In the heat of a desert summer, you can go inside an adobe building and find relief. I lived in an old adobe many years ago, and the interior temperature was always 70. That’s a nice change from 85 or 90 outside. Adobe is part of the reason we don’t need air conditioning here. It is also the reason our heating bills can be so low in winter. What is it about mud that makes it so energy efficient?
Earthen walls use the same qualities to heat and cool. Sounds like a paradox, doesn’t it? In winter, the earth absorbs direct sun or warm ambient air. As night falls and temperatures drop, that collected heat is slowly radiated back into the room. The laws of thermodynamics come into play as warm and cool air do a constant dance, which keeps you comfortable.
Mud is the original building material
In summer, mud walls do the same thing. They absorb warm air, keeping interior temperatures cool. Heating and cooling from a stable temperature of 70 or so is more cost effective than trying to cool a 90 degree room or heat a 55 degree space.
Mud is the original building material. It was and is still plentiful. You can’t get any more local than building your home from the soil on your site. Even if you have to buy your materials, they don’t come from far away.
Eco-friendly building advantages of earth-based houses
Other eco-friendly qualities of earthen building materials besides low embodied energy: no waste (it biodegrades), durability, little maintenance, no toxicity, fire and insect resistance, and excellent acoustics. Mud walls also save trees from being cut down.
The earth can be used in many forms to create buildings. It can be formed into bricks (adobe brick or compressed earth blocks, CEBs), poured into wall forms and pounded down in stages to create a solid wall that is ready for finishing (rammed earth), or packed into old tires stacked like bricks and covered with mud plaster (earthship). Mud walls can also be built by putting handfuls of mud on top of each other in low layers (cob).
Adobe and CEB bricks
Adobe bricks or CEBs are the most common of the earth building materials. I have lots of friends who have built homes by making bricks from soil on their land. A form is made of 2x4s. It looks like a ladder with 8-10 spaces and closed ends. The soil is mixed, the form is filled then removed, and the bricks are laid in the sun to dry. The form is then filled again. You can make hundreds a day! It’s a great community project.
CEBs are bricks made with a machine called a presser, which compresses the soil to create a heavier, denser brick. Because the process is mechanized, the bricks are uniform. Builders like that! They also like that a brick can go from the machine to the wall. There is no drying time, so projects get done faster. House walls can be put up in a day!
Rammed earth and earthships
Rammed earth is not so much mud as it is gravel, sand and cement. After 7-8” of the mixture is poured into a form, it is tamped down to about 4-5”. Then another layer is added. The forms are removed the next day, and the walls strengthen over time. The layering creates striations in the finished wall, which gives it the look of sandstone.
Earthships are very common where I live. They were actually born here of recycled materials. Discarded tires are a problem wherever there are cars. Mike Reynolds decided to experiment with them by packing them with mud, then stacking them like traditional brickwork. Exterior walls are the thickness of a tire, which offers excellent insulation and thermal mass. Interior walls are of cob or concrete, also good mass. Earthships rarely need supplemental heat, since they are built into an earth berm and have a bank of windows on the south side.
My next building project
My next building project might be cob. I imagine a meditative practice mixing mud and applying it with my hands layer by layer. It’s a slower process than other earth building methods, but the builder is more involved and connected to the earth. I like the creativity that cob affords, too. Walls can be curved with benches built right in, and reliefs are easy to add inside and out. Design would be flexible.
Earth is one of the smartest building materials there is. It’s local, and earthen buildings blend in with their surroundings. Emergency shelters can be built from the earth anywhere. Mud makes a great community project like an old-fashioned barn raising. Buildings last for centuries and resist bugs and fire. They are biodegradable – if you have leftover material, just toss it out back! Abandoned adobe buildings here simply melt back into the land. The mass of earth makes buildings easy to heat and cool. Earth building is the intelligent choice.