The Dirt on Rammed Earth
by Lloyd Alter, Toronto on 02.20.08
After a couple of thousand years, rammed earth is making a comeback. It has so many advantages- it`s local, it has great thermal mass and acoustic properties. Dan Whipple writes about it in New West Magazine:
When you look around the West at all the treeless spaces, it's a little surprising that earthen construction hasn't taken a greater hold on the architectural imagination.
Linda Kiisk, associate director of facilities planning at the University of Wyoming describes it this way: "Rammed earth basically works like the formwork of pouring a concrete wall. But instead of concrete, you are using soil from the site. The material is tamped down. This can be done with sledge hammers by hand or with a pneumatic device. Then you pull the forms off, and you have a stable wall.
Nk'Mip Desert Cultural Centre by Hotson Bakker Boniface Haden Architects.
Whipple continues: Earthen homes are wonderfully energy efficient, said Tom Ward of Ward+Blake Architects in Jackson, Wyo. He has designed several for second-home seeking clients in that upscale neighborhood.
The walls of a rammed earth home are sometimes two feet thick -- the acoustics are wonderful -- giving the house what's called "thermal mass," Ward said. Throughout the day, as an exterior wall is exposed to the sun, it absorbs energy, and then slowly releases it at night.
In 1983 Brandjord studied and compared the energy use of rammed earth and conventional homes. He estimates an earth house uses one-third as much energy. ::New West Magazine via ::Materialicious
Some thoughts on rammed earth that come quickly to my mind. What, if any, surface treatment is needed? Are the walls resistant to earthquakes? What is their durability in more humid climates? What soil composition is most suitable for this type of construction? Moisture penetration, from either side of the wall, could be a significant problem. And a high-clay soil would seem to make a better wall than a high-sand soil.
There research available on rammed earth building. Go & seek.
Sim Van der Rynn (sp?) is doing excellent things with it in California.
It's been used for centuries in parts of France, among other places, where it gets cold & wet.
Soil composition is important. Some recipes for rammed earth call for mixing in asphalt &/or cement as stabilizers and to build cohesion and strength. Hand tamping is cheap, but greater compression and consistency that mechanical tamping can provide will yield a stronger wall.
Less labor intensive than adobe,, no water or straw needed, and none of the rot and pest infestation issues of adobe or straw bale building.
You could incorporate reinforcing into the walls or add other shear walls to provide earthquake resistance. Otherwise, it should perform similarly to other unreinforced masonry buildings.
In damp or rainy climates I'd certainly consider stucco or other rainscreen surfaces, along with broad overhangs, to avoid any water deterioration issues. It's a perfect candidate for exterior insulation systems, in order to bring all that thermal mass into the tempered interior of the building.
Check out Wikipedia's entry for additional info:
http://en.wikipedia.org/wiki/Rammed_earth
The soil needs to have a certain amount of clay to bind the soil. Unfortunately it also needs a "stabilizer" which is usually cement. It's a lot less carbon intensive than concrete, but it's not perfect.
On the plus side, the cement will make the material durable in temperate and humid climates. There will still be some moisture migration, but the wall won't melt away.
I've seen articles on rammed earth structures in California which has some of the strictest seismic standards anywhere, so I think that it can be designed to withstand substantial earthquake forces.
Check out the work of James Cutler, particularly Meteor Vineyards, for some really beautiful rammed earth construction.
http://www.cutler-anderson.com/
Also check out Rick Joy who uses the technique in nearly all his buildings. They're really a visual treat, too.
http://www.rickjoy.com/
(The firm's site is under construction but you can follow the link to an Amazon listing for a book about his work.)
Finally, check out this site with a lot of information on rammed earth, adobe, straw bale, et cetera:
http://www.eartharchitecture.org/
Foraker, some of your questions are answered in the article that's linked at the bottom.
Check out the Factor E Farm... they are working on an open-source compressed earth maching.
http://openfarmtech.org/weblog/?cat=13
To answer some of those questions, read the original article in New West Magazine.
