Terra-Dome Earth Shelter Build

[dave1949]

R-value is not everything. Thermal mass is an important factor. If you have sufficient dirt over the top the great thermal mass and its thermal inertia will phase shift temperature changes and delay their effects. Sufficient cover will keep the ceiling from getting hot in summer or really cold in winter and reduce the requirement for heating and cooling.

Pat

That is true, what some call the 'effective R value'. I think the same may apply to (big log) log homes. I live in a house bermed on three sides and enjoy the benefits

I think what Jake and I were more about is making the roof water-tight. There have been some posts about leaks and treatments. I hope they are solved, but if not, I threw out some ideas.
Dave.

 

[sajurcaju]

Pulling your leg Jake. Seriously, if building an earth covered structure, the first thing that comes to mind is how to keep it from leaking...

I think the best place to insulate would be on the inner surface of the roof.

Dave.

If you insulate on the outer surface of your roof, then the concrete adds thermal mass to the inside of the house.

Steve

 

[dave1949]

If you insulate on the outer surface of your roof, then the concrete adds thermal mass to the inside of the house.

Steve

That's true. It also adds to the mass you have to heat. But, from what I have read, outside is the preferred location. That's where I put my exterior concrete wall insulation. It's also why some don't think ICF is a good idea if you want to use the thermal mass of the concrete. Another possibility to keep in mind, with the right weather changes and humidity levels, you could see some condensation form on the interior concrete surfaces. Not a huge concern, but it wouldn't surprise me if it happened. I think the only way to prevent it is to have a decent level of air exchange going on or AC.

I think I am not clear on how your roof is actually finished. I was remembering a pic of soil on the roof and assumed there was nothing under it but a concrete water proofing material. Guess I don't have it right in my head. Apparently, you have foam or spray foam under the soil?

Steve, how is the btu heat load calculated on the dome home? For passive solar, I was able to find some rules of thumb for ratio of south glass to concrete area. Beyond that, the modeling required to get a more exact answer was well beyond my abilities or budget. There are some free software programs available, but the inputs are so technical and hard to ascertain that after looking at it, I decided I wouldn't be able to produce any valid answers.
Dave.

 

[sajurcaju]

That's true. It also adds to the mass you have to heat. But, from what I have read, outside is the preferred location. That's where I put my exterior concrete wall insulation. It's also why some don't think ICF is a good idea if you want to use the thermal mass of the concrete. Another possibility to keep in mind, with the right weather changes and humidity levels, you could see some condensation form on the interior concrete surfaces. Not a huge concern, but it wouldn't surprise me if it happened. I think the only way to prevent it is to have a decent level of air exchange going on or AC.

I think I am not clear on how your roof is actually finished. I was remembering a pic of soil on the roof and assumed there was nothing under it but a concrete water proofing material. Guess I don't have it right in my head. Apparently, you have foam or spray foam under the soil?

Steve, how is the btu heat load calculated on the dome home? For passive solar, I was able to find some rules of thumb for ratio of south glass to concrete area. Beyond that, the modeling required to get a more exact answer was well beyond my abilities or budget. There are some free software programs available, but the inputs are so technical and hard to ascertain that after looking at it, I decided I wouldn't be able to produce any valid answers.
Dave.

From the top, there is about two feet of dirt, 3" of rigid foam insulation, then about another foot of dirt. This varies across the dome; the edges have more dirt under the insulation to level the insulation surface a bit. Then waterproofing and concrete for the dome and you're inside.

I have no idea how they calculate the btu heat load. The radiant heat company (who supposedly has done these homes before) came up with some pretty high insulation equivalent numbers. I think adding a large thermal mass (three days or so time constant I'm told) to heat loss makes it not simple. Also these homes have a *lot* less air leakage, which improves heat loss--we have ventilation to give us fresh air.

Steve

 

[dave1949]

From the top, there is about two feet of dirt, 3" of rigid foam insulation, then about another foot of dirt. This varies across the dome; the edges have more dirt under the insulation to level the insulation surface a bit. Then waterproofing and concrete for the dome and you're inside.

I have no idea how they calculate the btu heat load. The radiant heat company (who supposedly has done these homes before) came up with some pretty high insulation equivalent numbers. I think adding a large thermal mass (three days or so time constant I'm told) to heat loss makes it not simple. Also these homes have a *lot* less air leakage, which improves heat loss--we have ventilation to give us fresh air.

