Note: I am not a professional architect. Do not follow these instructions to the letter unless you're very brave.
An underground home can save ridiculous amounts of money in energy costs and generally look unique and interesting, at the price of a larger initial outlays. However, conventional housing continues to dominate, in part because anything as unusual as an underground house must be extremely difficult to make and there will be unforeseeable disasters, such as cave-ins. That line of thinking is faulty. Underground housing is feasible with some instructions, such as these.
Underground houses fall into three categories: Envelope, Slope, and Bermed (Carter 38). Envelope consists of a pit courtyard open to the sky with rooms tunneling off. The house is almost invisible from outside. Envelope-type housing is best constructed on a flat space with a low water table. The main disadvantage is that circulation is more difficult to produce than in the other types (Carter 42).
Slope is a cut straight back into the side of a hill. The interior is like taking a conventional house, moving all the windows and doors to one side, then stuffing it into a hill. The main advantages are the superior heating efficiency (since almost all of the building is underground) and the view (Carter 40). The disadvantages are the greater pressures by the earth and condensation and drainage problems (Carter 43).
Bermed is, technically, underground, but only because earth is dumped over the top of it. This type could be thought of as taking a slope-type house, setting it in a field, and covering it with ground. Advantages are the greatly reduced pressures by the earth and the ease in installing ventilation and utilities (Carter 39). The only real problem with bermed construction is that earth must be trucked in to cover the structure (Carter 42). A minor disadvantage is that this type is visible above ground, though planting is possible on all types of earth homes to minimize visibility.
All types have several shared traits. Energy-efficiency is the name of the game with underground housing. Because earth stays at a crisp 50 degrees year round, a furnace is extraneous (“How it Works…”). In fact, depending on the size of the dwelling, a few people and a greenhouse may be more than enough heating, even in winter. In summer, extra heat will bleed off into the ground, and what extra remains can be dealt with by circulation.
Earth houses are extremely awesome. The earth is 100% soundproof. Sheer novelty will keep visitors in awe and thinking that the owner must be some kind of deity. In case of attack by hordes of Mongolians, underground houses are defensible, they slighly resist fire (they take it better than a normal house, anyway), and can include hidden escape tunnels. The roof of an earth house can be planted on- the only space that can’t be used twice is the face, and that doesn’t apply to Envelopes which can use the courtyard.
However, it wouldn’t be fair to not mention the disadvantages, especially ones this sizable. Moisture is the number one and number two concern- such a huge problem that it is counted twice. If an underground home’s water defense system has even the slightest flaw, the moisture buildup will require extensive (and expensive) pumping and repair, if not complete abandoning of the site. The third problem is air circulation. In a conventional building, this is hardly a concern because air is constantly flowing through walls and attic intakes. Underground houses don’t have attics. The fourth and final (although, technically, the first) problem is the initial expense, which may be up to 20% higher than a conventional house of similar size (USDE 2). These will be dealt with in the discussion of process.
Okay, so location, design, contractors, utilities, and types of televisions to include in construction of your underground house have been selected. Well done, now just contact whichever government has building code jurisdiction in the chosen site. If there are no applicable codes (for underground construction), or, worse, underground housing is banned entirely, there is a problem. There are options. First, check committee agendas. If nothing is planned, write letters and get an audience. Be warned that it will take an eternity and a day for the problem to be solved bureaucratically. A much more efficient plan is to completely ignore the disagreeing codes- go ahead and build an illegal house. The odds are that no one will complain, and, even if they do, razings are only done under extremely rare circumstances (Oehler 103-106).
Assuming there are no more legal hurdles, excavation is within sight. The prospective hole must be three feet wider on each side and two feet deeper on the bottom than the wallpaper-and-carpeting layer of the interior. That extra space will be occupied by wall and water removal compounds. Also, contact a local soil expert (DNR, well-drillers) and ask about the earth at the prospective site. Removing several tons of earth and replacing it with house, which has a different density, can have strange effects. If the house is less dense than the removed ground, weights might have to be added or the design may need revision. If the house is denser than the removed ground, excavate less so that when the house settles, it will end up in the correct spot (Carter 21). A good test of how much the house will sink is to calculate its final weight-per-square-foot, dig a test hole (less than a foot wide and several feet deep), drop a beam down the hole, and put a proportionate amount of weight on that steel beam. Then measure how far the beam sinks: That distance is how far the house will sink; excavate that much less.
