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Timber Towers Are On the Rise in France (citylab.com)
A reader shares a report: Spurred by concerns over climate change and the negative impacts of concrete manufacturing, architects and developers in France are increasingly turning to wood for their office towers and apartment complexes. Concrete was praised through much of the 20th century for its flexibility, functionality, and relative affordability. In France, the material ushered in an era of bold modernist architecture including housing by Auguste Perret and Le Corbusier. Today, however, wood is lauded for its smaller environmental footprint and the speed with which buildings can be assembled. "Wood had largely disappeared and was seen as a quaint material," says Steven Ware, a partner at the architecture firm Art & Build, whose latest wooden office building opened in Paris's 13th arrondissement earlier this summer. "[But] the energy it takes to put a concrete building up, to run it, and then dismantle it when it becomes obsolete was too much. Using mass timber in office buildings seemed like something we had to do." The production of cement, one of the main ingredients in concrete, generates an estimated 5 percent of the world's carbon emissions. Trees, in contrast, capture CO2, helping offset emissions produced by a typical building process. And then there's the string of other construction advantages that make wood economically appealing. It's lighter, which means digging smaller foundations in the ground. Crane costs come down, as they're no longer hauling blocks of cement hundreds of feet in the air. Driving a nail into a slab of wood requires a lot less energy than driving one into concrete. Months can be knocked off the construction timeline.
Sounds like a good way to have a towering inferno. The stuff we put inside large buildings burns quite readily. But the fire generally stops in a single room. But if you suddenly make everything out of wood, what's to stop the fire from spreading everywhere?
Lumber supply forests are harvested and replanted these days.
>> Today, however, wood is lauded for its smaller environmental footprint and the speed with which buildings can be assembled.
There's no reason we can't just stack IT people in cubes in pole barns. Fortunately, nobody with any talent actually needs to work in a crappy office, so most companies are smart enough not to try this.
Recently, as in this week, they completed a low-emission earthquake-resistant timber tower in Portland, Oregon.
Fire risks tend to come from inefficient fire suppression systems and lack of coatings. Or inadequate emergency exits. As we've seen from London, England, concrete towers clad in flammable plastic are more of a fire trap than wood timber buildings are. It really depends on the full architectural design.
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I recall a prominent global warming alarmist getting kicked out of the group he was in because he advocated the using of wood as a building material, since using wood in this way is an effective carbon sink.
Using wood as a building material only causes deforestation if people don't plant new trees in their place. No one does that since it's not only bad for business, they'd run out of trees, but it's illegal in any place I can think of. If there is a place in the world that allows for clear cutting of trees and not planting new trees in that space then I'll show you a place that lacks any real government.
Using wood for buildings is good for the environment. If you believe that steel and concrete is better then I'll ask you to show me your math. If you believe that we just shouldn't be building new structures then I'll ask you to show me your age. Saying we shouldn't need new office buildings and homes is something that I'd think would come from a child or someone suffering from senility.
If someone knows who that was that advocated using wood as a building material as a carbon sink, and got shunned for it, then I'd appreciate a reply on who that is.
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CLT and mass timber is the shit. They are also working on LVL veneer based types that are like super plywood vs. the current finger jointed lumber version You trade material cost for labor but you can have a house framed in a day. Also concrete is a carbon emitter for a long time. It is not prone to fire. You can have them CAD CAM all the windows, doors, conduit, and plumbing into the walls at the factory, and it is renewable.
Wood can be grown and harvested sustainably on tree farms where generation after generation of trees selected for structural properties and rapid growth are cultivated. Any such "green" inspired building program should/would ensure that all the timber used comes from such sources. And so yes, building permanent structures out of wood does lock up CO2 as long as the structures stand - whereas CO2 released in the production of concrete is in the air for centuries.
