Subterranean homes face a number of water control problems. Each source of water,
each place where water is likely to show up, has its own characteristics that must be
addressed if all water problems are to be solved. Not all moisture problems are caused by
an excess of water either. Sometimes things may be too dry. This is also a water problem
since we want to keep some things moist and other things dry. Thus all the water should
The sources of water control problems include:
- Rain water.
- Stagnant surface water.
- Running surface water.
- Subsurface water on the roof.
- Water flowing over the home.
- Water flowing through the earth around the home.
- Water in the drainage system.
- Natural ground water, the aquifer, the water table.
- Moisture in the soil.
- Indoor moisture producers: bathrooms, kitchens, hot tubs.
Uncontrolled water can cause these major problems:
- Desert or swamp-like surface conditions.
- Structural failure.
- Waterproofing failure, dampness, dripping, or flowing water inside the home.
- Clogging of underground drainage systems.
- Mold, mildew and insect invasion.
- Flooding and drains that back up.
- Overly dry or overly humid interiors.
- Loss of stored heat and failure to achieve annual heat storage.
So, practical water control cannot be handled by mere waterproofing alone, but only by
a comprehensive water control program.
Keeping the Surface Water Away
The most common source of H2O, is the sky. Since it is still popular to build
underground homes on hills, and hills are great water catchers, they have a real affinity for
funneling all that rain water right down on top of that lovely building site you’ve selected.
Would you like to have a WHOLE MOUNTAIN of water pour over your home? Yet, that’s
exactly what some of them have especially when the snow melts in the spring.
So, avoid this problem from the very beginning. When you pick out that beautiful spot,
and you take all your relatives to where they are sure you’ve planned your “hermit’s cave,”
don’t take them there on some sunny sunday afternoon. Take them there IN THE RAIN!
Then, while they are laughing and pointing their fingers at the rushing torrent that’s
inundating your preciously picked place…TAKE NOTE! A little adjustment in the
prospective position may preclude a big bill for “excavational earth reorganization.” Don’t
plan so that you have to move a mountain. It’s far easier to move the plan.
The land that is to be moved around should be sculptured to facilitate the easy runoff
of rain water which falls on the roof, and to prevent water that gathers elsewhere from
running onto the home, INCLUDING ITS HEAT STORAGE MASS. Always encourage the
water to move AWAY from the home. This is done naturally by any good excavator. But
other items he can’t change such as the elevation of the house with respect to the land, the
location and shape of driveways, entryways, window wells and the like can back up tons
of water in some of the least desirable places, so these must be planned carefully. But
don’t use the word “sculptured.” Excavators charge more for “sculpturing” than for
What if you’re stuck with a big collecting bowl like a patio or something, and you have
to do something with all that water? Outdoor floor drains are very popular, and often quite
sensible if installed properly. But, all to often they are put at the bottom of a staircase,
ramp, driveway or other outdoor water collector with the lowest part right smack against the
Have you ever seen such a drain that worked? Aren’t they generally all clogged up with
leaves, dead grass, old plastic sacks, and cigarette packages? If you are forced to use
them, and use them only when you are FORCED TO; take positive steps to prevent them
from being clogged up. A drain cap with large holes will help reduce clogging, but not with
holes so large that they allow the pipe itself to clog. Make sure that the drain entrances are
located in the spot where the water is actually going to be, especially after the concrete and
the earth beneath it have settled. This collection place must be deep and wide enough so
that the water doesn’t back up under the door or even the insulation/ watershed umbrella
before it has time to drain away.
One should watch carefully what he hooks these storm drains to. Sumps are popular
but if they are in a soil that doesn’t drain too well they probably aren’t going to drain any
better through a small sump. So one will probably have to make the drain-pit much bigger
to give the water that is collected more time to soak into the soil. If you use a sump, make
sure you can open it up to clean it. Silt can very easily clog a whole sump, even a big one!
Never connect a storm drain to a septic tank or a city sewer. A friend of mine had a
indoor drain on the floor of his basement (about the same level where it probably would
have been had it been an underground house.) This floor drain was connected, along with
the rest of his home’s plumbing, to the city sewer system that also had storm drains
connected to it rather than to the city storm-sewer system as they should have been.
During spring run-off the sewer was very nearly full so it wouldn’t take even the normal
amount of waste water. So, through the floor drain, every time they did the laundry, the
Tide would come in.
How much better it would be if one could avoid catch basins altogether, or at least use
a large storm drain even if it just goes around the house. If you do, you must keep all
drainage sumps and pipes out of the heat storage zone, otherwise they will become
unwanted earth tubes extracting heat just as if all this water were loose and flowing around.
