Well, hopefully Sherri and I will love our underground house. “We don’t like our underground house” was the title of a blog by MizBejabbers who wrote about the pitfalls of her underground house.
MizBejabbers’ earth shelter in Arkansas. Check out her site for more pics, but this was the best one ;^(
Miz tells about how they moved into an earth sheltered home 18 years ago (built by TerraDome for a previous owner, who may have covered up the problems to sell it) and how it has not lived up to the earth sheltered promise. She writes about how it had all the fears (leaks, mold, etc.), but without the benefits of energy efficiency. She also talks about increased construction cost, severe depreciation, pests (bugs, rats and nosy people), etc. She does have a section on “happy things” such as feeling safe during storms, enjoying the peaceful quiet, etc. but concludes that these were not worth the pain.
She even blogs about mini tremors, which she thinks are earthquakes cracking the house, but I suspect it is the house cracking and settling as the soil underneath is slowly eroded. No earthquakes required.
For someone like me who is considering a similar investment, this could be a blog from my future, so I read it very carefully…
My conclusion was that this house was just designed and built really badly and in the wrong time and place. By time, I mean that it was built in the early 1980’s when few people had worked out how to do these properly. Lets go thru the issues, as far as I can tell from the blog.
in an underground aquifer, like a wet pebble in a stream. Try a quick Google image search for “artesian well diagram” if you are not familiar with the concept. Miz acknowledges that the french drains are not sufficient in capacity or well placed to drain water away before it enters the house.
This house is set below the road on the side of a large hill overlooking the Arkansas river. The U-shaped design that Miz mentions sounds perfectly designed to catch all the surface runoff from the hill above and funnel it toward the front door. What is probably happening under the ground is even more threatening… Hills do interesting things to water tables and an earth sheltered home may be sitting
Our site doesn’t have such a majestic view, but it is on the top of a hill, and our hill is very permeable sandy loam that will dry out nicely. Before I bought my land, I walked around during a thunderstorm and made sure the water didn’t collect or run. After buying the land, and looked “deeper” and buried moisture sensors more than 10ft down for my Soil Temperature Experiment.
In the comments after the article, she mentions that the house was built on fill (to make a terrace on the side of the hill). If there was water flowing down, around and under her home, fill soil would wash away more easily and would lead to further settling and cracking and leaking. My home will be built on undisturbed soil with a high compression rating and no erosion threat.
She also blames a “bad batch of concrete” for the living room roof crumbling. I am not sure if that was really the problem (or if the bad conditions just wore down otherwise adequate concrete), but The TerraDome homes are monolithic structures which are poured into proprietary modular forms. If the concrete is not carefully mixed and poured, there is no good way to fix it later.
My home will use shotcrete, which (when done right) is considerably stronger than any poured concrete because of its lower water content and the way it is compressed as it is shot onto the wall.
Miz mentions metal ducts rusting and falling apart, I will be using only HDPE ducts that will never rot or leak. We also plan to heat our home with radiant floor heating, a method better suited to the heavy concrete construction. We will still have ducts, but only for ventilation and de-humidification.
She mentions drywall rotting and molding, internal wooden walls being eaten by termites, etc. we won’t have any of that in our all concrete house with a specfinish gunnite surfaces.
umbrella. Instead they insist on more traditional methods used for waterproofing regular basements, glued or sprayed directly to the walls. These include bentonite clay or a “tar modified polyurethane elastomer applied as a liquid”. These directly applied methods are pretty useless if the concrete cracks more than 1/16th of an inch. Even applying something like a pond liner right over the concrete before backfill is not as good as an umbrella (away from the concrete) because it can be torn by the movement of the concrete and does not help with thermal mass.
TerraDome, like other earth sheltered builders (including Formworks) with “proprietary systems” does not use a waterproofing
Applying the waterproofing and insulation directly to the structure also excludes the surrounding thermal mass and allows water percolating thru the ground to strip it of its heat, both of which reduce thermal performance when compared with an insulating umbrella.
