Ultra-efficient underground earthbag cones

Well, here goes my first post. Like a lot of people, I've been lurking awhile, and one of my first exposures to permie concepts was Mike Oehler's 50 buck underground house book, which I read some 30-odd years ago. Kind of neat to reconnect all these years later and see how things have advanced, thanks to the internet.

So, here's my deal: After wanting to move off-grid and underground for my entire adult life, the opportunity seems close to presenting itself. My dear old dad has been strongly hinting for years that I'll inherit our cottage and lot in Prince Edward Island ("Well, son, we lose about a foot of bank a year, but by the time the cottage goes over, it'll be your problem!" or "Here's where the septic tank is, if I'm not around when it needs pumping.") The lot is about 125'x400', powered, with the cottage, well, and septic system, red sandy soil overlooking the Northumberland Strait about 25' above sea level. There's soft red sandstone bedrock about 20' down, when you go down the bank to the beach, you can see it poking out. That's what I've got.

This is what I want to do: Build an underground earthbag home as efficient as possible; Conserve and reuse power, water, heat, etc. Energy prices on PEI are steep, and I want to avoid being dependent on external utilities as much as possible. Now, while I'd be fine in a small PSP with a composting toilet, hand pumped well, etc., I've inexplicably become inextricably involved, and the wife, while quite enthusiastic about a rural, more self-sufficient lifestyle, has made it known in no uncertain terms that there are certain standards below which she will not stray, viz: NO PSP. Can't say I blame her for this one, we have carpenter ants all over the place; She MUST be able to bake, so the kitchen can't be skimped on; Indoor plumbing is mandatory, as is a tub/shower. (Ok, she'd be fine with just the shower, but I like to soak!); and assorted other niceties that I'll remember if they're brought up. We're basically a pair of (currently urban) hermits who live most of our lives in a 200 sq. ft. room with everything running off of 1 15A circuit, so our power needs (other than cooking and heating) are already pretty modest.

So, on to the plans so far (see attached diagrams): 6 earthbag domes/cones ranging from 6' to 15' diameter, 5 of them connected 6' below (existing) grade for living space, and a separate one 12' below grade for a utility room for power, HVAC, water, and waste management. Except the pantry and utility dome, I plan to insulate them, probably with pourable polyurethane foam. As detailed on the assorted earthbag sites I've read, the slope of the 'dome' can't go past 60° for underground use, so rather than actual domes, they will come to a conical peak. Because of the 60° limitation, the two 15' main domes will be about 20' tall, if brought to a peak, and this suggested to me the idea to use this 'excess' height as skylights: Where the diameter has reduced to 4', which will also be the finished grade level, I will pour a bond beam, then build a 4' cylinder upwards to 5' above finished grade, angling the top towards the south. To keep our heat from escaping up the skylight 'tubes', I plan to build a many-layered, transparent plastic false ceiling 7'-6" from the floor, and another at the level of the bond beam. All the walls above the ceiling to be lined with reflective foil to bounce the sunlight down to the whole dome. Everything will be backfilled to a minimum 4' depth. Incoming air to be brought in via 4"x100' earth tube 10' to 12' below grade, which should supply a fairly constant 8-10°C at that depth. Incoming air first goes to the uninsulated pantry/cold storage, then exhausted from the top into an HRV scavenging the heat from the outgoing air. As you can see in the second diagram, the ventilation is set up as a serial system, taking warm air from high in one room and injecting it low in the next. The bathroom is last on the chain, and then exhausts the warmest, moistest air into the HRV for heat recovery. Power will be a combination of wind and solar, with the following supplements: We have wood free for the cutting, and bottled LP gas is (probably, I'm still working on the conversion math) cheaper than electricity, so heating/cooking will be mostly LP. I want to use a biodigester for sewage treatment, and there will be some gas produced in that process.)

Anyway, enough about the systems, since this is the 'earthbag' section. I just wanted to fill in a bit of background, but I'm going to have questions all over the place; Here, in the solar, wind, biogas, etc., forums, but here are the earthbag-centric questions:

Basically, is this doable, from a structural point of view? I plan to stabilise the bags with 10% cement, and the covering soil is fairly light and sandy, and I plan to run supplemental waterproofing about 6" deep, which should keep the soil mass bearing on the domes relatively dry.

C'mon, people! I have a dream, I need you to shoot holes through it so I know where to patch it, if practical. Thanks a bunch!

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This is fascinating.
The sequential ventilation through ever higher levels sounds very interesting.
Two big comments:
Water, and freeze-thaw.

