Dumb idea for earth sheltered house?

Started by mvk, December 16, 2013, 01:27:29 PM

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Hi all

Haven't been on here for awhile, my plans for building on our land in NH fell through for various reasons.

New plan,  I should be moving next August, there is a sweet spot for an earth bermed small house with a living roof.  I'm more interested in the aesthetics in this case rather than any energy efficient stuff. Truly any other kind of house would ruin this spot. NO PERMITS REQUIRED!!! Sorry for the outburst.

While thinking through the idea in the initial phases a light bulb went off. Might be a really stupid idea but I thought of Glen Kangkauser and how he would be the perfect person to tell me how stupid? Ordinarily you would have a masonry wall as your back wall, in this case north wall, and most if not your entire east and west walls. Well I was thinking about including a root cellar and pondering how to build it and I remembered a shop that is dug in the side of the same hill 400' or 500' away. This left an exposed bank that is almost vertical and 14' high. It has been exposed for about 5 years or so. There is no caving at all to speak of. It is a stony clay soil. I haven't tried to really get a formal geologic description yet, but it doesn't seem like it is going anywhere soon.

So I was wondering if I could just have a "horizontal" dirt cellar around my house, maybe a eight foot wide room around the house, then maybe some way to stabilize the bank somewhat, maybe a kind of cribbing that ended on some kind of plate, cut back into undisturbed ground, where the rafters would meet the hillside.  Think of an old wooden bridge abutment, or mine cribbing. Moisture control would be a consideration of course, no idea of how to apply a vapor barrier to the earth yet .

As I said as long as it doesn't fail anything is good, also this allows me to substitute site gathered materials for store bought. If I can avoid the hard cash cost of the masonry, it might be a win?  I would be waterproofing the walls anyway, so that part might be a wash with the cost of the extended roof?  I would need more insulation I think. The rear wall could be log post and beam, with whatever, I would kind of like to try lime plaster, cob?  It's a smaller house, so it could always use storage, pantry, laundry, and bath, utility?  If you think of this as a horseshoe around the building, the entries could be on both ends, through this area.

Anyone know what size rafter I might need to span 18' 3' o/c and carry 185 lb's per sq.ft. using southern yellow pine. The weight is from Rob Roy's log cave, he used 5"x10" rafters on 30" centers to span 10'. He has all the calculations but  I don't trust my math, I have an engineer at work who will sit down with me, but we are so busy, and I'm driving him nuts. I just want some idea for now to ponder ??? 

Hi again and  I would appreciate any comments especially from Glen



For the beams, this should work
It sounds like you'll be using uniformly loaded simple beams.
Base design values for #2 SYP heavy timbers (5x5 and larger) are
Fb 850
Fv 165
E 1.2

I'm coming up with 10x14's, the span at that load is killing you.

The earth walls sound like trouble to me.


Thanks Don, that calculator is pretty cool, I have never seen it before.

I figured that that would be some big sticks of wood, guess that's why Rob Roy went with a 10' grid.  I would prefer no posts. The 18' span is from a room at a friends cabin, it is a large room in a small space if that makes any sense. The 3' rafter spacing is to accommodate slider replacement glass panels and also to spread the large sticks out a bit visually, I would prefer 4'. I'm planning on using logs so I should pick up some strength over  sawn lumber and I can use the natural taper of the logs visually also. Rob Roy's design load, with those snow loads, is quite a bit higher than what I need. I will also look into anyway to lighten the soil. Helps me to think, to just have a size in mind, so thanks. I work with a guy who bought a high end underground house, I will go see it, probably after the holidays. It appears to have huge spans in pictures, he says he has plans.

