Lately, I have been thinking about where creativity comes from. I have read articles on the subject, sat in on Ted talks, etc. but this is my take on it.
Creative attributes
Creative people have a creative mindset that is open to ideas and looking for inspiration all the time. If you were a painter, you would pay much more attention to the visuals around you, you would see more colors. You would pay much more attention to how things look. I remember going to an amusement park after my first year of engineering and all I could see was trusses, momentum, metallurgy and free body diagrams everywhere. Since heading down this earth sheltered path, I constantly come across earth sheltered ideas including everything from welding and concrete to container gardening and tile setting and all the plumbing, HVAC and solar in between. In the old days, it was a lot harder to find relevant new ideas, but the internet has changed all that. Google and YouTube are really stimulating creativity by increased your chances of stumbling across things related to your earlier interests. The world is at your finger tips…
Creativity is also a collaborative process. Yes, you can create something on your own, but even then you are building on earlier ideas you probably got from others. When you collaborate, your creative juices flow more freely. If you don’t collaborate with your spouse during the design of your earth sheltered home, you’re probably gona’ have a bad time. If you collaborate with experienced builders, you could save a lot of time and money. Collaboration with engineers or other earth sheltered building enthusiasts is a great way to get ahead of the learning curve. I tend to have surges of productivity after good discussions with potential trades people who have a specialty in a certain area… No one is universally creative. Instead, we are creative within certain fields. Someone who is musically creative may not be great at decorating or cooking. There is also such a thing as engineering creativity or design creativity… Again, this all goes back to your focus. The more passion and focus you have for a given area, the more creative you can be within that field. When building something like a home, you may need to tap into the creative fields of others to get the job done well.
Passion for an idea helps by compelling you to put more effort into it. Building an earth sheltered home is not for the feint of heart and you should not even consider it if you are not at least a bit passionate about it.
The creative process
Creativity is much more than just a flash of inspiration. In truth, there is a long process of working thru ideas that come in sparks and need work to bring to reality. There has been research into this field and I probably got some of these ideas from various books, but since I was in the mindset, I have been subconsciously scanning for them in my own experience. If you leave out elements of this process, it will stunt your creativity. The inverse is also true. You can stimulate your creative by consciously putting effort into these steps.
Preparation is the first step. It could be research on the topic or practicing essential skills. It could just be your full life experience that puts you in the position to be creative in a certain area. For my earth sheltered home, I have a couple engineering degrees as a good solid foundation, but then I have read more than 2 dozen books on the subject and as many magazine articles as I could find. Every bit of information helps me interpret later knowledge, and new information may lead to a rethink on earlier concepts. I have become an expert (at least a theoretical one) on many related topics. Actually building an earth sheltered home will add to my experience. Reading this blog counts as preparation for building an earth sheltered home. Your background may be unique, perhaps it is in a trade that would be just as useful as my engineering degrees, but you will probably want to read a few books anyway. Passion for the subject will compel you to prepare.
Next comes the incubation phase. This could be over night (sleep on it) or during your daily life between preparation. I get a lot of good thinking done in the shower without computers or other people to distract me. Since you are in a creative mindset, your brain is tuned in and scanning for relevant inspiration. Your subconscious is working to put everything together. Opportunities for collaboration come up and ideas come to the fore. No one really knows how it all works in our heads, but we have all felt it. It is my number one excuse for procrastination. It is why people can spend years designing a home, and then still want to make changes as it is being built (which can be pricey).
After you incubate all that important preparation, you get sparks! Some people would have you believe that the creative spark is the most important part of the process, but it is just a result of doing the first two steps right and then being open to what comes out. It may be that more “creative” people are just more “open” to their sparks (along with having more passion and doing more preparation/practice). I remember the day that I figured out that I would use the open ends of my radiating vaults as dormers… It solved a design problem that I had been mulling over for a while and it was great feeling.
Some people get too many sparks, not all of them are good and too many can be distracting. I guess it is key to know the difference. You need to carefully select the right sparks to develop. Here again collaboration can be helpful. Running a crazy idea by your spouse can help. In many cases my wife (who is smart, with her own masters degree, but doesn’t have the same preparation in the earth sheltered field as I have) has no idea what I am talking about half the time, but I find that just explaining the idea out loud to someone else can help me decide if I should keep it or trash it. Some ideas have been trashed and then dug up later when other information increased their value.