The actual material used for framing a structure has nothing to do with the fire safety (or lack of same) in an inhabited structure. Metal and concrete framed structures are no safer on that count than wood. The fire hazard that threatens life is entirely due to the furnishings and utilities inside the structure. By the time a frame of wood frame building starts to burn the interior is already destroyed, and the inhabitants have either escaped or are dead. Note that modern construction techniques using fire proof gypsum board that isolates the structure from the interior (gypsum does not burn and actually absorbs energy as it decomposes).
Wood is a pretty remarkable material. It is in fact an advanced composite material produced by natural nano-factories. It compares favorably with far more expensive synthetic composites, and beats them all in cost. Used properly (taking advantage of the anisotropic properties of wood beams) a good wood beam comes with a factor of 3 in stiffness/weight ratio of the best performance ofunidirectional carbon fiber epoxy composite, and beats structural steel. Sitka spruce is used in the upper stage of Trident II SLBM missile since it had the best properties for the role, over all other candidates.
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Also there is a fair amount of carbon sequestered in the building itself. That's assuming the building doesn't burn, which is why I won't get into a tall wooden structure.
Are they really comparing the energy cost of driving a nail?
Wood has a place but IMO if you want a durable structure use reinforced concrete. Maybe this wave of construction is only expected to stand for 30yrs?
My (small) multi-unit in Canada is built with wood timbers and is 218 years old. As long as you keep it dry, wood can be very durable.
Nails are better for framing because the fastener allows greater flexibility. Nails shift, twist, and flex; screws tend to take greater load from expansion and sway, and then shear.
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It would be ironic if you write that from a deforestated suburb!
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Nobody is questioning the fact that concrete is a good material from a structural and construction standpoint.
But wood, properly maintained, lasts quite a bit longer than 30 years. The oldest wooden building in the world is 1300 years old, a five-story pagoda in the temple complex of Horyuji in Japan.
There's no question concrete is more durable with less maintenance, and people are working on lower carbon-footprint concrete. Switching to non-carbon energy sources for converting limestone to cement would eliminate most of the carbon footprint of cement, and is probably the best long-term solution.
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That's solid wood, however, possibly dense old-growth wood. These are modern composites. I have no idea if that makes them more or less durable over a century.
What it likely makes them is hard to repair, unless the particular composite method they used becomes the dominant one. With a quick skim, I see about 4 competing technologies for pre-engineered, mass-produced wood composites. If you build with one and it falls out of favor, it might be tricky in the future to do any repairs. If nobody is making nail laminated timber and you need to sub in cross laminated timber, what are the ramifications?
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Wrong. They 'inhale' CO2 and 'exhale' oxygen during photosynthesis. All photosynthetic organisms do so.
Only when the sun is out. Most plants consume O2 and expel CO2 at night.
Nevertheless, trees are a net producer of oxygen (and a very good carbon-capture device) if you don't account for them rotting after they die. But oceans and marine plants are a more important producer of oxygen.
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I've seen a lot of this in my area, generally what they call podium construction, where you have a 1 to 3 stories of concrete construction and then build wood frame up to the maximum height allowed, typically 5 stories of wood. As TFA outlines, it is cheap and very fast compared to all concrete, and has become a go-to for mid rise residential. Unfortunately, it makes it possible to cut corners to an even greater degree when it comes to flooring, and fire safety is entirely dependent on active suppression. I have actually seen one of these buildings survive a fire during construction (with a great effort by the fire department), but afterwards it was demolished back down to the podium.
In the end it comes down to labor cost, concrete is surprisingly labor intensive and labor costs are a huge part of construction in first world countries. I've seen some beautiful concrete work done in South America that would be impossible in the US simply because of labor costs - Imagine a 20 story concrete facade entirely finished by hand: Beautiful, but impossible to do in the states.
Also there is a fair amount of carbon sequestered in the building itself. That's assuming the building doesn't burn, which is why I won't get into a tall wooden structure.
