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What Makes a Wood Burning Stove a Rocket Stove?

The coziness of a “rocket mass heater” (aka “rocket stove”) is something we would love to have in our house. So when Lasse Holmes, esteemed natural builder and teacher of this DIY technology, said he was going to be in the area, we decided to sponsor him to teach a rare workshop here in Western North Carolina on the theory and building of the rocket mass heater.

rocketmassheaters-evans-jacksonLasse is featured (among others) in Rocket Mass Heaters, a book by by Ianto Evans and Leslie Jackson. Leslie has cheerfully agreed to let us use a little excerpt with a link to the complete article explaining these wonderful wood-burning stoves at rocketstoves.com. In fact, we are including a copy of Rocket Mass Heaters in the price of our upcoming Rocket Mass Heaters workshop (April 7, 8-9, 2016) since it is an essential resource for anyone serious about understanding and building one!

»Learn more about Lasse Holmes and our Rocket Mass Heater/Fire Play Workshop…

Excerpt from Rocket Mass Heaters by Ianto Evans and Leslie Jackson:

What Makes a Wood Burning Stove a Rocket Stove?

The rocket stove burns cleanly and almost completely, and it does so by means of a combination of materials that is it built with, and geometry. The chimney is insulated, maximizing its interior temperature, thus helping the fuel burn completely. The wood is small, dry and straight. The chamber in which the wood burns is of a size to reflect back on itself, also maximizing the burn by helping it stay hot. The opening in the stove in which the fuel is fed, the chimney on which the cook pot sits and the gaps–around which the gases flow past and around the cookpot–are very carefully sized to control the amount of oxygen mixing with the burning fuel. The stove’s “L” shape or “J” shape contributes to an ideal mixing of the combustion gases for clean burning. It’s all about the proper conditions for complete combustion…
»Read complete article at rocketstoves.com

rocket mass heater diagram

What is Earthbag Building?

When the Mississippi floods, people use earthbags to hold back the water. And when you buy a sack of oats for your horses, it might come in a polypropylene bag—the same kind that they fill with sand or soil and use to direct the flood waters. But did you know you can build permanent structures with the same bags? In fact, you can get the material they make the bags from in a big roll—it is one long continuous tube at that point! This is before they cut it into smaller pieces and sew it to make bags—and that’s often even easier to use than the bags!

This building technique, which can use a wide variety of soil types, is called Earthbag Building. You can build foundations out of it, retaining walls, square houses, round houses, amoeboid houses, arches, vaults, domes, sculpture, benches, privacy “fences.” The list goes on!

Once you cover the sun-vulnerable woven polypropylene bags in either earthen, lime, or cement stucco, you have a very durable mass wall capable of carrying heavy loads such as cob, or adobe. And you can put the bags directly in contact with the ground, but you can’t do that with any earthen materials or straw and expect them to last. Thermally, earthbag acts a lot like adobe, cob, rammed earth, or earthships (tire houses), but is easier to build.


In the late 90’s, Steve built an earthbag house in the Bahamas with Carol Escott. They had heard about it at a natural building colloquium from Kaki Hunter and Doni Kiffmeyer, who had built an earthbag dome in Moab, Utah. So Steve and Carol asked them to come teach them their tricks and help them start it off—which they did! Eventually Kaki and Doni wrote a great book on the subject, and we highly recommend it! It is called Earthbag Building: the Tools, Tricks, and Techniques, and you can get it here at Amazon.com. Since then, Steve and Doni have also taught earthbag building in Jamaica.

Though we love straw bales for lots of functions such as houses, studios, wine rooms, etc. (they insulate so well!), they really don’t do well in contact with the ground. Since we moved to our place in Asheville, NC (which had absolutely no flat spot!), we have done a little grading and built some nice dry-stacked stone retaining walls, but we need more! So we have been thinking about and planning out some earthbag retaining walls. Earthbag is one of the few natural building techniques that can be in contact with the ground and not suffer.

We look forward to sharing our earthbag expertise with workshop participants on May 2-3, 2015 in a very affordably-priced two-day workshop called Earthbag Construction: Basics and Beyond. We are going to use mostly tubes, actually. We will probably only use bags for the arch demo we are going to do. (See our Upcoming Events page for more info about this workshop).

Preparing for earthbags

Preparing for earthbags

Steve and four work exchangers (who are attending the workshop for free in return for help preparing the spot) did a ton of digging the other day, as you can see from the photos! This resulted in no less than four piles of soil in our yard. It is always astounding how soil “expands” when you dig it up! Some of these piles will get used to fill the tubes, but we will fill a good percentage of them with gravel. Also, we will fill the footing trench with gravel (and a drainage pipe).

Steve Kemble in trench dug for upcoming earthbag workshop

Steve Kemble, Natural Builder and Instructor

If you want to read a bit deeper into the earthbag method, check out this informative and fun article by Kaki and Doni—they are excellent writers. And good people too! And you can always subscribe to our Hug Some Mud newsletter to stay informed about our next straw bale, cob, earthen paint, lime and earthen plaster, or other workshops (just go to the Subscribe link at the top right on any page of mudstrawlove.com). Plus, we’ll be writing some more blog articles about natural building. Don’t worry, we won’t inundate you with too many emails!

