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Straw bale Earthship hybrid....?  RSS feed

 
Greg Canicio
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Hi everyone,
My wife and I just got ouselves a little piece if land where we dream of building a multi-family homestead.  We have wanted to build different types of dwellings and we will have small cottages made in different natural tecniques for sure.
For our own house we were thinking of making an earthship/straw bale hybrid.  Has anyone here done this or have a bit of knowledge and experience with it?

The idea is to go with the earthship floor plans and technology but to replace the rammed earth tires with straw bales.  Can we still berm the house with straw bale walls?

Thank you for your time it is appreciated.

 
Gilbert Fritz
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I'm not an experienced builder, but I would guess that berming a straw bale wall would be a bad idea for moisture. Straw bale walls, like cob or adobe, need a good hat and good boots.

Hopefully somebody more knowledgeable shows up.
 
Roberto pokachinni
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Consider doing an couple rounds of tires first, for a solid foundation and get your bales off the ground.  You can berm or build underground with anything, but there are things like tires and stone and concrete that lend themselves to it better than things like straw bales.  Just sayin' 

It might be worth investing in The $50 and up Underground House Book  Probably the best 20 bucks you could spend to get some tried and true underground building knowledge.  If you have more cash look for  Passive Annual Heat Storage  In the latter link it shows that the latter is available as a kindle E book for 8 bucks.  A steal.   Check out the Wofati stuff on this forum.  Lots of good ideas there too.  With these resources you should be able to come up with a plan that works with your ideas.   

In my thinking (and this is just throwing stuff out there.  I can't advise you on something I've never done), but this is basically what I would be thinking if I was considering it:  

What you will need to do with the bales is to provide a barrier between them and the earth.  I was part of an Earthship Build in my valley.  We did this even with the tires.  We used waxed cardboard tree boxes (the sort that tree nurseries pack lots of trees into for tree planting forest companies to plant out).  We impact screwed these like shingles into the tires.  We laid plastic in the gap after that, and the plastic went out over the earth so that the earth behind the Earthship gets drier and drier as time goes on, and acts as a way better thermal battery.  

This last point is super important, especially if you are using bales.  Any moisture will kill your project, especially with bales.  Make a gravel trench outside of your tires, or whatever (concrete?) foundation you plan to put your bales on.  A round of Big 'O' drainage pipe would be a good investment in this trench.  To further ensure dry material near your bales, you could add only dry material to fill the trench behind your walls, and have it between two sheets of plastic.  I would definitely cob your bales, and maybe make a stucco plaster for the exterior to seal it.  Ensure that this is dry before you put all the plastic in.  I know, it's a lot of plastic, but you can perhaps salvage it like we did from large dairy operations who use silage.

If you are planning to have lots of things growing in your space (Earthship greenhouse...), then you will need to be especially careful with ventilation.  Keeping your bales dry, but 'breathing' is super important.  Breathing means that the bales can transfer heat and moisture.  An RMH is a good idea, or any wood heat, or drying heat source, will be handy to keep your space dry.  Super important.  In the Passive Annual Heat Storage book, he goes into detail on venting and creating a dry umbrella behind/around your house, with vent tubes in the berm.  Most up to date Earthships have incorporated these techniques as well, as far as I know.  We had a guy from the Earthship Academy finish the build, and he pretty much said as much. 

 
Kaye Harris
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I was actually hoping to use a combination of straw bales & a partial berm myself. Mostly because straw bale is faster to build with than, say, earthbag.

One thing I was wondering about was the potential pressure of the earth against the straw bales. I remember mike oehler in his book talking about how the pressure of the earth would slowly press in on some of the walls. To mitigate that, could you stair-step the bales (see photo) to take add some structure to the pressure? Of course you'd have to line it with a water barrier, but then wouldn't you have breathe-ability issues?

It kind of seems like each solution presents a new problem.

Also, straw bale is insulating. So, if you put it inside a berm, wouldn't it be insulating you from all that great thermal?

Why not do a house with cob-coated straw bale walls (insulating & thermal) on rammed earth floors (thermal), with an earthen roof (thermal)?
Bermed-Strawbale-Foundation.png
[Thumbnail for Bermed-Strawbale-Foundation.png]
Bale-Berm.png
[Thumbnail for Bale-Berm.png]
 
Roberto pokachinni
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You may be right about breathability issues, Kaye. You would have to super insure that your bales are dry beforehand.  Stepping them up, like a classic retaining wall, would be a good idea, for the purpose of relieving the pressure, but I'm not sure how practical it is with breathability concerns.  One way to maybe deal with this is to cob the stepped up structure, and add say a 6 inch layer of dry dirt on top of the cob, after it dries.  Then protect that layer of dry material with a few inch layer of loose super dry straw, and a layer of plastic before adding more material.  That way, you only have to super insure that a small portion of dirt is super dry, and the rest can dry slowly, later, under a larger umbrella of plastic. 

Straw bale is not simply insulating; it is both insulating and thermal mass, just as loose earth is.  You are right that your rammed earth is pretty much straight up thermal mass, but the loose (hopefully dry or drying with an umbrella) earth in the fill is both insulating and thermal mass. 

I agree with your last statement. 

There are simpler ways to build efficiency into a system.  Two of the great ideas of permaculture are to look at what you have in abundance and utilize that to maximize efficiency (do you have lots of access to cheap straw, or to logs, or to tires, or to...), and another is to do the least amount of work for the greatest possible gain, and so look at what is going to be the most effective use of time/energy/money/resources.
 
Stuart Ogier
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My understanding is that the berme in an Earthship is for thermal mass? I'm not sure that the two ideas are compatible due to the high insulation values of Straw. For what reason are you proposing a berme? A way around the breathability issue might be to put a stud work wall between the bales and berme, with some kind of tanking on the earth side, with good ventilation, might be vulnerable to vermin though, alternatively, providing there is really good ventilation in the interior side of the straw wall (with heat recovery) that might also do the trick. With a waterproof barrier on the outside of the bales the moisture of the internal air will want to breathe through the straw, gotta get some good air circulation in there, maybe hollow passive solar floor might do the trick.
 
Greg Canicio
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Thank you so much for your replies...  Just realized I never answered any of you and now it's almost a year later.  

We have changed our plans a little. I don't know how I couldn't see that burying a strawbale would simply be a bad idea when facedbwith moisture!

I really lile the wofati, we have a lot of rocks and boulders ...  So i'm thinking now of using rock in stead of tires and build an earthship/wotafi hybrid. 


Thanknyou again for all your replies
 
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