Building an Earth-Sheltered Home: Part III

Waterproofing and insulating the energy-efficient home, plus energy-saving details.


| March/April 1984



Earth-Sheltered Home Emulsion

The asphalt-bentonite emulsion is applied to the stucco surface with brushes. It's not a fun job.


PHOTO: MOTHER EARTH NEWS STAFF

Is is possible to achieve food and energy independence on one acre? Well, with imagination, hard work, and the right one acre, we think it can be done . . .and that's what this project is all about. Of course, providing most of the basic needs for four people from such a small piece of ground is a tall order. Still, we think it's a goal worth pursuing, and we're hoping that in this series of articles about our low-cost homestead we'll be able to help some of you in your struggles to increase your self-reliance . . . by doing some of the experimenting for you.  

In previous installments (see Part I and Part II), we discussed both our plans for the project and the construction of the building's shell. This time around, we'll go over the important tasks of waterproofing and insulation, and also describe a couple of the home's special energy-saving details.  

Effective waterproofing is crucial to the longevity of any earth-sheltered home, and leakage problems have traditionally been the major complaint voiced by owners of such structures. Fortunately, there are numerous quality waterproofing systems on the market today, two of which we used successfully in our last earth-sheltered building construction project (see My Mother's House Part I, Part II, Part III, Part IV, Part V, Part VI and Part VII).

Of course, good commercial waterproofing systems are expensive . . . but, in general, they're probably the wisest expenditure you can make when building an underground home. However, for our ultra-low-cost earth shelter, we decided to take a risky but very inexpensive approach. As an experiment, we chose to use two applications of an asphalt-bentonite compound in conjunction with a layer of 6-mil polyethylene. The total cost of the adhesive and the plastic was less than 15 cents per square foot of wall . . . as opposed to the $1.00 per square foot (or more) price tag on proven commercial systems.

We probably won't know whether this gamble was completely successful for years to come. So far, at least, the building's walls haven't leaked. Over the years, however, the asphalt could gradually dissolve in the water around the walls. In the meantime, we do not recommend that you follow our lead with this system. We can afford to risk having to pull out the backfill and install another waterproofing material . . . and this experiment is one way we can serve you, our readers. But we doubt that most folks would be willing to gamble with us. (Updates on the system's performance will appear in future issues of this magazine.)

Then again, we did give our experimental waterproofing setup the best backup possible, by installing a thorough drainage system around the walls. A perforated, 4" ABS pipe runs all the way around the junction of the footing and foundation, lying in a 12" bed of gravel. This pipe helps channel water away from the crucial joint between the concrete footing and the block foundation. Another 4" ABS pipe is set four feet above the footing on the fully bermed eastern portion of the wall. This pipe is also positioned in a bed of gravel to prevent it from becoming clogged with mud.





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