Living in Rammed Earth Houses

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PHOTO 2: Large windows on the southern side of the house capture as much solar heat and light as possible. PHOTO 3: The living room of the Miller house.
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PHOTO 1: The north view of the Miller's rammed earth house looks similar to other ranch-style homes except for a lack of glass.
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LEFT: Diagram depicts container forms used in rammed earth construction.  RIGHT: A section of rammed earth wall.
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PHOTO 4: The sill in this bedroom window reveals the 14" thickness of the rammed earth wall. PHOTO 5: David Miller was a practicing lawyer in Greeley, CO at the time of this picture. PHOTO 6: Lydia Miller was a retired foreign language instructor. PHOTO 7: The Miller's extensive pantry of home grown and home-canned foods.

In an era which tends to celebrate the new
and shun the old, rammed earth construction stands out as a
paradox: After all, the millennium-old building method
may well also be the technology of the future …
which we are just now returning to. 

No one knows exactly when
the first rammed earth edifice was built, though historians
agree that the process was employed by the
Romans–during the heyday of that nation’s
empire–to build structures in conquered lands. In fact,
the Romans spread the use of earth construction throughout
Europe … and today, in France (where rammed earth is known
as pisede terre), numerous 400-year-old rammed wall
houses still shelter their occupants with a measure
of comfort and security which no “modern” frame edifice can
offer.

You see, because rammed earth has such a low rate of
thermal conductivity (it’s actually near zero), warmth takes
almost 12 hours to work its way through a 14″-thick wall. The
half-day rate of heat transfer makes the material a perfect
substance for providing thermal mass in passive solar
construction … since the sun’s warmth will actually be
reaching the interior of the house during the cold hours of
the night.

In addition, the compressional strength of rammed
earth can be as high as 625 PSI, which–though it’s only
two-thirds the value of a similar thickness of
concrete–still makes a rammed earth building nearly as
durable as a bomb shelter.

Why then–if rammed earth
construction is so strong and so time-honored–hasn’t
this building method caught on in the United States? Well,
the fact is that it did … once. Ralph Paddy (of South
Dakota State College) conducted extensive research into earth
mixtures and building forms back in the thirties.

Then–
in 1938– the U.S. Department of Agriculture actually
erected an experimental community of rammed earth buildings.
The results of that test were quite positive: The USDA’s
final report noted that rammed earth structures–which
would last indefinitely–could be built for as little
as two-thirds the cost of standard frame houses. The earthen
abodes were also shown to be considerably less expensive to
heat and cool, and–because the homes were labor (as
opposed to material) intensive–it was clear that they
would allow do-it-yourselfers plenty of opportunity to save
money.

We can only speculate as to why postwar America
snubbed the rammed earth concept: Perhaps the modest
pise technique seemed too basic in the face of our
newly formed technocracy. Or it may have been the
construction industry–which depends so heavily on
material intensive methods for its livelihood–that
helped deprive rammed earth of its rightful position in
building. Furthermore, the public’s then increasing yen for
miracle synthetics certainly had something to do with the
lack of acceptance for so “earthy” a technique.

Fortunately,
attitudes are changing. People are returning to any number of
time-tested ideas and techniques that have been scorned
for the last several decades … including the
concept of rammed earth construction. And at the center of
this “back-to-the-land-for-building-materials” movement stand
David and Lydia Miller, who have been proponents of rammed
earth homes for more than 40 years, and occupants of such
dwellings since 1945.

The Millers initially encountered the
“building with soil” process in an article from a 1937 issue
of American Home magazine and–during trips to
eastern Europe in the late 30’s–their interest grew as
they corresponded with several English and German architects
who had used the method.

In 1940, David and Lydia met the man
who would design their rammed earth homes: J. Palmer Boggs
… an environmentally oriented architect (and professor of
architecture at Oklahoma State University). Together, Boggs
and the Millers built their first house in 1945.

Then, in
1949–after David and Lydia had been airlifted out of
Berlin (where David had spent two years as a civilian legal
analyst for General Lucius Clay)–the architect teamed with
the Greeley, Colorado residents again … to build the rammed
earth structure the Millers live in today.

Earth Solar

Since David and Lydia’s present home was Boggs’s second
collaboration on a rammed earth dwelling, the architect made
use of his previous experience to produce a design that could
still be called advanced by today’s standards, but that was a
downright radical departure from normal building
practice back in 1949.

From a distance, the Miller
home–which rests atop a gentle knoll on the outskirts
of town–looks similar to many of the sprawling
ranch style houses built in the late 50’s. But as you turn up
the tree-lined driveway, you can see several external
features that set the structure apart from any
run-of-the-mill residence. For example, on the east side of
the building–where two perpendicular walls
meet–the thickness of the bulwarks (14 inches of earth
plus an inch of stucco covering) becomes apparent. In
addition, there’s a surprising lack of glass on the front of
the house … to prevent heat loss from that northern
exposure.

