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CCAT rocket mass cobb bench heater

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Background[edit]

This will be the site of the cobb bench with the back of the bench against the face of bricks. Shown here is the full view of the existing chimney and ancient stove from before CCAT days.

In the Spring semester of 2019, our Engineering 305 Appropriate Technology course at Humboldt State University was asked to design the following project as a living and evolving installation of appropriate technologies. The project reflects integrated teamwork, strong communication across the institution, creative problem solving, and over 150 hours of physical labor.

Team Rocket Power was assigned the Rocket Mass Heated (RMH) cobb bench on the grounds of Humboldt State University's Campus Center for Appropriate Technology (CCAT) in front of an existing outside fireplace. CCAT is a student-run instructional home that demonstrates appropriate technology to promote sustainable living and design. The cement foundation and plastered brick chimney will serve as foundation backrest for the bench where the back of the bench will be set directly against the fireplace.

Team Rocket Power Completed bench

Site Potential[edit]

This area is currently underutilized at CCAT as it could potentially be a communal workshop space and interactive recreation area that demonstrates appropriate technology. By interacting with a rocket mass heated bench, students and community members can learn about how appropriate technology and design stacks functionality.

Scope of Project[edit]

The Cobb Rocket Mass heated bench will provide functions of heated lounge space, cooking, and a place to bring community members together. Cobb is a building material consisted of all natural components: clay, straw, sand, and water. Thermal mass heating has been used all over the world to heat beds, floors, and earthen home structures.

Team Members[edit]

Team Rocket Power consists of Ben Nguyen, Aidan Belleau, and Michael Perez.

Team Rocket Power will design, prototype, and implement the aforementioned technology during the Spring Semester of 2019.

Overview Video of Finished Project[edit]


>>>>CCAT Rocket Stove Mass Heated Cobb Bench 2019<<<<


Problem statement[edit]

The purpose of Rocket Power is to design a locally sourced, aesthetically pleasing, and fully functioning rocket mass heated cobb bench at CCAT.

We hope this demonstration of appropriate technology will have both a utilized purpose for accessible and comfortable seating, as well as an educational tool for future generations of students.

Project Evaluation Criteria[edit]

It was important to order the priorities of the CCAT community, as well as weighing what appropriate goals are for our team. The following criteria were chosen based on initial conversations with the CCAT Co-Directors, project manager, and the project team. The scale (1-10) represents the importance level of meeting the constraint of each listed criteria (10 meaning the most crucial).

Criteria Constraints Weight
(1-10)
Function Stacking Integrate at least 4 Appropriate Tech designs
7
Safety Building method approval from risk management
10
Structure Modifications/Use of existing structure (chimney)
8
Seating Area Four or more seating spots
10
Maintenance Weather resistant
9
Cooking Capability Stove function-ability
10
Materials Logical transportation and sourced locally (on site)
10
Aesthetics Artistically inspired finished product
7
Signage Minimum of two permanent educational displays
10
Operation Clear directions and operations manual
10
Chillability Want to stay on the bench for at least an hour
5

The CCAT Co-Directors and Project Manager emphasized student and community safety, learning accessibility, and project functionality as the main priorities. This is shown in our project criteria to be the most important to achieve. Operation of the system itself is crucial to maintaining the efficiency yielded by rocket stoves, so the order of operations must be clear and concise. This will be achieved through signage and accessible resources. The current location for which the bench is central to CCAT, however, the original fireplace is underutilized. This project will aim to invite more people to relax and engage with space while learning about appropriate technology.

Literature Review[edit]

Rocket Mass Heater Overview[edit]

A rocket mass heater, or rocket stove, consists of a right angle ‘J’ shaped combustion chamber inside of an insulated container. This insulation container creates a draft in which the heat gasses are drafted and then pushed through piping into the mass. This concept can be applied to heat earthen built furniture in homes that contain high thermal mass. [1]

Testing and Certification of RMH[edit]

Testing of rocket mass heaters for emissions efficiency is very difficult to come to conclusive data as each system will vary. Not one scenario will be exactly the same as fuel, operation, and structural design are variables. The testing would also be very expensive, ranging from $8,000 to $30,000 and would be targeted for builders who are in the business of licensing and patenting particular designs. [2]

Basics to Clean-Burning[edit]

The following was adapted from the book Designing Improved Wood Burning Heating Stoves by Mark Brayden et al.[3]:


“A good combustion chamber changes wood or other biomass into heat without creating much smoke or creosote (condensed wood tars). Complete combustion of wood results in two byproducts: carbon dioxide and water vapor. In contrast, incomplete combustion creates unburned particles that cause pollution and creosote that fills chimneys and can cause chimney fires if it ignites.”