Steve

Thanks Steve, Sorry I lost track of how the roof is finished. The way it sounds, the frost should never get below the rigid foam. That's basically the same configuration as a shallow frost protected foundation on your roof.

Ditto on the air leakage. I think that is why earth sheltered homes have a totally different temperature versus feel inside, the usual through the wall air infiltration just doesn't happen. Plus, the relative lack in temperature variation in interior surfaces is the heating equivalent of surround sound It's a good thing. I predict you will really like it.

I bet you are anxious to get moved in, must be coming soon. I think your last estimate was late Jan. or early Feb.

The btu calculations are tough because the simple modeling packages don't contain plug-in values for bermed construction, it's coming back to me Good to hear the heating folks made an adjustment in their calcs otherwise you would probably end up with more boiler capacity than you need.

Do you know how many kbtu's your boiler is rated at? Mine is 90K and that seems to be plenty the few times we have used it. We've never had all our heat zones turned on since the attic got insulated and we were done drying out the residual moisture from plaster and concrete. Hard to compare our houses though.
Dave.

 

[patrick_g]

I run an ERV 24-7 at a low (inaudible in living areas) fan speed that only goes faster and then just temporarily if the humidistat in the master bath goes above its set point. There are 4 registers connected to the exhaust side of this ventilator. Three of them are in the master bath: above the Jacuzzi tub, above the comode, and on the ceiling of the shower. There is no supply register to supply forced air to the master bath. Conditioned air is slowly exhausted from the rest of the house via the master bath. This flow supplies conditioned air to the master bath. The floor of the master bath is heated hydronically as are the floor and walls of the shower.

The other exhaust register is in the walk-in closet of the master suite. Air flow due to that provides a gentle flow of conditioned air to the closet. There are no supply registers in that large closet.

Pre-conditioned outdoor fresh air is supplied to the inside of the house 24-7. It is a great way to improve indoor air quality and avoid "sick house" syndrome. I designed my range hood. It has two blowers, both remoted, both variable speed. One exhausts air from the hood and the other supplies air to the periphery of the hood which forms an air curtain to separate room air from "above stove air" and supply make up air so you don't pull a partial vacuum when the powerful exhaust fan is turned up to a high speed.

My design ideas for the hood were formed when I thought I was going to build a home that was earth sheltered and not part ICF, part cast concrete (earth sheltered), part red iron. As infiltration can be extremely low in concrete structures like earth sheltered residences, getting fresh air needs to be considered and designed in as you don't get it for free by accident with infiltration through leaks. I tried to build a tight house so I still needed to give consideration to an engineered solution for fresh air and exhausts.

A really tight structure can get a backdraft in a gas hot water heater when you run a conventional range hood. Not a good idea.

Regarding the insulation on the inside vs outside of the concrete. Insulating the outside insulates you from the environment and its rapid changes. You do have to heat and cool the mass of concrete then but just once per season and then there is no difference on heating or cooling inputs except not having to respond to rapidly fluctuating environmental conditions which is a good thing.

In the traditional stick built section of our house (a little over 1000 sq ft) we have hydronically heated tile floors. Wide excursions in outside temps can cause under or overheating. With a constant outside temp the floor will be heated sufficiently such that it sheds the requisite Btu's to maintain the T'stat at its set point. A rapid change in outside temps gives rise to a large change in the delta T (inside to out) but due to the long thermal time constant of the slab the room will either be too hot or too cold as it can't respond quickly. I have two stats in this space. One is for forced heat and air conditioning and the other for the hydronic floor. I set the air stat a couple degrees below the floor stat and if the outside temp drops the hot air comes on to keep the room from getting too cool while the floor is catching up.

In a concrete structure the thermal mass of the walls will prevent changes of outside temp to rapidly effect inside conditions and my hot air supplement strategy is not needed. One thing is for sure with a concrete structure with the insulation on the outside is that night time temperature set back is not at all practical due to the long thermal time constants involved.

Regarding ICF: I have over 1000 sq ft enclosed by ICF (8 inches of concrete, no waffle or post and beam, just 8 solid inches of concrete with 2 1/2 inches of Styrofoam on both sides. This part of the house is the easiest and fastest to heat and cool. I used in-ceiling hydronic heat in this section due to thick carpet and pad and lots of floor covered by furniture. The thermal characteristics of the ICF are a little more complicated than concrete with insulation on one side. The one side example can be modeled as a single stage low pass filter. A resistor and capacitor in series with the input to the end of the resistor away from the capacitor and the output from the junction of the resistor and capacitor. The resistance is the R-value of the insulation and the capacitance is the thermal storage characteristics of the concrete. The ICF example adds a resistor in series with the previous example's output.