It also sounds like the soil around this home was not properly drained. The French drains mentioned are not well placed or of sufficient capacity to handle the location on the side of the hill. This moisture increases the weight and lateral (hydro-static) force on the walls. Cycling moisture levels are even more damaging.
An interesting side effect of applying the waterproofing directly to the structure, and then draining around it, is that you need to make a choice about the moisture level of the soil above the water proofing… Do you want it to be dry for the structure beneath or do you want to keep plants living on the surface? It is difficult to have both. Miz ended up shutting down her sprinkler and letting her plants die. Eventually, they had to remove the covering soil completely. The umbrella solves the problem by requiring that you drain only the soil under the umbrella and allowing you to maintain the moisture in the soil above.
My home will use an umbrella with three layers and I plan to go overboard on the french drains under the umbrella. It also helps that my soil is very permeable.
I think I can avoid the problems shown in this blog, but I need to keep my eyes open and be as careful as I can. I am sure the builder of this home didn’t expect these problems… And neither did poor MizBejabbers when she and her husband bought it.
Caveat Emptor! Buyer beware! When buying an earth sheltered home, you must be doubly careful to check it out before buying.
What is the latin phrase for “this may be harder to sell?” There is always some mistrust between the seller and the buyer, but this gets worse when the item, your earth sheltered home, is difficult to inspect, because it is buried, or difficult to compare, because it is unique or custom built. Economic Game Theory would suggest that because the seller knows much more about the house than the buyer (informational asymetry), he would only be willing to sell the home at a deflated price if the actually thought it was worse than the buyer thought. Sellers who’s homes have no issues would be less likely to sell for less than they thought the home was worth. This would reduce the percentage of good earth sheltered homes on the market even further. Buyers could deduce this and realize that a large portion of earth sheltered homes on the 2nd hand market are likely being dumped by their owners. Therefore, sellers would be willing to offer even less. This is why earth sheltered homes tend to suffer heavier depreciation than other homes even thought they should last longer. Blog articles and anecdotes and even random experiences with cold damp basements only make it worse.
If you want to prevent or at least reduce the depreciation of your earth sheltered home, just in case you ever need to sell, you can do things to reduce the buyer’s doubt. I will start by taking detailed photos of the construction. I also plan to bury sensors (temperature and moisture) and keep good long term records. Other maintenance and utility records also help to establish the efficiency of the home. Not painting, or other wise covering, the inner surface of the home will also help to preserve trust during the sale process. The effect of these efforts would be similar to the effect of selling a used car and including a full set of records; including gas mileage for every fill-up, maintenance records, a car-fax report, etc. Increased buyer cconfidence will translate into higher offers. Of course, it only works if you actually build a good earth sheltered home ;^)
The blog mentions their attempts to enforce a warranty or get money from TerraDome or the builder, or the previous owner, but all failed. I don’t expect to get a warranty and I will have no one to sue but myself, so I will need to select the builders carefully and make as sure as I can that the concrete mix is a strong one.
A wood stove for our earth sheltered home?
The building inspector, mortgage company and common sense will probably dictate that I should have a “proper” automated heating system in the home. I would call that my “backup” since I am hoping that I have designed the system well enough to call passive solar my primary heating system. However, I also assumed I would have a back up to the back up in the form of an efficient wood burning stove. We have a lot of “free” wood on the property (4 acres of Oak and Cherry) and you never know when power will go out rendering the other “backup” useless. There is also this idea that it may take some time to “charge” the thermal storage soil around my home (some earth sheltered homes report a 3 year period before the home stabilized), and a wood stove would be a “free” way to do that. Of course, there is also just something nice about sitting around a wood fire…
So here is my first choice, picked out several years ago… I liked that it was a full 360 degree stove. I had mentally situated it between the entry, dining and living rooms so that we could sit around it like at a camp fire. It looks simple, but has many of the advanced features you would expect from a more traditional stove (blower, outside air intake, re-burner, etc.) Its manufacturer, Focus Creation, has a lot of cool wood stove designs. I expected they would cost more than a more traditional wood stove, but this one turned out to be nearly $15k and the one on the next page of the catalog (similar, but telescoping) was $44k… It is an advanced stove, but you could get a 2012 Mercedes Benz SLK for a lower list price than that. “Ooo, but it telescopes!!!” Anyway, maybe if I already had that car, I wouldn’t mind shelling out for the unique stove…
We continued to shop around for more standard domestic wood stoves and found that they are generally inexplicably expensive… They are about the same weight as a motorcycle, but much much simpler mechanically and yet, more expensive. They are nothing compared to the technology or entertainment potential of a high end 3D TV, and yet cost much more… I wonder why that is?
