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Waterproofing the underground house

PSP constructionThe outer skin of Oehler's houses is a layer of polyethylene which is used as a moisture barrier to keep the walls from rotting.  Initially, he was using 4 to 6 mil plastic, but had upped that thickness to 6 to 10 mil by the time he wrote his book about greenhouses, and noted that he's now using EPDM pond liners for one of the two roof layers.

After making the framework of the house out of posts and beams, Oehler digs another narrow trench behind the walls and layers mill-ends (or other cheap boards) against the outside of the posts.  The plastic goes directly outside the mill-ends, and the whole wall is held together by the force of the earth rather than by any fasteners.

The roof gets a bit more fancy treatment, starting with a layer of building paper and polyethylene, covered by four inches of earth, another layer of plastic, then fourteen more inches of earth.  Eventually, plants will take hold there Living roofand create a living roof.

While a thin layer of plastic doesn't seem like much to keep an underground house dry, the design seems to be working, at least in Oehler's location.  As he points out in his book, you have to take his system as a whole rather than pick and choose if you want it to work --- presumably polyethylene wouldn't be enough to keep water out if you didn't plan the entire structure so water's always flowing away from the walls.

Stay tuned for another lunchtime series soon about his followup book, covering earth-sheltered greenhouses.

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This post is part of our The $50 and Up Underground House Book lunchtime series.  Read all of the entries:

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I have been reading all of the posts about Oehler's theory on building below ground. I also know of a bunch of companies that are going a different direction with underground structures, and building earthships. I also know of the though of building up the ground to the structure, instead of sinking it in, so it is less likely to retain water and a few other advantages. Now assuming that we are smart and build our structure below the highest point on our property, for water catchment and gravity distribution, which direction do you think you would go with the structure? Also, if I remember correctly, you have a roof build above your trailer to get the sun off and allows ventilation to keep hot air away as well. Do you think it would be a cool idea to have one above an earth structure? "Check out my Survivalist Blog at the Clever Survivalist and read daily Survival Guide content."

Comment by Clever Survivalist Blog Survival Guide Fri Mar 29 22:35:49 2013
I'm wondering what the rational is behind haviing a soil layer sandwiched between two layers of poly? Seems odd.
Comment by Chris Sat Mar 30 08:16:22 2013
Making a barrier between the two layers so a puncture in the top layer doesn't immediate damage the bottom layer as well.
Comment by Roland_Smith Sat Mar 30 17:27:06 2013
I wonder what the usueful lifetime of buried polyeth is? Cost is low for polyeth, but more expensive liners intended for foundations may be worth it. And roots from plants on the roof may be more likely to penetrate a polyeth sheet that has become brittle with age.
Comment by doc Sun Mar 31 05:34:55 2013

PE can resist a whole lot of very aggresive substances pretty well. Peroxides (30%) and acetone are often sold in PE containers. You'd need nasty solvents to dissolve it. So it does not easily biodegrade (without the help of UV).

Ultraviolet light is the bane of all plastics, because its photons have enough energy to break the chemical bonds in the plastic. So if it's not exposed to sunlight it could last a long time.

Investigations done in Austria and in the US on water and gas pipes that had been buried for 30 years found that they were still in very good condition. For modern PE pipes lieftimes of 50 years are taken for granted and 100 years is seen as possible.

So at a guess I'd say that even PE foil should be able to several decades.

However, a thin film could relatively easily be pierced by stones, roots and possibly burrowing animals.

Comment by Roland_Smith Tue Apr 2 17:40:14 2013

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