PSP issues? Possible solutions...

Hello Permies!

I have Oehler's books, yes, (as well as nearly every single book ever written on the subject of earth-sheltered construction, the collection takes up a whole shelf) and have been over and over it and read all the threads on it here and elsewhere. I am involved in a group project and heavily pushing for earth-sheltering in our buildings (as is one of my obsessions!). My best friend, who is also an experienced builder (of both standard modern structures and earthships) is completely NON-SOLD on Mike Oehler's PSP method with the following (it seems to me quite valid) objections.

Firstly, he will never agree to the putting of posts directly in the ground, treated or otherwise. Clearly eventually such posts will rot, even with an absolute minimum of moisture, as wood when exposed to soil WILL rot. Are we incorrect about this? For this problem, we can at least agree on the use of a foundation using concrete and/or stone as a reasonable and acceptable solution either above or below the ground. Agreed?

Secondly, he insists that the wood planks of a PSP structure, directly in contact with plastic (or pond liner or whatever specific kind of vapor barrier) will eventually rot due to condensation from LACK OF AIR-FLOW against the plastic. This seems to me a reasonable point, am I wrong?

This second issue is more of a problem, as I really otherwise quite like the simplicity of PSP, and going with a more "eastern school" (as Oehler puts it) paradigm of lots and lots of concrete is quite out of the question mostly due to high cost (among other reasons not worth getting into here).

Here is my proposed solution which I want you all to give me your thoughts on before I suggest it to my group. Basically a nice and thick layer of FELT between the wood and the plastic, to create BREATHABLE layer to prevent the wood from rotting. This would need to resist compression fairly well and yet be breathable enough to allow significant air flow allowing any condensation to evaporate and never reach the wood. It would probably want to be a SYNTHETIC felt to eliminate the possibility of IT rotting, though probably a very thick wool felt would work just fine.

Thoughts?
--Joshua

Hi Joshua, great questions and valid points. I agree with your builder for the most part. Wood performs best when protected from soil and excess moisture.

Its certainly possible to have wood against Earth. There are many examples where it has been done successfully. There are FAR more examples however of long lasting structures that use masonry as the earth connection.

I like your thinking of providing an airspace between the plastic and wood but thats much easier said than done. I think even a 1" thick felt material is going to have a hard time providing enough ventilation. Where will it be getting its air from and where will it be going? There would be some pretty difficult details to get this to work although Iam sure its possible.

Who says you need so much Concrete? Pre-cast concrete panels and CMU block are pretty thrifty with material use. They are also accepted by codes and are familiar to traditional construction trades.

Good points.

Unfortunately i did not read the book you are referring to.
I see the problem with the lack of air exchange. But condensation happens for a reason. If enough ventilation occurs in the interior and the walls are warm, this should not be an issue.
Conventional ceilings have vapor barriers and wood making contact. And condensation happens there only if there is not enough thermal insulation over the vapor barrier. So the main point is, the vapor barrier should be on the inner most side of a nice insulation. Also depends on how thick a wood material we are talking about? (Since the more insulation is on the inner side of the pond liner, the colder its surface will be, and more condensation will happen.
Are the walls insulated in the design you are talking about or is it more naturalistic?

I wonder if a cob plaster would solve the problem? We know that woody materials can last a long while in (dry) cob walls. So if the liner material is warm enough in normal use, the cob could buffer some short abnormal situations.

I am a builder and to begin with I have built many pole barns and even after 30 to 40 years the posts show no signs of decay even in very high humid areas such as the midwest (aka the rust and rot belt) that being said I grew up in Montana (Red Lodge and Livingston) and have even better success stories there.

I have been a builder in the Chicagoland area for over 25 years and know of a builder there, who at the time guaranteed your heat bill would not exceed $100 per year. He has built several communities and most of his homes have wooden foundations. If installed correctly you can ensure a lifetime of success with this type of foundation. If you don't follow through with staying away from marshlands etc you will find yourself getting into trouble. I would give you his name and web but I don't want to step over the line with spam.