Solving Ponding Problems
Ponding problems occur whenever there is an accumulation of water in an unwanted
place. The most familiar ponding problem shows up in the earth cover on top of a flat
roofed underground home. Ponding has been a severe problem in some homes because
most subterraneans have flat roofs. Flat things are not very efficient at holding massive
amounts of earth–especially heavy, wet earth. A large accumulation of water can actually
cause a structural failure.
Water collects in the center of a flat roof. The roof, due to the increased weight, sags
ever-so-slightly. The puddle gets bigger. The roof bends ever-so-slightly. The puddle
becomes a pond. The roof flexes ever-so-slightly more. The pond becomes a lake. Then
all of a sudden the lake goes away, to become an indoor pool!
You wouldn’t build a perfectly flat above-ground roof, why build one below ground? If
you do use a flat roof, set it at an angle so the water can run off of it, just as you would
above ground. However curved roofs like domes, culverts, and other shell structures work
much better, not only because they can be made stronger, and require a lot less materials,
but because they shed the water rather than allow it to accumulate.
If however, you design for a small storage zone on the roof, as well as a moderation
zone (by including some earth between the insulation and the roof,) potential ponding
problems can be prevented by using the insulation/watershed umbrella because it
encourages the water to drain safely away.
Roof ponding is not the most serious water control problem now, mainly because so
many fine texts have brought it to the fore. However, another sort of ponding has not been
dealt with to such an extent. This is the kind of problem that is all to often designed into
some homes, ponding that usually gathers less water, but occurs in sensitive, hard to deal
Surface ponds or flowing streams of water can cause difficulties at those places where
a portion of the home must protrude through the earth. The intersection of earth, flashing,
waterproofing, and building can be hard enough to handle, without collecting water on the
roof and then directing it right smack into these sensitive areas. Unfortunately, the earth
tends to angle down toward these delicate places, because we like to have lots of earth
cover that tapers off at the front of the roof. Retaining walls are especially famous for this.
They can easily form a water control problem that can be handled easily by simply directing
the run-off some place else.
A good retaining wall has “weep” holes at its base so that water will not build up behind
it, and as often happens, bring down even the biggest ones. Selective, controlled, run-off
will reduce this amount to a trickle, and will prevent water from backing up along the
retaining walls into the house. To accomplish this, we must keep the water flowing on top
of the umbrella a little ways back from the top of the wall, and not right against it where the
collected run-off could seep down between the umbrella and the wall.
Surface water, collected into little streams on top of an earth shelter can eat away the
carefully placed earth cover to expose the insulation leaving a gaping crevasse at the
corners of the roof and down behind the retaining walls. Erosion is sneaky. It is slow but
relentless. We can try to keep the velocity of the water to a reasonable level, but all such
collection streams should be lined with a good stone or gravel base. Such stream beds will
be a very functional part of the landscaping. But the best way to prevent erosion and
control the surface water, in addition to proper sloping and direction is with green plants.
The Green Solution to Drainage Problems
Earth sheltered homes CAN be more beautiful than any above ground home. Do I say
that just because of personal taste? No. The primary decoration of a properly designed
underground home is green vegetation. Well laid out landscaping is composed of natural
things: trees, bushes, grass, rocks, flowers, vines and shrubbery of all types. Drive down
a quiet street, the most beautiful one in any town. What is it that makes it beautiful? Isn’t
it the huge trees hanging like decorated arches over the street, the well manicured lawns,
and the great variety of shrubs and flowers that make such a place so much more desirable
to live in? Even in the older sections of town, where the homes are beginning to look a little
shabby, isn’t it the landscaping that has remained beautiful long after the luster of new
construction has worn off? Who wouldn’t want to have a park-like home in his
neighborhood, one with the most beautiful of decorations as its major feature?
However…ten hours behind a growling grass gobbler is not my idea of a “pleasant
weekend at home!” There is no reason why all that newly found green space has to be laid
out like a golf course, unless you golf a lot. Now, you certainly don’t have to mow bushes,
and the slightly longer growing season on the roof makes it a fine place for a vegetable
garden. Remember though, to keep the moderation zone deep enough to save your
insulation umbrella from your shovel! But even if you do have to use a lot of grass,
remember, a well designed earth shelter needn’t have any maintenance that can’t be done
by a sheep!
A marvelous variety of plant life is available from little tiny seeds, but before you select
your favorites, you should take into consideration:
- The root system.
- The amount of water and sunlight that each needs.
- The climate and the new longer growing season on top of the storage zone.
