I am building a small shed (11′ round) out of earth bags. Gravel (or any kind of stone) is cost prohibitive in this area. As well the the ground will freeze to 5 or 6′ deep here. Is it possible to fill a trench with sand (which I have here in abundance) with a sloping drain (also filled with sand)? Can I build with earth bags directly onto this? I can stabilize the first two courses with lime above ground level. Or should I fill earth bags with sand down to 5′ and back fill the soil around that?
I have no earth bag building experience, but I do know that sand can wick moisture upwards.
In addition "building a house on sand" is an idiom that suggests that suggest that the very basis or foundation of a plan is so flawed that the plan itself will fail.
That being said, bagging the sand/stabilizing it with lime could make all the difference.
What kind of soil are you building on/into?
Is it already sandy and well draining?
A couple of options to consider to fill your trench could be using chunks of cement (urbanite) from a local construction site or contractor that could be broken up further and dumped into a rubble trench and/or used to build a stem wall with before starting on your earth bags.
- Since its a small shed, another option could be to find a local creek out in the woods (not on private land of course) and collect rocks.
- Have you cruised any classifieds for people wanting to get rid of rock from their property? Only the price of hauling it away and a little elbow grease to load it.
Michael Smith of Cob Cottage Company has said "Even if it (water) should freeze in the trench, it can expand into the air spaces between the drain rock, rather than heaving up a solid foundation."
A recommended dept would be around 2'. I don't know if I would trust this for a house foundation, but a shed... could work?
I know the 16' wide earthbag dome I built in southern BC that gets on average a temperature of --10 C to -35 C in the winter with such a trench has had no problems whatsoever in the 8 years it has been built.
As William pointed out, the type of subsoil you have will also play a role in how fast the water that does get under the foundation drains away. A percolation test is a good way to find out.
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