Now excavation can begin. Have a professional excavator do this unless (a) you are a professional excavator or (b) you want to dig by hand to save money. For the hole dug for the recent addition on my (conventional) house, excavating costs around $5 per cubic yard, and we were given a deal because a relative did it. A dwelling 50 feet by 30 feet could cost in excess of five thousand dollars.
Whoever digs, the single most important caveat is to dig as exactly as possible. If earth has to be filled back in, that dirt will settle more and the house will be fatally lopsided (Carter 49).
Now there is a hole in the ground. The next step is to place ventilation/circulation pipes. Moisture and stagnant air are the 1, 2, and 3 largest problems with an underground dwelling. The best way to eliminate them both in one fell swoop is to install tubes that run from outside, underneath the house, and into the back in the corners. The pipes’ exits into the house (currently a hole) stick out of the bottom of the hole about three feet from the back wall of the pit for now. The intake should simply be a metal pipe with a chicken-mesh cover to keep out rodents (Carter 67-70).
Footing is the next step. Depending on soil type, there are several types of footing that may be needed. In very stable earth, none might be needed at all. A concrete grid like a waffle is recommended in exceptional soils. In any case, the walls will need the strongest footing. Place, about two feet from the edges, steel reinforced concrete beams around 1 foot tall running parallel to the walls. The top of the beam must be as wide as a cinder block, which is 8-10 inches, but they should be measured to find the exact width. The bottom will be twice as wide; the final shape, from the side, is a trapezoid (Carter 46-49). In shifty or otherwise untrustworthy soils, put scrap plywood underneath the footings to help distribute weight. Also, put these beams under any interior load-bearing walls.
All that remains is to build the walls, fill in the gaps around the walls, put down a floor, slap on a roof, build interior walls, and furnish. This is the home stretch
Building the walls is the simplest step, though by no means the easiest. Essentially, stack cinder blocks on top of the footings. Approximately 150,000 cinder blocks will be needed, or, at least, it will feel that way. A more realistic number is eight cinder blocks per foot of wall; a dwelling with 90 feet of load-bearing walls will need over seven hundred blocks. Purchase extra because every dropped block will break, without fail.
Stack the cinder blocks on the footings until the tops of the walls are level. For added strength (and added cost), drop hollow metal tubes down the holes in the cinder blocks to reduce shift. Build around the circulation vents. Coat each wall surface with a spray-on fiberglass bonding agent to keep the cinder blocks together and provide a better surface to work with (Carter 52). Be sure to include a rear emergency exit, accessible by stairs or a long tunnel to the surface.
On the other side of each exterior wall, the two foot gap will now be filled with waterproofing systems. By order of interior to exterior, they are: bentonite, polyethylene, earth, and gravel. Bentonite is a miraculous clay that expands when it contacts moisture, sealing it out. It can be sprayed on, painted on, or applied in sheets (EERE 7). Polyethylene is waterproof plastic sheeting. Wrap the walls in it. The earth here is a buffer between the walls and any moisture that finds a way past the gravel. The gravel is a system called the French Drain. Essentially, water that hits the gravel falls to the bottom, below the house (Oehler 50). Wrap the ventilation pipes in polyethylene and fill in surrounding gaps with bentonite, then fill in the dirt and gravel.
Install any interior support beams (if the design calls for them) now. This is a job for a real architect. Insufficient support has obvious dire consequences.