Cross section showing the sloped front of the house with the vault end as the dormers. It may not seem like much now, but I liked it much better than the large flat front or fake mansard roof I have seen on most other earth sheltered homes.
After an idea/spark is selected, you need to elaborate on it. The devil is in the details… You think you have a good spark, but just wait until you CAD it up, or do the math/trig, or combine it with other ideas. It will either develop into something useful or be proven a bad idea. Elaboration takes work, planning and maybe even some experimentation. In my case with the spark of treating the ends of the vaults as dormers, I quickly found that if I sloped the dirt (like earth on a roof) at something near the angle of repose (lets say 45°) from the large end of a vault, it meant that I had no dirt at the edge of the roof and significantly reduced coverage on the outer half of the roof. Visually, the dormer was too large and I still had to deal with how to retain the earth at the end of the vaults. I was just about to give up on that spark, when it occurred to me that I could bring the front edge of the roof forward. Suddenly, the dormers looked right and the earth coverage on the home was sufficient… Of course, now I had to work out another problem (which some architects call a “pattern”), how to create an overhang strong enough to support that earth?
Architect Ludwig Mies van der Rohe (1886-1969) is famous for saying “God is in the details”, I like that better.
This process of preparation, incubation, spark, selection and elaboration is not just a linear one. It gets repeated over and over again iteratively. Problems appear and creative solutions are found. Costs are estimated, ideas are scaled back, etc. It takes time and work. It is a journey and I am enjoying it.
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.
The site: 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 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.
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.
The construction: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.
The waterproofing: TerraDome, like other earth sheltered builders (including Formworks) with “proprietary systems” does not use a waterproofing 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.
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.
Conclusion: 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.
Earth Sheltered Umbrella Basics
Umbrella Origins
The idea of extending the insulation out horizontally from the roof line of an earth sheltered home (an earth sheltered umbrella) was first presented to me by Earth Sheltered Housing Design, prepared by the University of Minnesota. (In Minnesota, with its very cold, but very sunny, winters, passive solar earth sheltering makes a lot of sense. This lead to government incentives and funded research which further increased its popularity.) The idea is very similar to the “Frost Protected Shallow Foundations” idea that has been widely used in Scandinavian countries since the 1940’s. John Hait is the most famous for developing and popularizing this idea, I think he also coined the “Umbrella” name. In his book, he talks about originally coming upon the idea as a way to simplify the application of insulation to his geodesic dome home. I hope to further improved on the concept with my “by-passive” heating idea that avoids overheating the home.
Umbrella Theory
The basic idea is to use a few inches of rigid insulation to form an underground thermal umbrella that further separates the home and the soil around it from the above ground air temperatures. It is also important that the mass of earth be thermally connected to the home its self. When summing up static R-values, the order of the layers is not very important, but by placing a thick layer of earth between the home and the insulation, the thermal inertia and dynamic R value increases dramatically. This is simply taking the basic concepts and components of an earth sheltered home and rearranging them for even better performance.
Soil is a poor insulator compared to modern expanded or extruded polystyrene (EPS or XPS), but it does have some R value (which is why it was used historically and by animals). The R value of soil is proportional to many things, including the distance the energy must travel thru the soil, the moister content, density, soil type, etc. Above the soil, vegetation, and even snow, can add additional insulation. In terms of “dynamic” R value, soil brings low cost thermal inertia to the design.
Soil can also absorb and retain warmth like a capacitor. You know that heat flux thru a medium is inversely proportional to its R value… but Fourier’s law also states that it is proportional to the temperature difference across the medium. Just as pressure pushes flow or voltage pushes current, it is the temperature difference that pushes the heat thru a conductive medium. However, in a material with high thermal capacity, such as soil, some of the heat is absorbed instead of transmitted. As the material heats up locally, there is less and less local temperature difference remaining to drive the heat transfer. In above ground cement walls, this is known as “dynamic R value” and can dramatically improve the thermal comfort of a building in certain situations. Below ground, the much greater mass leads to a much longer cycle and an almost steady state R value improvement. This phenomenon is the same one that leads to the soil temperature profiles we discussed in the Earth Sheltering Basics.
