A Critical Look at MOTHER's Underground House

Now that exterior work is finished on the underground house MOTHER EARTH NEWS started planning in the late 1970s, we're making a comprehensive assessment of its cost and performance.


| March/April 1983



underground house - exposed southern face of completed house

The southern exposure of our earth sheltered/underground house is dominated by a row of greenhouse windows.


Photo by MOTHER EARTH NEWS Staff

With the MOTHER EARTH NEWS underground house pretty much finished, some of the people involved in its design and construction got together recently to analyze the project (with the benefit of hindsight). Here, then, are some of the topics that were raised at that meeting, as well as a breakdown of a few of the costs involved in building that structure.

The Costs

Our accounting department's records show $48,855 billed to the earth sheltered house project, which includes materials, contracted labor (such as painting, excavation, and the application of one waterproofing system), and tool rental. Items that have not been installed are cabinetry, finished floors, closets, bathroom fixtures, light fixtures, and appliances. We estimate that it would take another $10,000 to $15,000 to complete the residence.

Furthermore, by applying common ratios of materials-to-labor for construction, we can figure that it would have cost between $115,000 and $125,000 to have had a house like ours built by a contractor with no owner help whatsoever. The average person who decides to put up his or her own home, however, would likely find the price falling somewhere between our out-of-pocket expense and the contracted figures we just mentioned. Consequently, the cost per square foot for a structure built to our exact (and purposely impractical) specifications would amount to between $40 and $85.

Of course, the building could have been constructed for considerably less money, and we'd like to examine some of the design options that would have resulted in a lower per-square-foot price. Bear in mind, however, that most of the changes we'll mention involve compromises; you'll have to decide just what represents real economy to you.

The Walls

The house has very strong walls. They're built from dry-stacked, 12" retaining-wall blocks that are surface-bonded and have their cores filled with concrete and rebar. Some preliminary calculations suggest that an 8"-thick poured and reinforced concrete wall might have been substantial enough for our residence. (Please remember that each building site requires specific stress computations based on the soil type and hydrology, and that an 8"-thick wall might not be strong enough for your shelter.) It cost $4,380 to build the back and side retaining walls for My MOTHER's House, but we could have built forms from 3/4" plywood and poured an 8"-thick wall for about $2,750. What's more, we probably could then have reused the plywood for subflooring and/or roof sheathing.

On the other hand, the Surewall surface-bonding cement we used on our block walls gave us an interior surface that we felt no need to finish further, which saved the cost of paint or other coating. In addition, the surface-bonding cement also helped in waterproofing the exterior walls. Finally, the 12"-thick wall provides half again as much thermal mass as would an 8 "-thick one.





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