Have you spent a winter/spring/fall on PEI?
They currently get about 50 freeze-thaw cycles per year, depending upon location.  Temperature can fluctuate 20C in 24 h (-10C to +10C is common; -25C to +15C happens).
So any sort of masonry related structure (10% cement to stabilize bags) is very prone to cracking, heaving, crumbling etc.).
There is a good reason why a bunch of Scottish settlers abandoned stone houses within 1 generation.

And related, drainage?  A hole 15' deep on PEI is going to be well below the water table in most places.  I fear your structure will be a pool.
I think many of the earth dome/earthship/earth cone ideas are coming from much drier places.

Building practices in the maritimes are conservative, partly because conditions are so inimical to experimentation.
If I ever build another structure in the region it will be on an insulated slab, completely above ground, which is a practice starting to spread.
I have friends nearby who have a straw bale house on a slab with wide eaves for rain shedding.
cheers, Doug

Hi, Doug, and thanks for the two big comments!

So, concerning water: I know for a fact that the water table is about 25' down; First, the lot is up high on a bank overlooking the strait, and you can see the water level; and second, we do have a well on the property already drilled, and it hits water about the same depth. I'm only going about 12' down - halfway to the water table - at the deepest (the utility room), so I think I should have enough leeway. Most of the house will only be 6' down, relative to the original grade. Note in diagram 2 that I've included a perimeter drainage system (french drain/weeping tile) for the foundation to handle any runoff. I'll also be including one or more additional waterproofing layers over the whole thing as I backfill.

Concerning freeze/thaw: I've been on PEI only in the summer and fall, but I lived in Halifax, a similar maritime climate, for a while, and I get the privilege of painting the cottage from time to time, so I have a rough idea of what the climate is like and can do to buildings, which is why I want to isolate the house from the climate as much as possible!   . Most of the house will be under 4'(ish) of dirt, below the frost line, so I'm not too worried about freeze/thaw, except on the exposed areas, viz: Around the doors and skylights. The diagram doesn't show it, but except for the pantry, the domes will be covered with 4" (R20) of pourable foam, and 8" (R40) where there's less than 2' of soil cover, and the exposed foam will then be parged with stucco (smooth stucco: I don't like 'dash coats', it's less work to just trowel the finish coat smooth than to mix a whole 'nother coat to hide your trowel marks, and water just runs off smooth stucco).

So, I've put some thought into the issues you've raised. But is it enough?

I should also clarify: The ventilated rooms are all on the same level, so I'll need small booster fans to help the air along. One of the wife's edicts was: No stairs! So, except for the utility cave, there are no stairs.

Have a great day,
Bob

Looks like a very interesting plan.  I would consider using well tiles for the large skylights and maybe something like a solar tube for the bath.  If I remember right from Ken Kern, you can get up to five times as much light from a skylight as compared to a window.  Another thought, how about "Flowerbed" insulation?  Insulating foam sheets slightly under the surface and slightly sloped for drainage.
Good Luck,
RWC

Thanks Richard! Well tiles, you say? Do you mean the precast concrete ones? I actually ruled those out as being too heavy. If I recall, the 48"x48" ones weighed, literally, a ton, not something I can easily move . I can get a 48"x144" sonotube for about $500. I can cut it in half on an angle, and get both skylights out of it for $250 apiece, which is cheaper than a well tile too, if I recall. It'll be sat into a rabbet in the bond beam, with the angle cut on top facing south, and foamed and stuccoed in place, and topped with a sheet of plastic. I plan on a kind of a drop ceiling made of many layers of 6 mil plastic 1/4" apart to hold the heat down, and everything above the ceiling will be covered in foil, so it should be plenty bright.

I really like the flowerbed insulation idea! I was thinking of a waterproof layer of landscape cloth/plastic/landscape cloth about 6" down (and probably another a couple of feet deeper for redundancy) so could I lay sheets of 1" foam under the plastic? Is that the right idea?

Hi;
If you have an elevation, why not drain to air, rather than to a sump?
A sump is going to be a big electrical draw, compared to running your drains out to air at a lower point.
I would think carefully about multiple layers of insulation that could trap water between them.
Maybe better to have a single layer that can drain above and below.
I would also think carefully about stucco.  If you get any water infiltration between the stucco and the foam, the freeze thaw will peel it off in sheets.
cheers, Doug

Hi Doug,
Two reasons I don't want to drain to air: The bank is about 300' from where I'm thinking of putting the house, and a 12'+ deep trench 300' long is just too much earthworks to contemplate. Also, I'm planning to pump the sump up to a IBC container on the surface to use for irrigation.
I plan on making sure both layers of waterproofing are sloped away for drainage. I like the idea of a second layer in case the first ever leaks.
Good point about the stucco, I'll have to think of alternatives, maybe some sort of plastic coating. It'd have to be UV resistant. . . I don't want wood because of the carpenter ants, and I like the idea of something I can roll, spray or otherwise spread over a rounded surface. Any ideas?
Thanks,
Bob

Are you planning on digging a 6' deep patio outside the main rooms, or will they have a view straight out to the horizon? "No stairs" sounds to me like there has to be at worst a gentle ramp all the way down to floor level. If no view, are you sure you would both be okay with never seeing anything but a bowl/ramp and some sky from inside?