- The weight.
- The usefulness for control of erosion, animals and people.
- The beauty of each.
- Their positions relative to each other and the home.
Many conventional earth sheltered homes are deserts up on top, the “brown spot” on
a green hill, because the roof with its thin waterproofing protection must be drained
completely dry. The insulation/watershed umbrella will keep the home and the earth near
it dry, but the moderation zone on top should be made with a high humus soil which will
retain just the right amount of water for good plant growth. The earth cover on the roof
should NOT be drained dry, but the umbrella’s interior should.
Trees and some deep-rooted bushes should be avoided because the engineering may
not allow for the extra weight, and we want to confine the roots to the two-foot-deep
moderation zone. The plastic insulation umbrella will tend to localize roots in the
moderation zone, while preventing them from growing into the umbrella, because it is dry
both in and under it, and roots follow moisture.
So, you can landscape a subterranean home as if you were painting a picture. Just use
your imagination and those natural tools…green plants.
Solving Multiple Problems With the
If you look out toward the Geodome you’ll see that
it is a green spot on a brown hill. The reason is that it has an insulation/watershed
umbrella. Five moisture sensors were placed in the earth around this building. The top one
in the upper earth-layer, the moderation zone, has been moist since the first rain storm
after construction. The earth there is about two feet deep to allow room for good plant
growth. Under the umbrella it is bone dry, or nearly so, all the way down to the footings.
The home’s entire earth environment is dry in spite of the clay hill in which it is buried,
where the water comes down in sheets during spring run-off.
The proper level of moisture in the moderation zone can be controlled by placing the
insulation/watershed umbrella between that which we want to be moist, (the top layer of
earth called the moderation zone) and that which we want to be dry, (the storage zone, and
the home in it.) This plastic barrier will solve our dilemma by separating these two major
water-related earth functions:
First: Keeping the EARTH around the home DRY makes waterproofing very easy,
eliminates ponding, and prevents transportive heat flow from robbing our heat storage bin.
Also, dry earth has a higher R-value which reduces heat loss out the end of the umbrella,
while allowing the establishment of a permanent warm storage zone.
Second: The moist earth on top insures a well functioning moderation zone, prevents
erosion and fire, reduces the amount of watering needed, and keeps the roof beautifully
Underground Water Control
Pick up any text on underground houses, and you’ll find the same pictures of
subterranean walls with footing-level drain tile, loads of expensive waterproofing…and a
river of water drenching the house. (I suspect they were first drawn by waterproofing
salesmen.) Water flow problems persist. Conflicting claims by the waterproofing industry
haven’t helped much in solving the water troubles, and rapidly rising waterproofing costs
have made earth sheltering even more difficult, and costly. Just lately we’ve seen a
number of pictures in magazine articles, that show a second drain tile near the TOP of the
wall to reduce water flow, both for thermal and waterproofing reasons. That is a little better,
but still far from ideal.
Look closely at the picture below. Note that there is NO drain tile around the perimeter of the
insulation/watershed umbrella, but there is a layer of gravel. Drain tiles remove water much
faster than gravel, too fast for keeping the proper moisture content in most soils. By using
gravel, the excess is drained away, while the moderation zone will retain just enough water
to make those “deserts” blossom.
The SHAPE of the umbrella is also important. It is round, and like a fireman’s hat, it’s
designed to make the water run off of it. Why else would it be called it an “umbrella?”
Generally, people do not always equate the way things work above ground and the way
they work below ground. But, despite the difference in position, materials, and installation
sequence, the principles of operation are the same. The water will run off the underground
umbrella just like it does off the roof of an above-ground home.
Use Plastic Underground
The best construction material for use in underground water control is PLASTIC. No
one I know personally, would screw in a light bulb by turning the ladder because every
product has its preferred method of application, and its individual attributes. Yet people
persist in installing plastic improperly even showing it installed wrong in many
how-to-do-it-books. Then they belittle it for the problems that result (or they think result.)
While it is bad-mouthed by the waterproofing salesmen, they generally, when all is said and
done, recommend that at least one layer of it be put over the top of their super-good
Polyethylene sheet plastic, often called “Visquine,” is generally used in very large sheets
(20′ x 100′) (6 x 30 m) and .006 inch (0.15 mm) thick. This thickness is usually chosen
because it is the thickest, and toughest of the garden variety plastic you can get for a very
reasonable cost. It has some fine attributes:
- It is the least expensive of any commercial water-control material.
- It is not biodegradable and will last a long time.
- It is fairly slippery.
- Almost nothing will stick to it, even glue.
