Sweden wants to build an entire city from wood | Hacker News Reader

Sweden wants to build an entire city from wood

economist.com

35 pointssohkamyung70 comments

I do wonder what fresh new health conditions we will learn are caused by that "engineered" fire-resistant wood in a couple of decades.

I'm also not fond of "engineered" as a form of sanitising what is really happening: the wood is either sprayed with or treated with some sort of fire-retardant that will remain on the wood for its usable lifespan. Unlike other terrible things that we use in constructions but then cover up, the wood is also more likely to be left exposed in the interior of the building as a stylistic choice.

CLT burns, like glulam, but it just burns very slowly. Importantly it also retains it's strength for a long time while burning. So basically: you have combustible buildings but you have buildings you can get out of while they are burning. I have not heard about use of fire retardants on CLT/Glulam even in highrise construction, but I do know that many wood highrises "cheat" and use steel beams where it makes sense.

Is this really exotic enough to even warrant discussion? What is it that makes it stand out? There are of course large developments with wooden houses (rows and rows of thousands of apartments/townhouses) that are only slightly lower at 2-3 floors, but that have existed since the 40's and 50's. Is it that it's within a city rather than more suburban? Or that it's 4-5 floors? Or that it's mixed residential/commercial?

I'm considering to build a house with light-frame monocoque technology, which is unfamiliar/unpopular and somewhat new here in Hungary. My fears are also along these lines, I wonder if the glues used in the KVH "engineered timber" beams, or in the OSB boards would have health impacts. Not to mention the insecticides, the fungicides, flame retardants.

Also there is little to no experience in long-term maintenance costs of these building technologies in Eastern Europe (only with more traditional log-house wood building methods), I'd be happy if I could get any info on it from people with experience on this (maybe from the Nordic region, or the USA probably).

Oh the technology is basically:

- wood frame from engineered timber,

- OSB for lateral structural integrity (both inside and outside),

- semi-permeable humidity closing layer

- rock wool insulation

- few centimetres of dense EPS foam on the inner side, over the OSB (this is where the wiring/plumbing is done in, traces cut with heat-knife),

- and wood or drywall finishing on the inside

- outer finishing can be wood or anything used for traditional buildings

As per current building code automated continuous ventilation needs to be added with heat exchangers, which I think alleviates some of the VOC (formaldehyde) problem.

(sorry for the possibly bad translation, I don't know the proper industrial lingo)

This technology promises 20-30% cost savings from traditional brick based technology used extensively here, better net area (less lost on wall thickness for same level of heat insulation). On the other hand its longevity has no well-known track record here, so insurance costs may be higher, etc...

Yes, it is very possible that "engineered" fire-resistant wood (and all the added chemicals that come into play with that) could be toxic, one way or the other, we are already using in construction lots of "engineered" (composite) wood, and I am personally not much convinced that even that is really-really "safe".

As a reference, for formaldehyde emissions:

https://en.wikipedia.org/wiki/Formaldehyde

https://en.wikipedia.org/wiki/Formaldehyde#Safety

it took decades to categorize them as toxic/carcinogen and then put limitations in Laws and building codes.

What exactly is euphemistic or sanitizing about saying out right that a chemical engineer engineered some chemicals for a generally desirable purpose.

I guess a more specific term would be “composite”.

Fire resistance with CLT is not provided by chemicals. When it burns, the wood chars on the outside which then insulates the rest of the wood. So, it takes quite some time for this to escalate to the point where the structural integrity is compromised. And it takes quite a bit of heat to keep it burning to begin with. Basically, eventually it would fail if you don't extinguish the fire. But this takes quite some time. CLT is basically rated for how long that takes.

As for toxicity, CLT is basically laminated wood with modest amounts of glue (compared to other laminated woods that people use in their homes without much issues). Mostly the glue stays on the inside where the layers are. And of course the glues used have all sorts of desirable properties with respect to not being toxic, bad for the environment, etc.

I don’t think it gets its fire resistance by things sprayed on.

https://www.greenspec.co.uk/building-design/crosslam-timber-...

I'm really confused by the "sanitising" comment - I understand "engineered" to refer to the whole manufacturing process, the fact that it resembles and functions similarly to "raw" solid wood but has been broken down and rebuilt with different properties (of which fire-resistance is just one). What would be a better name? Is "pressure-treated" sanitized because it doesn't really convey what chemicals are involved? I'm having a hard time envisioning how the general name for this class of products would be expected to better reflect the potential presence of fire-retardant chemicals.

