Earth berm house and ground insulation

[EcoHeliGuy]

Hi guys

Need the power of some minds here.

I have read a couple places that if you are building an earth bermed solar passive home, that you should place plastic and insulation under ground in a 20FT radius from your fountain.

The plastic is to keep moister out of the soil, and the Insulation is to keep the frost out.

So here is my question, If you are keeping the moisture out, why worry about frost? I know that there could be ground water. Maybe the insulation is too help with your thermos mass, but I would think at 20ft out, even 10 ft out your house is having very little effect on ground temperature.

To me both materials are pointless and just adds head ache and expense.

I would think its better to just insulate the wall and lay some plastic just below the surface to help shed water away possible 5-6 feet.

Thanks for any input 

[pagan]

My research has led me to believe insulating out twenty feet is beneficial because you can artificially raise the temperature of the surrounding ground. You're really looking at the thermal flywheel of the earth and using that to assist in heating your house.

Check out these sites.

http://www.earthshelters.com/Index.html

http://www.greenershelter.org/index.php?pg=1

[speedfunk]

pagan is right.  You need dry , thermal seperated mass (earth) to store heat in.  If it gets wet the heat gets washed away. 

I'm in the process of building with the 20' insulated "umbrella" or in my case "skirting" would be more accurate.

http://countryplans.com/smf/index.php?topic=5690.0

I'd be happy to try to answer any questions you might have.  We are not up to the insulation part yet..and won't be until next year most likley as we our building ourselfs on limited budget.

I want to add that John Hait quotes a study done by the university of minnisota (sorry for spelling) where they took insulation in different configs and compared the results .  The best way to insulate was straight out horizontally.  Hait and others (naturalhome.com) run it at a pitch to drain water as well.

[Bishopknight]

I brought in 60 tons of sand for my earth berm house and I plan on having a 4' insulation skirt around my house to further protect against frost heave.

Frost heave doesn't affect hardpan clay very well because there is very little way for the moisture to penetrate it. I think if you were building right on top soil, you'd have to be concerned about frost heave since the first 3' has alot of air and moisture in it.