ICF still uses the thermal mass to phase shift the thermal load but allows for easier short term changes in indoor temps. It does accommodate T'stat setback strategies. With one side (outside) insulated concrete a space that is used once a week has to be heated 24-7 because you can't heat it quickly. ICF accommodates random use patterns and you don't need 2-3 days advance notice to heat a room.

Regarding water control in concrete structures. Concrete always cracks even if only microscopically. Plan for it. The are admixtures to add to concrete to improve its "water proofness" but that may or may not help after cracks form. There are products that "lie in wait" for a crack to start to pass moisture and then the substance reacts and forms crystalline growth that plugs the leak.

So long as there is a head of pressure behind the water (can be provided by just a small vertical expanse) a crack, even microscopically small, will pass water. A good strategy is to ensure there is no head of pressure. This is the route I took with my basement. My basement floor is 5-7 feet below the water table and has no water problems. A patch of sheet plastic taped to my slab floor or outer basement walls for a week, when removed, reveals no condensation, not even a slight darkening of the concrete when done during a record setting wet season. My walls were cast with "snap-ties" to hold the forms so I have holes through my walls on a regular grid but they don't leak.

I used a product called Insuldrain. It is 2 1/4-2 1/2 inches of rigid foam in 4x8 sheets with tongue and groove to interconnect sheets One side is plain and flat while the other has vertical and horizontal grooves (water channels) covered by Tyvec filter cloth. The grooved/filtered side goes to the outside and the smooth side is to the concrete. Any underground water that comes in contact with the outside surface of the product is filtered by the Tyvec to keep fines from plugging the channels and then falls through the channels to the bottom where I have perforated drain pipe in a filter sleeve buried in washed septic gravel wrapped in geotextile. A non perforated extension of this pipe drains to daylight (just above a backyard pond well over 100 ft away.)

Even if you hammer drilled a hole in my basement wall it wouldn't leak. There is no standing water. There is no head of pressure to force water through any cracks (or the snap-tie holes). Be it ceiling or wall or floor, if there is no head of pressure due to a depth of water, however slight, there will be little or no leakage. In my view it is very important that an earth covered roof have no areas that are concave which hold water irrespective of waterproofing method. Where there is standing water it doesn't take much of a flaw to be a significant leak. With proper "fall" and no concavities to retain water the risk of significant leak is seriously reduced.

Pat

 

[dave1949]

Very cool post chock full of good info Patrick. The description of how concrete behaves thermally in various configurations is great info and well written. I haven't searched in a couple years, but I think a person could look a long time to find those nuggets of knowledge.

The body of knowledge and good standard practices continues to build for earth sheltered construction. That's been lacking in the past.

I like the sounds of your range hood. The average new construction range hood is a waste of sheet metal and electricity IMHO. They don't accomplish their intended task.

The sick house syndrome is right on. People are slowly becoming aware there needs to be some attention paid to the materials used to build and furnish a home in addition to providing air exchange.
Thanks, Dave.

 

[patrick_g]

Very cool post chock full of good info Patrick. The description of how concrete behaves thermally in various configurations is great info and well written. I haven't searched in a couple years, but I think a person could look a long time to find those nuggets of knowledge.

The body of knowledge and good standard practices continues to build for earth sheltered construction. That's been lacking in the past.

I like the sounds of your range hood. The average new construction range hood is a waste of sheet metal and electricity IMHO. They don't accomplish their intended task.

The sick house syndrome is right on. People are slowly becoming aware there needs to be some attention paid to the materials used to build and furnish a home in addition to providing air exchange.
Thanks, Dave.

Dave, Thanks for the compliments. Consider anything of value I contributed to be a tax rebate. I attended classes paid for by my employer (Federal Government, DoD) that were by the AIA (American Institute of Architects - like AMA for doctors) in energy efficient architecture. The instructor was a consulting architect in energy efficient building. My interest piqued, I bought a small library of books on the topic of energy efficient architecture with a specialization in earth sheltered residences. I studied the topic for years in my spare time but eventually ended up with just a little over a thousand square feet of earth sheltered floor space, a walk-out basement with concrete slab ceiling (floor to great room above.) Many passive solar earth sheltered designs (not the dome homes) are essentially walk-out basements with dirt on top instead of more home.

