What is Rammed Earth Construction?
Rammed earth
construction is once again gaining in popularity for home builders looking for
eco-friendly options. With rammed earth, you're using the dirt under your
feet (or from a local quarry) to build a house. This is certainly a
"green" practice since it usually makes use of local materials (local
dirt!) and you don't need lumber, quarried stone, brick, etc. to be transported
from long distances.
Rammed earth
construction has its pros and cons of course. Let's take a look at the
positives and negatives.
Pros of
Building with Rammed Earth
- A
properly sited and designed rammed earth home is ideal for passive solar
strategies, so it can be great for an off-the-grid house. The thick,
dense walls absorb the warmth from the sun all day and slowly release the
heat into the interior of the house at night. This helps keep
heating bills low in the winter, and these homes tend to stay cool in the
summer as well.
- Dirt
is an easy-to-acquire material and while there are some requirements (not
all dirt is going to have the right mix of sand and clay), you ought to be
able to get it locally, so this tends to be an eco-friendly building
material.
- And
let's not forget the coolness factor of having a house that is built out
of something unique. In many cases, homeowners wanting to save money
help with the building process, and there are even DIY sites out there
that will tell you how to make a house on the cheap using rammed earth
construction.
Cons of
Rammed Earth Construction
- Soil
selection needs to be done carefully, and if you are able to use dirt from
the building site, you'll end up with some big holes you need to figure
out how to work into the landscape.
- Though
it might seem that a house made out of dirt would be cheap, rammed earth
construction actually tends to cost 5 to 15% more than conventional
construction (due to the labor-intensive process of creating the rammed
earth forms).
- It's
difficult to impossible to create rounded or sculpturally shaped walls the
way you can with other materials. Homes made with rammed earth
construction are going to be boxy in nature.
- In
colder climates, you'll probably need extra insulation (it's typical to
add foam insulation to exterior walls and then cover it up with stucco).
An alternative
house building material that we haven't talked about before is rammed
earth. And, yes, it's exactly what it sounds like. The walls are
made from earth that is smashed into forms.
Rammed earth has a
long history around the world and was popular in the United States before
railroads made the transportation of lumber and other building materials
commonplace. In recent years, the material has been seeing a resurgence
as an eco-friendly option for home building. It doesn't get much more
natural than building a home right out of the ground around it!
How Building
a Rammed Earth House Works
The building
process starts out with a concrete foundation that protrudes above grade six to
eight inches as a "stem wall." The rammed earth wall will stick
to the stem wall via gravity and pressure.
Mineral-laden soil
(not topsoil--save that for the garden) is used for the walls. A mixture
of mostly sand with some clay works well. On sight soil often isn't of
the right consistency, so you may have to get it from a local quarry (this
saves the problem of correcting gaping holes in your landscape anyway).
Typically 3-10%
portland cement is mixed into the soil for stabilization. The mixture is
then moistened to lubricate the soil particles and help with compaction.
The earth is placed into box-like ramming forms (similar to forms used for
creating concrete panels), which are attached to the stem walls. The wall
depths will be anywhere from 18 to 36 inches (in a two-story building the
first-story walls are typically wider). Plumbing and electrical are
usually run within the forms, and windows and doors are framed out before the
earth is rammed home.
In the end, the
rammed earth walls will have a slightly textured surface and striations left
from the ramming process. Wall color depends on soil mixture. You
can, of course, paint but many homeowners want to be able to see and admire
their natural rammed earth walls and will simply apply a clear sealant to
interior walls to prevent flaking. In cold climates, foam insulation is
often added to exterior walls, which are then covered with stucco.
Rammed earth houses
are a unique and eco-friendly way to build a home.
Source: Living
Homes: Sustainable Architecture and Design
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