The type of wood buildings they're making nowadays don't burn very easy. (not talking about timber framed houses like the US, but the kind used for taller buildings such as this article). They take wood- cut it in strips, arrange the strips in alternating directions (for added strength) and then glue them together with a fireproof glue.
They're actually more fire-safe than steel buildings. Steel will melt or lose strength with fire (as in 9/11 twin towers)- the modern timber buildings resist fire at higher temperatures than it takes for steel to lose integrity.
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How long can a concrete and steel building last?
How long do even well engineered wooden structures last before succumbing to rot or burning down?
Well... There are wood buildings that are 1,500 years old. A properly taken care of wood building can last a long time. Wood doesn't rot if it is not exposed to water. The secret is proper waterproofing. As for fire, the modern wood buildings use flame retardant glue and are safer than steel at high temperatures.
Wood is also more earthquake resistant because they sway easier. Wood is more resistant to wind damage.
"That's the way to do it" - Punch
You're on the right track to some of the "devil in the details".
Soft woods like pine grow quick, but the wood is, you know, soft. Wouldn't want to live in a skyscraper made of that!
Calling pine a soft wood, and implying that it wouldn't serve well in a structural sense, is perpetuating a myth. SPFs (spruce, pine, fir) are highly regarded for their structural properties. Douglas fir, Southern Yellow Pine, Sitka Spruce, Hemlock...all have excellent MOE/MOR ratings, while yes, having low Janka Hardness ratings. Along with time-to-yield and price, these structural properties are why SPFs rule the US stick-built construction supply.
AFAIK, the hardier the wood, the longer it takes for the tree to grow. That means a long-term investment in your re-planting, and a lot can happen to your plot of re-planted little sprouts (bugs, deer, fires, suburban sprawl, drunk kids on ATV's, massive natural gas deposits) while you wait the lifetime or two for your trees to grow to full size.
Harder wood trees, do "generally" take longer to grow. However, today's new-growth trees pale in comparison to the mostly gone old-growth trees from a properties comparison. The hardness may be there, but their MOE, MOR, and density are usually lower, and their stability and durability are much more volatile. But, again, those are generalities. The science behind wood is quite fascinating; much more in depth than I imagined when I got into woodworking.
The Wood Database is a great resource.
The vast majority of CO2 emissions from cement manufacture is not from the energy used to heat the kiln but as a produce of the chemical process itself when limestone (calcium carbonate) is decarbonated into lime (calcium oxide).
This means that it is not enough just to change into using clean energy for heating the kiln.
Luckily, cement could be produced CO2-free using a heated electrolysis process but the process if very new and untested and it would require that the a huge chunk of the cement factory would have to be rebuilt. The world can not wait 20 years for clean cement.
"We mustn't be caught by surprise by our own advancing technology" -- Aldous Huxley
The article says that a huge benefit of wood is that it can be taken down/disassembled much more easily and with less energy than concrete. I believe that's what the OP was referring to when he said "Maybe this wave of construction is only expected to stand for 30yrs?". I don't think he meant to say that wood wasn't durable.
Personally, I still think that wood is a luxury. It may not be a luxury in Canada, but in France, wood is still a lot more difficult to buy than cement and rebar. So I still expect cement and rebar to be the default for low-income housing and lower budget office buildings.
And even in the picture of the article in question, or in a better picture of the same building I found here, cement and rebar are still being used for the lower floor and the stairs/elevators shafts, not just the foundation, so obviously the promoters of this pre-fab wood idea still think that cement has a place.
And my second concern would be the chemicals used in those slabs of cross-laminated timber (CLT) panels.
Wood construction has been propelled forward by the growing availability of cross-laminated timber (CLT). These enormous, prefabricated panels, made from several layers of wood glued perpendicular to one another and measuring up to 20 inches in thickness, are strong enough to hold up bigger buildings and arrive on site ready to be assembled like Jenga pieces. It’s also this heft that helps make CLT fire-resistant: the outside layers char slowly, protecting the wood inside from burning.
