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Comment by ehou | Hacker News Reader

The article doesn't mention one alternative: CLT (cross laminated timber) as a building material for houses and flats. See https://www.bbc.com/future/article/20190717-climate-change-w... for example.

Using CLT (and passive house principles) can reduce the total CO2 emmissions of a house by 90% in its total life span. The wood in CLT stores carbon and the passive house principles reduces energy needs.

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Yes. And better than that using this at scale is going to require massively scaling up wood production (i.e. forestry). This too will help with capturing a lot of co2 in the soil. A lot of countries would end up restoring farm land to production forests and probably end up using sustainable practices for this.

For those unfamiliar with CLT, this is a high tech building material suitable for making e.g. sky scrapers or other types of buildings. It's much lighter and stronger than concrete. Because it is lighter, you save a lot of fuel transporting it. It's fire resistant and rot resistant because it is chemically treated. It's also much easier to work with as you can drill, glue, saw, etc. it. Additionally, you can do this off site meaning actual onsite construction activities are a lot more straight forward, less noisy, and much less wasteful. Think Ikea for buildings.

To sketch you a picture of how awesome this stuff is, the Japanese are planning to build a 1100 feet skyscraper made of wood, steel, and clt in Tokyo, which is of course a city that regularly sees earthquakes and tropical storms. https://www.archdaily.com/889142/japan-plans-for-supertall-w....

The biggest challenge is going to be simply scaling the production of this material and transitioning the construction industry to mostly using this instead of concrete. Right now it's kind of a novelty / niche thing and it is going to take a while to reach efficiencies and economies of scale we have with concrete today. It's not exactly cheap (yet) but it could become cheaper long term; especially if you consider all the benefits (technical and environmental).

What are the long term health effects of the chemicals used in the production of CLT, on the residents of the houses?

According to this article: https://www.bbc.com/future/article/20190717-climate-change-w..., it's less than 1% vs 10% in things like plywood and does not use dangerous chemicals:

" Other engineered woods such as plywood and MDF are around 10% adhesive (glue), often urea-formaldehyde, which can produce hazardous chemicals during recycling or incineration. CLT, however, is below 1% adhesive, and typically uses a bio-based polyurethane. The planks are bonded together under heat and pressure to fuse that small amount of adhesive using the moisture of the wood. To look at, smell and touch, it’s as pure wood as a child’s tree house – knots and all. "

In any case, there are already quite a few buildings that use this so, I'd say this is a non-issue.

Good question.

There is also CLT without glue. Check https://www.youtube.com/watch?v=4j_UjIshzMc where Matt Risinger is visiting a Swiss factory where they use wooden (berch?) nails and dowel pins in stead of glue. And by using more layers they also need no insulation. Gives R=24...

Some adhesives use formaldehyde, but you can also get formaldehyde free adhesives. It's no different than plywood or OSB which is greatly used in the construction of most wooden stick framed houses where that's common (i.e. North America).

It's the same chemicals used in the production of plywood (glue), only there's a lot less of it. It basically is plywood, just with fewer and thicker layers so a lot less glue is needed.

At least per 2019 when it was opened Mjøstårnet[1] is the world's tallest timber building. It's only 85.4m (218ft) though[2].

There's also a report[3] about a glulam burn test, something I was quite curious about.

[1]: https://www.moelven.com/mjostarnet/

[2]: https://en.wikipedia.org/wiki/Mj%C3%B8st%C3%A5rnet

[3]: https://www.moelven.com/mjostarnet/glulam-can-withstand-a-bu...

The wikipedia page you link to says it has a concrete core.

I think you misread? The concrete core is in reference to a building in Austria.

"As the main vertical/lateral structural elements and the floor spanning systems of Mjøstårnet are constructed from timber, the building is considered an all-timber structure."

I misread. I appreciate the correction.

While CLT has been certified for 60 years, I don't know how the adhesives they are using are certified for that long. The working life of common industrial adhesives is remarkably short [1]. The key is not just moisture control, but also temperature regulation.

With rigorous humidity and temperature regulation, some adhesives have an as-yet undetermined lifespan. I'm still looking for transportable passive designs without active mechanical assistance that keep humidity at or below 40% and temperature variation to within ±10° C in temperate zones.

[1] https://www.bhhomeinspections.com/building-materials-life-ex...

[2] http://www.woodcentral.com/woodworking/forum/archives.pl/bid...

There is also CLT without glue, see my other comment. Check https://www.youtube.com/watch?v=4j_UjIshzMc.

"passive designs without active mechanical assistance" - do you mean passive (highly insulated, air tight) designs without mechanical ventilation?

Thanks, I follow Matt so I saw that, but couldn't figure out how they made the exterior wood stand up to the elements.

Yes, PassivHaus or even NetZero type standard, but without an electrically-powered ERV. I don't think it is possible, so I've been looking at minimizing the power requirements.

Using actual timbers in a place like Canada should be the norm. Many of the biggest trees are left after a clearcut because they're just too big. When everything around them is cut they tend to die quicker (due to exposure). If they do get cut and milled, they often get processed into dimensional lumber (2x4s) instead of being used as timber.

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