I sort of chronicled my home building experience on the sister site http://www.countrybynet.com in the Home building section in a thread titled Oklahoma farm house.

Typical consumer grade range hoods are like bathroom exhaust fans. They make a lot of noise and don't do much. Commercial hoods have make up air supplies to replace what is exhausted. I wanted to use the "air curtain" concept to separate the fumes and hot air above the stove from the ambient air of the kitchen and to provide make up air to avoid a partial vacuum. I was was blissfully unaware of the make up air arrangement of commercial hoods till I got into the topic. I guess I was once again reinventing the wheel. The sheet metal shop owner I took my design to had built several commercial hoods and was fully aware of what I was trying to do. I bought grease filters from Sears and keep a second set for spares. Easy to get more of the right size and no custom charge. I use three to get the cross sectional area I wanted. You have to do some contortions to see the metal of the hood as it is covered with oak cabinetry. The actual exhaust fan and motor are on the roof so you mostly hear rushing air in the kitchen and a faint drone of the motor. The make up air blower is inside the front porch attic and is even quieter than the exhaust unit but oversized and has to be run at lowest setting. One day I may swap it out for a smaller unit.

It will be hard to build and furnish a house without formaldehyde and other things I'd rather not breathe. There is so much outgassing of fumes from so many materials; carpets, pads, particle board, and on and on. The only gas flame in our home that is not a direct vent gas log (we have 4) is the 5 burner cook stove (twin ovens are electric) and we always run the exhaust fan, at least on a low speed, whenever we have a burner going to exhaust the byproducts of combustion. I think there should be mandated codes on how tight a house must be to be "to code" and some sort of whole house ventilation system should be required, preferably an ERV or HRV. The ERV I run 24-7 uses less than an amp at 120VAC. Passive vent systems working on convection and ambient wind are simple to engineer if you want to dodge the small electrical consumption.

Pat

 

[Zaster]

Hey all,
I was that guy a few months back who posted about asking questions then disappeared. Not sure how but every time I visited the page for the next week or so it never updated so I figured the thread died. If I may still ask questions, I certainly do have a few. (Some basic background, I plan on using a two 28'x28' modules, sheltered on 1.5 sides and the roof. Not looking to build for 2-3 years, but want to do as much work as I can myself)

-I do still plan on using Terra-Dome. How has your experience been with them to date now that you've had some time to really look at their work? Would you recommend them?

-Waterproofing: What have you guys learned about it so far. I read the 10 or so pages after the web error and see there has been some problems. I've been doing my own research, but have no idea what to use. Everything sounds good, but there is just so little posted about actual experience with product/technique X. What would be your ideal drainage/waterproofing system if you did it all over again?

-HVAC: I really want Hyrdonic Floor heating (radiant floor) especially since there will be such a large concrete mass, but am having a hard time justifying the extra cost since a forced air ventilation system is almost required for safety and dehumidification. What convinced you to do in-floor heating? (By the way, I have been using http://zurn.com/images/pdf/ZPM02101.pdf as my reference for designing the hyrdonic system.)

- How are you finishing the interior? I plan on using metal studs for interior walls (low/zero smoke in the event of fire and no worries of mold damage), but are you using drywall or plastering the walls? Using products from Dietrich, I am just thinking about using plaster (also no worries of mold damage) for all the interior walls.

-What is the cost of insulating, waterproofing, and draining? They don't really mention it which scares me. I have been trying to get a cost estimate going, but if they don't include it, I worry it has to be a significant cost addition if they don't mention it.

-How good were the concrete forms? Did you lose any receptacles/box cutouts due to sloppy side wall forms allowing concrete to pour into them? This was a concern I read on another source I found. Do I need to plan on losing some so add extra?

-What solar tubes are you planning on using? I found a company that offers a really nice product, Solatube. Are these what your using, and if so, have you had any experience with them? I plan on using these in the bathroom because They can have a built in light, 110 cfm fan, and a dimmer for the natural solar light. Probably expensive as sin, but meets my bathroom requirements.

-Did Terra-Dome provide any HVAC analysis with their design? It says they provide a HVAC plan, so I'm guessing they must have sized an Air system.

-Where is the HVAC plenum located? Is it located in the concrete slab, or below the slab? (aka.. will it interfere with Hydronic in-floor heat or conduit/cable?) I got the impression it's located under the slab, but wanted to confirm that.

