Comment by myshpa | Hacker News Reader

Comment by myshpa | Hacker News Reader

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I think one of the solutions may be based on hemp, currently known as hempcrete or hemp concrete - essentially a mix of hemp hurd (the woody essence of the hemp plant), hydraulic lime, and water.

You mix it up and then all you need is just the wooden frame (if you're building load bearing walls), then you wrap it in hempcrete (floors, walls & roof), apply some mud plaster and you're done. No need for 6-10 layers full of plastics & glues.

Thanks to use of lime instead of cement the building even captures CO2, as the walls literally turn into stone over time.

Some hemp buildings are 200+ years old, in some cave in india they've even found 1500 y.o. hempcrete, and you can compost whole building at EOL.

Some other benefits: non-toxic, no off-gassing, no solvents, mold resistance, high vapor permeability, humidity control, durable, sustainable, carbon sequestration, fire and pest resistance, passive self regulation of temperature and humidity, great insulator

Can hempcrete be made from Mars or Moon aggregate instead of lime, and 4d printed?

FWIU, lime requires coral for production? Is lime sustainable?

Alternative solutions for: structural wood frame in a hempcrete structure: stacking hempcrete blocks on structural forms that are stronger and more insulting than structural concrete; green concrete, a carbon and thermal gradient sink; and Hempwood, which is apparently stronger than spec lumber of the same dimensions as well.

most lime comes from limestone, extracted by quarries/mines- although sometimes it is sourced from coral

the process of producing lime can involve a number of not-very-sustainable steps, hopefully which can be substituted for more environmentally responsible alternatives

Hempcrete is great for many things, but it produces very thick walls -- like a foot or so.

And they're pretty solid, so snaking a power or network line through the walls after the construction is done -- that's not really very feasible.

And it takes a long time for the hempcrete "bricks" to dry. Although once dried, they are sprayed with a mixture that makes them pretty waterproof, IIRC.

If you can design around the very thick walls, then I think it's wonderful. But you've got to make some changes to your design and assembly process to accommodate the building material in question.

I think Matt Risinger has some nice videos about hempcrete on his "Build Show" channel on YouTube.

How thick the external wall is depends on your insulation requirements - for residential building a foot is not much, not in central/northern europe, because you don't need additional insulating layer, as is the case with other, more traditional building materials. If you build with traditional bricks here, 20cm+ wall then needs 16+cm of styrofoam to have good insulating properties, so 30cm of hempcrete is a plus. I've got a hundred y.o. house, with 45cm brick walls ... and would need to add 16-20 cm of styrofoam to make it an energy efficient.

> And they're pretty solid, so snaking a power or network line through the walls after the construction is done -- that's not really very feasible.

It's not as hard material as concrete is, so with some hand tools it should be easy enough [https://www.youtube.com/watch?v=NDfzgZ8d0Cc].

> And it takes a long time for the hempcrete "bricks" to dry.

Yes, that's true. It may take weeks/months, depending on the weather conditions. But ... all "wet" building techniques require some time for drying, so in my country it's non-issue.

> Although once dried, they are sprayed with a mixture that makes them pretty waterproof, IIRC.

If I remember correctly, I've seen some video, where hempcrete building stood directly on the beachfront, with no special treatment, and it withstood the elements admirably.

I agree that a great deal depends on your local area and what the normal construction methods are, and that's radically different between the US and some parts of Europe.

When my wife and I lived in Brussels for almost eight years in a townhouse that was built just after the turn of the 20th century (1910?), one thing we noted was the extremely thick walls. That kind of construction made sense at that time in that location. Modern construction methods in that same area would be thinner, but probably not like what we would typically see here in the US.

Many people in the US don't realize how far north a lot of Europe is. For example, Brussels is on about the same latitude as Toronto and Seattle. And Belgium is not part of what I would consider Northern Europe.

So, hempcrete construction in Europe might be a lot closer to the type of wall thickness you would normally see over there. And the fact that this is a solid construction material versus the hollow "balloon stick framing" technique we see for most home construction in the US -- that might be less of a problem for you.

I personally would like to see a lot more PassivHaus class building here in the US, and a lot more hempcrete in general. But both of those things are going to require a huge shift in the mindset of most builders here in the US.

Doesn't US have big problems with air conditioners in the summer?

Hempcrete is not only for winter months and keeping heat inside. It's also very good for keeping the heat outside of the building in summer.

