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Is it a bad idea to build a rock cabin on top of an earthbag basement?  RSS feed

 
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Planning on excavating a hole and building a 12 x16 ft earthbag basement, then doing a one foot deep 18 inch wide concrete footer on the top run of bags which will be about ground level, then building a 12 x 16 stone cabin on top with a loft and a wood and tin roof. The rock will last forever but I'm concerned that I might be risking having problems with the bags below grade in the future. If the bags fail there's absolutely no easy fix considering there's who knows how many tons of rock sitting on top that would have to be deconstructed. I love the idea of an earthbag basement and rock cabin above but God help me if I ever have an issue with the earthbags, so I'm going back and forth questioning whether is even worth the risk. Would the bags support that kind of weight without bursting? And if so, for the sake of simplicity, id like to keep the earthbag straight, squared and vertical. I would think the weight of rock above would keep backfill pressure/settling from pushing in the walls. But if I have to curve them and lean them slightly inwards, but straightening and squaring up as it gets closer to the top run to meet up with the 12x16 footprint of the stone cabin, would that be better?? Any thoughts or ideas
 
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It could work.
If it were me, I'd consider climate, soil composition, moisture, topography, access to suitable earthbag fill, and the loads that it carries ( eg. 12" thick single wythe stone masonry, one story tall, etc). We're you thinking about plastering the exterior side of the EB, backfilling with drainage stone, or adding a membrane?
I'm not an engineer but have a good working relationship with EB. If you want free structural and construction advice, then what are your structural conditions, anticipated basement uses, priorities, resources?

(depending on reasonable soil conditions, I'd be comfortable doing what you propose, with regular 50lb bags, however there are larger sizes... If soil conditions, climate, no termites, swayed me, I'd also be just as happy with icf for the basement which depending on your stone wall thickness, could be only 5-7 times the concrete as your 12"x18" bond beam...)
 
nick bramlett
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I'm 45 minutes outside of atl ga. Humid and hot. 50 inches rain/year. Sandy clay soil. Plaster inside, no plaster outside, just a couples sheets of polypropylene sheeting and the back filled with same sandy clay. Bags would also be filled with sandy clay. Single heavy duty 18x30 bags. Thinking of making earthbag section a 12x16ft oval meeting up with 12x16 oval stone which squares up to 12x16 rectangle as it nears roof.
 
nick bramlett
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What is icf?
 
nick bramlett
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Planning on 8 to 12 inch thick stone walls
 
nick bramlett
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Basement will be for fridge and freezer and a bed.
 
nick bramlett
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French drain would be wide enoough for inside and outside perimeter and underneath earth Bags. Water table could come as close as 3ft from beneath basement floor
 
gardener
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The foundation of a building should be the strongest thing in the building, instead of the weakest. Doesn't seem prudent to build a stone building on a plastic/clay/sand foundation.
 
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I'm inclined to agree with Joseph.

I have a lifetime in conventional building, and my rule of thumb is to make it stronger than you think it needs to be. "It might work" is a tad cavalier when considering potential catastrophic failure. A bed in the basement? I wouldn't sleep too soundly, myself. The worst case scenario makes it a foolish gamble. Actually, the other way round is ideal; rock basement, EB domicile atop, but you seem set.

 
nick bramlett
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Found a group of people that did experimental tests on the strength of polypropylene sandbags. Most polypropylene earth bags look to be 49 gsm (grams per square meter of material) tests were done with 70 and 100 gsm bags. Heaviest duty bags I can find are 75gsm so using the 70 gsm experiments as my guide, an 8 stack of 100% sand filled bags show failure at 20,800 pounds. From what I understand, in architecture, a materials working load is typically rated at 1/10 of its load to failure, so 2,800 pounds per bag is im assuming a safe working load limit for a sand filled 75gsm earthbag. However, my bags being filled with not only sand but also a good portion of clay as a binding agent should substantially raise that working load capacity (I would think to at least double). My rock is mostly granite which is roughly 200 pounds per cubic foot, so given the dimensions of what I'm planning, about 4000-5000 pounds is i think about the max weight any one bag would have on it. I think one bag would suffice but I could double bag to err on the side of caution.
 
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what is the reason for wanting the earthbag construction as opposed to something more solid?
 
