The Efficient House: A Passive Solar, Earth-Sheltered Log Cabin


The idea of building my own house wasn’t born out of any nostalgic notion, it was simply my frugality in its most radical form. Years ago, I read a book called, Mortgage Free and that’s when the seed was planted. The passive-solar designs in Michael Reynolds’ Earthship confirmed what I knew a house could be, but I didn’t like the idea of hammering dirt into thousands of tires to create a wall of thermal mass. This, along with Mike Oehler’s ideas and examples of underground housing using logs proved it was possible to take a log cabin approach with alternative building styles. We bought some property in the mountains with plenty of timber on it and I started planning how to blend several of these ideas into a highly efficient building without sacrificing aesthetics. My Dad (who was invaluable during this entire process) worked out many of the engineering details and we got busy cutting and peeling trees for the passive-solar, earth-sheltered log cabin.

If you’re not familiar with these terms. Passive solar is simply orienting the long axis of your house to solar south and putting the vast majority of the windows on that side to collect the free heat from the low angle winter sun. Since the sun angle is much higher in the summer months, you simply place a nice overhang on those same windows to block the hot summer rays along with the undesirable heat. 

The earth-sheltering part plays several roles. First, the earth keeps a fairly constant 50-55 degrees Fahrenheit year-round, so this helps keep the house cooler in summer and during winter, the interior only has to be heated an additional 20 (ish) degrees. A traditional house would have to pump in a lot more heat to make up the difference between the freezing temps outside and the 68-70 degree comfort zone inside. Another bonus of earth-sheltering that pays off during our hot, dry summers is fire protection. Wildfires are one of the primary threats to rural homes in the Pacific Northwest, so I opted to bank the earth up to the eight-foot mark on the North, East and West sides. Concerning fire-protection, the South side of my house is sided using the Japanese technique of Shou Sugi Ban where you char the wood making it more resistant to fire, rot and insect damage. I think it gives it an awesome rustic look that blends with the natural design and the tones of the surrounding environment. 

The 65 x 25 structure uses logs (Larch, Doug Fir and Cedar) with butt and pass joints that utilize rebar “nails” down the length of the log and at joints to affix them to the log below. We built the South wall of the house out of dimensional lumber knowing that if we used logs, most of them would be removed to frame the vast amount of windows for the passive solar effect. The below-grade exteriors of the earth-sheltered walls are protected by 45 mil EPDM with a french drain pipe at each base to carry any water away.

The plumbing is a little different in this house as well thanks to the book: Create an Oasis with Greywater. We don’t have a septic tank or drain-field. Instead, we use a grey-water system with an outdoor (downhill) soak-away that irrigates ornamental trees and other vegetation. We use a compost toilet system based on the Humanure Handbook and it’s worked out great. My Dad convinced me to rough-in the plumbing lines so I can add a traditional toilet and septic system if the romance of the compost toilet idea wears off or I get old and want a more hands-off system (whichever comes first).

The building police reading this are probably developing a sink-hole sized ulcer thinking, “How is any of this legal? What about codes?!” Well, we specifically chose property in a county that prioritizes the privacy and independence of its citizens, so our house is an unpermitted structure without the hassles and costs associated with asking permission and padding the pocketbooks of people who tell you how to build your own house.

I’m proud to say that every stage of building was accomplished by just my dad and me. From the dozer work clearing the land to foundation work, plumbing, flooring, roofing and electrical, we never used a contractor and saved a ton of money in the process. Since we were cash-flowing this project, my family and I lived on-site for 16 months in a 36 foot RV and even hauled our water until the well was finished! After the house was livable, we sold the RV to keep the project moving forward. 

The inside of the house is fairly normal save for the rocket-mass-heater we use to supplement the passive solar heat. I was able to build this myself using the book Rocket Mass Heaters and other tips from You can deep dive this using the links mentioned, but basically, it’s a stove that uses a fraction of the wood that a traditional stove would and it captures the majority of that heat in the thermal mass (rocks and pea gravel in my case) before it goes up and out the chimney. We light the stove in the evening for about 4 or 5 hours and the mass stays warm long after the fire is out, slowly releasing heat until we’re ready to light the following evening. A typical 4-hour burn uses about a milk-crate amount of wood, so we only use about 2 cords of wood to get us through the winter.

The house was a tough build, but very rewarding and in my wife’s opinion (which matters most), a huge success. In addition to my dad, I had some additional help along the way from both of my fathers-in-law and even my wife and kids. I’m grateful for their support and effort to see this through and I can’t begin to explain how awesome it feels to live in a house that I built and be mortgage-free as well!