- It is a complete water and vapor barrier.
- It comes in very large pieces.
- Water will not only drain off the top of it, but will run under it too.
It also has some drawbacks that require the installer to be cautious.
- It can be punctured quite easily.
- It cannot be stretched, and will hold no weight.
1. Sunlight. The ultraviolet light from the sun will eventually turn it to powder. If stored
out in the open for a long period of time it will deteriorate and not work as well when it is
used. Now, the sun doesn’t shine underground, so, only where the plastic has to protrude
above the surface must it be protected with flashing.
2. Burrowing animals. If you live in an area where there are a lot of ground squirrels or
gophers, don’t put out a trap line. Remember, that they were smart enough to live
underground long before you discovered subterranean living. But they don’t have any
plastic to control the underground water for their homes, so they like to dig where it’s
already dry. Ah ha! If you keep the roof of your home moist, as suggested, then they will
move out to become your neighbors, rather than pests. If you plan your landscaping to
match the arid climate that you already live in, and would like it to blend in with the scenery,
protect the umbrella with lots of big rocks. The little fellows are tough, but usually not that
tough. Now, it is true that muskrats and beavers burrow too…but if you have trouble with
these, I’d suggest that you have a big enough water problem to warrant building elsewhere.
3. Frost. Frost will destroy it. When plastic gets cold, it gets brittle. When it moves it
breaks. If it moves a lot, it breaks up in little pieces. Frost is accompanied by both low
temperatures and movement. Of course, the purpose of the insulation in the “insulation
umbrella” is to keep the earth beneath it at a higher temperature than the earth above it.
With the storage mass at about 70° (21° C.) some heat will pass through the insulation into
the moderation zone. This accounts for the longer growing season up there. It also
prevents freezing close to the umbrella. Also, the formation of frost requires the presence
of water, and as we shall see, the entire umbrella will be so well drained that it itself will be
dry. If you are in an area of extreme cold, like the Yukon, a small layer of round river gravel
placed on top of the umbrella should keep that earth somewhat dryer. So a balance must
be found between the requirements for drainage and for water retention based on the site’s
4. People who like to dig holes on their roofs. So keep the dirt on top of the umbrella
5. People, by improper installation or by stomping it full of holes!
To expect plastic to do a job that it was not designed to do is unwise, like the lightbulb
and the ladder. In all but a few of the examples I have seen, the plastic has been
INSTALLED IMPROPERLY. So, proper installation is vital if we expect it to do the job for
The biggest complaint that people seem to have about plastic is that it gets holes in it.
There really is no reason outside of just plain carelessness why it need be perforated. If
the workmen are aware of its importance, and know how it should be installed, then it will
survive construction to do the fine job it is capable of doing.
The plastic will soon be covered with dirt, dirt that could cause some holes to develop.
Therefore, it would seem wise to avoid using a layer of crushed-stone gravel that has a lot
of sharp pointed rocks in it, right on the plastic. The covering soil should only have round
river stone, if any, since it will make fewer holes. However, holes–at least some holes
WILL be made.
Do you worry about holes? Let’s consider some of the ways that plastic has been used
in the past, and determine if there is an improved method of installation that will lessen this
Some earth shelters have been waterproofed with just a single layer of plastic. Even
today, thousands of homes have been built with All Weather Wood Foundations. They
have been very successful. Their primary waterproofing system is…gravity drainage, and
a single layer of plastic.
Some earth shelters have been built with a multi-layer system, where six or eight layers
of plastic are laid on top of each other for greater protection. But…what happens when a
rock or something punctures a hole it it? And it WILL HAPPEN. If you have one layer, how
many holes are punched in the plastic? ONE. If you have 8 layers of plastic, and a rock
batters an opening, how many holes will you now have? You guessed it…EIGHT HOLES!
Eight CONCENTRIC holes! So, just using multiple layers is probably not a whole lot better
than a single one. Certainly, the top layer is the most effective.
Second problem: MULTIPLE HOLES. Over the entire surface of the insulation/
watershed umbrella quite a number of holes may be made. Care will keep it to a
minimum, but holes will be made. How much water will be funneled through these holes?
Well, what is the total surface area of the first plastic sheet in comparison to the total
surface area of all the holes put together? Obviously, the river of water that would
ordinarily slosh over the home has been immediately REDUCED TO A TRICKLE!
Plastic sheets should be laid like shingles, so the water which is missed by one shingle
(goes through a hole,) is captured by a layer beneath it.
When a hole is made, especially by a stone, it usually doesn’t penetrate very far.