Randje Mitchell
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Yup...double-bagging would put you over the top I'd aver.
Pun intended. You well free of seismic activity? Be tough tying rocks to the bags...
 
nick bramlett
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Yes there is pretty much no chance of an earthquake here. Reason for earth bags instead of something more solid is to save money. Maybe I'll be able to find enough on rock on property to do the whole thing in rock but I doubt it.
 
nick bramlett
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If I covered outside of sand bags with a couple layers of polyethylene sheeting, what kind of plaster would you recommend for the interior? A highly water resistant plaster is preferable.
 
nick bramlett
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*meant to say earthbags
 
gardener
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Not covering the issue of underground earthbag strength and rigidity over time in a humid climate, I would be loathe to put living space underground in a hot humid climate, as the air would tend to be cooled and the relative humidity raised in such a space. I would be concerned about mold growth.

I can believe that polypropylene earthbags would hold the instantaneous load of a stone wall above, but I expect that the fill would never dry out and truly solidify, rather creeping under the load and possibly eventually stressing the bags too much. How many decades do you expect the bags to retain their full strength?

How many houses in your area have basements? How many have living space in the basement? I suggest you investigate that before building.
 
Randje Mitchell
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Good point. Humidity never sleeps. Good venting is crucial to this scenario. I'd think about stabilizing the bags wirh lime or (horrors) even cement, for insurance.
Yes, it ups the cost factor, but this is a permanent dwelling you're shooting for, and some chances are not worth taking.
 
nick bramlett
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Basements are pretty common around here so long as the house is on high enough ground to stay out of the water table. Living space in basements is common too.
 
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I'm not a builder...although I wonder if the reverse would work?  Starting with stone from the basement up and then finishing with earth bag if you are unable to find enough stone?  A stone house could live forever and seems a shame to have a less durable foundation.
 
nick bramlett
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Yeah. That's a good idea too. Only reason for putting the stone up top is bc it's prettier. But practically speaking, putting it below makes more sense.
 
nick bramlett
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If hate to bury such prettiness.
 
Judith Browning
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nick bramlett wrote:If hate to bury such prettiness.



It seems like I've seen a style of house with stone up quite a ways and then plastered above...covering something...might as well be earthbags? 

Your family will see the stone work in that room from the inside and appreciate...good craftsmanship is good craftsmanship whether anyone sees it or not.

Either way this sounds like it will be a beautiful home...
 
Glenn Herbert
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Various cultures have a style with stonework at the lower part of the walls and something else plastered above it... this can be beautiful when handled well. Stone for the basement would obviously be the best option for durability - you wouldn't want to have to rebuild the upper stone structure if the foundation settled or shifted. There may be a lot of stone that wouldn't be presentable as exterior finish but is still structural for use below grade, depending on the character of your local stone. If it will be plastered inside, the appearance becomes irrelevant.

An oval basement wall would obviously be stronger than rectangular; just don't try to cantilever the upper wall at the corners as this would likely cause cracking. I would transition the exterior of the foundation to rectangular over several feet of height so the exposed walls will be well supported all around.
 
Christopher Steen
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nick bramlett wrote: I'm 45 minutes outside of atl ga. Humid and hot. 50 inches rain/year. Sandy clay soil. Plaster inside, no plaster outside, just a couples sheets of polypropylene sheeting and the back filled with same sandy clay. Bags would also be filled with sandy clay. Single heavy duty 18x30 bags. Thinking of making earthbag section a 12x16ft oval meeting up with 12x16 oval stone which squares up to 12x16 rectangle as it nears roof.



Nick, hey I forgot to check back on your forum post. My building experience is not in your climate. But I believe a few things with regard to your climate:
1. Insulation needs to be on the outside of your basement mass walls/floor to prevent dew point and moisture from condensing there. I believe this is a big reason for many moldy earthen projects above grade and basement funk.
2. Grading
3. Drainage
4. Backfilling basement with clean aggregate, appropriately sized. Not backfilling with clay.
Is your clay expansive, does it crack it slabs and basements and block crawlers in your area?
5. Mechanical ventilation or drying in basement.

Should all be pretty standard in your area.

6. I still stand by ICF basement under your stone hut. Hey it's 12x16. 14 block per course if you cut and glue your corners. I could have stacked them in the time that I spent typing this out. When it's all done, that is just a drop in the bucket

7. Hey I love good mass in a house. I also appreciate exterior insulation. If your dead set in single wythe stone exposed on both sides, then some diy icf downstairs might be welcomed for a number of reasons.