The dirt walls do seem crazy, but it seems like cheap space. I don't think the whole hill sliding would ever be a problem, that could be a killer. The roof of the living space will be supported by a wall, a log post for each rafter, so that collapsing isn't a worry. I think that the dirt peeling off could be a PITA. A way to stabilise that would be nice, a clay based layer maybe? Using that space was a thought after looking at Rob Roy's book, and thinking about all those blocks and bonding agent. I really will be in a situation where I can build what I want, how I want, so kind of just thinking out loud. I could build a log crib wall as a retaining wall and set rocks behind it to keep the dirt stable and also keep the wood away from the soil. If I was to build some kind of beam for the rafters to set on I could then crib up the hill say 8' into undisturbed soil. I could use railroad ties for this since the would be outside both the living shell and the storage shell. This is all observed tech from old mines and my brief time as a miner.

There would be more to work out and it might just be too much work, fun work though.

What would I do with the water coming down the hill, look for a natural swale or build one to divert most of it, then let the water on the roof flow forward and away I think.

I'm just in the preliminary stage here, it's been years since I even thought about an earth sheltered building except to check into the Malcolm Wells forum from time to time. My Mike Oehler book had disappeared, and guess which two characters I saw the last time I checked into the  M.Wells forum, and after I started to think about earth sheltered. So I thought who better than Glen to run this by. 



Hi I have a couple of new thoughts on this bank idea.  So now I'm going to support the earth bank with a retaining wall, but does the bank give me any advantages that I can exploit? As I said it is compacted, and unlikely to move in the short term. I could probably sculpt it?

I would like to use wood against the bank, like Mike Oehler.  I once again have his book, the $50 and up underground house book. I'm thinking the easiest/cheapest way might be to smooth out the wall somewhat and then put the boards against the bank. I'm going to be using log rafters, on 3' centers at least for this planning stage.  If I just posted from the rafters down as Mike does, I could then use wedges between the log post and the 2 by boards to keep them against the dirt, and built it from the outside in.

If I do this right it could keep me from having to back fill. But is this a good thing? How do I keep the poly intact? Would I need a drainage plain/ channel, it would be pretty hard to put gravel,  maybe some of that new stuff, it's like a fabric I believe, that they put on concrete walls to provide water channels?  I have no experience with it other than see this old house; I would imagine it's expensive?  Is there a DIY way to provide drainage to a vertical wall that would allow you to build in place and outside in? Maybe felt paper, poly, XPS foam, poly, shoring? Maybe place another layer of building paper inside the poly to protect it during assembly? I'm planning for all the surface water to be either diverted or to flow downhill over the roof. And I will have at least one perimeter drain.

I think water pressure and freeze thaw would be the reasons to worry about building right up against the cut bank? Whatever happens with water in the soil will now happen at the poly barrier I would think? I've dealt with hydrostatic pressure before, it always seems to win! As I said before the existing cut bank hasn't had any water flowing, weeping, etc, but what if anything should I have to consider here, soil saturation that's above normal?  Would water from just damp soil exert pressure at the poly barrier, I wouldn't think it would be much? Would it collect and condense? I'm assuming that the vapor barrier stays intact, and that the dirt bank is stable. The ground around the walls should be insulated from the frost cycle, the wedged boards should keep contact to prevent dirt from moving.

I first thought about exposing the cut bank because it seemed like low cost space, I should say lower, because it's certainly cheaper to build up. After a little thought it seems I'm just building a bigger Mike O house with the exterior walls forming a kind of basement and separated from the living space by an interior wall. I think I'm getting a way to upgrade the wall insulation that's cheaper than using XPS, plus it would be like building an air lock/basement around your entire house. The roof insulation could run both up the hill a little and down the wall a little with maybe a minimum going all the way down the wall to try to avoid summer sweat?

That whole space which is say 8' wide could be storage/utilities, and could be built like a basement meaning lower cost. Perhaps with a gravel floor and a second French drain above the foundation drain? The whole space could be X braced it could also be used to brace each rafter against moving down hill I would think. Doing this should prevent any side to side movement, which would allow me to use wedges and nail the wedges to the planks. It would also allow me to use square edge planks and not worry about having to create a finished wall surface. It is just a barrier to prevent dirt from coming in and to hold the water proofing.