"Fellow municipal council members, I don't want to start the blame game, but in retrospect, perhaps it wasn't the best idea for our city to host the International Arsonist Convention"

Ah, but that convention is already hosted by another Swedish city every year (voluntarily or not).

https://en.wikipedia.org/wiki/Gävle_goat

Imagine the size of that flat pack box and the weird wordless IKEA instruction sheet.

The "weird wordless IKEA instruction sheet" is actually a thing of genius, because it's universal: it allows them to sell their furniture anywhere they like. Contrast that to the typical approach of American or British companies, who start by printing their instructions only in English, and are then surprised that there are other languages and they have to provide instructions in those languages too if they want to sell to non-English-speaking countries...

LEGO was one of the first ones I remember that did this. Almost all their promo material was pretty language agnostic if I recall. Even now the sets have multiple languages on the box

> weird wordless IKEA instruction sheet.

Where did this trope come from exactly? I can't remember the instructions being unclear, really.

It usually works pretty well unless it’s complicated. The classic example I give of “complicated” is anything involving a spring loaded or roller mechanism like a drawer.

Though even the weird wordless complicated is almost always better than the alternative, which is English words poorly described

Perhaps it's just reality.

The instructions are purely graphical.

Which is completely natural to anyone who’s grown up with legos.

This has nothing to do with carbon footprint. They chose laminated wood for development cost reduction. Prefabricated parts require a lot less labor on site and can be put up a lot faster. This moves costs from the developer to the buyers, as they will have to do a lot more maintenance over the life time of the building. Said maintenance and repairs contradict the carbon footprint reduction claim if you consider the total cost of ownership.

I'm not convinced, do you have any numbers to back that up?

It's your problem that you are not convinced. The trade-off between concrete and wood as to initial vs subsequent costs are not exactly a secret for even an owner who had both, let alone a civil engineer.

Numbers: 1, 2, 3...

There are wooden houses that are centuries old.

Reinforced concrete doesn't really have a reputation for lasting long. See https://theconversation.com/the-problem-with-reinforced-conc...

There are multiple books about it: https://www.taylorfrancis.com/books/mono/10.1201/b15160/conc... and https://www.taylorfrancis.com/books/mono/10.1201/97814822714...

Finally, here's a study doing the exact cost comparison: https://meridian.allenpress.com/fpj/article/70/4/482/454349/...

"...However, because of its estimated much higher end-of-life salvage value compared with the concrete building, the TLCC calculated for a 60-year study period reversed the cost and showed about a 2.4 percent cost advantage for the mass timer building. ..."

And (1) it looks dope.

It doesn't. All of the modern wooden/eco houses with wooden facades I've seen in Sweden look really shabby and rundown after as little as one year. Because for some reason modern construction prefers to just expose wood to the elements.

In contrast all the traditional houses look pretty because no one thinks that painting your house is an abomination in the eyes of the Lord.

Yeah, i can see that being a problem. The renderings always look sharp, and weathering can give a much different and more uneven/random look. This ofcourse is al subjective.

In the computer renderings only? Wood exposed to atmospheric conditions quickly looks badly. All it takes is 3-4 cycles of sunny summers and freezing winters, with mild humid periods in between.

I can see why Sweden would ... in 1920s, forests covered 35% of their land, today they cover 70%, of this 80% is in active use [-1], employing 4% of the workforce [-2].

Makes sense in low-rise construction - of two otherwise identical buildings (4 story, ~15 flats/apartments), one with timber-frame construction has no carbon dioxide emissions, whereas the concrete-frame yields 96 tonnes [-2].

[-1] https://www.forestindustries.se/forest-industry/facts-and-fi... [-2] https://www.ksla.se/wp-content/uploads/2015/08/Forests-and-F...

I sometimes get an idea and think "why haven't we done that?"... and perhaps we have.

Venice is built on wooden stilts that are sunk into clay so tightly that the clay is essentially reinforced by the stilts and this allows them to support the stone structures on top. The clay also protects the wood from rot in a long-term way, which provides the longevity that Venetians obviously needed.

Given that reinforcing clay with wood produces such qualities, why not produce taller organic structures where instead of concrete reinforced with rebar we have clay reinforced with wood?

Is this something that has ever been tried above ground for tall buildings? (i.e. not driving stilts down, but lifting clay up and boxing it in before driving stilts into the box).

https://en.wikipedia.org/wiki/Wattle_and_daub

Not quite the same thing, and I meant for tall buildings.

Venice is built entirely on a clay swamp, the wooden piles support the full weight of absolutely massive stone structures including St Marks Square, the tower and cathedral.

https://sites.google.com/site/engineeringvenice/

Given that the relatively short wooden piles combined with clay produce such strength... what's stopping very tall wooden buildings existing?

> the wooden piles support the full weight

You kind of answered your own question. The clay is just supporting those piles, and the clay is supported by the substrate surrounding it, etc.

