My Mother's House Part III
The most important challenge facing anyone who builds an earth-sheltered home is waterproofing, including rubber on the roof, mud on the walls, blood in the snow.
November/December 1981
By the Mother Earth News staff
At the end of the discussion of MOTHER's earth-bermed, passive solar house presented in the last issue of this publication, the building was roofed in and ready for the application of waterproofing materials. And—because the sealing process is generosity considered to be the most critical step in earth-sheltered construction—we announced that we'd dedicate most of this issue's story to a report of how we chose to keep water out of our subterranean structure.
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The house's split—level design—which provides for earth bermng on three sides and a partial sod roof-presents two separate challenges to the would—be waterproofer. The vertical bermed walls must shed both surface and ground water (including drainage from the high land behind the building's dug—in location) and esist the pressure of some 13-1/2 feet of earth and rock backfill. The sod roof, on the other hand, will gather water only from direct rainfall, and won't suffer any great hydrostatic pressure. However, since its surface is nearly horizontal, the roof's natural drainage won't be as thorough as will that of the bermed walls.
Consequently, we decided to use two different kinds of waterproofing. And although either of the substances selected could conceivably have been used in both applications, we think that each material's unique qualities make it particularly suitable to the separate task for which we chose it. Besides, by working with two different products, we've gained twice as much information to pass on to you.
RUBBER ON THE ROOF
Specialized elastomeric membranes have been used in conventional built-up roofing applications for quite some time, and several rubber manufacturers have elected to market the products as earth-shelter waterproofing solutions, primarily in response to the burgeoning demand caused by new enthusiasm for the "underground" homes. We contacted the Carlisle Rubber Company (Dept. TMEN, P.O. Drawer 5583, Greensboro, North Carolina 27403) and investigated several of that firm's compounds . . . and, at the recommendation of regional representative Marshall Abee, we opted for the company's 0.060" EPDM (ethylene propylene diene monomer) material, which is resistant to degradation from ultraviolet light and remains flexible through a wide range of temperatures.
With Mr. Abee's direction—and the assistance of workers from a local roofing company who were interested in learning the procedure—we laid down the rubber mat on the to-be-sodded surface and sealed it in a little more than one morning's time. The membrane was rolled out atop 1/2" particle-board sheathing, with protective patches of the rubber added at each junction of the 4' X 8' wooden panels to prevent the possibility of a corner's lifting and puncturing the EPDM. Two different adhesives are used when working with Carlisle's elastomeric membrane. One cement bonds the EPDM to itself (for use in situations where two sheets of the mat must be joined to span a wide roof), and the second glue sticks the rubber to other materials.
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