What are the limitations? I assume one story only (which is fine by me). I hear straw bail is not a great choice for very wet or humid climates. What about dirt? It sure is beautiful.
What about Earthships? They're some of the most innovative, creative, smart housing designs I've seen, and they use old tires and packed earth as the basis for the walls.
I am a great fan of earth as building material, and intend to make my own home out of earth some day. That said, rammed earth does have a few issues. The labor intensive nature of building with rammed earth can be prohibitive for many people, and may also drive up the embedded energy cost of the building if machine powered tools are used. The soil must have a proper proportion of clays in order to be used. (Subsoils can often be used.)
Another, newer technique is cast earth, in which earth is mixed with gympsum, a small amount of portland cement, and a drying retardent that prevents the slurry from setting too quickly. It is then poured or pumped into molds like concrete. This is still a proprietary process, and it requires a fair degree of mechanization, but it does make for some very durable and attractive buildings.
Either technique can be used to create a very robust and energy-efficient building that will last for many hundreds of years with fairly minimal upkeep. It's wonderful stuff!
Foraker; You may coat the outside/inside with a lime base material (white wash, it can be pigmented any colour). It may also be treated with Linseed Oil to seal out water. If the structure is in a dry or protected area it may be left as is. If damage does occur under chip the damaged area and apply fresh earthen material.
I too plan to build my home with earth some day, but rammed earth has certainly been removed from my list of possibilities. After working on a foundation for only two days I was too sick of it to continue (finished the foundation with stacked rock).
It is a very very time and energy intensive process. If you had a pneumatic device it would be better, but we were in the jungle in Thailand with no such luxury (or any power source).
I agree that the pictures are beautiful and I love thermal mass earth homes, but I'll go for cob an day. It's more fun and you can build much faster.
I grew up in another version of a "rammed earth" home: a house made of adobe bricks with walls 18" thick. The bricks were made by pressing a mixture of a sticky mud and straw into wood forms 18" X 9" X 4" thick. The bricks were held in place using the same sticky mud as mortar.
Our home was warm in winter and cool in summer. The house was built back in the twenties in the high desert of New Mexico. In the thirties, a pre-Columbian pit house was excavated on this farm and the walls were made of adobe bricks. This building method has been practical for centuries in the Southwest.
I grew up in another version of a "rammed earth" home: a house made of adobe bricks with walls 18" thick. The bricks were made by pressing a mixture of a sticky mud and straw into wood forms 18" X 9" X 4" thick. The bricks were held in place using the same sticky mud as mortar.
Our home was warm in winter and cool in summer. The house was built back in the twenties in the high desert of New Mexico. In the thirties, a pre-Columbian pit house was excavated on this farm and the walls were made of adobe bricks. This building method has been practical for centuries in the Southwest.
Too bad rammed earth is so expensive to build with. It's also really pretty. But because labor is so amazingly expensive these days it's pretty much only for the richest people, or people that have tons of time on there hands.
We have a group locally here (North Texas) that builds a very green home (Monolithic Dome Homes). I visited the dealer site several times and have decided on this type of building system for my next home. It combines all the best aspects of the rammed earth, bail, earth ship, etc but with out the draw backs. Only problem is they use concrete as the shell. I know the school is out on the energy and pollution for the concrete industry however, these homes are nearly earthquake proof, highly energy efficient, nearly indestructible to the elements (fire, wind, hail, tornadoes, hurricanes, etc). I've seen pics of a couple that have been through major hurricanes, forest fires, tornadoes and most come through unscathed. Also, they use approximately 60% less energy to heat and cool.
Just my 2 cents ....
Interested parties may wish to check out wardblakearchitects.com to see our take on seismically stable Rammed Earth.
I designed and built my home out of rammed earth in Canada.
Here are my blogs about it:
general interest:
www.rammedearth.blogspot.com
project specific:
www.sonoramarammedearht.blogspot.com
get informed!