More About the Instructors
One of the things Steve and I (Mollie) really love to do is pass on our knowledge, tips, techniques, and enthusiasm about natural building—straw bale, earthen paints and plasters, cob, earthbag, and more. We have been teaching for a long time (about 44 years worth between the two of us!), and doing natural building for a bit longer than that. We have learned a lot in those years, and taught a lot too—and still think we have a lot to learn. So we encourage our students/workshop participants to glean whatever is most helpful from us, and also to think for themselves and let us know how they think we could do it better. We love to see people excited and empowered by gaining the knowledge they need to make their own dreams come true in an environmentally conscious way.

Natural Building 101

This article gives you a crash course in the terminology and basic concepts of Natural Building, providing a glossary of common terms, a materials and methods reference guide, and descriptions of natural building materials and finishes.

Common Terms in Natural and Green Building

‘Natural building’ and ‘green building’ have their roots in the broader subject of ‘sustainability.’ Sustainability means harvesting or using a resource so that the resource is not depleted or permanently damaged. Even renewable resources can be used in a way that is unsustainable, such as harvesting trees faster than the forest is able to regenerate itself. Sustainability can also be applied to the subjects of energy and water use in a building, and to the waste products of that building.

‘Green building’ focuses the principle of sustainability on reducing the impact that our built environment has on the rest of the planet. Green building reduces environmental impact both in terms of the energy that is required to operate and maintain a building, as well as reducing the ‘embodied energy’ of the materials that go into building it. The embodied energy of a building material includes all of the energy that goes into extracting it from the environment, the manufacturing and processing of that material, its transportation costs, and the costs of recycling or disposal of that material at the end of its useful life.

Green building utilizes renewable and lower impact materials, renewable energy and reduced energy use appliances and design, water and waste recycling, rainwater collection and climate-tempering and climate-appropriate landscaping. It also makes use of some highly processed manufactured products; however, they are lower in environmental impact than their more commonly used contemporary counterparts.

Natural building is green building that places particular emphasis on using materials which are found locally in nature, and used in a raw or minimally processed state. Natural building places a higher value on human labor, craft and creativity rather than specialized skills, capital and technology. Natural building also places a high value on the ongoing health and well-being of the building’s inhabitants, as well as the surrounding environment. This concern also extends to the builders.

A Handy Reference Guide for Common Natural Building Materials and Methods

The most common elements used in natural building are: subsoil (various combinations of clay, sand and silt), grasses (including straw and bamboo), stone and gravel, wood (often rough-milled, and used sparingly unless you have a plentiful supply), and building lime (from limestone). The local availability of these particular elements, along with climate-specific design needs and the skillsets and sensibilities of the builders, are major factors in determining how and of what materials a natural building is made.

The following is the beginning of a glossary of common terms, techniques and materials used in natural building. These building blocks are composites of the above earthen materials, and some of the ways they can be used most effectively to meet different needs. In future articles we will talk more about the specifics of how these materials are used.

Natural Building Materials

Adobe: sun-dried mud bricks made of clay, sand, silt, straw and gravel, set in mud mortar to make massive walls which can be planar or curvilinear, and which can be structural or non-structural. Adobe can also be used for the roof of a dome or vault, eliminating the need for wooden roof framing.

Rammed earth: a moist mixture of clay, sand and silt which is tamped into forms to make massive, planar structural walls.

Cob: a wet mixture of clay, sand, silt and long straw which is hand-formed in place to make massive structural walls and other sculptural elements.

Light-clay, slip-straw or straw-clay: long straw that is coated with a clay slip and packed into forms to make planar, lightweight, insulated non-load-bearing walls used to infill between structural vertical elements of another material. Light-clay can also be used to insulate roofs and floors, and can be formed into insulated bricks.

Straw bale: Large compressed bricks of straw, bound with twine or wire, which are stacked to make planar or curvilinear walls. Straw bale walls can be either load-bearing or infill, and are highly insulated. Straw bales can also be used to make vaults or dome structures in areas with little rainfall.

Earthbag: Polypropylene or burlap grain sacks which are filled with damp earth and tamped to make linear or curvilinear foundations and load-bearing walls. Earthbags can also be used for the roof of a dome or vault.

Stone masonry: raw or cut stones which are dry-stacked or set in mortar to make linear or curvilinear foundations and load-bearing walls.

Compressed earth blocks: a mixture of dampened clay, sand, silt and gravel which is compressed by a machine into bricks, and used much like adobe.

Cordwood: short logs cut to uniform lengths which are set in mortar to make massive and insulated structural or infill walls.

Wattle and daub: A framework of stiff vertical sticks woven horizontally with thin, flexible saplings or split bamboo and covered with plaster to make thin non-structural walls and partition panels. Wattle and daub walls can also be left unplastered for ventilation, or used to create a double wall construction in which an insulative material is stuffed between the two wattle and daub walls.