1.) Metering the fuel– Splitting wood up into small pieces (no bigger than the wrist and 16 inches long) and feeding them at a consistent rate.

2.) Creating a hot fire-Managing the combustion zone where fuel, flame, and air are mixed to create a fast burning and efficient coal reservoir.

3.) Insulating the combustion chamber- Crucial for mass stove heaters that store energy in materials with high insolation properties (see Understanding R-Values)

4.) Igniting escaping smoke- To ensure that the ignition chamber reaches optimal efficiency, the exiting gases from the exhaust should be just CO2 and water vapor.

5.) Providing sufficient oxygen– Starving the fire slows it, cools it down, and produces smoke.

6.) Warming and increasing velocity of cold air entering the fire– Air is warmed as it passes through a small opening (usually the same entrance where wood is fed) into the combustion chamber. For systems without a fan, make enough small holes under the door into the combustion chamber so the holes have as much cross-sectional area as the chimney exiting the stove. Position the holes so that primary air is sucked into the coals and up into the combusting wood.

7.) Creating sufficient draft– Use a tall enough chimney, double the height of the width of the internal vertical combustion chamber. An insulated chimney creates much more draft than an uninsulated chimney. High air movement entering under the fire, up through the coals, to create mixing which reduces emissions. Do not use a damper in the chimney. Design the stove to run efficiently with enough air entering and leaving the stove to burn fuel cleanly.

Do not block the air intake, reducing primary air and blocking the necessary amount of intake volume will create particulate air pollution!!

Types of Mass Heated Rocket Stoves[edit]

Different designs of the J-shaped combustion chambers have been refined by hundred of permaculturists and homesteaders worldwide. To assess the success and meet the main goal of longevity for overall design, the below project references display ideal qualities and strategies. The examples begin with low cost and minimum design complexities and advance to high expense, technical, and professionally engineered.

J-Type Combustion Chamber and 55-Gallon Barrel[edit]

J-Combustion and 55-gal Drum.jpg

Our design was based mostly off of this layout. With an 8-inch stove pipe ducting through the bench as the exhaust. The draft in these systems allows for the most efficient and complete use of fuel energy. The J-type combustion allows for fuel to burn from the bottom-up while the horizontal flame reached high turbidity while traveling around the 90-degree riser stack.

[4]

Efficiency of Combustion, and Heat Transfer Efficiency[edit]

The Rocket Stove, created by Dr. Larry Winiarski, features an insulated firebox and short chimney (14”). Low mass insulation such as wood ash help to keep combustion temperatures high and improve burning efficiency. The high combustion temperatures also greatly reduce smoke and lead to saving of wood, making a more efficient stove. [5]

Solunit Rocket Stove[edit]

Our vision and project scope have incorporated some of the design aspects of this example into the final bench layout.

Solunit Rocket Stove (2011).jpg

Overall cost = $700

Materials:110 firebricks, 55-gallon drum, recycled water heater core, about 20 ft 8” diameter ¼” Steel Pipe, concrete, pumice, and multiple tons of cobb


[6]

Basics of Cobb[edit]

Cobb is regarded as the first earthen material used for construction. Cob buildings from the 1400s are still standing to this day and serve as an important reminder that cob does have longevity.[7] In its most popular form it is a combination of clay for strength, and sand to reduce cracking by shrinkage, for strength and water to create cohesiveness. [8] Together these four material create a medium that is easily malleable and self-drying. It must be noted that while straw does provide other tasks such as decreasing weight of the mixture and aiding in the drying process its main purpose is to provide tensile strength. Thus many materials can be used in place of straw as long as it has tensile strength properties (i.e. herbs, pine needles, various types of grasses).

