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PSP Earth Sheltered Building

 
Simon Johnson
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Another little bit from my blog. This time on PSP buildings. Enjoy!


When it comes to building yourself a debt free home, cost is a major factor to be considered when planning the build. The best way to reduce cost is to not buy expensive building materials! To avoid buying expensive building materials, you will need to use as many locally available, free materials from your land and nearby community as possible. Two free materials from your land, which are readily available (in Ontario anyway), are trees and dirt. These two sources can comprise the majority of the materials needed to build an excellent home following the PSP method.

PSP buildings are earth sheltered homes using Posts, Shoring and Polyethylene, pioneered by mike oehler in the 1970's and shown to the world in his book The $50 and Up Underground House Book. Here Mike builds a home for himself for under $50 using the logs and earth from his land! The post part of PSP refers to the main structural components, which are post embedded in the ground to carry the load of the earth back fill. The shoring are the boards that cover the span between posts to hold back the earth. And the polyethylene is the plastic that is placed against the shoring to keep the water out of the building. So using logs from the land as posts and shoring as your main structural components, the polyethylene, nails and windows might be the only products you need to purchase. With some good scrounging skills, you could also find these for super cheap/free. Now we are talking debt free!

Let's examine these buildings further. They are essentially pole structures, in that you build a skeleton frame of poles. The vertical ones are buried in the ground for structural stability and to support the walls, with others running horizontally across these as beams to hold the roof up. This is the main part of the building and is constructed using simply logs from your land and some fasteners. No need to purchase expensive boards or concrete from home depot. Here is a picture of the pole skeleton to illustrate what I mean.



Once the main pole skeletal structure is erected, it is time to add the shoring, or boards/small logs which make up the walls and roofing. These boards will span the gaps between the main posts and hold back the earth which will be covering the structure. Again, you would want to use what you have readily available. If you have a lot full of small sized trees, then you could use those logs as the shoring, or if you have access to a sawmill, you could get rough cut lumber to use as your shoring. It doesn't really matter, as long as what you choose is strong enough to hold back the earth over the span between posts. Let's have a look at what the pole structure covered in the shoring looks like. Here is a good shot showing the walls and the roof filled in with smaller logs.



The next step in construction is the polyethylene layer to cover the shoring. The polyethylene is the main barrier to keep out moisture and the dirt used when back filling. It is important to make sure the layer(s) of poly remains intact and doesn't get holes in it from things like sharp stones or little parts sticking out from the shoring logs. If the poly gets holes in it, you may have a moisture problem. There are different ways to go about protecting the poly, like using multiple layers, or laying down a thick layer of newspaper or cardboard on the logs before the poly is placed. This polyethylene can be a variety of different plastic tarp like materials such as vapour barrier, tarps, or pond liner. Again it depends on what you can get your hands on for a good price/free.

Once the polyethylene layer has been put over the shoring, it is time to start back filing the structure. Here you will want to be careful to not puncture holes in the poly. Try to use dirt which doesn't have lots of stones or other sharp materials in it. Starting with the walls, work your way up to burying all parts with shoring and polyethylene. That will be three sides and the roof minus a gabled doorway on the opposite side of your windowed side. Here you can see the structure covered in poly and being back filled. This is the gabled doorway end.



Once the entire structure has been back filled with a few inches (4+) covering the roof, there are a couple things you can do. If it's cold where you are, you will want to insulate your home some. Those first 4+ inches of dirt covering the first layer of poly will act as somewhat of an insulator, but more insulation is better, so adding something on this dirt to add insulating value is necessary. You could use some free materials here as well, like wood chips, saw dust, or layers of cardboard. Adding thick enough layers of any of these materials will add some insulating value for free, but you could go out and buy board insulation for better results.

Once your insulating material is down (or if the first 4+ inches of dirt is enough), it is time for another layer of poly to keep this material dry. Not only will this second layer of poly keep your insulating material dry, but it will also keep any water from getting anywhere near the actual structure. This layer of poly will extend way out past the walls of the building a good 15+ feet. With the entire building back filled, it creates a kind of a hill reaching all the way down to the original grade of the ground. So laying poly over this hill, out past the edges of the building to follow the newly made hill down to the original grade will create a kind of umbrella to keep any rain water falling on the roof from coming in contact with the wood posts of your building. This greatly extends the life span of the wood posts as well as keeping the interior of the building dry.

Here is a second layer of poly going on and you can see the hill created by the back filling of the building.



Now you have a wooden structure wrapped in plastic with a layer of dry dirt back filled to bury the building. On this you have a few inches of insulating material, covered by another layer of poly which extends down the back filled hill, keeping any water well away from the building. It's time for the final layer of earth. This final layer will be quite thick. Anywhere from one to three feet of earth is now put over the second layer of poly. This earth acts as your main buffer between your home and the elements. When it rains, the water will follow an uninterrupted path of soil directly to the ground level and far away from your building. If it rains hard enough to saturated the three feet of earth on your roof, the water will come in contact with a layer of poly and then again flow downhill to the ground away from your building. When it's really hot out and the sun is beating down on your building, that three foot layer of earth will keep you nice and cool in your home. It will take an awful long time to heat up that much soil, especially once it is all covered in a beautiful layer of lush greenery.