Therefore, a protective layer put between TWO layers of plastic will provide:
- Protection for the second layer of plastic, so it will not be punctured.
- A second layer which is also an UNDERGROUND SHINGLE, to catch the few
trickles that make their way through the top shingle.
- A means of drainage BETWEEN the layers so that the plastic can do its thing.
Often waterproofing salesmen are down on plastic because the water will travel beneath
it for quite a long ways. True, if it is just laid on the house as is usually done, with a torrent
of water flowing over it…and a leak occurs, it is just about impossible to find because where
it goes in is usually a long way from where it comes out. Certainly it would be expensive
to dig the whole thing up to find one hole.
So why does the water run just UNDER a sheet of plastic? For the same reason it
always runs down your arms to drip off your elbows whenever you’re trying to wash your
Should you then go out and buy some ooie-gooie-sticky stuff like tar or bentonite to
put…all under it…to prevent the water from moving? No, this would only PREVENT the
plastic from doing the dandy job it was designed to do. On the contrary! Provide a means
of drainage under the plastic, between the separate layers used on the
insulation/watershed umbrella. The top layer will encourage the water to travel just
underneath itself, and the lower layer will catch any water that gets through, so those drops
can trickle out of the way, just as they do on cedar shakes.
Conveniently, right between these two layers of plastic is the exact location where we
want to put our insulation! Also, rigid insulation comes in convenient 4′ x 8′ or 2′ x 8′ (1.2
x 2.4 & .6 x 2.4 m) boards that will encourage the water to runoff between, above, and
below themselves until these few trickles reach a more desirable location. A very
In most installations it is generally recommended that about 4 inches (10- 11 cm) of
insulation be used in the insulation umbrella. Since these boards come in convenient
thicknesses like two inches (5 cm)…it would seem sensible to use THREE LAYERS OF
PLASTIC with TWO LAYERS OF INSULATION sandwiched in between. This third layer
of plastic would be the “back-up” layer, and would also be protected by the second layer
of insulation which is above it. Each successive sheet of plastic will catch what
trickles through from above, and each will drastically reduce any water flow eventually
keeping the entire earth environment about the house D-R-Y!
Failure to use these fine attributes of plastic sheeting is like leaving your best tools out
to rust…or trying to drive nails with a rock!
Once upon a time, while building a house in Helena, Montana, we watched some hard
working fellows roof a garage across the street from where we were building. They worked
hard and soon had their back-breaking task complete. However, they had installed their
seal-down shingles…starting from the TOP of the gable! For those readers who have never
roofed a house before, shingles work well, only if the water from each shingle is allowed
to run off onto the TOP of the shingle beneath it, and soforth down the roof. In order for
the shingles to be thus installed, one MUST begin at the EAVE, so that each succeeding
shingle overlaps the one below it. Had it rained on this garage, the owner would have had
a near-perfect indoor sprinkling system. The next week the guys were back, installing a
second layer…starting from the eave.
Underground shingles, in the form of large plastic sheets, work basically the same.
Even underground, water flows down hill. It never flows up hill unless you seal off its
escape route so that it fills up the space between the plastic layers of the umbrella.
Nevertheless, given proper drainage, large plastic shingles will move the water from where
you get it to where you want it just like their above-ground counterparts. Thus the plastic
should be laid as if it were large shingles, with the upper shingle overlapping the lower adjacent
one even though it is underground.
Unlike above-ground shingles, the underground shingle in the insulation/watershed
umbrella, must contend with some new problems. The earth over which it is put will settle.
This settling will be uneven. If you do not watch closely during installation, to see that a
steep enough slope is provided, the earth may settle enough to back water up under the
overlap of the adjacent up-hill shingle, or maybe even create a lake.
The earth will move some, so it is important to provide an arrangement that will ALLOW
for it. Since plastic will not withstand ANY stretching. The overlaps (slip-joints) between
adjacent plastic pieces must be fairly large (1 or 2 feet [30-60 cm].) Then as movement
does occur, a gap will not suddenly appear between them. Please note carefully the
Umbrella Drainage and Underground Gutters
Each of the three successive layers of plastic MUST HAVE DRAINAGE. The
insulation will provide that drainage space in the main body of the umbrella. At the outer
edges of the umbrella, the insulation should be tapered in one inch increments until there
is just one inch left. (The thermal reasons for this are explained in chapter 5 under:
developing the thermal arrangement.) Therefore, at the outer edge of each insulation layer
there MUST be a layer of round river stone, wherever there is no insulation between the
plastic shingles, to allow drainage into a plastic gutter which is an extension of the bottom
layer of plastic. Otherwise, the earth will press the outer layers of plastic together,
and the insulation will fill up with water. Each drainage layer should be terminated inside
this perimeter gutter to catch all of the water that trickles its way out.
