So, at some point, I decided that I wanted to build myself an earth sheltered home. This is not like saying I would like to build a colonial or a bungalow or something that has some know design DNA, or that uses known systems and processes… This is a wide open endeavor with a wide range of possibilities and even more unknowns. I have always been an Architecture buff, so it would have to be nice looking and functional. The engineer in me wanted to build an “engineered house”, what ever that is… I wanted it to be light, but authentic, and a bunch of other vague ideas that would have left any architect scratching his head. Of course, this wouldn’t just be my vage want list, I had a wife and kids who were also giving vague input. My kids wanted tunnels that connected things impossibly (they were not worried about the engineering or cost). My wife’s wants were harder to nail down, but she knows when she doesn’t want something ;^). But everyone was pretty supportive of the overall idea, so I started trying to add specifics to the vision…
Of course, I started by searching the web for other examples (check out my links page). The range was quite wide, from free-form (curvy) shotcrete vaults without a straight line in sight to more “practical” homes with concrete block walls and simple flat roofs. Some basically just buried Quonset huts (maybe a nice cottage idea some day). I have a big folder full of pictures in my computer. I wish I could share them all here, but getting permissions would be too much pain. Instead, here is a google image search, and here is another. The variety is amazing.
Many of the photos came with detailed blogs about their construction. Many were home builders who kept their budget low and did all the work themselves. I did like that idea, but I am full time employed and too busy to build my own home by hand. I am willing to spend a little more (not mortgage phobic) and wanted something more architecturally interesting. You could also see that many had a lot more money than I did (Bill Gates lives in an earth sheltered home), so I won’t be on that end of the spectrum either. There was also a strong contrast between those that were built without any compromise on the scientific principles (no north windows, brown cement floors, insulating shutters, tromb walls, etc.) and those that were built as art, without any consideration for the scientific principles. I wanted to stay married, plus I am a little artsy myself, so I plan on compromising where I need to. For instance, I plan to have a number of windows on the north side to capture the view even though I know they will leak precious heat. I also plan to have rugs on my floor although they inhibit solar gain into my storage mass…
I shared these ideas and pictures with my wife in an “agile” way, trying to get as much input as possible. For instance, i found it interesting that my wife really liked the concrete block or “ICF” idea because she liked the simplicity of the Lego-like construction method. I also discovered that she thinks about thinks like curtains very early in the design process… ;^) So, we initially co-imagined a rather rectilinear cement home (but with fibonacci proportions) with an undefined roof type (research pending) covered in some unspecified thickness of earth…
We cut these standard room sizes out and arranged them on the dining room table
For the actual layout of the home, I got some plan books and looked at single story homes that were about 2400 square feet. I took the room sizes from those and made a bunch of scale room tiles. Sherri and I printed these out and shuffled them around endlessly as we talked about design concepts.
- How do we divide the public and private areas of the house?
- How do we keep the TV noise out of other areas?
- Where can Simon’s office go? (I work from home 80% of the time)
- Why do people put laundry rooms by the garage instead of next to the bedroom?
- Do we need somewhere for our guests?
- How can we keep it affordable and make it interesting?
Also, we didn’t like the idea of an entry that appeared to be leading to a bunker. We wanted the functional areas of house to be on one floor, but I liked the idea of a “storm room” like a gazebo/conservatory on the roof that would give me 360 degree views. I thought a zero flush urinal in the boys bathroom would be a good idea. I really wanted a courtyard, but that idea morphed into a more practical green house or sunroom.
We some how expected that we would be entering from the North side (the earth bermed side) and wanted to avoid the bunker look, so we came up with the idea of the entry cottage. It would look like a little house to disguise the entrance to the underground portion of the house. I liked the idea of a modest little cottage concealing the larger home inside it.
We worked out the look of these rooms with extensive notes (in ppt) for each room.
Layout from Nov 2007, featuring the entry cottage and a decent sized courtyard. It also had a lot of small sunrooms… Funny now to look back at this.
By Dec 2007, I had realized that the courtyard wouldn’t work well in our norther climate, and moved it to the south side
By July 2008, we shrunk the courtyard, tilted some rooms (solar angles) and added the start of the rotunda idea. The walls were still straight because I had not yet figured out a roofing plan. I was considering individual square shotcrete domes for each room.