Here is a picture of a finished product all buried in.



Here is a drawing showing a side view of the basic idea.



There are a couple key points that I need to mention here now that the main concept of the building has been covered. This type of building is generally built into the side of a hill and with that, the front wall, with all the windows in it, faces up hill. This is very important. It allows for the building to be built so that the water falling on the roof has a continuous downhill path to follow without coming in contact with any hard edge. When water comes in contact with a hard edge it leads to problems; you don't want water backing up against the side of your home with only a layer of plastic to hold it back. This will inevitably fail and the house will get wet, or the logs will rot much faster as a result of getting wet. So by facing the building up hill, the water can run away freely without any chance of getting to the logs.

When facing the building uphill, you must excavate in front of the building, further uphill a ways and create an uphill patio as it is known. This uphill patio can serve many functions, but the primary one will be to catch and divert water running down the hill from above, around the house. Here you will want to install multiple drainage trenches similar to what is shown in the drawing below. Don't want to rely on just one. This will again prevent any water from coming in contact with any of the structural logs, thus making the logs last much longer.



This uphill patio can act as a nice place to grow vegetables and be a cool hangout spot, sheltered from the wind and any prying eyes. You could also turn this area into a greenhouse to help warm your home, extend the growing season and keep even more water out. There are many options here, but it is imperative that you build this patio to catch and divert water.

Here is an example of what happens to the water if you don't face your building uphill and have a continuous downhill path for the water to follow. As you can see, there is a pinch point where the water comes from two directions and has nowhere to go but build up. Don't do this!



The next important thing to mention is the inclusion of a downhill, gabled entrance to the building which has windows. With this addition you will have two exits from the building as well as light coming from multiple directions and the ability to create a cross breeze for ventilation. All of these things are important for the comfort level of the home. Having two ways out is always good. Getting light from more than one direction is also very nice, especially if you are on a south facing slope and most of your windows are facing north. Being able to get a cross breeze going is essential in the summer time to keep down on the humidity and to just get some nice fresh air. Making this entrance gabled still allows for the water to have a continuous downhill flow from the roof.

One last key component to keeping your nice new home dry is the extended roof overhang protruding out over the uphill patio to keep your wall with the windows in it nice and dry. It also helps reduce the amount of water that gets in the patio area. You will want to extend this overhang about three feet. Don't skimp here, it's important. If your building is on a north facing slope, this overhang will also help keep out the hot summer sun.

This is just a general overview of the building technique. There is lots of room here for customization and site specific alterations. With the right site and enough money, your imagination is the limit to what you could build. Think multiple stories with downhill views, rooftop gardens, uphill patio greenhouse and much more. This is an amazingly simple method of constructing a beautiful home with almost all natural on site materials that integrates perfectly with the surrounding landscape, while at the same time being very energy efficient, durable and long lasting.

For more information on and pictures of these types of structures check out Paul Wheaton's article, Mike Oehler's website, my review of Mike Oehler's book, and the forums at permies.com.
 
Bill Bradbury
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I am a big fan of using the earth to buffer the elements and it seems that earth-bermed architecture is best of these, but I have to question the use of a vapor barrier on a breathable wall assembly. See Terry Ruth's excellent thread on breathable walls

Where does surplus indoor moisture go?

Maybe change the PE to troweled and sealed lime/clay below a gravel drainage plane. Or stones could be set into the clay, shingled much like clay roofing tiles.

I think that I would add to the deign a semi attached workshop with a dark metal roof that is used for solar heat gain(piped in underground tubes, 4" super ferritic stainless flue vents) and water collection. I bought a big box of these from the local plumbing supply for $200 because no one is using them anymore, they're just going with PVC. I used them for earth tubes for my shop, connected to a hi-efficiency fan they blow fresh cool air from the orchard into the dusty/smelly shop in even the hottest weather. Since they have a heavy silicone rubber gasket, they don't smell musty. I think a more permies solution might be clay pipes though, cast them yourself and seal with clay. These could help with the ATI if they travel through the mass.
 
Simon Johnson
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Thanks for the link Bill, there is a ton of information to digest there.

Let's see if I understand what you are proposing.

Instead of covering the wooden part of the structure with plastic and then back filling, you are suggesting the wooden structure be coated in a cob like material. Basically plastering the entire outside of the wood and having that act as the last line of defence against moisture?

Once the the structure has been covered in cob/plaster and back filled with 4+ inches of dry dirt (plus insulation on that), do you think the umbrella layer of poly on top of this and running down the sides of the newly formed hill that is your back fill is still a good idea? This would be the main defence against moisture from above. The walls should be able to breathe still with this layer of poly not being in direct contact with the wood, but rather 4+ inches away on the roof and a matter of feet away from the walls. It seems to me that at least one layer of impermeable material (polyethylene or pond liner or some other such material) would be necessary to keep rain water from soaking through and direct it down hill off the roof.

