[bradknowles]

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.

[myshpa]

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.

[bradknowles]

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.

[myshpa]

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]

[bradknowles]

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.

[dvdkon]

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.

[bradknowles]

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.

[stuaxo]

Depends on the country.

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

[seszett]

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.