When I met my architect/engineer Ken Woods he lived in Naperville IL and it was -20 at 7pm in January when his furnace kicked on for the first time that day. He showed me his fuel bill including hot water and it averaged between $100 and $150 per year. Now he had a concrete foundation but he designed it to be energy efficient.

The point to my story is whether you use wood or masonry you can achieve these types of savings, and wood against dirt isn't the problem. There are many variables you need to consider when putting wood in the dirt. Even though I have built under the strictest building codes in the country and tend to be sort of a snobbish builder I plan to use a lot of Ron and Perry's plans in my next endeaver.

I guess I don't understand the concern since if you are building a post and beam building, you always set the posts in concrete. At least every post and beam building I ever heard of is set in concrete. It's standard building code here in Wisconsin. In fact, I think I could probably get Oehler's plan passed for permit before I could get an Earthship passed in this area depending on the county. However, I think they both have there merits along with the many other natural or recycled building structures out there. With weather extremes and high humidity in this area, I always am concerned about using certain materials as well.

Newbie here... I have no direct experience with the problems mentioned but thought I'd pass along this thought. Elsewhere on this forum I read about an option to chemically treating posts used by builders in East Africa. Tom Rampart wrote, "... we plastic coat the portion of posts to be placed in the ground. We scorch the ground end of a post over a fire - not burn, just scorch. Then we wrap that portion with plastic grocery bags and heat the wrapped end over a fire. If the plastic ignites and burns - too hot. Just want it to melt/shrivel and adhere to the post."

My suggestion - Why not do the same thing to the backsides of shoring boards? Melting the plastic so it is in intimate contact with the wood seems like a great way to prevent condensation between the materials.

jack vegas wrote:Newbie here... I have no direct experience with the problems mentioned but thought I'd pass along this thought. Elsewhere on this forum I read about an option to chemically treating posts used by builders in East Africa. Tom Rampart wrote, "... we plastic coat the portion of posts to be placed in the ground. We scorch the ground end of a post over a fire - not burn, just scorch. Then we wrap that portion with plastic grocery bags and heat the wrapped end over a fire. If the plastic ignites and burns - too hot. Just want it to melt/shrivel and adhere to the post."

My suggestion - Why not do the same thing to the backsides of shoring boards? Melting the plastic so it is in intimate contact with the wood seems like a great way to prevent condensation between the materials.

The idea being the PSP system is keeping toxins out of the home, if you're willing to compromise there it's very easy to make the wood last indefinitely.

Concerning condensation, I would suggest that because there is no insulation between the wall and the dirt, then the dirt (especially right against the wall) is going to be at the same temperature as your interior air ALL THE TIME, and it is temperature differential that causes condensation. And, remember, you will have several tons of dirt pressing that plastic against the wall. There will not be room for condensation to form anyway. A third issue that comes to mind as I'm sitting here is that my understanding is you need to have microbial/bacterial activity for wood rot to occur, am I correct? I've heard tales of people storing logs under water in a lake for decades, so water alone doesn't cause rot. As mentioned, there is no space between the walls and the plastic, and there shouldn't be access for the proper bacterial activity to cause rotting either, and assuming you are using a suitably rot-resistant wood for the siding, and the above factors mentioned, I cannot see rot ever being a problem for the plastic-against-wood-walls situation.

Regarding the posts in the ground, the PSP method specifically calls for wrapping the posts in several layers of garbage bags and taping the top tight around the post. If you don't tear the bags during install, and have the posts on the INSIDE of your house where it is always dry, how will moisture ever get to them to rot them out? Keeping the soil dry around the outside of your underground house is a primary objective in the first place, otherwise you won't receive any of the benefits of building underground.

Mike's original house is over 40 years old, and does not suffer at all from either of these concerns (rotting posts or rotting wood siding.) And, btw, I'm speaking from personal first hand recent inspection of the structure. There are other points in his system that are consistently failing, but these two issues aren't among the faulty ideas.

...interesting topic !
Edward: what are those failing concepts in Mikes underground design? (I am very interested cuz I am just about fired-up to build one, so would be nice to know the "leaks" and consider possible solutions)

thanks