Most of the north-facing glazing is set
around the front door, which is framed by a pair of beautiful
sandstone columns (mined in Lyons, Colorado). However, the
northside bedrooms do have windows to admit natural
light, and a line of glazed vents runs along the roof level
in the living area.

Despite the lack of glass on the street
side of the house, the home’s interior is kept bright by
extensive south-facing glazing. In addition, because the
house arcs gently to match the sun’s path, light tends to
penetrate deeply into particular portions of the building at
specific times of day.

For example, the morning sun shines
into the bedrooms in the east wing and heats both the
wool carpet-covered floor and an interior
12″ thick rammed earth wall. By the afternoon, however, ol’
Sol has slipped around and is beaming in through the living
room’s huge thermopane picture windows. More of the woolen
floor covering–as well as much of the inside north wall
and the massive sandstone fireplace– catches
these rays and stores their warmth away for future use.

While
visiting the Millers, two of MOTHER EARTH NEWS’ staffers inadvertently
discovered just how effectively rammed earth does
hold the sun’s energy. A photo session was held on a chilly
October afternoon, and the doors to the living room and
kitchen had to be left open to admit more light for the
photographs. Throughout the course of the camera work, the
home’s inside temperature dropped from 65°F to 45°F.
However, once all the pictures were shot (the job took till
just about sunset) the house was closed back up, and the
hungry workers paused to sample some of Mrs. Miller’s
homemade bread and plum jam. Amazingly enough, within less
than an hour after shutting out the evening’s chill, the
inside temperature rose to 60°F with no source of heat
other than the warmth stored in the walls!

Furthermore, even
at only 60°F, the dwelling was surprisingly comfortable.
With heat radiating from the walls, the air temperature
actually seemed substantially warmer than the
thermometer indicated.

Of course, on really frigid days, the
Millers can produce additional warmth by circulating hot
water through pipes embedded in the four-inch concrete slab
floor. This auxiliary heating system was initially served by
a gas-fired boiler, but the Millers have recently
installed additional water-heating components: A local
company, McCreery and Sun, is in the process of placing three
4′ X 8′ collectors (from Solar Energy Products) on the
Colorado couple’s roof, and has also installed a
water-heating device in the living room fireplace … all of
which will tie into the originally gas-fueled heater. Though
the Millers have used a minimal amount of natural gas in the
past, they anticipate using next to none of the nonrenewable
fuel this winter.

Naturally, rammed earth walls do just as
fine a job of cooling as they do of heating. The
excess warmth of a particularly hot day doesn’t reach the
interior of the house until nightfall … when the outside
air has cooled. Plus, Palmer Boggs designed a few
special features into the Miller home to help the
walls do their cooling work. The southern side of the house
is equipped with eaves to prevent light from entering during
the summer months, and louvered vents are located at the
bottom and top of the wall to provide convective ventilation.
However, Mrs. Miller claims that it’s never necessary to open
more than one of the vents, and that not even a number of
successive 95°F days can raise the inside temperature above
75°F!

Proof in the Living

There are also a number of subtle advantages to
the use of massive earthen walls … pluses which contribute
to the comfort of this venerable form of passive solar
living. Besides doing a great job of insulating and storing
heat, pise also allows more air exchange than does any
comparable material. Thus a rammed earth house breathes (and
doesn’t tend to become clammy like a concrete structure)
without suffering any significant heat loss.

The thick walls
also provide a feeling of security which goes beyond their
warmth and strength. It’s hard to beat a 14″ layer of earth
for soundproofing, yet the material’s ability to protect
inhabitants from the less desirable aspects of the
out-of-doors (such as extremes of temperature and noise)
doesn’t–perhaps because of the native soil in the
bulwarks themselves–seem to intrude upon the residents’
relationship with their environment.

Down to Earth

Perhaps the best feature of rammed earth is that almost
anyone can build with it! As you’ll see in the sidebar,
constructing the massive walls is actually rather easy, and
most people have the necessary raw materials in their own
back yards! And, if you’re willing to supply the labor, a
rammed earth dwelling can be far less expensive than a
conventional (energy inefficient) house of the same size.

According to Lydia and Dave, rammed earth homes lend
themselves particularly well to construction on the community
level. Because digging, sifting, and tamping the earth
requires a relatively extensive amount of labor, a work
exchange arrangement among a number of potential rammed earth
builders can offer a way to construct pise dwellings quickly
and economically. Better yet, the spirit of such a
group effort harks back to the days of house raisings in the
formative years of our country.

Even though the Millers
employed numerous laborers to help in the building of their
home, and used costly custom woodwork extensively (as in the
magnificent pentagonal ceiling that Boggs designed), their
3,200-square-foot abode was completed for $32,000 … a price
which is slightly lower than that of a comparable
conventional residence of the time. But the point which David
and Lydia would wish to make–and that their house seems
to emphasize–is that rammed earth is not just an economy
construction technique … it results in some of the most
pleasant, comfortable, and energy efficient buildings
available at any price.


