My lot is completely flat, sandy soil. Is it still possible to build an underground house? Would it flood? Water tables are at least 25 ft down. All the references I've seen sit the home on a hill. Anyone try it on flat land? Sue

-- Sue Landress (Sulandherb@aol.com), November 11, 1999

Answers

my earth sheltered house is on essentially flat ground - the rock that it is built on slopes 6-8 inches in forty feet. the surface of the ground slopes about the same. landscaping to have surface water run away from your structure is the only necessity to ensure a dry house. the plan of my house is basically a circle with a covered atrium and greenhouse on the southwest side. next to the greenhouse is the entrance and the steps down 4 feet to the floor level of the house. The sides of the house that are not the greenhouse have the removed earth piled against them so they are completely buried. The roof waterproofing extends out a foot or so beyond the walls so that rain water doesn't run down the walls and overload the drainpipe that encircles the house. the soil in our area is mixed loam with some clay and little sand. the material removed by the cat that dug the hole was either limestone or clay. There is very little top soil in the area that our house occupies.

-- kirby johnson (kirby@selco.lib.mn.us), November 12, 1999.

Sue, I think it will be fine to build UG in your circumstance, so long as you are careful with the waterproofing...as a matter of fact, look at it this way: rain falls on the roof in either case, but a hillside may be directing MORE water down to the house....the reason its usually done on a hillside is mostly just been evolutionary - but the house is actually more ON the hillside than IN it, likewise, your flatlander house should be more ON the ground that in it (floor 4 feet below ground?) (ie dig in some & overfill some).... in the CA Borrego State Park there is a visitor center pretty much that way. Good luck.

-- Guy Winton III (guyiii@home.com), November 12, 1999.

Guy, I respectfully disagree. The reason to build on a hill is so that it is practical to divert any water which tries to fill up the area outside the walls can be diverted away from the house (downhill). If the ground is completely flat, that is impossible, unless the house is built aboveground, then backfilled.

A compromise is to build the house part ways underground, then backfill the rest with the soil you have excavated. But be sure to have a sump pump unless you are ABSOLUTELY SURE that the rain will never exceed the permeability of the soil to the extent that the soil around the house becomes saturated with water, or the walls may be destroyed by the water pressure, which is EXTREME if it is very deep.

Be careful in designing where the sump pump is located, too. My son has a full basement on flat ground up in Washington. During a particularly severe rain (the Cowlitz River reached a "300 year flood level") the water ran into his basement faster than the pump could pump it out.. The water rose enough to burn out the pump motor, then the water filled the basement four feet deep. The building inspector told me (and he's probably right) that, had the pump NOT failed, the walls may well have blown in from the pressure. As it was, the water INSIDE the basement relieved at least most of the pressure from the outside. So don't let the soil OUTSIDE the walls get saturated. Put drainage all around the house to divert any water present to the sump pump.

We have a lot more rain here in the Northwest than a lot of you folks do, so I am a bit paranoid, perhaps, but what the heck; bette safe than sorry.

-- jumpoff joe (jumpoff@echoweb.net), January 25, 2000.