For instance, what is the glue used in those panels? And is it only the glue and the wood that make those structures fire-resistant? Or is it something else?
Prefabricated slabs of CLT, which form the framework of most timber buildings, are usually shipped in from Austria. “CLT manufacturing isn’t sufficiently developed in France,” says Viguier. “I’d like this project to help revive wood consumption and trigger the growth of factories in the region.”
Usually shipped from Austria? Are they sure about that? Aren't those slabs of CLTs going to come from China instead where they usually don't have good records of what chemicals are used in their manufacturing processes? That being said, those CLT slabs are as likely to be coming from Ukraine or Finland also.
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Just to reinforce dj's point - hardness and strength are two completely different engineering qualities and usually have very little to do with each other. Aluminum for example is both fairly soft (the surface deforms readily in response to concentrated pressure) and fairly strong (in bulk it can withstand fairly impressive compression and tensile pressures)
In addition, hardness does tend to correlate with another, far less attractive quality: brittleness. The more rigid something is, the less it can temporarily deform in response to sudden stresses, which causes much higher spikes in the forces involved, and a much greater chance of breakage. Glass is actually very strong, but also very hard, and any sudden impact causes it to shatter. Oak has a similar weakness - it's not nearly as brittle, but an equivalent strength worth of SPF will survive considerably more abuse.
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This is actually not that big of a deal because the carbon that was used to form it was atmospheric, and not sequestered in the earth. Also, these types of materials are very hard to burn.
Now I'm not the original guy but I think it's a choice of words here. Some of the newest treated wood ignites at 500C. Now steel won't melt at that temperature, not even close, but at 550C it loses 50% of its strength. So I sort of get where guy is coming from but yeah, it's an iffy argument. However, I think we can all agree that at either temperature, no one is going to exist very long. That said, I'm not sure about France's standards but I would assume that the level of planning that has to go into the fire suppression system before the blueprints are okayed has to be dizzying to say the least. However, I don't know the linked article is really shallow on information and I'm at work so I don't have the time to look it up.
You don't rate a fire-resistant structure by its ability to sit baking indefinitely at a certain temperature, but by the number of minutes or hours it provides safety while people evacuate and/or extinguish the fire. And once you have a fire-safe structure that doesn't collapse and compromise its egress paths, you worry about fire safety of the building which includes ventilation, fire suppression, and materials to avoid asphyxiating the occupants in a poison gas chamber.
Thick timber chars on the outside when exposed to extreme heat. This is almost a self-healing, temporary insulation to slow the heat transfer to the rest of the wood on the inside of the timber. That's why a big log in your fireplace burns for many hours and doesn't immediately explode your house from over-pressure. The timber continues to be able to bear most of its rated load while this outer surface is burning.
Meanwhile, steel will quickly conduct heat throughout and soften until it suffers a load failure, long before it has reached its liquid phase. The twin towers didn't collapse because the steel was solid one minute and liquid the next. It collapsed because it became soft enough for large horizontal spans to sag and separate from their supports, fall a whole story, and exceed the load-bearing capability of the level below.
Steel structural members have to have fire insulating layers to mitigate this type of problem and allow people to escape. The violence of the plane impacts in the twin towers destroyed egress routes, trapping people. It also tore away a lot of the fire insulation (asbestos) meant to protect structural steel, so the collapse happened sooner than it might have in a typical fire.
Look into "insulated concrete forms".
You get a 6-8 inches of concrete wall with insulation (bound to a structural webbing) 2-4 inches thick (with thicker options available both for concrete AND for insulation).
But the base wall is rated at R-20.
Also, being a monolithic wall, there's are no "hidden" breaks in the air/vapor seal of the building. Just at windows, doors and utility penetrations.
This makes the house far more easier to make airtight. And while mechanical ventilation is required, it requires FAR less energy to regulate the indoor temperature.
