Hello everybody,  this is my first post at this forum. 

     A quick intro: I am 27 and looking to live around Hanover NH in Grafton or Windsor county.  I have built/finished/repaired furniture for eleven years as well as worked various construction jobs in rough and finish carpentry as well as siding.  I thouroughly enjoy working with tools, raw materials, and design.  Consequently I have gravitated towards the Earthship style of housing.  The way the walls and interiors are built naturally lends itself to curved flowing walls with strong imposing wood beam framing. And yes I have pounded tires for days before,  daydreaming in the sunshine while I swing a sledgehammer is anything but "work".


   SO to the point of this post.  Being in Zone 4 and having an average frost depth of 5-6'  I have large concerns about keeping the heat in the house.  The basic design of an earthship dictates that all but the Southern side of the house be buried almost to the roof and sloped down away from the house.  Not having a land plot to plan with directly, I am assuming the current trend of building the earthship on grade and burying the tire walls as they are built up.  The previous convention being to dig into the ground and having a large part of the house below original grade.

  My idea so far is to put down two layers of 2" rigid foam (~ R-10 per layer) on the entire footprint of the house with the vertical insulation of the buirlal being three layers of 2" rigid foam.  A 10ml plastic vapor barrier would go on top of the floor insulation and between the inside and middle layer on the burial insulation. From what I've read the vapor barrier should be on the warm side of at least 2/3s of the insulation.  To ensure the water from rain and the soil does not push into the house I also will put a 4" drain around the entire buried perimeter.



   My question(s) is does this look like an appropriate insulation plan for the floor and perimeter?  And if it is, what ground preparation is usually done before laying the rigid foam down?  I have had a surprisingly hard time finding an explicit explanitation of that. 

     Thanks,

          Brian

First, Hannover NH is in US climate zone 6, not zone 4.

Second, vapor barriers below grade are there to block ground moisture from diffusing into the conditioned space, not to block moisture from conditioned space from condensing in the soil.  It doesn't matter AT ALL from from a moisture transfer point of view where it is relative to the R-value of the stackup, since only moisture-impervious insulation can be used under slabs.  (EPS is the greenest choice, with less than 1% the lifecycle greenhouse gas footprint of XPS, due to the differences in blowing agents used- pentane vs. HFC134a.) 

EPS is only R8 at 2", not R10. XPS is R10 at 2", but in a sub-slab application it's lifecycle greenhouse gas of 4" of XPS will FAR exceed the lifecycle carbon release from the energy reduction it offsets, even if you were using electric resistance heat on a 30% efficiency coal-fired grid (which you ain't.)  Stick with EPS- go 6" if you have to for getting the R-value up- even 50" of EPS would have a lower greenhouse footprint than the first 2" of XPS.

The 2/3 R rule is a really crude measure that applies only to above grade assemblies, and is highly local-climate and wall stackup dependent. In your floor configuration you have the poly correctly placed, since if you spilled a tub of water it wouldn't get trapped under foam taking forever to dry.  But you don't need the added complexity of wedging it between layers on your wall structure- putting it between the compacted fill and the exterior foam is just fine.

You would ideally have ~6" of 1/2- 3/4" screenings/gravel under the floor foam, extending all the way to your perimeter drain, and put the drain at an elevation below the floor foam. This acts as a capillary break between subsoil and your floor structure, and allows moisture that may well up under the middle of the floor to drain freely.

I'm not sure how you would adequately air-seal the roof & exposed wall, or how that's normally done in EarthShip designs. With high-R high-mass earth ballasted walls air infiltration out the rest of it is likely to equal or exceed the conducted heat loss out your  high-R above-grade south wall.

Also, the wall-R to floor-R ratio would usually want to be about 2/1, but perhaps you're counting on the R-value of the soil to make that up?  With R20 floor you should be looking at R40 for at least the above grade portion of any walls, at least down to a couple feet below grade.

Since you're going to be using a lot of EPS, investigate buying a truckload of reclaimed roofing EPS (insulationdepot.com, or talk to local commercial roofers, or search the local craigslist materials section for "rigid insulation").   Take care to only use EPS or XPS below grade- there's a lot of polyiso used in commercial roofing too- it's great stuff, but will eventually waterlog if buried.  Reclaimed goods typically run 1/4-1/3 the cost of virgin stock.  At R20 you'd be looking at about $2/square foot if virgin stock, but about 50-65 cents/ft with reclaimed goods.  It adds up pretty fast!

Also, ants and termites will tunnel and sometime even nest in rigid foam (any type), so it may be important to put some sort of hard-finish & mesh on the exterior sides to deny them access.  There are borate-loaded EPS variants available that will mitigate against wood boring species, but usually only appropriate in high termite-risk areas.