Above Ground Note: Dynamic R value is often “sold” by ICF dealers and proponents. It basically describes the additional thermal inertia (resistance to change) in the wall during temperature swings from one side of room temperature to another. For instance, in the southwest, you may have a very cold night followed by a very hot day. High mass walls cool down during the night and provide dynamic insulation into the hot day as they warm up again. If the following night is cool, the warmed up walls continue to stabilize the home temperature as they cool down. However, this benefit is dramatically reduced in areas that are colder (or warmer) than room temperature both day and night. In temperate areas like Michigan, air temperatures do fluctuate over any 24 hour period, and dynamic R value can bring some moderation, however, both daily extremes are typically on one side of the desired internal room temperature, so the energy transfer is one way and “dynamic” effect doesn’t really happen. In temperate regions, wide temperature changes are seasonal and the Static R-value and the temperature outside the walls is much more more important for calculating heat loss. On the other hand, an earth sheltered home provides a lot more mass than an ICF wall, enough to moderate seasonal changes. Also, 6 inches of insulation with static R-values of 60 to 100 are typical for an earth sheltered umbrella and the dynamic-R value of the soil on both sides is a bonus.
When you bury a wall, the deeper portions are further from the surface. The heat must travel further to reach the surface. Distance to the surface increases the resistance to conductive heat flow presented by the soil (aka R-value)…
Uniformly applied insulation is a throwback to above ground construction and is less efficient for an earth sheltered home
Due to the longer path to the surface, the total resistance (R-value) is greater near the bottom of a fully insulated wall. Taking the path of least resistance, heat flux is therefore greater at at the top of the wall. We could reduce the heat flux at the top by adding insulation there, or we could make better use of the same amount of insulation by taking some from the bottom and using it higher up the wall where the heat flux is greater. (Again this is similar to what many smart above ground builders have done for years in terms of concentrating insulation under the perimeter of the slab.)
Re-position the insulation for improved efficiency
Re-positioning the insulation further up the wall can balance, and overall reduce, the heat loss without increasing the quantity or cost of materials. It is important to note that, for conduction, The R values are simply added up (commutative and associative properties of addition) so it doesn’t matter what order the R value components come in, the total R value is the same regardless of the order of the layers. These two concepts open a world of possibilities for optimizing both the insulation and the thermal mass.
Increased thermal mass increases thermal stability and capacity for passive solar homes
We can increase our thermal mass simply by including some soil under the insulation. Heat energy follows the path of least resistance and will either pass thru the the rigid insulation or take the longer path down and around the insulation to the surface. The parameters of the design (thickness and extent of insulation) can be adjusted to minimize the heat loss for a given quantity (cost) of insulation. One major flaw with this idea is that it could be difficult to install.
Extending the insulation horizontally past the edge optimizes the amount of thermal mass between the interior and the insulation
Another idea is to take the same quantity of insulation and extended it out horizontally from the edge of the buried roof. The R value of the earth plus insulation can be the same or greater, but the thermal mass is definitely maximized. This can be done after the walls are backfilled so that construction is as straight forward as laying insulation on the ground. Tilting the edges down a little at the perimeter would help with diverting any sub surface water away from the home.
The University of Minnesota wanted to use about the same amount of insulation as a regular home, so they tested this with a 5.6ft extension and showed overall thermal performance, particularly for the summer time. John Hait was trying to insulate a geodesic dome, so he included some soil over the dome to simplify the shape and then extended the “umbrella” 10 feet past the sides. He also saw very good results, but wished that he had extended 20 ft.
John Hait’s schematic to illustrate the layering of his umbrella (on the left)
Rain Umbrella
One topic often discussed with these earth umbrellas is water penetration. The concern is that cold water (from cold rain or snow melt), with its greater thermal capacitance, would percolate thru the soil, steal much of the absorbed heat from the earth, and dump it into the water table. This is why John Hait used his three layers of plastic sheeting to waterproof his umbrella. I also plan to layer my insulation with waterproofing, but I am less concerned about this theory since conducting a full scale experiment. In my experiment, I buried temperature and moisture sensors at various depths below ground. I had two sites. One was the control site and the other was covered in a few hundred feet of plastic water proofing buried 1 ft below the ground. I expected to show how much heat was lost from the earth due to this percolation. However, watching the data come in over the past year, it is clear that the effect of the rain on the soil temp is only in the first few ft near the surface.