-What are frost footings and where might they be needed? I am guessing they would be required on the exposed walls, and normal footings on the earth sheltered walls, but haven't been able to get a clear answer from Terra-Dome on this when I asked.

Well I think that's about it for my off-hand questions. I have been having a lot of fun designing this house in AutoCAD. I have the layout done, now I'm just preparing the different plans now (electrical, plumbing, Hydronic Heating, etc.) Seeing all your projects really makes me excited to move forward soon with mine own. They all look amazing and I've learned a bit from reading all these posts!

 

[sajurcaju]

Hey all,
I was that guy a few months back who posted about asking questions then disappeared. Not sure how but every time I visited the page for the next week or so it never updated so I figured the thread died. If I may still ask questions, I certainly do have a few. (Some basic background, I plan on using a two 28'x28' modules, sheltered on 1.5 sides and the roof. Not looking to build for 2-3 years, but want to do as much work as I can myself)

-I do still plan on using Terra-Dome. How has your experience been with them to date now that you've had some time to really look at their work? Would you recommend them?

-Waterproofing: What have you guys learned about it so far. I read the 10 or so pages after the web error and see there has been some problems. I've been doing my own research, but have no idea what to use. Everything sounds good, but there is just so little posted about actual experience with product/technique X. What would be your ideal drainage/waterproofing system if you did it all over again?

-HVAC: I really want Hyrdonic Floor heating (radiant floor) especially since there will be such a large concrete mass, but am having a hard time justifying the extra cost since a forced air ventilation system is almost required for safety and dehumidification. What convinced you to do in-floor heating? (By the way, I have been using http://zurn.com/images/pdf/ZPM02101.pdf as my reference for designing the hyrdonic system.)

- How are you finishing the interior? I plan on using metal studs for interior walls (low/zero smoke in the event of fire and no worries of mold damage), but are you using drywall or plastering the walls? Using products from Dietrich, I am just thinking about using plaster (also no worries of mold damage) for all the interior walls.

-What is the cost of insulating, waterproofing, and draining? They don't really mention it which scares me. I have been trying to get a cost estimate going, but if they don't include it, I worry it has to be a significant cost addition if they don't mention it.

-How good were the concrete forms? Did you lose any receptacles/box cutouts due to sloppy side wall forms allowing concrete to pour into them? This was a concern I read on another source I found. Do I need to plan on losing some so add extra?

-What solar tubes are you planning on using? I found a company that offers a really nice product, Solatube. Are these what your using, and if so, have you had any experience with them? I plan on using these in the bathroom because They can have a built in light, 110 cfm fan, and a dimmer for the natural solar light. Probably expensive as sin, but meets my bathroom requirements.

-Did Terra-Dome provide any HVAC analysis with their design? It says they provide a HVAC plan, so I'm guessing they must have sized an Air system.

-Where is the HVAC plenum located? Is it located in the concrete slab, or below the slab? (aka.. will it interfere with Hydronic in-floor heat or conduit/cable?) I got the impression it's located under the slab, but wanted to confirm that.

-What are frost footings and where might they be needed? I am guessing they would be required on the exposed walls, and normal footings on the earth sheltered walls, but haven't been able to get a clear answer from Terra-Dome on this when I asked.

Well I think that's about it for my off-hand questions. I have been having a lot of fun designing this house in AutoCAD. I have the layout done, now I'm just preparing the different plans now (electrical, plumbing, Hydronic Heating, etc.) Seeing all your projects really makes me excited to move forward soon with mine own. They all look amazing and I've learned a bit from reading all these posts!

Steve with (not yet in) the Maine house:
I think Terra Dome has a reasonable product, but wish they did better concrete work. Our house is 3 24x24 modules, a fourth one is the garage. The house has a 7x24' flat extension. Also part of the same structure is a 28x28 shop with a 12x28' flat roof extension and a 28x28 barn. Specific flaws in the concrete:
1. Flat areas don't drain right. The one in the back of the shop has two problems--first, 3" deep puddles and second the drain pipe that services that area of the roof is an additional 3" above the flat roof area! Pretty useless drain. These are fundamental flaws in their work.
2. One retaining wall and one parapet wall ran out of concrete during the pours. The retaining wall additional pour looked really bad (we ended up covering the whole wall with some sort of trowel on stucco product since it was in the entry area). The parapet wall leaked along the pour line, a lot. My contractor fixed it, but why should he have had to?
I guess I'd still recommend them, but go into it with eyes open (and supervise, don't let them run open loop). I'm continually bothered when I talk to Jay and ask him specific questions about TD houses and he answers by saying "talk to the folks on my link page". He gives me the impression what he is selling is concrete work, not houses.