Rammed Earth From the Ground Up

Though the composition of finished rammed earth walls has
frequently been compared to that of sandstone, it actually
more closely resembles the geological rock type called
conglomerate. Sand is one of the major soil construction
components and clay does bond the materials . . . but
aggregate, with rocks up to an inch in diameter, is also
included in pise.

The earth in a rammed wall can usually be dug from the
excavation that’s made for the home’s foundation. Topsoil,
however, can’t be included in the mixture and should be set
aside for gardening uses … while the ground that is used
must be composed of about 30% clay and 70% sand and small
stones. Such a ratio is common in many parts of the
country, but roadbed aggregate must be added to especially
clay-heavy soils.

Once earth with the right composition is located (or
mixed), the material must be broken up with a rototiller
and sifted through appropriately meshed screens to remove
any large rocks. (The Millers have stones as large as an
inch in their walls, but some rammed earth builders specify
using nothing larger than half inch pebbles.) After the
consistency is smoothed, water is added to give the mixture
the proper adhesion. The ideal raw material is just damp
enough to ball up in your hand … but will still break
apart when dropped. Such a consistency is usually reached
by using about 12% H20, but the ratio varies depending on
the exact proportion of clay in the soil.

Rammed earth walls are built on a foundation that is at
least as wide as are the bulwarks themselves (remember, the
soil–in its final compressed form–will weigh
about 140 pounds per cubic foot). The foundation can be
composed of either poured concrete or specially prepared
rammed earth that has been fortified with the addition of
10% cement.

To build the wall, the forms are clamped onto the
foundation–the top of which is dampened
slightly–and from four to five inches of earth is
dumped directly atop the moistened concrete.

This dirt is then tamped with a flat bottomed device (such
as a concrete filled bucket with some sort of handle
embedded in it) which provides about

two pounds of weight for each inch of its diameter. To tamp
properly, just lift the ram and then let it drop …
continuing the process until the tamper no longer makes any
indentation in the earth. Ramming will compact the loose
dirt to about 50% of its original height, so each layer
will eventually take up between two and three inches of
space.

To continue raising the walls, dampen the previously tamped
earth, throw in more dirt, and repeat the procedure. Once
the form is full, take away the wedges, slide the boards
off, remove the 118″ steel straps, and move the form up for
the next level.

The ends of the walls are truncated by sliding a vertical
board inside the outermost metal straps and packing the
dirt against this barrier. Then, once you’ve squared one
wall, a corner can be formed by simply butting the next
wall perpendicularly against the original one.

The Millers now believe that it’s not necessary to cap a
rammed earth wall with concrete, though their 30-year-old
home does have a six-inch layer of the mix poured
on top of the compressed soil. (Some rammed earth builders
are still employing the concrete cap on their walls, while
others compromise by mixing cement in a 1 to 10
ratio–with the last couple of beds of earth.)

You can incorporate windows and doors into the massive
walls by framing the proposed openings with 2″-thick lumber
(of appropriate width) and tamping the earth around the
frames. Plumbing and wiring may also be built into the
unpacked walls … but both junction and switch
boxes should be temporarily plugged–with a piece of
lumber to prevent them from collapsing during the ramming
process.

It can take as long as several years for a rammed earth
wall to dry completely (and the strength of the material
increases during the curing period), but the forms can be
removed as soon as you’ve finished tamping. Then–two
days after the wall is completed — framing, nails,
and other connections can be added. You’ll have to act
quickly, though, because within another two weeks the
rammed earth will be too hard to get a nail into … unless
you first drill the wall with a masonry bit.

After the initial 14 days have passed, it’s no longer
necessary to protect the rammed earth from rain … though
moisture will still be able to penetrate the pise.
Therefore, exterior and interior coatings are more or less
a matter of your own aesthetic preference. The Miller home
has an external covering of stucco (over chicken wire) and
a layer of plaster on the inside, but David and Lydia plan
to leave the walls in their next house bare. They find the
natural light brown color of the rammed earth to be quite
pleasing.

The limitations on size for rammed earth buildings come
more from practical than from structural concerns. There
are “soil skyscrapers” In Europe that are as tall as five
stories, but building a structure over two stories high
involves lifting that would be prohibitive for the
do-it-yourselfer. In addition, because it’s difficult to
set floor joists directly Into a rammed earth wall, most
two story pise buildings use a ledge created by narrowing
the wall thickness on the inside –to brace the
support timbers at the second level. Thus a three-story
building with a 12″-thick top wall would have to have a
16″-thick bottom wall to allow enough material to form
joist ledges … and would be too thick to be
heat-efficient (heat from the sun doesn’t have time to
reach the Inside surface of walls over 16″ thick).

Unfortunately, there’s just not much written information
available to the owner-builder. The excellent
pamphlets put together by Ralph Paddy at South Dakota State
College are out of print, and the USDA never published much
instructional material on its test community.

Need Help? Call 1-800-234-3368