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).
I keep checking with my wife and a few other people (architect, engineer, builder, friends, etc. but no qualified psychiatrist yet) and I am told that I am not crazy. So then, why would I want to build an earth sheltered house?
Origins
I had just bought my first home when the “Northeast Blackout of 2003” occurred. My new home was poorly built and thinly insulated and had no backup systems. The blackout clearly demonstrated that my home was not designed to keep us comfortable without consuming vast amounts of energy. Maybe at some point I will share some of our regular electricity and gas bills, but suffice it to say they are large. However, I was thankful that the 3 day power outage had not happened in winter, because we also had no backup heat. Since that time, there have been several shorter-term winter power outages where I felt my homes temp drop to the low 50’s in just a few hours. A number of other times we have had the natural gas shut off while the gas company was doing repairs. Our furnace (like most) was designed so it would be worthless if either the electricity or the natural gas stopped flowing. I thought back to the Quebec power outage of 1989 where 4 million people lost power in the middle of winter for up to 33 days. Can you imagine if some freak storm did that in our area? Neighborhoods like the one I currently live it would be devastated. I became interested in moving my family to somewhere more stable.
In 2006, Al Gore released his award-winning “inconvenient truth” about global warming and sea level rise and then (several years later) infamously purchased a 9 million dollar, 10,000 square foot ocean side (sea level) home in Malibu CA. The irony between his stated belief in an impending carbon-induced global-warming seal level rise and his actions to purchase such a huge (carbon footprint) home right at sea level helped push the story all around the world. While others were laughing, I had to think, “If you really believed in global climate change bringing extreme weather, what sort of house would you build?” What if you also believed energy prices would continue to rise? Or if you believed our energy distribution systems were crumbling or threatened?
There have not been very many generations that made it thru their whole lives without being impacted by war or weather or at least a fuel shortage. Consider England 100 years ago… In 1912, two years before the first world war, England had the largest army in the world (and its first airforce), the most advanced education system, a large number of colonies that kept resources and fuel flowing cheaply to its shores, the Titanic had just been built, but not yet sunk, non-stop flights to Paris had just begun, etc. England was on top of the world and I am sure that many Englishmen assumed it would stay that way, but the only constant is change.
If we look at our current situation, do we expect things to remain stable for the rest of our lives? What do we expect will happen to the costs of energy (barring the invention of a
nuclear fusion power plant)?
Every one expects energy prices will continue to rise. Do we see our energy distribution infrastructure getting better?
Nope, crumbling. How about our governments ability to look after us?
Soon they will be struggling just to pay the interest on the debt. Taxes will rise, jobs will be lost, etc. If you agree that one or more of these things are likely, then what sort of home should you build?
How about the weather? Regardless of if you agree that global warming is caused by our pollution or just some natural cycle thousands of years long, the data does seem to indicate that it is getting more extreme… (perhaps weather like this has happened before, but can we at least agree that extreme weather is possible?) More tornadoes, hotter summers, colder winters (the winter between 2011 and 2012 was an anomaly with the jet stream (arctic oscillation) that kept the bottom half of Michigan very warm by keeping all the cold further north, but next winter could very well see the Jet stream come lower and blast us with a colder than usual Canadian winter.) The thought of riding out any of these sorts of events, or even a regular Michigan summer, where my AC struggles to keep the house at 80°, in my flimsy 2×4 and vinyl siding home was not appealing. Tornadoes and strong winds could easily rip my home apart. We had a hail storm last year that put a number of holes in my siding. I always chucle when I see people on the news after a storm (or fire) vowing to “rebuild” after their homes were totally destroyed. Why do most of them build the same type of weak structure that blew away last time…? “Oh no, ya see, this time I used these here hur-can’ straps to hold my roof down…” “Great, much better.” Instead of just hoping for mild weather, why not build a safer way?
So I started looking around. I started with more traditional passive solar concepts, along with the super insulated “
passivhaus” concepts. Some how, I don’t even remember when exactly, I became aware of this “earth sheltered home” idea as a way to moderate the volatile environment around the house. I liked it and started researching, casually at first, but then heavily. I couldn’t find an “off the shelf” idea that I liked. For instance, many of the homes combined earth sheltering with passive solar. This was a good combination, especially in sunny/freezing Minnesota, because the passive solar energy could be stored by the massive cement structures needed to support the earth, and then returned to the home over night. But in S.E. Michigan, we only have 21% sunshine in January, so traditional passive solar with a daily cycle probably wouldn’t work very well. Then I discovered this idea that I could cheaply incorporate the earth around my home into my “solar mass” so I could store even more energy, perhaps several days worth. John Hait takes it further by suggesting you include enough mass to hold the home thru a cold dark winter. I liked that idea, but it called for letting solar heat gain directly into my home during the summer. This would result in over heated summers, and then thanks to losses found in any system, colder than comfortable winters. Then I started reading about solar hot air collectors and it occurred to me that I could reserve my home for
living in and build an external solar collector to “by-passively” heat the earth under my home. If the pipes were buried the right distance under the home, the stored heat would take months to reach my floors at just about the time that I needed it. Also, since I could push the solar heater up to much higher temperatures, I could drive much more heat into the earth (ΔT), and I could be charging up the earth away from the home to take greater advantage of the earths heat conduction lag time. I will talk about many of these ideas in the “Tech Notes” pages of this site, such as
Earth Shelter Basics,
Umbrella Basics,
Passive Solar,
Soil Properties and
Earth Tubes (still working on this last one ;^).
I now had the basic idea, I would look to build a “
by-passive” (my own term) solar earth-sheltered home in S.E. Michigan… I shared the idea with my
wife and she actually LIKED IT! Well that was helpful. This is not the sort of thing you embark on without your significant other. Of course the kids were on board, they put in their requests for secret rooms and tunnels. So I started planning. I used Autodesk Revit for the drawings and tried a number of different configurations. I crunched numbers for engineering and cost, etc.
Back in 2007, I told my friends that I would probably start building in about 2 years… Well, breaking ground as been at least 2 years away for quite a while now. The 2008 housing crash slowed us down on the sale of our current house (
its value dropped to 1/3 of its 2003 purchase price), but it did make it cheaper to
buy the land we would need. Buying the land in 2009 was clearly a serious step, however, the orientation of the lot forced a serious redesign. Now that we have hired an
architect and an
engineer (two serious steps toward the final goal), had meetings with a builder, got quotes on windows (and more), I would adjust that estimate down to less than one more year (giver or take a few). In fact, we would like to start building in 3 or 4 months, but a lot would have to fall into place for that to happen.
This website will journal my progress as I prep for building and then eventually (Lord willing) as I break ground and begin to actually build this crazy home… We will probably start with some past-tense posts to catch you up to where we currently are…
“The distance between insanity and genius is measured only by success.” Bruce Feirstein