The water which runs off any roof should be caught in a gutter. So it is with the
insulation/watershed umbrella; the first (top) and second layers of plastic, out at the edge
of the umbrella, empty onto the third sheet. This bottom layer is extended out from under
the umbrella in the shape of a GUTTER. Because that is exactly what it is–an underground
gutter. It must be shaped like a gutter or ditch full of rocks, so that the water will not simply
run over the edge.
If you live in a particularly wet area, you may wish to make this gutter fairly large, and
use large stone, 3″ (8 cm) or more, to encourage faster removal. If you live in a VERY
WET climate, the plastic gutter should be extended quite a distance past the end of the
insulation to keep the water as far away from the home as possible. Even a drain-tile could
be included; after all, if it gets to dry on top you could always stop the tile up a little bit at
the end to slow down the drainage.
This gutter must contain the water in it, and it MUST RUN DOWN HILL along the
perimeter of the umbrella. It should start at a high point in the center, unless there is a
reason why you don’t want the water to run out both sides. Angle it just like drain tile, one
quarter inch to the foot (2 cm/m), and bring the end to “daylight.” It may be more
convenient to “daylight” a short stub of tile, but it would be cheaper and look far nicer to
bring the gravel to daylight using big rocks.
Often a single layer of newspaper or straw is put on top of underground drainage gravel
before the top soil goes on. Its purpose is to prevent the fine soil from sifting down to clog
the gravel, until the soil can become packed tight enough to prevent it naturally.
The outer edges of the umbrella should be installed carefully, especially where they
meet retaining walls, parapet walls and other protrusions of the structure through the earth
cover… because they are gathering points for a LOT OF WATER, and the last thing you
want to do is funnel it UNDER the umbrella, behind the walls or cause it to run down over
the front of the house. Here too, a similar underground gutter should be used, along with
the surface contouring, so the accumulated water can be kept back away from the building.
These are the difficult areas that must be designed with great care, and installed with even
Now the home and its storage mass should be DRY.
The Vapor Barrier
The last layer of plastic that any moisture may encounter, and the first layer to actually
be installed, is the vapor barrier. Keeping the running water many feet away from the
actual structure will certainly make waterproofing much simpler, and far cheaper. However,
moisture, usually non-moving moisture, will still exist in most soils. Therefore, a vapor
barrier is vital. This is the layer that is draped over the house itself.
Installing the vapor barrier is a little more difficult than the umbrella. We must not
actually “drape” it over the structure and then backfill. The heavy backfill will pull the plastic
down, stretch it, and if not right away then later when the dirt settles, it will TEAR OFF like
a paper towel from a rest room towel dispenser.
Form a gutter at the bottom of the footing, under the drain tile if you choose to use one.
At the footing, the top of the walls, and whenever the shape takes a major change in
direction, an OVERLAPPING FOLD should be included along with a 1 or 2-foot (30-60 cm)
wide slip-joint (shingle overlap) wherever a new piece of plastic must be added. As you
work your way up the wall, these folds and overlaps should be arranged so that they will
be able to slip or UN-fold as the dirt settles, thus at no time will there be any tension on the
plastic. But don’t fold it like a catch basin. Fold it so that it will always allow the water to
run off of it. And keep it away from sharp edges. In fact, try to avoid building any
sharp edges in the first place.
Unroll the plastic as backfilling is taking place. Don’t try to hold up the earth with it. It
won’t work! Allow it to settle down with the earth as backfilling is in progress, while being
careful to allow enough folds and overlaps to remain for future earth settling.
Now that we’ve taken care of the surface water, the running underground water, the
vapor and the moisture in the soil, you next must deal with the moisture which can be
sponged up by the concrete itself…and the water table.
A Concrete Sponge
Can you imagine a concrete sponge? Concrete is a fairly effective water barrier for the
most part. It has only two drawbacks. First: It will soak up water from the bottom of the
footings by capillary action, allowing it to evaporate into the dwelling, and Second: It cracks.
There are several ways of preventing the capillary action. The first is very effective, but
not generally known. Almost all concrete is made in what is called a “5 1/2 sack mix.” That
means that for every cubic yard of concrete that is made, there are five and one half 94
pound (42.6 kg) sacks of portland cement in it. If the amount of cement per yard is
increased to seven sacks its waterproofing ability is increased several MILLION times,
especially if you use as little water as possible when mixing it. A less expensive method
is to use a concrete additive that will make it waterproof.