Hanover NH is USDA Zone 4, which is different than a climate zone. I'm not sure why we need two different sets of numbers, but it causes a lot of confusion.

Dana1,
      I was using the USDA zone map , I just finished a long permaculture course and my mind is still trying to change gears.  I had been leaning towards the EPS foam already, but you definitely sold me on it.  Three 2" layers is not much more work than two layers.  As for the burial wall, money permitting I would like to have double the insulation of the floor, but it is not 100% necessary.  The burial is going to be about 7 or 8 feet high where it meets the back wall, so in theory it should push the frost line back away from the wall and slow the heat loss associated with normal exposed walls.  There is a small exposed part just under the roof but above the burial that will need the extra foam.  ALSO I had not even considered the ant issue with the foam, I do NOT want to be making a glorified ant farm under my house.

     The insulationdepot.com is a great site for sure, and I think it will shore up the slow collection of building supplies I am already accumulating.  I've got time to build my supplies as my only goal this summer is to find and purchase a 5 - 10 acre lot.  Dana1 I really appreciate the time you took in your response and I will be back in a day or two with a new sketch.


jdebree - You know what's up.  Meters and feet and zones oh my!

Ants generally prefer a moist environment, so the better the drainage of the backfil and the bigger the roof overhangs, the less risk you would have (but it's never zero risk.)

IIRC there are now high-density rock wool panels rated for sub-grade soil contact- using them for the outer layer would probably mitigate further against insects. (I'm not sure where to get 'em though.)

Plant hardiness requires considering many more factors than would make sense for general climate & heating/cooling energy use distinctions, so it's not surprising that USDA zones maps are different (and much more detailed) than climate zone maps used for building-code distinctions.

Alrighty, many other fun projects and research trails aside, I've got the new back tire wall foundation detail mostly worked out.  I have decided to go with the 2" rigid EPS foam of course.  The sub-floor EPS is now on top of a 6" layer of 1/2-3/4" gravel, and the perimeter curtain drain sits 12" below the bottom level of the sub-floor gravel layer.  The vapor barrier is now between the innermost EPS layer and the dirt compacted fill/subfloor.  I have made the subfloor deeper as it occurred to me that I will be putting some plumbing into the floor and need to keep it inside the insulation envelope until the final black-water out piping.  When I am at the point of planning the actual in floor plumbing I will adjust the final sub-floor depth accordingly.

   




As for the insect prevention measures, I have two ideas.  First is to use a chemically treated foam for the two outermost layers.  From my research it looks like termites/ants can exploit a 1/8th" gap in most anything, so just doing one layer of the treated foam leaves a lot of room for an 1/8th" gap between boards.  With the two layers placed level and cleanly on top of each other, there would be two flat surfaces compressed together with the weight of everything above it, or behind it for the vertical insulation.  Second is to use a physical barrier,  steel mesh or accurately sized crushed rock.  This would be in addition to the treated foam, if budget permits.  The barrier would be placed between the drainage gravel and sub-floor foam, and between the back burial and vertical foam.  The mesh would be "easily" placed between the layers, while the crushed stone would need to be kept from filtering into the drainage gravel and back burial.  I would imagine some sort of hardware cloth or similar permeable barrier would hold the crushed stone back.

     Overall I am confidant now that I have the general plan laid out.  Next up is the front greenhouse tire foundation . . .

If you use copius amounts of liquid latex waterproofing the little critters will not attack the walls. Seems the little fellows get their crunchers clogged up because the liquid waterproofing never really dries to a hard shell

It doesn't matter AT ALL from from a moisture transfer point of view where it is relative to the R-value of the stackup, since only moisture-impervious insulation can be used

Up to the point where you get enough condensation that it starts leaking into the interior. Your moisture barrier is usually your best air barrier - so put it on the warm side.

Posted By smartwall on 03 Apr 2013 09:24 AM
If you use copius amounts of liquid latex waterproofing the little critters will not attack the walls. Seems the little fellows get their crunchers clogged up because the liquid waterproofing never really dries to a hard shell

I could see using that on the vertical burial insulation,  but would there be a way to get under the floor insulation and paint the underside in a continuous coat.  Also would waterproofing on both sides of the foam insulation, vapor barrier on inside and waterproof paint on outside, cause water to become trapped with the insulation?

 Still, that's 103' of steel mesh/crushed stone that could be replaced with much less $$ in paint.  

Posted By jonr on 03 Apr 2013 09:51 AM

It doesn't matter AT ALL from from a moisture transfer point of view where it is relative to the R-value of the stackup, since only moisture-impervious insulation can be used

Up to the point where you get enough condensation that it starts leaking into the interior. Your moisture barrier is usually your best air barrier - so put it on the warm side.

And thankfully it is.