I suspect the multiple layers of plastic for a ceiling would quickly acquire some bugs and spiderwebs between them, beside the possible condensation pooling. I would not count on complete hermetical sealing of the space above the ceiling, and I think it would be an even more attractive space for bugs and spiders than a dark basement.

I understand the utility room being lower than the main floor, but why 6' lower? If you want more earth above, you could easily mound it higher there and have only say 7' of stairs down instead of 12'. A sump for drain collection can be a 2' diameter pipe sunk in the floor, it doesn't need to be the whole floor.

If you are talking about having to dig 12' deep for 300' to drain to daylight, does that mean you have 300' of practically flat land? In that case, you will have a huge amount of earth to dig up to get a gentle ramp down to floor level, which can add significantly to the fill available for covering the dome/cones. I would venture to say that you could easily dig up enough earth to cover the designed spaces without going down more than 3' at the rooms, and get a very spacious patio, even possibly a daylight slope for the patio to drain. Are you set on being so far underground that there is hardly a visible mound? Would a small hill in that spot be a conspicuous feature of the landscape once grown in with plantings?

Hi, Glenn,

Yes, the large arcs at the top of the first diagram are retaining walls to hold the 'roof' on, and I planned a sloping front yard 20' or 30' up the slope away from the doors to level. The wife wants a couple of big hobbit doors with big windows for light, and that side will be facing south. (So my diagram is south up.) 6' up over 30' is a foot up every five forward. Too steep? (But see below: You're right, I might not have to go quite so deep, per your suggestion.)

The plastic panels will be removable for cleaning/maintenance, I suspect I will get the odd bug up there, but I'll be screening over the vents for those areas, so I don't think I'll get enough bugs to be an ecosystem. If there's only a couple of flies up there, they won't feed a spider for very long. The wooden frames will be sealed with a soft 1/2"x1/2" foam weatherstrip in a 1/4" deep notch - there's a detail of the edges in the upper left of the ceiling idea diagram, the foam is the dark gray, shown compressed to 1/4" by the panel - so there can be 1/4" of play before bugs could get through, well within the limits of my carpentry skills. I plan on venting the ceiling areas with the rest of the house to keep the humidity down, but I'll have to keep an eye out for condensation. Now that you've got me thinking about it, I think I'll vent the ceiling spaces with the 'raw' air from the tube (via the pantry), before the HRV and the rest of the house: It'll be cool and dry, having lost most of its moisture in the tube, and any heat that leaks through from below will get passed back into the house via the HRV. Thanks! That's a great idea!

I chose the 12' depth for the utility cave because that's the depth my earth tube has about 6 months of temperature lag, according to the chart I found for Charlottetown (the closest location I could find data for), so my 'raw' air will be at its warmest in the winter and coolest in summer. The condensate drain has to go in the low spot, so the sump's got to be lower. . . The floor will slope slightly towards the stairs, and the low spot and sump will be just at the bottom of the stairs with a grate over it for easy inspection. I was going to just form and pour the sump as a 2'x2'x2' pit as I get ready to pour the floor. I plan to put a large garden shed over the stairs with an IBC or two to pump the sump up into for irrigation use, and another couple for effluent and sludge from the biodigester for batch sterilisation and use as fertiliser. It'll also have a sink/garburetor to feed garden scraps, lawn clippings, etc. to the biodigester.

Yes, the lot is almost perfectly flat, about 125'x400', then drops about 25' to the beach. I hadn't taken into account the earth from the 'patio' area, so you're right. . . I can probably go a bit shallower, eh? I chose 6' because it 'looked' about the right depth to get the amount of fill I needed (and fill the earthbags.) I think I'm going to have to do some math. . . Pi R squared, here I come! Even 4' deep would save a day or two with the excavator, and If it still went the 30' from the door, that'd be 1 foot up for every 7-1/2 feet forward. As far as depth and appearance go, I don't mind making a bit of a hill, but I don't want it to look too steep and artificial.

Thanks for your input! Food for thought.

So I did the math for 4' deep, and it indeed looks like I can get away with it:

Earthmoving-cu.ft.