There are a number of fine products on the market called “integral waterproofers.” After
considering a number of these, we settled on a particular one called Berylex. It is fairly
inexpensive; it makes concrete waterproof; it makes it stronger; it bonds old concrete to
new concrete like you wouldn’t believe and it coats the steel with chromium to help
preserve it. It is available from Berylex National Sales, Kansas City, MO. You just pour it
into the cement truck before you pour out the mud, and it does the trick.
(p.s. they didn’t pay me to say that. It did for us exactly what they said it would and you
sure can’t say that for a lot of other people’s stuff we bought!)
However, cracks can still occur, and it is these cracks for which so many of the
waterproofing people have tried to design their products. The Berylex will help reduce
some types of cracking. However, bad cementing practice has more to do with cracking
than any other problem. Making good concrete is a little like baking a cake. A little change
in the recipe can make a big change in the taste, and if you jump on the floor at the wrong
time, the whole thing can fall. So, know your concrete!
Some other methods of crack control include good engineering, and the use of prestressing
and post tensioning techniques. Without these special tensioning methods,
concrete MUST crack.
YIPES A CRACK! Why on earth MUST it crack? Because the steel in it will not begin
doing its job by go into tension until the concrete cracks. These cracks are just hairline
cracks. If they spread to a eighth inch (3 mm) or so wide you’ve got real engineering
headaches. The whole problem with cracks is that water will run through them. If the
entire body of earth around the home is dry because of the insulation/watershed
umbrella…so what if the concrete does crack? No water…no leak!
However, in critical areas, like where the home protrudes through the earth, it is far
more difficult to keep these parts a long way from the water. Here special water proofing
agents may be prudent.
If you dig a hole for your dream home and you hit an Artesian well…I suggest that you
make beer, and move the house some place else! Just because the umbrella wipes out
the problems of water which comes in from above is no reason to ignore the water which
comes up from below. When you are investigating a site to build on, one of the priority
prerequisites should be that the water table is sufficiently low to permit construction.
Check it out! and not in the dry season either when the water table is low.
Earth sheltered homes are NOT made to withstand hydrostatic pressure. Actual
hydrostatic pressure occurs when the home is submerged in water. NEVER should such
a condition be allowed to exist. The tremendous force of actual hydrostatic pressure will
buckle a concrete floor, crack a wall, or at the very least bring springs of the watery deep
into your living room.
Some waterproofing salesmen will boast that their product will withstand such gigantic
amounts of pressure that it could float your home in the ocean. Are you designing an
underground submarine? Why waterproof for something which (structurally) must never
be allowed to occur anyway? Gravity drainage is the ONLY proven way to prevent
hydrostatic pressure. Water that isn’t there can’t cause problems.
Unless there is some way to actually find out, one hasn’t the foggiest notion what’s going
on behind the walls of an underground home. However, the drainage system will tell, if it
has its drain-exit outdoors. If a well designed sump must be used, it should be one that can
be examined easily to see if any water is or has been present. By watching it, one will be
able to find out if any water is getting back there at all. Since no one wants to stay up all
night and watch a pipe, a small piece of cloth may be laid a foot or so up into the pipe; one
that that won’t clog it. If any water does run over the cloth, it will remain moist for quite a
while so it can be checked at leisure. Most importantly, if you bring the drainage system
to “daylight,” out in the open so you can see it, you will completely drain the back fill.
A popular drainage system is the so-called French drain. French drains are simply a
gravel-filled trench a foot or so from the building, and as deep as the wall. They will do the
job in all but the worst of circumstances. But in most cases a full gravel backfill works
better, and easier to install. If the soil on the job site drains fairly well, it can be used in
stead of straight gravel. The backfill can be daylighted with a ditch full of big rocks at the
opening, or a short piece of pipe can go from the bottom of the backfill gravel to daylight.
At the bottom of the wall where the water collects, it is a good idea to make a small gutter
out of plastic so it can catch any running water that may get under the umbrella and
channel it to daylight. Otherwise it would probably just drain into the earth and not speak
to you about what’s going on back there.
If the soil you build in has a high clay content, it will exert an abnormally high lateral
(sideways) pressure on the walls. Gravel on the other hand will reduce this pressure to
where it will have a pressure of about 20 PSF per foot of depth (320 kg/m2/m), whereas
even regular soil will press at about 30 psf (480 kg/m2/m), and much more in clay. Gravel
will exhibit little or no settling, does not require a special trench, and it’s cheap. If you do
not have a fast draining soil already, a round river gravel backfill is the best idea.