Creating and Mixing of Cobb[edit]

The creation of cobb is specific to location, materials at hand, which makes environmental and economic sense, preferences, time allowance, and desired outcome. Due to the extreme variability of the medium, there is no universal standard of cob mixture. [9] From review, it is understood that mixtures containing more straw and water tend to see the most amount of shrinking.[10]We will, therefore, be mindful of our straw and water content and create sample bricks of different mixtures to determine the best combination for our task, materials at hand, and desired outcome. However, through research and experience, large scale mixing process will be done by foot on a tarp.

Impacts of Moisture (concerns for maintenance)[edit]

It is a well-known fact that Arcata, California has high humidity and precipitation for more than half of the year.[11] This is due to the fact that Arcata is located in northern California on the western coast of the United States. Moisture and humidity can affect rates of drying and can alter mixtures causing unexpected shrinking and drying outcomes mostly seen in plasters. [12] Again plaster samples of varying recipes will need to be created and subjected to tests that will be determined on a later basis. The fact of the matter is the climate of Arcata will permit a structure made out of cob to be successful in enduring heavy use for several years.[13]

Understanding R-Values[edit]

R-value measures the thermal resistance of a material. This can also be expressed as the temperature difference that will cause one unit of heat to pass through one unit of area over a period of time. Using earth to capture heat inside an RMH is essentially using different R-values to capture the thermal radiation emmitted by the combustion chamer and throughout the stove pipe to heat the seating bench.

InspectApedia provides a comprehensive R-Value table with different insulation materials and various common construction materials. [14] [15]


Thermodynamics[edit]

Heat, Temperature, and Thermal Energy Thermal Energy is an energy of the system due to the movement of its atoms and molecules as a form of energy. In this sense, a system can still sustain thermal energy even in an isolated environment. According to the first law of Thermodynamics, work or heat that changes the thermal energy also changes the pressure, volume, temperature, and other variables. This explains how high pressure inside a rocket stove chimney generates extreme heat and forces it up and out into the isolated container surrounding it. This is crucial to gaining high combustion temperatures in a small space. [16] [17]


Construction Process[edit]

The Rocket Stove[edit]

The project started with designing, building, and prototyping the rocket stove. This consisted of first arranging the firebricks into a J-shape that makes the combustion process in rocket stoves more efficient. Once this J-shape was achieved we tested the prototype with a small fire and even with visible cracks we were able to get a steady consistent draft. Throughout combustion chamber prototypes, the overall J-shape remained, but the brick pattern and arrangement changed a few times before permanently mortaring them into place.

We built this system using an 8" stove pipe heat conveyance. The cross-sectional areas are crucial to measure and maintain throughout the RMH. The opening of the feed chamber cross-section ended up being 5" by 7" (A). The burn tube cross-section dimensions are 4" by 5.5" (C). The chimney riser cross-section dimensions are 5" by 5.5" (F). The space between the top of the riser chimney and the 55-gallon drum was about 1.5" (G). These dimensions matter greatly in terms of getting the correct draft and suction through the entire system. A good reference we used is found in Ianto Evans Book [18] where he explains the correct dimensions needed for a working 55-gallon barrel project (we highly recommend to see pages 35 through 42). The entire system measures about 42" tall and 40" from the wall behind it.

The Letters correlate to the part of the stove and dimensions mentioned above

After solidifying the dimensions we placed the barrel and stovepipes in their determined places and temporarily closed up gaps with raw clay in order to prototype the system as a whole. We were able to get the system up to desired temperatures (above touch-able temperature on the pipe). Once the design was finalized, agreed on, and prototyped we moved on to the mortar with our final mortar.

The recipe for our refractory cement used to set bricks in the J-combustion chamber is depicted below:

Mortar Materials 1 part portland cement 3 parts sand 1 part fire clay 1 part lime

The use of fire clay in the mortar mix allows for a mortar that can withstand the expected temperatures within the burn chamber (in the barrel). Lastly, on the exterior of the barrel, we used stove paint (rated at 2,500F) to add a nice matte finished look.