Aside from the wattle and daub examples (of which I have seen 4-story examples) there are many large structures built with clay (in the form of bricks for load bearing walls, pillars, etc) and timber framing.

Also, consider the density with which those piles are packed in venice - you would essentially end up with a building with no interior space - just piles.

Bricks are cooked clay.

Venice substrate is wet clay.

I don’t think that required clarification, but yes that is almost correct, in the sense that bricks don’t need to be cooked (the term used is “fired”) as they can also be left to dry naturally.

Sure, though the fired ones are much more resistant than naturally dried ones.

The note was more about the fact that clay in different states (wet/fired/dried) has very different properties and that the parent comment was ignoring that.

BTW the way a foundation may work (wooden piles in a wet clay substrate) is very different from how a vertical structure (pillar/wall) or a horizontal one (beam/deck/slab) behaves.

In the case of the foundation, the wooden piles distribute the vertical forces through lateral adherence (as opposed to applying it directly to the top surface) over all the inserted length, and in the particular case of the tight grid used in old Venice buildings, the wooden poles act also as containment, they are also called "friction piles".

> what's stopping very tall wooden buildings existing?

Buildings are generally valued for the space they create internally. Filling the inside with clay and piles is rather less convenient, you might as well put those in the ground.

Which is exactly what we do.

> Is this something that has ever been tried above ground for tall buildings? (i.e. not driving stilts down, but lifting clay up and boxing it in before driving stilts into the box).

I’m not sure it’d work for actually tall buildings as clay is quite heavy.

But timbered and half-timbered commonly have wattle-and-daub, clay, or unfired brick infill (adobe, mudbrick). Though actual brick, stone, plaster, … are also common. As well as the infill changing as the building goes up (e.g. stone or brick on the low floors, with wattle or plaster on higher floors.

In a country where this[1] is a thing, it that seems like a bad idea.

[1]: https://en.wikipedia.org/wiki/G%C3%A4vle_goat#Timeline

"Entire city" is a stretch, of course. It a large city block, at most. They're basically building over a parking lot of a shopping center[1], a dozen or so buildings[2].

[1]: https://goo.gl/maps/ZmwJZiNi24xV1ahT7 (it does include the three rectangular buildings in the middle)

[2]: https://www.al.se/sickla/ scoll down to the image

Amusing to see this development mentioned on Hacker News, one of my best friends here in Stockholm worked as an architect for this Sickla redesign. The entire area of Nacka is under heavy development of new housing, it's a deal between the city of Stockholm and the Nacka municipality where Nacka builds housing and Stockholm foots the bill for the expansion of the tunnelbana's (metro) blue line to it.

I'm curious to see if there will be any impact to housing prices, I think the plan was to add some 50k new units until 2030, I personally believe it won't make a dent, the rise in interest rates from Riksbanken seems to have had a much major impact in housing prices than any new development done in the past 10 years.

Sweden already has plenty of "wooden cities" (i.e. from quarters to cities built mostly or entirely out of wood, viz. Haga in Göteborg, Vänersborg, Alingsås, Eksjö, Hjo, Nora and many others) so this is not a new thing. Buildings tend to be lower, 2 or 3 floors instead of the 5+ floor glazed boxes shown in the image in the article. They are made of wood as it comes from the forest, not wood which underwent industrial processing. They also tend to be quite old with plenty of 200+ year old buildings.

I live on a 17th century farm, the (wooden) house was moved from its original location to the current one during the great land reform in the early 1800's, most likely around 1823. The house itself is probably from the late 1600's or early 1700's but parts have been added and replaced in the intervening years. Whe I put a new roof on it in 2015 I left the old plank roof ("locktak" - overlapping planks with grooves to catch rainwater and lead it down) in place, it now lies sandwiched between two layers of insulation for the next generation to be found. As long as you keep moisture, arthropods and fire at bay wooden constructions can last for a very long time.

Don't not about wood, but thanks to the abundance of cheap lumber half of Vancouver is built from plywood.

Not the sky-scrapers or residential towers, but low-rises and individual houses in suburbs are that way. So much so that back in the day it was recognized as a "Canadian approach" to home construction that they even tried to export to other countries, but I don't think it took.

The main issue with it is sound-proofing. Even if you don't hear neighbors one floor up talking, you do hear them walking. There are ways to deal with that, but it drives construction costs up and makes it more expensive than using the concrete.

Is it plywood or OSB?

Plywood is expensive.