Drain Tile and the Shape of the Backfill Hole
Drain tile (usually 4″ (10 cm) plastic pipe with holes in it,) is often used with gravel. It
drains faster, but may only be needed in wet climates. However, it seems to be easier to
explain this arrangement using tile than just gravel on top of the plastic gutter, so let’s talk
about how to install the tile while remembering that it works the same with drain tile as
without. If you choose to use tile or not, the plastic gutter must be laid out just the same.
That is, the bottom of the backfill hole must be shaped like a gutter, and the gravel (with or
without tile,) is put on top.
Just about every text I’ve seen which describes how to keep underground walls dry,
shows the drain tile being placed at the footing level, the bottom of the hole you’ve dug to
put the house in. If some one were to install your sewer line, and lay it out with a transit to
make it lay PERFECTLY LEVEL, how long would it be, before you threw a fit because it
was all clogged up? Sewer or drain pipe is laid with about a quarter inch to the foot drop
so the fluid will run down hill. When the footings were laid out, wasn’t considerable time
and effort used to lay the footings PERFECTLY FLAT? Then why on earth would anyone
want the drain tile to lay beside the footers…perfectly level? The place where the tile lays
must be sloped, and the same holds true for the bottom of a gravel backfill unless the
ground is all gravel anyway. The pipe’s elevation with respect to the house determines how
well it will work.
Lowering the Water Table
Let’s consider the draw-down lines below. These are lines that are supposed to
show how the water table is altered by the insertion of a drainage system. The water table
(the dotted lines) represent is the level of underground water. It is the water table that
determines whether the earth around a subterranean home will be continually wet or dry.
Above the draw-down lines the earth is relatively dry, and below them it is wet. In gravel
these lines are flat, because the water flow is so fast that it is like a bucket with a hole in
its side. The level of water in the bucket will not rise above the hole. In a clay soil the lines
curve down to the pipe, since the flow to the side is not as quick as with gravel.
In soil which is not gravelish, and a draw-down curve exists, AND the pipe is located
next to and level with the footing, is the floor wet…or dry? Since the curve goes
upward from the tile…the floor is wet. Do you want a wet floor? When the drain system
goes all the way around the house and the water has a way to drain under the footings, it
is a lot harder for water to get under the floor. Dropping the tile a little, and/or putting gravel
under the floor if the home is to be built in clay, levels out this line and keeps the floor dry.
The drainage system, whether just gravel, or gravel and tile, must also slope down hill
from its highest point in the back of the house all the way around the home to daylight.
That beginning HIGH POINT MUST BE AT LEAST A FOOT BELOW THE FOOTINGS,
unless the home it being built in a gravel soil, and even then, it should NEVER START
HIGHER THAN THE FOOTING. Otherwise you will have a WET FLOOR.
There is another factor which is all too often ignored in the site selection for an
underground home. Insertion of the drainage system into the earth may significantly alter
the natural water table. You have paid a lot of money for a nice green, plant covered
site…then you insert a drainage system which lowers the natural water table, the aquifer,
and what do you get? Dead trees. The drainage system is vital for keeping the home dry,
but it should be designed to keep it moist where you want it moist as well as dry where you
want it dry. So raise the house up and berm it if you must, but don’t significantly lower the
natural water table.
A Clay Cap
A few people will be afraid of using just plastic, thinking that it will not last as long as
they would like it to. Yet, there is no reason to believe that the plastic, which is NOT
BIODEGRADABLE, will be any less permanent than clay. If one feels that way, then a
couple of inches of clay could be put right over the top of the umbrella. It doesn’t have to
be pure bentonite (the stuff in clay that makes it stop water,) nor should it be bought by the
bucket full. Buckets cost too much. It should be gotten as close to the building site as
But what about waterproofing?
I have just described a complete water control system designed to take care of every
water source, except the kitchen sink! These methods not only work better but are less
expensive than the conventional way of running a river of water over the home and then
waterproofing the house as if it were a battleship! This ENTIRE program of water control
IS the waterproofing! You must use ALL of it. For what reason would you need any more?
After all that, some of you will still want to put regular waterproofing on the house. As
you wish, but be aware of what it actually does and then use it only where it is really
needed. Otherwise, you may be just wasting a lot of money and still not getting the job
A complete program of water control IN the earth environment is essential, not only for
keeping you dry, but for keeping you warm too.
Post adapted from chapter 4, “Water, Water Everywhere– So Control It!,” in the book,
Passive Annual Heat Storage Improving the Design of Earth Shelters, by John Hait.