I used my ppt “skills” to record/share our ideas and layouts for each room in a rudimentary, but useful way. We could edit these easily as we tweaked our design.
I really spent the most time thinking about the structure of the house. I was I going to safely hold up all that dirt without spending too much money or having a house that looked like a bunker? I ended up with this idea of a central tower (the rotunda), with site-cast concrete ribs radiating out from it. There would be shotcrete arched vaults between the ribs passing the load to the ribs, which passed the loads to the ground. It was this central “structural umbrella” concept that changed the design from angular concrete block to the more circular layout built with shotcrete. It was somewhat of a Eureka moment for me as I saw it all come together in my head.
From there, I spend few minutes here or there each day for a month researching shapes for the ribs. I ended up looking into the mathematics of natural shapes such as shells or eggs. These had been studied by ancient mathematicians and Renaissance men and there was a lot of information on the web and in books. Since the ribs would need to be cast on site and lifted into place, I was particularly interested in designs that could be drawn in the field with just a piece of wire (or a stick) and a pencil. I tried these shapes (such as the golden egg, a mathematically sacred shape based on the golden ratio) built into arched ribs at many different angles and simulated loading the ribs with an estimated 68000 lbs of load until I eventually settled on a particular orientation of a 2300 year old euclidean 5 point egg design that had the right proportions.
Golden Egg design
“Golden egg” on its side as part of a rib. However, the heights at the ends were not right, so I would need to tilt it up…
Golden egg, 19 degrees tilt, but still not the right proportions…
Golden Egg, 38 degrees, still not right…
I tried a lot of other eggs, the Euclidean 4 point, the Moss Egg, etc. But this Euclidean 5 point egg, tilted at 41 degrees, had the right clearances, proportions and strength…
I created computer simulations for most of the promising candidates and loaded them with the estimated 68000 lbs that I expected they would each need to carry…
Eventually, by the end of 2008, I got into Autodesk Revit where I could CAD up the model in 3D. Now it was getting interesting. We had spent a lot of time discussing each little detail and there was a reason for everything. All the rooms had purpose, even the angles of the windows were designed to line up views thru the house (and even functioned as a solar clock).
An early version in Autodesk Revit, windows are missing, furniture is still sitting outside, but you can get the idea.
At some point, I hit that little button that calculates the square footage. Ouch, 3917 sqft, plus another 1035 sqft for the garage. We could not afford that much house… How had this happened? We had started from the rooms of a 2400 sqft house, but then probably added a few feet with each alteration. We ended up making some drastic cuts to get it back under control.
Our original footprint was much too large, the house had to go on a diet. The purple outline is the original floor area, the white walls are the shrunk down version… At least for a few days… A lot has changed since then.
Then we went out to shop for some land… I will save that story for another day, but the punch line is that the lot we bought had primary access from the south and best views were to the north, so we had to scrap much of what we liked about these these early designs… More on that later.
Sherri looking at our new pond back in 2009. Buying land made the whole thing a lot more serious, if no more immanent.
The point of this site is to assemble and share some of what I have learned about earth shelter design and construction (as well as my extrapolations), in addition to journaling the design and construction process of my own earth sheltered home. My wife, Sherri, is a big part of that; so I just hooked her up with a log in so she can post also. Hopefully she will find time between all the other tasks that already keep her very busy.
We have not really got started on the construction yet, so things are pretty quiet right now. We are really somewhere in early phase II development with the architect and structural engineer and I am still waiting on getting drawings that look like what I have in mind. Working with an architect after getting so far on your own is a lot like taking one step back so you can take two steps forward. In the mean time, I will probably try to catch you up on the back story of earlier steps that we have already taken.
I have not told any of my friends about this site yet (because the content is not ready), but when it does get going and my list of subscribers are not all living with me, I hope it can be a little interactive.
I am sure you are not all as interested in the technical aspects as I am. Some are probably just interested in following the story as we build this crazy house. The Technical aspects will mostly be cordoned off in the Tech Notes area. The story is under the blog… If there is some particular aspect you are curious about, let me know and I will write about that also.
For now, it is a nice evening outside, so I am headed out there.
∞Posted on July 2, 2012 by
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).