[https://www.youtube.com/watch?v=_5lDwBiQNc0 - Israel, no need for air conditioner, hempcrete keeps inside temperature between 20-25C all year round]

In the South, yes -- air conditioners are definitely the biggest cost we have for electricity.

I do feel that hempcrete would be a good building choice for a lot of places in the US, based on insulation capacity and relatively low cost of materials.

But the cost of labor to build with it would be higher, due to lack of familiarity with the materials, and it would take longer to build with -- especially compared to prefab or other higher speed building methods. And then there's the increased cost in labor to do the interior fittings.

I am a fan of hempcrete. But it will take significant adjustments to the building process here in the US.

A foot (~30cm) isn't too much for exterior walls, right? A brick wall with more traditional insulation would be about that thick, maybe more with concrete. Running cables is also a challenge with bricks or concrete, hopefully people building/renovating today will have enough sense to build in conduits.

Look at old thatched roof buildings from the 1600s in the UK. That's the kind of wall thickness you're looking at here.

Modern "stick framing" construction is much thinner. Interior walls are four to five inches thick, depending on the actual dimensions of your 2x4 "sticks" and the drywall on either side of that. Exterior walls tend to be a bit thicker, depending on what kind of exterior surface you've chosen to put on the face.

If you want to build to PassivHaus standards with modern construction, then Matt shows examples of that in his video series, and yes the walls are thicker than we would normally see. But still not as thick as you'd get with hempcrete.

I'm not saying hempcrete is bad, I'm just saying that there is a factor there you have to take into consideration when you're looking at doing hempcrete construction for your walls.

The problem with running cables and pipes through hempcrete is that it is a solid material throughout. In modern "stick frame" construction, there is typically no interior insulation and nothing between those two sheets of drywall, other than the 2x4 sticks that are 16 inches on center. So, with all that empty space in the walls, it's much easier to run cables and pipes.

Again, not a deal breaker. But it is something you have to account for. And your current architects and construction crew will have to think and work harder now, in order to make life more livable for future architects and construction crews -- and future owners.

Depends on the country.

In a crowded Island like the UK, doubling the wall thickness absolutely makes a difference.

Are walls generally 15 cm thick in the UK? Here in Belgium, which is certainly not less crowded than the UK, my exterior walls are 30 cm thick. 40 cm for the back wall that was insulated further recently. That's for a town house in a city center.

How does hempcrete respond to water?

It seems fundamentally difficult to have a material that can hold up for decades but then biodegrade once we decide it is EOL.

Not about hempcrete specifically, but I can see how you could potentially make a material like this. All these materials used in construction we can assume have an environment with a range of variables they operate in. If this material will never be exposed to high temperatures for example while in a typical operating environment... then maybe you can design the material to be able to biodegrade when heat is applied?

Just think about how even typical composting works where the point is to keep temperatures of the compost pile going in order to aid the process of breaking the material down in an acceptable timeframe.

It is waterproof ... please, see my other comment in this thread for a link to a relevant article.

It's a poor insulator.

Mineral wool is just hot rocks, a far better insulator, and completely immune to water.

As it turns out, hempcrete is a great thermal insulator. Less heat flows through it than through other insulators, e.g. wool or cotton. In winter, the temperature of the outer walls of hemp houses can be around 5C lower than in the houses (heated the same way) with standard insulation. This means that less heat leaves the interior of the building. Indeed, with comparable heating intensity, houses insulated with hemp-lime material maintain an average temperature higher by 2C.

[https://ecoreactor.org/hempcrete-2/]

Hempcrete is waterproof. It is highly versatile and features desirable structural and moisture-handling properties. Depending on the mix variables, hempcrete makes an ideal choice for insulation, flooring, drywall, and roofing. Hempcrete is also fireproof and rot-proof.

...

Unlike Portland cement that needs water to hydrate, hempcrete takes on moisture when it exists and releases it when the conditions allow. Research indicates that hempcrete blocks fabricated and stored in different weather conditions – without any coating – for a few months showed water vapor pressure between 1000 Pa for the drier block and 1600 Pa for the moister one.

...

Besides, hempcrete cannot be overwhelmed when it comes to adsorbing of moisture thanks to the vast storage capacity with a sustained elevated humidity of 93 percent. Therefore, high levels of moisture don’t propagate deeply into the hempcrete.

...

The lime coating in each hemp block creates a surface that resists the development of mold, even when the conditions cause decay. The resilience to tackle humidity and liquid moisture makes it a desirable choice and a unique insulation material in hot and cold climates.

[https://www.builderspace.com/is-hempcrete-waterproof]

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