The sustainable cities made from mud | Hacker News Reader

The sustainable cities made from mud

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17 pointsclouddrover5 comments

From what I understand the pros are that it's a sustainable material, you get great insulation from temperature and sound and good durability against earthquakes, and you can easily extend or modify the building; the cons are that it needs a lot of maintenance work, it is vulnerable to heavy rains (the reason for the yearly maintenance work on the Great Mosque of Djenné) and it needs good planning to resist flooding.

I think the insulation is the most interesting property, for me at least, being from a country where summer temperatures can reach 42 degrees C easily. Anecdotally, stone has similar properties although it tends to stay cold in the winter. Intuitively, I expect you need to have thick walls with both kinds of material if you want to benefit from their high thermal mass, otherwise once your clay walls are heated through by the summer sun, they will keep radiating heat throughout the night. That would in turn mean that more space is needed to build a house with thicker walls than normal.

The real problem is, of course, I don't really see developed world cities tearing down all their concrete buildings to live in mud high-rises, sutainable and well-insulated though they may be. It doesn't sound like something that can be easily adapted to big cities, in other words. Perhaps it's possible to change the way we build newer houses, to use more sustainable and economic materials like mud and stone, but we already have way too many concrete buildings (and steel and glass towers) and I dont' know how realistic it is to expect that those are going to be retro-fitted with earth- or stone- based insulation.

>That would in turn mean that more space is needed to build a house with thicker walls than normal.

Yep, and until (this is slowly changing nowadays) building permits will depend on the external surface of the house or internal surface+half of the external walls (it depends on local building codes), having "better" homes even in the countryside may be problematic.

A "raw earth" house typically has 1 m thick walls, to be compared to the 30-40 cm of houses built in the '60's up to - say - 2010 and the 50 maybe 60 cm of houses built more recently including the (stupid) external foam insulation, this difference in wall thickness is very relevant.

So you have a building lot of 900 sqm (30x30), and according to local Laws you can build on it 20%, your allowed 180 sqm, that is roughly 14x13=182 sqm, has 2x(14+13)=54 m of external walls.

182-54x0.3=165.8 net inner (floor) surface <- old

182-54x0.5=155 net inner (floor) surface <- new/insulated with foam

182-54x1=128 net inner (floor) surface <- raw earth

In a nutshell, you lose one or two rooms.

good durability against earthquakes

Unreinforced masonry is pretty much the worst class of building materials in an earthquake.

Hence it is largely prohibited by modern building codes for occupied structures and severely limited when allowed.

Mud buildings aren't cake to modern construction's bread.

The old city is made of mud because mud buildings are better than nothing (except in an earthquake) and better than nothing is better than nothing.

I am surprised. How can mud withstand rain?

Set aside Yemen ones (of which I know nothing, but that likely has not that much rain), "mud" houses (which were once common in some regions of Italy, Abruzzo as an example) are usually plastered (with clay, and painted with lime), and have a roof that is usually protruding outside a little bit more than other types of houses in order to better protect the walls, but periodical maintenance/repainting was required to keep the walls dry.

Check this (Italian, but understandable via Google translate):

https://www.cronachepicene.it/2018/02/07/memoria-del-territo...

If you search for "raw earth house" or "rammed earth" you will find similar examples in a few more "rainy" countries, including the UK.

https://www.motherearthnews.com/diy/earthen-homes-zm0z12aszm...

> First, the old adage: Give your buildings a good pair of boots and a hat. That means lifting your earthen walls up away from water on a solid foundation and covering them with big overhangs.

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