Jotul F100 wood stove.
Anyway, market mysteries of supply and demand aside; I eventually ended up going with something smaller and relatively simple… The Jotul F100. I liked the arches on the door which would be similar to the vaults of the room. It is only supposed to keep 1200 feet warm, but that should be good enough for us. It does have decent efficiency, but not some of the advanced features that more pricey wood stoves had.
The main problem was the back of it… Actually, the back of pretty much all the domestic wood stoves I looked at… They all looked like junky old CRT televisions, many even had the big energy efficiency sticker like you would find on your clothes dryer. An that was before you added the even uglier blower assembly… The only solution is to put it up against a wall.
I spoke to the sales guy who was quick to correct my pronunciation… “oh, do you mean the ‘yot’l’ wood stove?” “Yes, sorry, I am not up on all the in-crowd Northern European wood stove name pronunciation”… Anyway, it “starts” at $1,168. But, at that price, you just get a paperweight. If you want the fan, that is 250$. If you want the “outside air kit” (to prevent it from sucking all the warm air out of your home), that is another $100. I don’t think the legs were even included in that base price. Then I asked about stove pipe… They sales guy said, “$800 to $2,600”. I asked him to break it down for me and he said that he could get me a deal on the first 8ft out of the stove for only $899. Well we were already past the low end of his estimate and I hadn’t even reached my ceiling yet. He said it was about 100$ a foot after that… I have since found double wall stainless steel pipe online for about 50$ a foot, so I will keep shopping around.
I also looked into the cost of a professional install… I love how they like to ask all sorts of questions and keep asking to come out and measure, but then really don’t have a very complicated formula for the price… “Well, I have never done anything like that [earth sheltered roof], but its usually either $500 or $1000.” Assuming that I look after getting the pipe thru the cement ceiling and out the outside of the dirt roof, he figured the rest of the work was on the low end, ~$500.
I don’t know if you have been adding that up, but I have to figure that my little Jotul wood stove will come in at close to $4,000 and that is before I put any gas in my chain saw… Hmpf, free wood heat indeed!
But Mr. Pronunciation did fill me in on some other rules that I was not very familiar with. The pipe must extend at least 3 feet out of the roof, but must be at least 2 ft taller than anything within 10 feet. Hmm… I have a 22ft radius house with a 10 ft radius “storm room” on the second floor. Since much of the other layout is already in place, this means I have three options for where to place the stove…
1) I keep it where it was, about 2/3rds of the way out in the living room… But then I have an ugly backed wood stove with a very tall (18 ft?) shiny metal pipe sticking out of my earth covered roof, probably with guy wires to keep it steady…
2) Move it to where the piano is currently and let the chimney climb right up the side of the storm room… I kind of liked this idea and imagined a traditional stone chimney as well as tapping into the pipe with a second stove in the storm room (some day when I find a cheaper one on craigs list). But the cost would definitely be higher and the stove would then be in a major transit path next to the kitchen. My wife was concerned about the logistics of sitting around a hot stove in the middle of a traffic pattern.
3) We move it out and put it agains the outside wall, pretty much 11ft from the tower and hope that any rising smoke doesn’t just impinge on the storm room… This is a serious problem because the prevailing winds will most likely drive it that way. On the bright side, the little pipe could appear to be coming out of the entry cottage (if we do it right). This also knocks out a window on that internal wall, or maybe reduces it to a high transom.