Installing the floor is the next step. Fill the waffle footings with gravel if waffle footings were used. If they were not used, there should be two feet of space. Pour in dirt to cushion the plumbing, which is laid out next. Cover the plumbing with earth and level to two feet. Level now. If the floor is not level and tamped by the next step, you will regret it for the life of the house (Oehler 88). Now cover the entire floor with a layer of polyethylene. Finally, place ¼ inch hardboard. The hardboard is the second-to-last surface: the last is linoleum tile or carpet (after the roof is installed) (Carter 65).
Finally, as far as the bones of the structure go anyway, a roof can be installed. This is the trickiest part that can cause ruination if done slightly off. There are several ways to build a stable roof. One is to lay concrete slabs (Carter 59). Another is to build roof beams out of logs (Oehler). Some of Carter’s builder’s wanted him to build a conventional roof (Carter 56). I recommend the concrete slabs with a poured concrete cap, for simplicity.
Before laying the slabs, have holes cut in them for Solar Tubes and the Solar Chimney. Solar Tubes (brand name Solatube) are essentially just flexible metal tubes with glass on either end. One was recently installed in my bathroom. Solar Tubes can be at practically any length and are relatively inexpensive, a far cry from the skylights that had to be used in the past (Solatube Intl). Use them in rear rooms that would have to rely on artificial light, and in closets at risk of mildew (which dies in direct sunlight). The Solar Chimney is a metal pipe painted black or covered in black material that sticks out of the ground above the dwelling several feet. The bottom is a vent in the ceiling inside the house. The solar chimney works with the underground ventilation pipes to continuously draw in fresh air, and cool the house in summer, using convection. The solar chimney can be constructed to be able to be sealed at will, such as by closing the interior vent (Carter 67-69)
The cement cap on the roof should slope down slightly toward the front-top corners, away from the front-top-middle, to remove water. Have an experienced cement pourer handle this phase of the operation. On top of the cement cap, drop another layer of polyethylene. Cover the complex with earth either to a smooth flow away from the top, or to match the slope of the hill.
Only people without tongues cannot taste conclusion. All that remains is the front, wiring, furnishing, and customizing.
The front (or interior, in the case of an envelope) will probably be a wall of glass, because the only other windows are skylights. Install energy-efficient double-pane glass and doors, as per your design. Make sure a professional carpenter is on hand to supervise since so many picky little errors can occur here that another essay would be needed to go over them all.
Have professional electricians install all the wiring and the phone and cable companies their products now. Have plumbers finish the interior plumbing. Build interior non-load-bearing walls, with (at least) instructions from a professional carpenter. Throw down linoleum, carpet, and flooring on the ¼ inch hardboard. Paint. Install cabinets, beds, televisions, bathrooms, computers, chairs, cats, tables, stoves, microwaves, silverware, refrigerators, stereos, and anything else necessary for life in the modern era.
There remains but one necessary component: A front summer-sun blocking overhang. Assuming the front of the house is to face south, the sun is higher in the summer than in the winter. Calculate the length of the overhang, which can be made of 2-by-4’s with a conventional (i.e. shingles) roof, based on the house’s latitude and depth. The overhang should reach across the width of the house (Carter 63-64).
An excellent idea is to install a greenhouse immediately inside the bank of windows. The plants look good, smell good, can provide some food, and, most importantly, help recycle air (Oehler 67-69).
Finally, the last-est step is to landscape the exterior and roof. Trees are incredible. In addition to the aesthetics and air-recycling and erosion-prevention they provide, trees can be used instead or in addition to sun-blocking overhangs: Trees block out summer sun with their leaves, and allow in winter sun because they dropped their leaves (Oehler 72).
Plant grass on the roof. Drink some lemonade. You’re done.
Carter, David. Build it Underground. New York: Sterling,1982.
“How it Works- Concepts: Ground Temperature”. Alliant Energy. http://www.alliantenergygeothermal.com/howitworks/groundtemps.htm
Oehler, Mike. The $50 & Up Underground House Book. Self published, 1977.
Solatube International http://www.solatube.com/home.htm
United States Department of Energy. Energy Efficiency and Renewable Energy. "Earth-Sheltered Houses". http://www.eere.energy.gov/erec/factsheets/earth.html.