Thatch: long stalks of water reed or straw which are tied into bundles and attached to a roof structure for an insulated and rain protected roof covering. Large leaves such as fan palm can also be used for thatch.

Papercrete: waste paper mixed with water into a pulp slurry, with sand and a small amount of Portland cement or lime added to make a lightweight, insulated material which can be formed into blocks, poured into forms, or used as mortar for non-structural walls, domes and vaults. Clay can be substituted for the Portland cement to make ‘fidobe’ (fibrous adobe).

Bamboo: the most useful plant on earth, bamboo is a fast-growing giant grass capable of spanning large distances and resisting large structural loads. Timber bamboo can be grown in temperate climates to replace structural lumber.

Natural Building Finishes

Earthen plasters: mud made from a screened mixture of clay, sand, chopped straw and/or manure; trowelled, hand-applied or sprayed onto earthen walls for protection from the elements.

Lime plasters: a mixture of building lime (made from limestone that has been burned and crushed), sand and sometimes fiber; trowelled or sprayed onto earthen walls for a weatherproof and durable coating.

Earthen paints: a coating made of either wildcrafted, screened colored clay or white pottery clay with pigments added, mixed with aggregates such as sand or mica and often wheat paste and powdered milk (to increase durability); applied like paint over earthen plasters, drywall or other surfaces to seal and beautify them.

Limewashes: a wash made of building lime and water, colored with natural pigments which can be painted onto an earthen wall to seal, protect and beautify them.

Earthen floors: durable and beautiful floors can be made using various combinations of earthen materials, poured or moist-packed into place, trowelled to a fine finish and sealed with oils or non-VOC sealers.

Choosing Natural Building

Building using natural materials comes from a desire to get closer and more connected to our environment; the natural patterns of life in and around us. Living in a home that fits into the landscape rather than being imposed upon it, that seems to grow out of the earth and keeps us comfortable with a minimum of environmental impact, can shelter and nurture us in a way that gives us a sense of belonging.

A growing sense of isolation in western culture has had a great many side effects, many of which are detrimental to the well-being of life on this planet. Environmental awareness and science have alerted us to such things as global warming, holes in the ozone layer and species extinction. The industrialized world is using the finite resources of the planet at an unprecedented rate, while contaminating air, water and soil along the way. And much of the developing world is hot on our heels. In a mad rush for progress, we act as we have forgotten that trees support us as much as our bones, that clean water gives us life as much as our blood does.

Choices Matter Over Generations

Even though we can’t always see how the choices we make in our daily lives affect our back yards, we can see the cumulative effects. Turning on a light or cranking the heater doesn’t immediately appear to pollute the air in our rooms or around our houses, but when we see a power plant in operation, or get a headache from chemical fumes coming from a building material in a new house, we begin to make connections. Today, we have more choices than ever before, and each has its own set of consequences, some apparent and some almost invisible. The more aware we become of the consequences of our actions, the more we are able to respond accordingly, and make choices that reflect a shifting consciousness towards connectedness and interrelatedness. Natural Building is an extension of this awareness into how we create our living and working spaces.

Most of us would agree that the most basic human survival needs are food, water, clothing and shelter. These issues are a daily concern of every human, and how they are dealt with has a cumulative effect over a lifetime and over generations. In the last century, western culture’s relationship to sheltering ourselves has changed dramatically. Prior to this, most housing needs were met by hand-crafting the natural materials available nearby (wood, rock, soil, grasses) into climate-appropriate structures that stayed relatively comfortable year-round. With the rise of industrialized society, new materials and methods have been developed that make building faster and easier than traditional building methods, meeting the needs of a rapidly growing population. The accompanying widespread availability of centrally generated power has lessened the need for climate-appropriate design to achieve comfort levels. These newer methods often rely heavily on resource extraction, manufacture and long-distance transportation. Compounded by population explosion and redistribution, the unintended consequences of modern industrialized building include planetary resource depletion (forest clearcutting, drilling, mining), pollution and other damage to the earth’s life support systems.

The use of highly manufactured materials and toxic chemicals in the building industry has also had unintended impacts on the health of factory workers, construction tradespeople, and the families living in these houses. Major emerging health threats include increasing chemical sensitivities and environmental illnesses due to toxins in our surroundings. Buildings account for one-quarter of the planet’s yearly wood harvest, two-fifths of its material and energy use, and one-sixth of its water use. Figures such as these make it clear that a shift in our approach to building could have significant impacts. A growing number of people in the western industrialized nations are now realizing that technological solutions to housing are not without their global consequences. The process of building a house represents the largest concentration of resource use that many people will experience in their entire lifetime. There is a movement towards blending more traditional building approaches with a judicious use of modern industrialized materials. Natural building is experiencing a resurgence growing from a conscious choice to honor the interrelatedness of our resource use, our own health and that of the planet.