We didn’t really have much option for where to place the wood stove…
Anyway, this third option is what I sent the architect…
At this point, it is in the budget, and I am expecting to put in the pipe to make a hole when we shotcrete the ceiling, but I also plan to save purchasing the stove for last… If we have any budget left.
Costing this out has really undone my theory of using the fire place for “free” supplemental heating while we charge the earth that first year. I could buy a lot of convenient conventional heat with my geothermal furnace for the cost of a wood stove. However, I would still like to get one eventually for its ambiance and grid independence.
We will see how it goes.
So, why not just go with a more traditional, above ground, passive solar house?
PassivHaus construction calls for a tight thermal envelope
There is quite a range of what is considered a passive house. On the “uber” end of the spectrum is the “Passivhaus” (or “Passive house” in English), which is really a performance standard for high-efficiency housing commonly applied in Europe where high energy prices (necessity) have focused a lot more interest and invention towards this sort of housing… There are tens of thousands of these built in northern Europe and some here in the USA also (a greater challenge due to our tougher climate). To be certified as a “Passivehaus”, the home needs to meet a few strict requirements including low annual heating demand, less than 15kWh/m2 (4746btu/ft2) per year, and be as airtight as possible, the building must not leak more than 0.6 times the house volume per hour, as tested by a blower door.
Basically these are just standards of energy efficiency, and “Passivhaus” owners typically claim a 90% reduction in their heating bills. I guess it is a good thing to have standards and metrics, but the more I thought about it, the more hollow it sounded. While I am interested in reduced energy bills, I am also interested in increasing my robustness against interruptions to the grid. I am even more interested in climate comfort, temperature stability and a healthy environment. Don’t get me wrong, when I am done, I will check to see if I met the “passivhaus” standards, they are just not my focus.
Passivehaus construction is typically boring because all the money is used up on the super insulated and sealed walls
A more interesting example, but still a simple square to reduce the cost.
When I studied examples of Passivhaus construction, particularly the American examples, I did not think they were taking the correct approach. For instance, they spent a fortune on R60 insulation all the way around… The insulation its self is only part of the cost, they first had to balloon frame the walls with trusses instead of 2x4s, and then sheath both sides for stiffness, then they created an airspace and a second wall (double envelope house). Most also used a “cold roof”, which is a double roof with an airspace between (and costs about as much as two roofs). Most use triple glazed casement windows which needed to be imported because they just don’t make those here. In some cases, they put 14 inches of rigid insulation under the slab and 6 inches around the foundation. A lot of expense is also tied up in making sure that the envelope is well sealed against infiltration, yet permeable enough to allow trapped moisture to escape. In terms of performance, they typically get large temperature swings on a daily cycle, the passive solar heating is also not uniform within the space. In one example, I read about plastic toys melting in the living room. Because they are trying to keep the construction costs manageable and the volume to surface ratio as high as possible, most passivhaus examples I have seen are very simple boxes ( upper left) although many can still make those boxes interesting like this one (right).
I am all for fuel efficiency, but some “fuel sippers” crack me up.
It reminds me of those automotive “fuel sippers”. These are people who spend thousands more for a Prius or other hybrid, then drive it very slowly (coasting when ever possible) and risking their lives as big rig trucks over take them, in order to save a few dollars in gasoline. I had one such colleague tell me that she is saving so much money on gas that she “drive[s] all the time now”, she didn’t understand why I laughed.
Leakage is the main obstacle to keeping a home comfortable in a challenging environment. Sealing a home above ground is a difficult challenge. Think of it this way, the strict PassivHaus inspectors are impresses when you only leak 59% of your homes air every hour! The average home has much higher infiltration rates. While it costs a lot to seal a regular stick frame home above ground, below ground construction is naturally air tight (instead we worry about bringing in enough fresh air). Also, an earth sheltered house has insulation and thermal storage. Thermal storage works as a sort of dynamic insulation. Our particular earth shelter plans also call for some cellular concrete (R~1/inch) and a rigid insulation umbrella. It should give an average roof R value of 47, but at a relatively low cost (more on that later).