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I was recently asked what I thought the advantages of straw bale construction are over earthbag construction. I have not done very much earthbag construction, so my response was somewhat limited. I’d love to hear from folks who have experience with earthbag construction as to the advantages and disadvantages of the technology. All comments are welcome, as always.
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Andrew Morison is a specialist in straw bale and green construction. He has shown thousands of people how to build their own straw bale projects through his comprehensive series of instructional straw bale, concrete foundation, and plastering DVDs. You can check these out at www.LearnStrawBale.com..
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February 25th, 2010 at 10:54 am
The beauty of natural and sustainable construction is that the disadvantages are few and the advantages endless. The major advantages of one particular technique over another may be primarily related to its availability or economic accessibility. in other words where ever you may be in the world will determine the advantages of using say straw bale over earth bag, or adobe over waddle and dob for construction. Bt the advantages of using any of the preceding natural methods over conventional wooden or brick and cement construction remain the same.
March 12th, 2010 at 11:10 pm
Basically, straw bales are good insulating material. It depends on what you fill in earthbags, but as a general rule, they store heat/cold rather than insulate. One more thing: building with earthbags will be slower than it seems. Also, in wet places, protection from the elements is every bit as tricky as with strawbales, and nuances with breathing and ventilation pop up. Basically, in an earthbag, you need a strong plan how to get moisture out, if you don’t livedry desert.
March 13th, 2010 at 5:03 am
The biggest point that makes straw bale better than earthbag is that straw is a much better insulator than earth. There is much debate on what the actual R value of straw is but for a 2′ wide bale you will have at least a R-value of 50. Earth has an R-value of .25 per inch so a 2′ wall would have a R-value of 6. The earth-bag wall would be better suited for hot climates – the thermal mass of the earth-wall would absorb the heat of the day and release it to the cooler night air. You can use materials that have better insulation properties in the earth-bag wall ( Kelly Hart used Scoria; a porous lava rock with an R-value of 3 per inch, in his earth bag home)
March 13th, 2010 at 7:05 am
I have been researching Alternative Construction Methods for almost 10 years including: Strawbale, Earthship, Earthbag & Monolithic Domes. Thru studying Michael Reynold’s book series on Earthships, the distinction between Insulative Materials like Strawbale & Thermal Mass Materials like earth, clay or concrete, was made pretty clear in my mind. Thermal Masses act as a Battery/Regulator/Conserver if you will, between Heat & Cold, while Straw acts as an Insulator between Hot & Cold. Once you introduce Heat or Cold to the inside of a well built Straw structure, it tends to STAY there, trapped by the Insulative effects of Straw.
Thermals Masses tend to draw part of their Heat/Cold either directly from the Earth, or mimic it closely enough that it acts like a Heat/Cold sink or Natural Heat Pump.
Earthbag structures then, are Thermal Mass Structures. Their main building component is also, ‘Dirt Cheap’.
The only structural fault I can see w/Earthbag is that altho it has great ‘Compressive’ strength, it has little ‘Tension’ strength in it’s current method of construction. (see calearth.org) Adding rebar within & thru each bag may mitigate that, especially if mixing a light concrete w/the soil as it’s filled. Also, mechanical grip of walls to footings on top of heaving soils (those that have a Freeze/Thaw) would also be a problem unless you used rebar & concreted the lower tiers to a concrete footing.
Along w/Andrew’s BYOC course I’ve purchased & enjoyed, I’ve chosen to go w/a monolithic dome (monolithic.com) for thermal mass & insulation & structural integrity. (Andrew, you totally need to market BYOC thru monolithic, calearth & earthship.)
Finally, if I didn’t have a good paying & steady job & decent credit @ the moment & didn’t live out of my rv (well, I’d probably still be in an rv) &/or couldn’t get construction financing, I’d probably look again @ calearth & strawbale, simply for economic reasons. Who knows, if my financing doesn’t pan out, I still may! In fact, I’d like to see someone combine earthbag w/straw! One of the ways it could be done is to use those skinny netted tubes filled w/straw for erosion control, coiled on the ‘inside’ of the earthbag coils & then plastered over. What do you think Andrew?
March 13th, 2010 at 7:49 am
Correction to my Posting above: Insulation (like coiled straw) should go on the OUTSIDE of a Thermal Mass like a coiled dome Earthbag structure then finished with water proof Plasters as per normal Straw bale.
Also, for heaving Freeze/Thaw soils, just make the footings deep enough (below the Frost line) & concrete & rebar in. Sheesh!! Didn’t have my 2nd cup O’ Mate’ yet!!
March 13th, 2010 at 3:39 pm
I think there was an article in the recent Dwell magazine about something like this. Not sure of the details but it involved s project that used bages filled with sand and then plastered over. Thought it sounded intriguing. Not sure re: pros & cons compared to srawbale. Would depend on location & other factors.