I don't really want to use treated wood inside wherever the MSDS (?) says, I'm perhaps not rational about it but I don't want to, even in a basement. Building like this I would only have one face of any wood that I couldn't see to somehow to keep an eye on.

I would prefer to not bury my posts or treat the ends. What else could I do, use Locust, White Oak, and not worry about it, buried they would outlast me I'm sure? Pin the post to a concrete pier?  This would get the post ends out of the dirt. Would it be strong enough to resist lateral movement? What could happen, the pin shear?
Could I use this space that would surround the living space on 3 sides as a type of plenum, and move air around or through it? Can I use it as a low tech air changer?  The ceiling will be one plane and unobstructed all the way up the rafter bays; this could be connected so as to vent the living space to the utility space or back the other way, and also outside. Since I'm going to be heating two relatively small spaces that aren't connected, could I put a wood stove in there and use doors to the living spaces to control heat flow? Maybe use a low flow fan of some kind? Since it wasn't living space it could over heat a little, maybe vented to the outside if needed, even in winter, or when unheated it could be used to help moderate the heat gain from the mostly south windows. Any masonry in the chimney could be exposed in the living space and act as a heat source?
I wonder what that space will be like in summer; it is pretty humid down where it will be built in Southern Missouri?

What alternatives to XPS are there for ground contact insulation? I would think that there might be more sophisticated ways to increase the soil insulation that have been developed over the years but I don't know of them yet. What about biochar?

Looking over Mikes book, what I was originally thinking of, wouldn't be much different then roofing over the dugout in one of the pictures.



Man thats a lot of questions on a lot of ideas, you talk cost and then do two walls instead of 1, if the outer wall is porus-wood then that U room is damp

By the time you've built a strong enough retaining wall and have it all waterproofed your almost doubling your cost as you still need a strong second wall to help with supporting the dirt roof.

A lot of the earthship houses are built in the desert......they have methods suitable for that climate.....having a little moisture wont be an issue, build the same house in a rainy area and you'll have issues

When looking at costing a project, the foundation basis of the house is the most important part to concider, money spent at this stage will prevent major expediture down the road if not done right.

I see a bare earth wall , even cribed with timber as creating a damp wet moisture laden cave at the back of the house anywhere accept the mojave desert !

When you move into EPDM liners to keep the moisture out, then still want a usable space, I'd just do the one properly built wall sealed against the water and backfilled, and add your extra spaces within the main foot print, you can still do creative wall coverings and get the molded cave look inside that wall.


Man thats a lot of questions on a lot of ideas

I expect a lot of answers and all of them right   :)

Once I got away from the unsupported dirt walls then it became apparent that I was increasing the cost quite a bit, thats why I said cheaper space. But where else do you go for space deeper?, up? These walls shouldn't be wet from the ground they will have a poly moisture barrier, this is Mike O's original tech. I'm skeptical of using the poly mostly because of the hassle of trying to install it without punctures.

If I go to masonry thats where the costs start to add up, and I give up that advantage of no code, and having a saw mill and timber on site.

I would love the idea of exposed dirt walls and no vapor barrier, it would be pretty easy to do, to bad it wouldn't work.

But what will happen in this space, that should have a continuous vapor barrier between it and the ground. It should be cooler than the house and the outside air in summer. If it was open on both the south east and west with screen doors and roof vents in the north wall could this keep the area mold/mildew free? For any fans of Mike O it's easy to see that it's not a great leap to adding a north side courtyard of some type.

And in winter if I did put the stove out there, that would sure keep it dry. It would be nice to circulate heat passively 

As far as adding cost to support the roof, I'm looking at a tree every 3' in the original design  if I add a 10'x10' section, roof and wall, to extend it, then I'm adding a half a tree per unit length ??? if I explained that right. Then I'm also adding additional planking that has to be sawn.

As far as thinking about EPDM or any other kinds of upgrade in waterproofing I did feel that the post was getting to long. But now that it's brought up what other ways of waterproofing are there?