More thoughts on this would be good. It wouldn't be much good to build a nice structure like this only to have the wood rot out prematurely at the point of contact with the poly.
 
Bill Bradbury
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Simon Johnson wrote:
Instead of covering the wooden part of the structure with plastic and then back filling, you are suggesting the wooden structure be coated in a cob like material. Basically plastering the entire outside of the wood and having that act as the last line of defence against moisture?

Yes, but only as your last line, so then on top of the insulating backfill would be the main moisture deflecting layer of clay/lime or clay/lime shingled with stone and a layer of gravel on that. Then filter cloth and the rest of the soil.
Simon Johnson wrote:
Once the the structure has been covered in cob/plaster and back filled with 4+ inches of dry dirt (plus insulation on that), do you think the umbrella layer of poly on top of this and running down the sides of the newly formed hill that is your back fill is still a good idea? This would be the main defence against moisture from above. The walls should be able to breathe still with this layer of poly not being in direct contact with the wood, but rather 4+ inches away on the roof and a matter of feet away from the walls. It seems to me that at least one layer of impermeable material (polyethylene or pond liner or some other such material) would be necessary to keep rain water from soaking through and direct it down hill off the roof.

An impermeable material in the vapor profile must be in the warm area or it will condense water and soak the nearby material, in this case soil. This is good if it is available to plants and microbes, but I think it could be a problem where there is no air or plants' roots. So, my answer is, maybe that one is fine, but I wouldn't.
Simon Johnson wrote:
More thoughts on this would be good. It wouldn't be much good to build a nice structure like this only to have the wood rot out prematurely at the point of contact with the poly.

Vapor will always try to find an equilibrium, this process is driven by heat and travels in the same direction. Bulk moisture travels the path of least resistance, mostly down. There is a delicate balance there, that you will hopefully be able to find while still using natural materials.
 
Simon Johnson
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Bill Bradbury wrote:
Simon Johnson wrote:
Instead of covering the wooden part of the structure with plastic and then back filling, you are suggesting the wooden structure be coated in a cob like material. Basically plastering the entire outside of the wood and having that act as the last line of defence against moisture?

Yes, but only as your last line, so then on top of the insulating backfill would be the main moisture deflecting layer of clay/lime or clay/lime shingled with stone and a layer of gravel on that. Then filter cloth and the rest of the soil.


This is very intriguing. I like the idea of using all natural and breathable materials. I wonder how much more work it would be though?

On this post Paul mentions filling the spaces between the logs that that cover the spans to hold back the dirt with smaller branches to help fill the cracks. This could reduce the amount of cob required to cover the wooden part of the structure.

And in this post Paul talks about filling the cracks between logs with cob to keep the cold air from coming in willy nilly. So maybe we are on to something here with using a natural plaster instead of poly altogether?

Do you think the main moisture deflecting layer of clay/lime and stone would be sufficient to hold back a lot of moisture? The natural plaster does absorb moisture right? But there are ways to help seal it? It wouldn't be much good to have the natural plaster turn back to mushy clay because there was too much moisture for it to handle. Maybe a thicker final layer of earth over the main moisture deflecting layer would help to mitigate the amount of moisture to actually make it to the plaster?
 
Bill Bradbury
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Simon Johnson wrote:

This is very intriguing. I like the idea of using all natural and breathable materials. I wonder how much more work it would be though?

Definitely more work, but is it worth it? In 40 -50 years when the PE starts to break down, it will be worth it for whoever lives there. I am imagining digging up the whole umbrella and redoing it, while repairing rotted timbers; the whole thing would probably be a write-off at that point.

Simon Johnson wrote: So maybe we are on to something here with using a natural plaster instead of poly altogether?

We are Permies!

Simon Johnson wrote:Do you think the main moisture deflecting layer of clay/lime and stone would be sufficient to hold back a lot of moisture? The natural plaster does absorb moisture right? But there are ways to help seal it? It wouldn't be much good to have the natural plaster turn back to mushy clay because there was too much moisture for it to handle. Maybe a thicker final layer of earth over the main moisture deflecting layer would help to mitigate the amount of moisture to actually make it to the plaster?

Underground moisture migration is a very complex process that is hard to understand for even professional hydrogeologists. There is gravity, but also deflection and don't forget the most complicated part; vapor diffusion. Although gravity is working on the bulk moisture(water), the water is vaporizing in the soil and rising up toward the surface in order to try and equalize moisture content. Vapor will also diffuse through poly, especially at the seams if untaped. This is a slow process as PE has a very low permeability, but the seams will allow a little more capillary diffusion. The main source of vapor is the interior of the home and as long as the soil is drier than the interior RH, vapor will diffuse through the entire structure, driven by heat and condensing on vapor barriers if RH reaches 100% at the barrier.
 
Simon Johnson
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Bill, I made a new thread on this natural plaster vs ploy discussion over here.
 
I agree. Here's the link: https://richsoil.com/wood-heat.jsp
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