The waterproof umbrella does have several other benefits. Primarily, it helps to reduce the amount of water in the soil around the structure. Any time you build below the earth, you need to be very concerned about water in the soil. Reducing the water content of this soil reduces the lateral pressure on the structure, it reduces the chances of water penetrating the cement and causing other damage, etc. Traditionally, earth sheltered home builders dealt with this water by severely over draining the soil around and above the earth shelter. In many cases, this actually lead to surface conditions that were too dry to support plant life. In contrast, the umbrella serves as a divide between the moist plant bearing soil above and the well drained earth shelter friendly soil below. As a bonus, the dry and almost airtight soil under the umbrella is also unattractive for most digging pests, tree roots, etc.
It may be a good idea to provide a vent in the top of the umbrella to let radon (if any) escape…
Umbrella Construction
The robust umbrella construction recommended by John Hait includes 2 layers of XPS rigid foam insulation (thickness tapers off toward the edges) between 3 layers of 6 mil plastic sheeting (or pond liner in some cases). The XPS foam is recommended because water absorption tests show that it will absorb no more than 0.3 percent (by volume), this is 1/1oth of what the EPS foam will absorb. Water absorption reduces R value.
Note: I have since discovered that EPS may actually be a better plan… For more info, see my page on insulation. A switch to EPS cuts the cost of the umbrella in half, so it is well worth considering. But when I started my own construction, I bought 2″ XPS ;^)
I suspect that thinner plastic (4 mil or 2 mil) could be used on the lower layers. The layered construction is intended to make it difficult to puncture the umbrella. If one or more layers are punctured, any drips that pass thru tend to run along the underside of the plastic which is sloped towards the perimeter. The primary downside to this plan is that if moisture does get thru, it becomes almost impossible to determine where a leak has happened because it may run along the plastic and enter the home some distance away.
I discovered that there are many places selling used billboard vinyls. These are 15 to 17 mil thick, waterproof and tough. They are way over designed for their short life on the side of the highway and still have a lot of life in them when they are taken down. Some companies will even glue them together into large 200’x200′ pieces… The prices are great, but shop around a little. I found that the store I linked to in this section had prices about half of what other more generalized building material re-sellers were charging.
The layer of soil below the umbrella is there to facilitate installation (easier fit was one of the reasons the idea came to John Hait in the first place) and to keep the umbrella from rubbing against the cement. It will be important to keep sharp rocks and other “dangers” out of these early layers.
Anatomy of our planned Umbrella (plans have changed a little now. I will redo this pic when I get a chance ;^)
Our early plan was to waterproof with Zypex (or equivalent) and perhaps even a layer of bentonite clay in some areas. However, I am now more likely to go with a painted on rubberized waterproofing… Additionally, many earth sheltered home builders also add a layer of used carpet over the top of the umbrella for further protection. I have not tried it myself, but I imagine that it is actually quite difficult to accidentally put your shovel thru polyester carpet. And the synthetic nature of most carpets ensures that the protective barrier will have a very long life.
Initially, my design also included some cellular concrete (aircrete) on the roof between the vaults to fill in the gaps without adding too much weight. This is not shown in the above image, but would be found below the top layer of cement. Cellular concrete has a pretty decent R-value and can also be formulated in a way that makes it naturally moisture resistant. However, due to the lack of availability of reasonably priced cellular concrete in my area, I briefly considered starting my own company and then decided I had enough on my plate and would just fill the gaps with EPS rigid insulation. Either method could be covered with a thin (2″) topper layer of waterproof cement.
So, in summary, the umbrella is an alternative placement of insulation that allows the many tons of earth around the home to be incorporated as part of the thermal mass of the home. An umbrella extending 20 ft around the home would be similar to an additional R100 (20 ft x R5/ft) against a normal wall. The high thermal capacity of the soil also stores heat and increases resistance to heat flux. While slightly reducing the volume of thermal storage under the umbrella, the edges are sloped down to enhance runoff (water management).
Simplistic comparison between direct insulation and umbrella insulation
