What are Earth Blocks?
Earth Blocks, or compressed earth blocks (CEBs), are machine-made adobes, a modern variation on an ancient building material. There are many earth block press machines on the market that produce a variety of sizes, shapes and rates of production.
The blocks are typically composed of soil with high clay content, sand, and lime or portland cement as stabilizers. The stabilizers enable the blocks to maintain their structural integrity when wet. The percentage of each ingredient will vary from region to region depending on soil composition.
How do Earth Blocks differ from adobes?
Sun-dried adobes are made by pouring a mixture of mud and straw into forms on the ground, with the frequent addition of asphalt emulsion, a petroleum by-product, as the most widely used stabilizer. The adobes cure in the sun for several weeks, the time varying depending on the weather.
Earth blocks provide the benefits of consistent size, quality, speed of production, and the option of non-toxic stabilizers. In addition, their uniform size speeds the building process, with associated savings in labor and mortar costs. The courses of blocks are uniform and only a thin layer of mortar between courses is required. A traditional adobe wall can contain up to 20 percent mortar. Compressed earth block walls can contain as little as 5 percent mortar. Finally, earth blocks have a considerably higher PSI (pounds per square inch), a measure of compressive strength, than sun-dried adobes. While sun-dried adobes are strong enough to meet the state of New Mexico’s code requirement of 300 PSI, earth block PSI test results typically exceed 750 PSI. We have recorded strengths as high as 2560 PSI for stabilized compressed earthquakes blocks.
How much does an Earth Block building cost?
“Costs” can be measured either for construction or over time. Masonry construction is typically more expensive than conventional lumber construction for the building phase. However, the lifetime costs of the building are reduced due to energy savings, maintenance, longevity, and health factors.
Building costs also vary depending on site location, soil composition, and architectural design. A single story rectangle will cost less per square foot than a complicated shape, such as an ellipse.
How does Earth Block construction compare to conventional building techniques?
An earth block building is not only healthy for the individual, but also for the planet. Soil, earth block’s primary ingredient, is a renewable, non-toxic natural resource. Earth block walls are breathable, soundproof, bug-proof, fireproof, and even bulletproof! Requiring less transportation of materials than conventional construction methods, earth blocks have a lower embodied energy than conventional building materials. Energy savings are immediate with thermal mass equating to lowered heating and cooling requirements. Earth block buildings can last for centuries. Ancient earthen structures stand today in many parts of the world. The average expected life span of a wood frame building is about 70 years.
Can I use my on-site soil?
Yes, sometimes site soil can be used. However, unless the plans call for a large excavation, such as a basement or a pond, digging and screening site soil might proveto be more expensive than having screened soil delivered. This process can also leave a large hole in your land.
If the site soil is not suitable for block production, soil can be delivered to the site or blocks can be made elsewhere and transported to the site. Trucking costs for soil or blocks can be expensive depending upon the location of the site and the amount of soil or the number of blocks needed.
What does it mean to have a ‘breathable’ wall?
A breathable wall is able to absorb and release water vapor. Water vapor molecules are no larger than air. Like human skin, the water vapor passes in and out, but does not transmit water molecules. This transpiration of vapor helps to regulate and modify heat and humidity. This benefit reduces the need for mechanical systems to maintain human comfort levels.
Clay maintains an equilibrium moisture content. If there is too much humidity in the air, the walls will absorb water vapor. Conversely, if the air is too dry, the walls will release moisture. Human health is optimized at humidity levels between 40% and 70%. Low humidity levels will dry out the trachea, contributing to respiratory issues. High humidity levels promote mold growth, again not beneficial to human health.
Cement stucco and other synthetic materials, such as closed cell insulation and paint, applied to earth block walls will hinder their breathability. Lime or clay plasters maintain an earth block wall’s breathability.
What is thermal mass?
Thermal mass is the ability of a material to absorb and store thermal energy. This creates thermal inertia that requires a much larger input of energy over time to change it’s temperature. This is sometimes referred to as a “thermal flywheel”. Therefore, if a wall is cool from a relatively chilly Summer night, it tends to stay cool well into the day. Conversely, If a wall is warmed by the afternoon’s winter sun, then it stays warm well into a cold winter night.