March 14th, 2010 at 7:49 am
A friend and I are about to start an earthbag project, and we’ve gotten most of our information from calearth.com…they’ve done extensive research on the subject, although I’m not sure I’ve heard of any sort of study that compares strawbale to earthbag. I’m thinking that it’s like comparing an apple pie to an apple turnover…they’re both really freakin’ good, but which one are you in the mood for? Also, in our case, bales aren’t easy or cheap to find, so I ‘d say availability of materials is one of the the biggest deciding factors of any construction project…I hope this helps!
March 16th, 2010 at 5:10 pm
Thanks. I love the comparison too! Yeah, they’re both really good.
March 16th, 2010 at 8:36 pm
This is similar to the sod homes the settlers used on the praries way back in the day. One difference is they did not have bags to put the sod in, they just piled the sod together like bricks in some cases 2 ft thick or more. The grass that it was cut from would become the glue that held the mound together after the first season. Sometimes the roof was made from what wood they could find to act as a support. Thermal mass does have its merrit and with the cone construction plus UV inhibitors used in plastic such as found on polycarbonate sheeting or good greenhouse plastic like I use from Northern Greenhouse supplies, it is viable in some areas. If you want to give this a go I would think that a material worth considering would be peat from a peat bog because when it is dry it has a porus airy factor about it which goes along the line of less thermal mass but more insulative than say sand or clay loam. The material is not found everywhere and there is a new view on peat bogs as becoming endangered and over harvested. It takes approx an hour to rip out 1 cubic yard that took mother nature 120 years to build. Perhaps a combination, Thermal solar wall facing south made with clay filled bags, then the rest filled with more porus materials. Hmn…. definetly worth pondering about.
March 17th, 2010 at 9:48 am
Hi Andrew,
I have had talks about this comparison a thousand times…
I believe there are two main things to take into account: avaibility of materials and climate.
The first doesn’t need any explanation I guess, but climate is something so often ignored when building that it really needs some attention…
I’m living in Belgium. We have moderate warm summers (30°C) and moderate cold winters (-10°C)… The temperature difference between day and night are not that big (more or less 5 to 10 °C).
I’m building a strawbale house with some thermal mass in the flooring system. The thermal mass in the floor will capture the heat from the sun directly during the day and keep it during the night. My strawbales keep as much energy inside as possible. Both systems (heating thermal mass and insulating) are necessary in our moderate climate to have an ideal energy-efficient house.
When talking about extreme conditions there are different approaches necessary…
An eartship or sandbag architecture are perfect for desert conditions where days are hot and nights are freezin’ . Thermal mass will level out the difference.
Now imagine the opposite.. living on the northpole… imagine living in an earthbag house over there… what will happen? In due time, the sand will get the same temperature as the outside air and you’ll get a fridge! You might want to put a fire inside, but you’ll only be able to heat the inner surface of the sand and you’ll loose all your energy to the cold mass around it.
So what you really need is good thermal insulation… in theory a starwbale house would work perfectly over there (only considering the insulating capacity, not talking about condensation and water issues).
So in short: extreme conditions need extreme solutions, moderate conditions need moderate solutions… make sense doesn’t it?
At the moment I’m working with a friend of mine on a theoretical model of sandbagconstruction and it thermal behavior… I’ll keep you guys informed as soon as we have some result…
Greetings and enjoy building!
March 19th, 2010 at 8:52 am
That’s an interesting idea. I imagine it’s a bit of each: mass and insulation. I wonder if the straw would provide adequate insulation at that thickness. It has a strong R-value based mostly on the thickness of the material. I’d be interested to see how it works if you do it. Thanks for the tip on the BYOC marketing. I plan to move that training forward in a big way in the coming year and get it in front of lots of people so I appreciate the heads up.
March 22nd, 2010 at 9:40 pm
Maybe someone has mentioned this, didn’t have time to read all the replies. A couple of days after I got this e-mail we had a minor quake. California imposes even more regulations for building strawbale in our earthquake prone zone, which I think is kind of funny- what would you rather have fall on you in a big shaker? personally, other than my tipi that I loved living in til they ‘regulated’ me out of it, I think that being burried under strawbale sounds better than just about anything else I see people constructing their homes of.
March 28th, 2011 at 9:40 pm
There’s no point building a straw house if you have plenty of soil or a soil house if you’re surrounded by straw. Take a look at your environment and go with what nature tells you. I’m no expert , we are earthbagging because of financial reasons, and climatic ones. good luck.:)
April 8th, 2011 at 8:14 am
True to some extent. Having a lot of earth around may not mean building an earthen house is a good idea. Keep in mind that if the climate one is in requires insulation as opposed to thermal mass, then straw bale will be much better than an earth house and if thermal mass is a better solution than insulation, the earthen house wins.
I agree that using local materials is a great idea, just be careful you don;t build with local materials and end up with a house than does not function well for your climate.