otherwise use a prefab concrete or steel/glass piece.
It is true that CLT is both "glued" and "laminated" (so it is a kind of glue-lam) but using just "gluelam" was established already as short for "gluelam beam".
That's literally what it is. You can do it in all sorts of interesting different ways, but the idea is, where with other techniques you'd use e.g. insulation, gypsum wallboard, oriented strand board sheathing or plywood, instead you just... put more wood on it.
I'm not sure you could use that building technique for anything over a few stories.
They all uses concrete though. Brock has concrete stairwell cores. Mjøsa apparently limited concrete to upper floor decks, for weighting (elevator shafts and stairwells are apparently CLT).
With those sorts of constraints, you're going to be limited by how high you can build.
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.
Laminated plywood has been used for a long time (70's?), and has been used as cross bracing on timber framed houses. There's also all the sorts of chipboard which although aren't structural are glued. So I suppose there's a fairly long history there with glued timbers. Its the usage as multi storey buildings that is new I guess.
Edit: apparently plywood was first made in 1797 https://en.wikipedia.org/wiki/Plywood, wow
But AFAIK those used different glue than what is used today in plywood production, not to mention 1797.
I'm not sure what's worse: a cheap wooden structure which lasts 50-100 years or a strong brick structure which lasts hundreds. Here in Europe we have a large stock of houses from the 1950's which cost 300 EUR a month to heat and cannot be insulated. For a modern passive house costs are closer to 30 EUR a month.
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.
Another e.g. concrete disintegrating due to use of mine waste: https://www.theguardian.com/money/2009/nov/29/mundic-test-cr...
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.
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?
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.
Do you mean steal reinforced concrete lasts 150 years or that the technology is 150 years old? My understanding is that reinforced concrete has a service life of 50 years and 80 years if protected with a sacrificial anode of some sort.
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 :)
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.
But your point is valid. Wood is susceptible to rot, bugs, fire, etc.
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.
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.
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.
[0] https://en.wikipedia.org/wiki/Acetylation#Acetylation_of_Woo...
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.
Also sprinklers.
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.
https://en.wikipedia.org/wiki/Grenfell_Tower_fire
Timber doesn't burn as fast as that, especially in a city as wet as London.
Edit: In building applications. Steel softens and loses its strength in the presence of heat.
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.
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.
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.
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.
Sustainable forestry generally involves replanting the trees you cut down, often several times over. Of course, as the article states it's pretty important that the timber comes from sustainable sources if it's to actually have a chance of benefitting the environment.