George Spencer wrote:One question I must ask is how these types of structures would perform in areas with lots of frost heaving?
How do we build an earthen floor without the ubiquitous plastic barrier?
The same as previously stated; packed stones?
Also, is that what we should use for the wall above the foundations and below the cob?
I would like to avoid concrete mortar. Is cob suitable for the mortar in the stone foundations?
...It seems to me that this is closer to a vented crawlspace, which can work great in certain climates (usually dry) but can create more problems than they solve for humid ones. Building codes require vapor barriers at the ground in vented crawlspaces and this is certainly a case to me (as most cases are) where its safer to follow code than ignore it. Am I correct that ventilation below the floor is how to deal with water vapor from the ground in these traditional systems?
Iam also curious why its ok to use geocloth which is made from plastic and has a shorter "proven history" than plastic vapor barriers. Thoughts?
For most locations, I believe the dominant direction of vapor flow is from the outside in.
The higher moisture levels of the ground will readily flow inwards towards a dry basement, slab or crawlspace despite any temperature differences.
My picture was not a plastic baggie of earth left in the sun. It's a picture of a building detail clearly showing underground moisture seeking equilibrium. This vapor is effectively being blocked and redirected to drainage.
Jay, are you suggesting that whenever you specify geocloth, you make it from "natural" materials?
Most geo cloth in use today is made from plastic and it has a shorter history than plastic vapor barriers.
I think some thicknesses of geo cloth probably use more of the earth's natural resources (plastic from oil) than these plastic vapor barriers.
A 4000 year old structure offers valuable lessons on structural stability in the region it was built. It tells us nothing about how much energy its used to keep comfortable or quality of its indoor air.
Plowing takes the top layer of soil, which is high in organic matter and field litter, and places it 8" below the surface. This layer of organic matter will completely stop the wicking action of the moisture in the soil, leaving the top 8" of dirt void of the needed moisture...Putting a layer of rocks in between the earth and your floor will also leave anything above the rocks high and dry. Because moisture cannot wick thru gravel.
Brian Knight wrote:I appreciate the thoughtful replies and I love the contrast between Bill and Jay's writings.
Bill, in your apple receiving post, you suggest that the main direction of vapor flow is from the inside to outside. For most locations, I believe the dominant direction of vapor flow is from the outside in.
Above grade, vapor can regularly travel in both directions. Underground things are different. Vapor is always trying to even itself out despite the temperature differences. I cant speak for the dry desert but most soils have moisture levels higher than what we want in our homes. The higher moisture levels of the ground will readily flow inwards towards a dry basement, slab or crawlspace despite any temperature differences.
Allison Bailes wrote:He (Dr. Joe Lstiburek) also showed a lot of photos (from the 1980's) of his early projects and the failures they had to work through. My favorite was the house where they were going to embed ducts in the slab and then had to fight to get them to stay down as they floated in the wet concrete.
While the law states that moisture does flow from warm to cold it also flows from more to less.
...Just be aware folks that gravel is a capillary break for bulk water and will not stop vapor...
Packed clay will certainly do better but it will not stop vapor flow as well as a true modern vapor barrier.
For the most part though, I think Jay is absolutely correct. Choose the right site, use the right methods and things will be hunky dory. I still think people need to take a very holistic view of materials, labor and costs when comparing and mixing modern and traditional forms.
Is there a hope that I could convince a council to allow me use this under an earthen floor instead of a plastic moisture barrier? We live in the sub-tropics in South East Queensland.