Walls that have low thermal mass, such as conventionally framed walls, do not have these properties and are easily effected by a change in temperature.
Earth blocks, on the other hand, will “flatten out” or buffer large temperature swings with their thermal mass capabilities and significantly decrease the need for additional heating in winter or cooling in summer.
What’s the difference between thermal mass and insulation?
Insulation is used to reduce a material’s thermal conductivity. The object of this systemmis to thermally isolate a wall from external temperatures.
In a wall made of lightweight materials, such as lumber, the insulation is the building’s only protection against external fluctuations in temperature. These lightweight insulated walls do not contribute to a building’s heating or cooling capacity. They attempt to stop the transfer of thermal energy.
A wall with high thermal mass, such as an earth block wall, is an integral part of the building’s heating and cooling system, by storing and releasing thermal energy as needed. In extremely cold or hot environments, earthen walls can be insulated on the exterior to minimize the transfer of extreme temperatures. Alternatively, a double earth block wall can be built and then filled with insulation. A natural, breathable insulation is preferable to a rigid, closed cell, synthetic insulation, and the cavity wall provides this option.
Does an Earth Block building require insulation?
No, typically earth block buildings do not require insulation, but can benefit from it in extreme climates. As mentioned above, a common technique is the use a double wall system, with a cavity between the walls. This cavity should be filled with an insulation that allows for the transfer of water vapor, so that the walls breathability properties are maintained.
Are Earth Blocks safe in earthquake-prone areas?
Compressed earth blocks are as good or better as any other masonry system in seismic zones. In high seismic zones, all masonry wall systems require reinforcement.
There are several strategies for dealing with seismic activity.
The first defense against earthquakes involves the height to thickness ratio of the wall. Shorter and thicker walls are more stable than taller and thinner walls. There are “rules of thumb” about this ratio and some building codes address it directly. However, a structural engineer should be consulted with any questions regarding seismic reinforcement. An example of the effectiveness of this thick-wall system is demonstrated by the survival of the California missions for hundreds of years. Of course, there have been repairs and upgrades over the years, but the truth is that they still stand in spite of the fact that many of them were built in close proximity to the San Andreas fault. The walls can be as thick as six feet.
A common strategy in low to medium seismic zones is to use horizontal wire ladder reinforcement. Wire grid is placed between courses of earthen blocks, the frequency of which needs to be determined by a structural engineer.
Another common defense against seismic activity is the containment system in which the building is supported by vertical columns of steel-reinforced concrete or steel Ibeams. In this system, the earth blocks, or other masonry units, serve as in-fill between the structural elements. While this system is prevalent in Latin America and other parts of the world, there are certain disadvantages. During construction, care must be taken to secure horizontal reinforcement to the vertical steel. Without this, a “cold joint”, subject to failure in a seismic event, is created at every intersection of the masonry units and the vertical reinforcement. Another disadvantage of this system is the thermal break that is created at every column. The steel I-beams or steel reinforced concrete columns will not perform thermally as well as the earth block walls. As stated previously, the design of such a system needs to be done with a structural engineer.
Alternatively, vertical and horizontal steel reinforcement can be installed within an earth block wall. This system is most easily employed providing the block machine used to create the earth blocks is capable of producing “holeys” and “U-blocks”. Care must be taken to ensure that the rebar reinforcement is completely contained within cementmmortar. The frequency of this reinforcement is, of course, the domain of a structural engineer. An advantage of this system, versus the containment system, is the continuity of the earthen wall. For instance, when plastering, the interior and the exterior of the walls are continuous earth and no cold joints are formed.
Shake table tests in Berkeley, California and Lima, Peru have demonstrated the effectiveness of “the basket” method of masonry reinforcement. In this system, mesh is fastened to the inside and outside of the walls and through-tied at periodic intervals, to be determined by a structural engineer. The mesh used can be either stucco wire or plastic geo-grid mesh. The advantage of the geo-grid is that it won’t rust over time.
The method of reinforcement of a compressed earth block building will be determined by a number of factors. These include considerations such as intensity of the seismic zone, location, design, and availability of local materials.
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