'Yard' - 30' x 50' x 2' = 3,000 +

2 main cones - 15'dx4' cyl. + 15'dx15' cone - 4'x4' cone x 2 +
707 + 883 - 67 x 2 +
3046

Utility cave - 10'dx4' cyl. + 10'dx10' cone +
314 + 262 +
576

Bath - 8'dx4' cyl. + 8'dx8' cone +
201 + 134
335

Pantry + Closet - 6'dx4' cyl. + 6'dx6' cone x 2
113 + 56 x 2
338

= 7295 - sqrt. approx 85

85' x 85' x 1' = 42' x 42' x 4' pile o' dirt, give or take. Oughta be enough.

.I will comment on the cliff because I am familiar with that, though I am on the opposite side of the continent and our cliffs tend to be yellow [iron sulfide] instead of red. We only get about 3 freeze thaw cycles on the cliff face around Puget Sound so that causes less loss than it probably does at your location. Major erosion seems to start with tree roots exposed and hanging over the edge. When the center of gravity topples the tree over the edge the tree roots in back then tear out a slope toward the edge starting water erosion.  So I think if you keep the cliff edge tree free and the ground sloping away from the edge a south facing cliff should be fairly stable.  I even considered building into one. It is the west facing windows that over heat in the summer time.

Hi Hans,
Attached is a pic of our cliff. We share the stairs with a neighbor, our plot is to the left of the stairs. There's a 5 foot band of red sandstone bedrock, overlaid with 15 to 20 feet of sandy red soil. In winter, the water near the shore freezes and the tides grind it into the bottom of the cliff. The province has aerial photography going back to 1935, and I've compared it to the most recent (2005) image, and frankly, there doesn't seem to be that much change, certainly not the 80 feet one would expect if we lost a foot a year, so I'm not overly worried about the bank erosion. Unfortunately, the county has passed an idiotic bylaw prohibiting cutting or trimming anything within fifteen feet of the bank, ostensibly to prevent erosion, but actually because some wealthy yuppies bought some cottage lots nearby and 'they don't like the look of piles of trimmings' on the beach. How they can tell which are piles of trimmings amongst the tons of other driftwood we get each year has never been adequately explained to me, nor has how letting dying trees fall naturally and pulling the bank down with their roots is supposed to prevent erosion.

Correct zoning ordinance are seldom created by experts with some knowledge of what the effect will be. The rich vacation home owners got a ban on burning on the beach because small pieces of charcoal washed up on their bech. So the people that were burning their brush just threw it in the water and it would wash up and get tangled in their steps.
It looks like the neighbor has more stones at the base of the cliff to buffer the waves so might surreptitiously angkor any large logs that wash up against your bank. We built up a nice natural looking sea wall that way. I remember when I was little my mother would stand on the bank and spear pieces of driftwood with a pike pole and pull them in at high tide. My job was to pull the small ones off and stack them behind the logs.
Maybe  some of those tall trees could be nudged to fall back instead of over the edge.

Practical? Define that... cost / sq ft?
Or within budget? (Allow 25-50% overrun on uncommon projects!)

Add a dwg of cross section of soil & blg elevation from anything inland above you to water level. Use as a reference. Rain can sometimes flow. Maybe make the subsoil sections w drain surrounds like a basement without a drain. Compact the soil-berm. Maybe add sloping water resistant membranes ( not contiguou$ but  overlapping)  to start at existing soil level and slope 1ft in 10 up toward cones to shed rain. Insulation inside needs a vapor barrier as usual. Add 1 exoskeletonic or hidden camera obscura.

Remote it via old tv antenna remote? Also add tv antenna for fm radio + disguises c.o. function. Add of dish antenna. At the LNA replace w mic and listen where you look. IF nursery camera and added IR leds. Add the low drain to bank if only for 10 ft to a dry well. It's a backup and stub is in place IF you ever wished to do it. Consider a well-digger for home... but drill sideways +slope to bank. Use grey pvc as last section... uv resis.
BillSF9c

I read out your dream to my (well read) husband...he asked me to ask you if you have read any Ken Kerns? Sadly he died inside his earth house and my beloved said unless you are a soil engineer he thinks you are taking a big chance. I totally hear what you are saying about going to ground though! My dream is a hobbit house half way into a hill...well dreams are good! necessary to keep us going huh?
Best of luck, your place and your dream sounds wonderful to me! All the best from BC
Snowpeach

As much as I love this idea, I think you would be better off with an earth bermed earthship style earthbag home.  You don't want water infiltration. It leads to all kinds of unhealthy conditions. You get much the same advantages and you get more solar gain. Your type of design is far more fitting where I live in dry windy cold UT.