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.
Im certainly no expert, but as far as terminology, mass timber seems to be a category that includes CLT as well as others:
>Katerra's mass timber product line will include cross laminated timber (CLT) and glue-laminated timber (glulam) at both architectural and industrial appearance grades.
> 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.
Terms are used a little differently internationally. However with that said typically "mass timber" is the catch all for both engineered and non-engineered timber.
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
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.
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.
UBC's Brock Commons opened in 2017 and has 18 stories over 53m. And Mjøsa Tower was just finished (March 2019), also 18 stories but 85m.
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).
Gluelam is usually used for the older (more established) technicque of just making structural wood beams that are larger than can normally be sawn in one piece. E.g. the largest dimension of regular lumber may be 50x200mm, but you can make a 100x500 gluelam cross section by simply gluing five 100x50 on top of each other. That also has the benefit of being stronger than the individual parts because their weaknesses are averaged (much like how a spun rope works).
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".
Mass timber technique goes beyond engineered wood. It can be simply piles of wood. I saw an architect’s own residence built entirely from sawn timber and pegs. It is also consider a mass timber structure. Engineered wood products may help span large distances and things like that but it seems like the category “mass timber” requires mainly the use of wood where previously one might have used another material, and the use of simply more wood instead of cavities. It is really the opposite of wood frame construction.
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?
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.
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.
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.
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.
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.
I had a home in the 90's that had laminated structural beams, I don't live there any more, but last time I drove past it was still standing.
I think its pretty common for housing in Australia, here's some info https://www.thefifthestate.com.au/innovation/materials/expla...
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.
Timber at least can last a very long time. There are houses in the UK which dates from the time of Shakespeare which are still standing.
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.
Any building can be insulated, you just have to spend the money and sacrifice some internal space. Frame the inside of the walls and put in insulation.
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.)
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.
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.
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.
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).
> - 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.
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.
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.
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.
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.
Concrete is very susceptible to freezing water, and steel rusts. All building materials have flaws, this doesn't seem any less manageable than the flaws of the current most popular building supplies.
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.
No. In the US the logging industry plants more trees than it cuts down every year. Wood used in building materials sequesters the carbon for as long as the structure stands.
I guess the argument goes that if demand for timber increases more forests will be planted.
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.
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.
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 :)
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.
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.
You can farm trees pretty easily and it’s done in my state with Pine. If you just clear cut the forest and don’t plant it back then yea is going to be terrible. Similar to the Palm Oil issues I hear about in the news.
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.
82 comments
[ 2.9 ms ] story [ 143 ms ] threadThe 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.
https://www.masstimberconference.com/
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.
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.
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".
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.
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.
https://en.m.wikipedia.org/wiki/Reinforced_concrete
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.
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.
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.
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.
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...
[1] https://www.accsysplc.com/
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.
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.
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.
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.
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 :)
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.