I think the biggest deal on waterproofing is make sure you have slope to the drains. I still can't believe that on a structure the size of ours they only put in two roof drains (one of which is useless). We ended up drilling the concrete front and rear in the shop to install additional drains. Amazing amounts of water flows through the drains we added. If you're in a climate that freezes, make sure your roof drains aren't in a position where they will freeze, bring them through a heated room's wall, with insulation on the outside. Do use a waterproofing product, but the best solution is to make sure slope is there to get rid of the water.

You put some dirt on the roof to smooth it out a bit, then put down insulation board and bury that. When it rains, we found that since the insulation board is waterproof, the water stays on top of the insulation, isolated from the drains! Given the poor soil we have in Maine, it essentially turned to quicksand. Next spring we'll have to figure out what to do (we're in the frozen north here), either punch holes in the insulation or add a second set of drains above the insulation.

Forced air heat and forced air ventilation are two different beasts. Heating with air takes a large volume of air, ventilation doesn't. Running forced air heat in the slab means you will be using small diameter pipe at high air pressure. This will be very noisy and annoying. These houses are supposed to be *very* quiet; imagine what it will sound like every time the furnace blower kicks in. If you're doing it yourself, I'm not sure why in-floor heat would be too expensive. You will want to insulate the slab either way, and that's a big part of the cost (but I didn't really look into it, we were decided on in-floor heat).

The interior concrete walls and ceiling in our house are finished with plaster. The same finish went on the metal stud framed walls. Apparently this means you need to use "blue-board" instead of drywall (plaster board vs. gypsum board) to make the plaster stick right. We're going to paint the shop and barn interior to lighten it up, but with some gloppy paint designed to cover concrete well.

Costs not mentioned by TD--I think they just don't want to get into it. Costs depend a lot on what products you use, who does the work, rates in your area, etc. Probably a reasonable attitude on their part, but they could at least provide examples.

We're using the solar tubes off of TD's links page (Sun Dome). We haven't actually gotten them yet. Someday my contractor will be done. DO put in enough (more than enough) tubes through the roof. Will you want to put solar panels up there someday and wish you had another tube? etc. Run a faucet and electrical outlet up there while you're at it. You might garden, or want to use power tools up there. Think about putting a safety railing of some sort around the edge--remember, when full of dirt, you can walk right up to the edge.

TD put some lines in our plans showing where hvac would be run, but they did not do any sizing. That is up to your hvac contractor according to Jay. Again, they should provide more info, at least some specific examples. You're left without a clue. We blew it on the ventilation--we said no forced air heat, so our contractor dropped the in-slab piping. As a result, we've got a couple of flat ceiling areas (bathroom, back end of the kitchen, places where you don't notice it). The flat ceilings give a little bit of attic space for vent pipes. The vent units themselves are in the MBR closet and the laundry room (two due to the size of the house and no way to run a pipe across the living room area).

I think we only lost one electric outlet, and the electrician is managing to work around it. I think what happened is that the conduit came unhooked from the box during the pour, but I'm not sure. We have a *lot* of outlets, especially in the shop. You're going to have to stare at electric diagrams in your house plans for a lot of hours to make sure they are in the right places. In general, I think their forms are pretty good. Pretty neat to see them pour the dome.
***Make sure they get their forms out in a reasonable time when the concrete is done. We were held up for several weeks waiting for them to move their forms out.

Frost footings are a lot different from in a stick house. They are supporting a lot more weight. Ours range in size from one to three feet across. There are internal footings under the center of the house as well (but they don't need to go to external frost depth, they are shallow footings not expecting frost). You say "haven't been able to get a clear answer from Terra-Dome on this when I asked"; sounds pretty familiar. Maybe in this case there is some proprietary nature to the info.

It sounds like you are trying to draw the final plans yourself. If this is what you're doing, I really question the idea. DO spend acres of time planning the house, but I think you'll have to hire them to at least check your work. These are specialized structures and need someone experienced with them doing the plans. Note on plans: we modified a window size that got lost in the final drawings--we now have this tiny window over the sink in the kitchen.

Steve