Hempcrete – eco-friendly material in Australian homes | Hacker News Reader

Hempcrete – eco-friendly material in Australian homes

abc.net.au

70 pointsclouddrover15 comments

> Hempcrete, made from mixing woody hemp fibre (from inside the hemp stalk), with lime and water, is then pushed into timber frames by hand to build an insulating wall.

So it's a reinforced lime mortar, rather than a concrete alternative. You can use it to fill space, but not to bear load. More practical and quantitative detail here:

https://greenbuildingcanada.ca/2017/advantages-building-hemp...

Curtain walling is used just about everywhere else, no reason it can't succeed in housing too. There was a Guardian piece about a hempcrete house just yesterday, with the hempcrete held in frames made from the hemp stalks and resin made from agricultural waste. Started out as a barn, so there was a steel structural frame to be filled in.

The prospect of carbon negative building has to be a huge plus.

https://www.theguardian.com/artanddesign/2019/dec/07/flat-ho...

Lime production is carbon intensive (heat + chemical C02 release from the limestone) and the hempcrete curing will take 50 years to fix back the second part. So it can be carbon negative (by fixing the carbon of the hemp itself) but only on the long term (50 years after production) and assuming that the heat used for lime production was from non-fossil source in the first place (which is not the case today: the cement industry typically produces heat by burning natural gas).

The heat could be produced from burning green hydrogen (hydrogen produced by water electrolysis using renewable power) but as of today is still too expensive compared to using fossil fuels.

A simpler alternative to get carbon negative buildings is to use Cross-Laminated-Timber (CLT) to build both the frame and the walls themselves.

I believe it can bear load, but it takes something like a decade to harden to that point. It's like very slow curing concrete.

I have a hempcrete extension on my house in Sydney. It's not load-bearing but it very effectively insulates. It's packed into formwork so there's no gaps or seams. This is in a city with mostly terrible thermally-performing buildings so, combined with double glazed windows (also rare in residential in Australia) we have an amazing house thermally. Regularly 10 degrees cooler than outside in Summer and the reverse in Winter.

We originally were going to use another high-performance technical product to achieve the same. The cost ended up about the same. Hempcrete has higher labour costs and the technical product cost more but went up much quicker.

how is this carbon negative? since lime is used for the mixture, doesn't it mean the carbon was removed earlier during production and released? so essentially any carbon absorbed was the carbon released during production.

The carbon released from the limestone. If your concrete kiln, say, burns huge amounts of fossil fuels to convert your limestone to line, that doesn't get reabsorbed.

Hemp is a plant which consumes CO2 from the atmosphere. Using it as part of a structure keeps it sequestered within that structure.

That’s the same as every other fibrous cement product, though. Is this different apart from using hemp for the purposes of marketing to a certain crowd?

It has other advantages compared to fibrous cement, like being a very good moisutre buffer, having a time shift of 10…12 hours, CO2 absorption as it cures etc. It can use natural hydraulic lime or pozzolanic binders.

>It will negate any carbon emissions we've had to make — for the concrete for instance; it'll be a carbon-negative house.

I wonder how that compares to geopolymer cement?

Neat... although I can't help but wonder what would happen if the structure catches fire. I mean, would the entire neighborhood end up smoking it secondhand?

There's very little to no CBD/THC on the stalk itself. Also, hempcrete isn't flammable.

Thanks. I meant for my comment to be humorous... and evidently, it wasn't.

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