Earth buildings
Jun. 26th, 2005 08:35 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
trixtahI love earth buildings, and if one day I get sufficiently rich enough to buy some land and build a house, it will be made of dirt. I can imagine all the "yeah rights" coming from the kiwi contingent, because, you know, in NZ, it rains. But so long as your earth building has a "good hat and boots", ie. it has a decent roof with wide eaves and a good solid foundation that doesn't allow water to pool, then your earth building will outlast you. One of the oldest buildings in NZ, Pompallier House, is made with a rammed-earth construction, and is still going strong over 160 years later.
So, there are two main earth building methods. There's rammed earth or pisé, which involved putting up formwork to lay out the wall courses (such as when pouring concrete walls), filling the forms with layers of earth (normally with 3-5% cement mixed in), and then tamping down each layer to half its original height, before shovelling in more earth and tamping again. Hard work, and you can imagine how hard it must've been in the days before pneumatic tamping tools! The advantage of this method is that you get nice flat walls and they go up fast, since you're building in situ. Disadvantages are that the soil must have fairly precise clay and sand proportions (high clay), and that the formwork and tamping can get pretty pricey.
Adobe is the process of making bricks out of mud, which again needs to have quite a decent amount of clay, with some sand and possibly straw mixed in. You mix up the mud, pour it into brick moulds, and then wait for the bricks to cure (a month, at least). So, the advantages of adobe are that you can do it in bits at a time (you don't need to make all your bricks at once), it needs bugger-all skill to make bricks and it's more flexible with doing nice shapes like curves in your walls. Disadvantages are that you can't start building for AT LEAST a month (assuming you managed to make all your bricks in one day (uh huh), and you have perfect weather during that month), you need to tote the bricks around to lay them, and you need to learn bricklaying.
Given the usual state of NZ weather, I always thought that rammed earth would be the way to go.
But wait...!
There's a company here in Oz who have come up with a method called Formblock. It's like a combination of the rammed earth and adobe methods. You get a basic assembly which consists of a block shape which is 600x300x300mm. These are then slotted together to form a run, and then a slurry of earth+10% cement is poured into the run. Next day, you remove the block assembly and slot it together for the next layer up. The assembly is offset in the same way that normal bricks are, so when you pour the next layer, the slurry runs down into the gap left between the blocks on the lower level, thus no need for mortaring. Wow. Much less labour-intensive than the other methods, reasonably fast (certainly faster than adobe!), no need for a high clay content (in fact, less is better) and it's reasonably flexible, since you can build the forms into curves. The only drawbacks are the higher percentage of cement needed (cost), the cost of the forms ($AU3500 for a kit that will do a 7m course) and the fact that the wall widths are only 300mm. I'm used to the idea of 450-600mm widths, although that might just be my being used to rammed earth ideas (you need to be able to stand between the forms to ram the earth down). It'd be interesting to see just what difference the narrower width makes to thermal mass properties. Although, if they use it here in Oz, which has much greater temperature ranges than NZ, then it must be reasonably decent.
So, yeah, if and when I ever build my house, that is how I'm going to build it!!
So, there are two main earth building methods. There's rammed earth or pisé, which involved putting up formwork to lay out the wall courses (such as when pouring concrete walls), filling the forms with layers of earth (normally with 3-5% cement mixed in), and then tamping down each layer to half its original height, before shovelling in more earth and tamping again. Hard work, and you can imagine how hard it must've been in the days before pneumatic tamping tools! The advantage of this method is that you get nice flat walls and they go up fast, since you're building in situ. Disadvantages are that the soil must have fairly precise clay and sand proportions (high clay), and that the formwork and tamping can get pretty pricey.
Adobe is the process of making bricks out of mud, which again needs to have quite a decent amount of clay, with some sand and possibly straw mixed in. You mix up the mud, pour it into brick moulds, and then wait for the bricks to cure (a month, at least). So, the advantages of adobe are that you can do it in bits at a time (you don't need to make all your bricks at once), it needs bugger-all skill to make bricks and it's more flexible with doing nice shapes like curves in your walls. Disadvantages are that you can't start building for AT LEAST a month (assuming you managed to make all your bricks in one day (uh huh), and you have perfect weather during that month), you need to tote the bricks around to lay them, and you need to learn bricklaying.
Given the usual state of NZ weather, I always thought that rammed earth would be the way to go.
But wait...!
There's a company here in Oz who have come up with a method called Formblock. It's like a combination of the rammed earth and adobe methods. You get a basic assembly which consists of a block shape which is 600x300x300mm. These are then slotted together to form a run, and then a slurry of earth+10% cement is poured into the run. Next day, you remove the block assembly and slot it together for the next layer up. The assembly is offset in the same way that normal bricks are, so when you pour the next layer, the slurry runs down into the gap left between the blocks on the lower level, thus no need for mortaring. Wow. Much less labour-intensive than the other methods, reasonably fast (certainly faster than adobe!), no need for a high clay content (in fact, less is better) and it's reasonably flexible, since you can build the forms into curves. The only drawbacks are the higher percentage of cement needed (cost), the cost of the forms ($AU3500 for a kit that will do a 7m course) and the fact that the wall widths are only 300mm. I'm used to the idea of 450-600mm widths, although that might just be my being used to rammed earth ideas (you need to be able to stand between the forms to ram the earth down). It'd be interesting to see just what difference the narrower width makes to thermal mass properties. Although, if they use it here in Oz, which has much greater temperature ranges than NZ, then it must be reasonably decent.
So, yeah, if and when I ever build my house, that is how I'm going to build it!!
![[identity profile]](https://www.dreamwidth.org/img/silk/identity/openid.png){kind=small}
(no subject)
Date: 2005-06-30 01:38 am (UTC)http://www.life.ca/nl/73/straw.html
(no subject)
Date: 2005-07-03 11:27 am (UTC)But, really, maintaining the "skin" of the straw bales wouldn't be that much different to other earth buildings. Mud render with a lime top coat should be reasonably weather-resistent. And it'd be possible to get around the issue of straw bale's lack of thermal mass properties (although it's an excellent insulator) by using one of the alternative building methods to construct the internal walls.
Hm, I think you've made me modify my grand plan. :-) Now, the only difficulty that remains is that NZ has a code for earth buildings, but not one for straw bale (although they're looking into that). Which means that you need to apply for a variation to the code to put it up, which involves more engineering approvals, council approvals and general hoops to jump through, thus more money. Hopefully they'll get one sorted out before I actually will be wanting to build (not for 5 years or so, probably).
Thanks for the food for thought!! :-)
(no subject)
Date: 2005-07-05 01:01 am (UTC)