Unusual and beautiful, "bottle windows" are a hallmark of cob houses. When colored bottles are used, the effect is that of a stained glass window, but even clear bottles make a pretty display. WARREN KRILENKO

Dirt is the original DIY material. In cultures all over the world, people have used earth to fashion everything from bowls to buildings. We know this because so many earthen homes are still around, including buildings hundreds and even thousands of years old. In recent decades, interest in earth construction has risen. What follows are some of the pros and cons of the different types of earthen building, including adobe, cob, compressed earth blocks and clay-slip straw, and some practical tips on things you may want to try as well as those you’ll want to avoid.

Earthen Home Basics

Some basic features and practices apply to most earthen building types. First, the old adage: Give your buildings a good pair of boots and a hat. That means lifting your earthen walls up away from water on a solid foundation and covering them with big overhangs.

I’m a fan of outdoor rooms, so I prefer large patio overhangs all around, except for the south side of the building if we need passive solar heat gain in the winter. To prevent water damage, keep earthen walls covered during construction. A sensible approach in wet climates is to build the roof first on a post-and-beam structure, and then infill with bricks, cob or clay-slip straw.

Second, dirt isn’t insulation. Light, fluffy and airtight assemblies prevent heat flow; massive, dense ones do not. Some people don’t get this. I think the confusion arises because of a unique feature of the most common earthen building climate: hot and arid. In such regions, exterior temperatures tend to fluctuate above and below desired interior temperatures (hot during the day, cold at night). Thick-mass walls can act as an effective form of dynamic insulation. In all other climates, in my view, earthen materials aren’t appropriate for exterior wall systems if your goal is to build the most energy-efficient building. They instead should be used inside the insulated envelope as interior walls, floors and plasters to add mass, soundproofing and beauty to the building.

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Third, earthen building is not easy, simple or cheap. Dirt is heavy, and you need to move a lot of it around to build. That’s not easy. Anything heavy that has the potential of falling on your head needs to be taken seriously. As for cheap, a big plus of earthen building is definitely that much of the material can often be found on site and is ubiquitous and inexpensive. But earthen building is labor-intensive, so what you save in materials, you may pay back in hard work. Of course, much of it may be slave labor (i.e., you), but to make an apples-to-apples comparison with conventional approaches, you have to value that time. I could make a free building out of gold if the gold were salvaged and the labor were unpaid.

Finally, the best earthen building approach is one that has a history in your area, because that means local expertise is available, and problem solving and code approval will likely be easier. Being a novice without elders to guide you along can be a lonely, difficult enterprise. Building is hard, serious work — wonderfully rewarding if done right and potentially calamitous if done wrong.