Interesting idea. But does a wooden structure, even if it is engineered, have the same lifespan of a concrete building? How does this affect prices, rent, management, maintenance of the buildings?

https://en.wikipedia.org/wiki/Kirkjub%C3%B8argar%C3%B0ur

Anything can last forever if you maintain it. At some point it's really a rebuild with nothing of the original structure, but that's debating semantics. The problem is the effort/cost to do so. Concrete and steel structures are maintenance free for more than their architecture remains acceptable by ever changing standards of living. Wood, even laminated, requires very frequent maintenance. And not just for aesthetics and insulation but for the structural integrity to remain intact.

I inherited my grandfather's axe, but I had to replace the head once and the handle twice.

As writing this in a 140y old wooden house in a neighbourhood of alikes (some of them even several stories high, consisting of many apartments), I would say that lifespan of 200+ years can be reached easily, as long the foundation and roof are checked regularly and maintained properly. Of course the modern wooden element engineering and it's lifespan is a mystery.

Wooden houses - if maintained properly - can last very long indeed.

The problem nowadays is that we don't maintain stuff. It's sexier to rebuild it (at a much greater expense in resources). I don't see this changing unless we're getting too poor (not just in money, also in resources) to rebuild and have to repair.

I've been to wooden houses here in Sweden that are 200 years old. If properly maintained the lifespan can be quite long.

A concrete building has a lifespan of about 50 years. Even so, most people wouldn't want to live in a 30 or 40-year old building anyway.

This is very dependent on location. There are places where, eg, the buildings from the 60s are rather well built, but the later buildings are terrible. It's not the age that matters. My previous apartment was brand new building, but cheaply built to cash in on certain developments nearby (new transport links, new faculty building at the university). I doubt it will still be there in twenty years. My current building is much older but much nicer to live in (thicker walls, better ventilation, no creaks and whistles when the wind blows the wrong way). I think it must be 40 years old or more.

In The Netherlands, anything post-WWII up to the 1980s is typically of very low quality. We had to quickly rebuild the country. And it was the start of prefab concrete, which had some teething issues. In the 1980s we had the Bouwbesluit, a set of rules for building residential homes. Everything built since the Bouwbesluit is of high quality and can usually be purchased without worry. Those homes are typically also well insulated.

Looking at pre-war the 1930s were great. Opulent homes with a high degree of finishing, including stained glass, beautiful mouldings, lots of wood finishing, en-suite doors.

I think it's quite normal to live in a 100+ year old building in a European city center. Though they're usually made from brick and not concrete.

And do people who have built their own house usually demolish it and move on after just 30-40 years? That's when you've just paid off your mortgage, heh.

At my parents' house, they just replaced the roof, which was well over 30 years old. The house itself is over 100 years old and completely fine to live in.

In Europe, people often pay extra to live in buildings which are several hundred years old.

I live in such a building. Only the facade is hundreds of years old, the rest has been completely redone multiple times over its lifetime. The entire building gets stripped, including the floors. New floors are placed, then the walls, then the interior walls. Even the foundation was completely replaced once.

You mean they pay to live in that 1 out of 100 buildings of that age that is still standing and on which multiple extensive renovations have been conducted.

https://archive.is/hTQku

https://archive.ph/hTQku

What I don't see mentioned and haven't found information on is how good these wooden structures are at sound isolation, especially lower frequencies like bass/kickdrum and compressor sounds. Does anybody have information on this?

Well then they're up for a challenge. Activists and environmental absolutists are doing their darnedest to stop or make it exceptionally hard to do any logging in Sweden.

Logging outside the country is fine tho...

Swedes source their wood from Poland, Romania, and other countries where their money goes far. Why bother with domestic eco lunatics when all it takes is one flight and meeting with state forests representatives.

https://en.wikipedia.org/wiki/K%C3%BCstendorf

Has Sweden never heard of the USA? They are acting like this is some magical new technology.

The US builds tons of buildings from wood. It works just fine, and the US does not have more fires than other places.

However concrete is better for apartments - it blocks sounds better.

And I'm not sure why they think building a wooden building is quieter, there's tons of noise - saws, nail guns, air compressors.

We haven't heard about Sweden for some time now, and here it is!

It worked well for Ankh-Morpork, what could go wrong?

Burning man is coming

Wood houses burn quite a lot worse than a lot of "modern" houses built with styrofoam insulation, plastic windows, and so on.

Wood has this wonderful property of charring, and the thick layer of carbon on a piece of wood prevents it from burning further.

Wood houses will also have the styrofoam insulation and plastic windows. If you're gonna give the wood houses rockwool insulation and aluminium windows traditional houses can also have those.

> styrofoam

Nobody would call that modern around here, PIR has been around for half a century now?

Hence "modern" in quotes. It's relatively modern, considering wood houses have been around longer than writing im guessing.

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