8. Your water table sounds like it could rise in a heavy rain. then again, I don't know your topography or drainage plan. Maybe I just see too many areas flooding in the news recently.

It could work, I stand by it. And I have high levels of acceptability. Depends on lots of site and construction details. I could bang it out and sleep soundly down there till the day I die. But considering all this talk of diy squinching an oval footprint into a a rectangle, already using concrete in your grade beam, high humidity, rainy clay area, high water table, clay backfill, guess work, I'd suggest you to just pour icf, I would without a thought if I was out your way. Then deck over that and be happy. Backfill and grade correctly. That icf won't cost much; over it's lifespan, it's footprint is justifiable, moreso than a slab. But I'm of the 'concrete for walls and roofs rather than floors' mindset. That's my free advice from a nut builder hanging around this forum. And I love earthbag, don't get me wrong.

To me, an earthbag basement is like an earthbag dome, awesome is the correct setting. Many materials can be used awesomely and correctly, but materials are also often used in situations when better options exist for that particular set of conditions, a trade off typically due to cost, time, availability, labor, ideology...

Or if you really want to have an earthbag basement, then have a good mix, , good high site, good drainage plan, and good backfill, and be prepared if you need mechanical ventilation or dehumidification.

If the basement is too daunting, rubble trench that clay and grade beam, and don't look back.

I like Glen's point about moist sub grade earthbags creeping under load over time. Aside from flood, I think if you have that kind of moisture, you would have serious mold issues already. I also think his honkin grade beam would not produce much creep. Plaster cracking due to wall creep settling don't really seem like an issue in eb, sb, re, Adobe, or tire construction. I haven't seen any. Not like drywall cracking, etc... Wood moves way more, though that's more a hygro-thermal deal. Plaster cracking in these wall methods is typically from lack of shear, or lack of reinforcement around windows/doors. Or bad mixes, attachment, cure, freeze thaw, weathering, etc. Plaster cracks in settling earthen walls would be apparent. Never saw any in the pueblos. Heck, the adobes under lake Mead look good still.
 
Christopher Steen
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Joseph Lofthouse wrote:The foundation of a building should be the strongest thing in the building, instead of the weakest. Doesn't seem prudent to build a stone building on a plastic/clay/sand foundation.



I bet 99% of stone buildings were over lots of clay/sand. All but those over bedrock.

If he excavated Adobe to pour a concrete foundation, there will still be Adobe underneath his concrete. His proposed grade beam over the earthbag wall is a good jumbo foundation, not chincy....

Many unreinforced stone masonry buildings succumb. So do reinforced concrete. So do earthen. So do framed. A well built earthbag foundation, wall or roof is nothing to sneeze at. Especially comparatively.

People do masonry over wood, everyday, everywhere. I think they are nuts, but it is done. Different expansion rates and wetting tolerances and elasticities. That doesn't seem prudent.


If moisture is dealt with appropriately, a good rammed earth wall can carry way more weight than he's taking about.
 
garden master
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The load forces of stone over Earth Bag are only part of the stress load, you also have to add the actual weight of the stone wall, the wood of the roof and the roofing material.
Most of the houses I've seen with foundation problems it is the sub structural medium that gave way and caused the settling. Clay will not do as well as sand when it comes to supporting a heavy structure, the clay will squish where the sand simply compacts.
This phenomenon can be observed in England's St. Paul's Cathedral, when construction started, the architect decided to go with clay instead of sand and that resulted in an almost 3 foot sinking of parts of the foundation.

The idea of earth bags would be best for above the foundation building simply because the bags will most likely fail due to pressure of the structure above them.

Redhawk
 
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If you ad enough portland to the mix it won't matter if the bag fails and it should be as strong as concrete if the clay and portland get along. 
 
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All this talk about how strong the bags are....The bags only purpose is to hold the adobe in form until it cures. After that the bags can rot away and it won't matter. The bags themselves serve no structural purpose.
 
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I was thinking of doing something similar. Can you build your stone cabin two or 3 feet out from your earthbag cellar? If the stones were resting directly on the Earth or whatever you would be using there wouldn't be any worrying about the Earth bags giving way. The perimeter of your cabin would be around the basement instead of on top. I hope you know what I mean it's not coming out quite right.
 
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