Also, as the AC who responded to you mentioned, with the concrete walls, you get a thermal mass effect, evening out the flow of heat through the wall.
A wall will ALWAYS migrate heat. What you want to avoid are major differentials WITHIN the structure of the wall. Because those are areas you'd get condensation.
Closer to the outside, you're subject to freeze-thaw, which could damage the wall. Closer to the inside, you get mildew and mold growth. which can render a structure uninhabitable, as well as possible standing water which can damage furnishings.
And wood in modern buildings isn't actually an especially good insulator unless you're going VERY thick.
A normal 2x4 (3.5" nominal) stud had a full-thickness R-value of about 4.
The R-value of 3.5" batt fiberglass is R-13 to R-15. So when you factor the R-value of a wall, every stud lowers the nominal R-value of the whole wall structure.
Basically, depending on how a wall is built, framing can account for 15-25% of a wall. And each % of wall it accounts for can be directly applied to how much it lowers whole-wall R-value.
So, assuming batt rating of R-15, and stud rating of R-4, with the framing accounting for 20% of the wall, what's our overall R-value?
On top of this, windows and doors also reduce the whole-wall value.
JUST the concrete in a 6" concrete wall has an R-rating of about 3. However, unlike stick framing, your insulation is applied whole-wall with no interruptions (save for windows, doors and utility penetrations). Usually in one of two ways.
Inside and outside, attached by structural webbing (the majority of the systems I've seen).
In the core of the concrete itself (Spider-ties).
Also, it's possible to build the entire building this way.
You build an insulation "raft" either for foundations or a combination foundation/basement floor.
You build the walls with the traditional ICF stacking. Then water/vapor barrier the outside walls. You can even build concrete roofs (just make sure your architect takes the additional dead-load into account when spec'ing the trusses). Let's see a tornado or hurricane rip off a concrete roof that's fully bonded to the wall structure!
Additionally there are options for various strengths of concrete (bog standard is 3000psi concrete that's backed with #4 and #5 rebar). You could go with higher PSI mixes (there's crazy-strong high-strength concrete up to (and possibly exceeding) 15,000 psi. There are also additives that can be put into the concrete to help control cracking, reduce reactions to things like road salts, improve ductility, and even replace some of the rebar structure.
As for strength and durability.
Here's a bog-standard ICF house that had a guy drive a Ford Excursion into it at high speed..
https://youtu.be/0B81NZUqT2Q
Images of the damage at this time point: https://youtu.be/0B81NZUqT2Q?t...
Standard 3000 psi concrete.
He ripped off the stucco and trim and took a few chips out of the underlying concrete wall.
Not saying concrete is a perfect building material. It isn't. And, built CAREFULLY, a wood frame building will share MOST of the benefits you'd see in a concrete building, and at about the same price point.
If you still disagree, that's up to you.
Hope you at least found this info dump enlightening.
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Laminated panels have very different properties than frame (aka mostly air) construction. It's hardly fair to lump them together.
In fact that's rather the point of the people pushing wooden construction today - they're not talking about wooden *frame* construction - there's good reason that was abandoned. But laminated timbers and panels solve pretty much all of those problems, and especially for tall buildings the strength-to-weight ratio of wood makes it extremely appealing.
Oh, and I looked up some info for another comment that you might find interesting:
Insulation: standard concrete has an R-value of 0.33-0.52 per inch (for 80-60 lb/cu.ft. mixes, respectively), while most softwoods have an R-value of around 1.4 per inch
Strength: pine and fir have a compressive strength of between 4,000 and 8,000 psi - quite favorable compared to standard concrete mixes. And unlike concrete it's tensile strength is about the same, giving it great durability in the face of flexing and vibration, while concrete fails at about 300psi (rebar obviously helps with that, but it's a deeply imperfect solution)
And of course pine weighs about 1/3 as much as concrete, so delivers about 6x the strength-to-weight ratio.
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