The Cobb Bench[edit]

Our overall idea for the bench was to use the least amount the cobb as possible. We practiced a common method reducing cobb mixing (a heavy laborious task) by inserting broken and used bricks into the cobb where it did not affect the bench’s structural integrity. Additionally adding a 2-inch layer of decomposed granite near the bottom. This method of infill wasn't as utilized as many professionals suggest and required for us to make many, many, many batches of cobb.

In terms of insulation, the bottom of the bench and the back of the bench needed to have a higher R-Value barrier to reduce heat loss. To meet our insulation goal we laid down a coat of straw slip (clay, water, and straw,) on the concrete about 3-4 inches thick before our first layer of cobb. The straw slip was also placed in between the back of the bench and the fireplace for the first twenty inches of the bench. A cross-sectional view of the bench’s layer starting from the bottom would be, 3-4 inches of straw slip, 1 layer of cobb, 2 inch layer of decomposed granite, cobb for the rest of the bench with intermittent pieces of bricks and urbanite (and of course our 8" stove pipe ducting about 3/4ths the way to the top of the seating area.

For the love of Cobb[edit]

Our clay was dug up on site at CCAT from both the Greenhouse during renovation and the center of the main yard. CCAT is hme to a nice consistency, high quality, low-sand content brown clay. We used 5-gallon buckets to measure 3:1 clay to river sand mix.

Cobb formula 3 parts sifted clay 1 part river sand rice straw as needed water as needed

NOTE: This mixture proportion will vary depending on the quality of sand and clay. We recommend you do a "shake test" with a mason jar and teaspoon of salt.

-- Instructions of Mixing Cobb --

1.) Place sand on the large, heavy-duty tarp.

2.) Clay on top of sand and dry-mix the two together.

3.) Once well-mixed start adding water from the watering can until softer consistency.

4.) Use bare feet to ensure the mixture is as homogeneous and lump-free as possible.

5.) Start adding a straw (about a basketball size to start off with)

6.) Mix, mix, mix and add water/straw until mixture is cobb loaf shape-able.

7.) Do a drop test of a cobb loaf from the waist and loaf should not- crack or split or flatten too much.

8.) Make all of the mixed cobbs into loaves.

9.) Repeat until you dream cobb.

Cobblife Hacks[edit]

Sifting stations are crucial- waist height, heavy duty metal screens with 2X4 construction, over a 30-gallon waste bin works well

The tarp mix and flip method of cobb were pretty efficient- what better way to actively use a tarp!?

A total of 5-gallon buckets was a good amount to mix within each batch.

Put cobb loaves of wood planks to both dry out and transport more easily

Cobb Takes Time[edit]

Although many of the hours of cobbing required the team members to commit to over 10 full work days each, we brought in extra hands. Collaborations with Engineering 305 classmates, volunteers at Volunteer Friday at CCAT, and many helpful peers made the laborious tasks of collecting, moving, sifting, mixing, applying and shaping cobb possible. Had this been a 3 person job, we would have been spending multiple weeks of full-time labor on just the cobbing process for the bench.

Construction with Step-by-Step Photo Gallery[edit]

Cost[edit]

The following budget breakdown has been formulated to cover all alternatives designed for the project. The tables are broken into two pieces; the first consists of the structural and natural materials needed for the rocket stove mass heated cobb bench. The second is the more expensive due to he steel stove components that will convey the heat/exhaust through the bench. Our team hopes to source donations, free, or scavenged materials to our best capabilities. While the stove piping is the most expensive aspect of the budget we have also acknowledged that used stove piping is less expensive and it's quality is questionable. Thus, we are incentivized to purchase new stove for a guaranteed quality.

Below you will find what components are necessary to build a rocket stove mass heated cobb bench and their local cost.


Bench & Plaster Materials

Material Quantity Source Cost ($) Total ($)
Local Clay 1.5 cubic yard CCAT Greenhouse Reclaim/Dug up from yard Donation 0
River Sand 1-1.5 cubic yard Wes Green Landscape Supply 40/cubic yard 60
Decomposed Granite 0.5 cubic yard Events Field Donation 0
Rice Straw 1 or 2 bales Eureka Farmstore donated after MayDay 0
Urbanite (concrete Chunks) As needed City of Arcata Donation 0
Fireclay 50lb bag Pheonix Fire Supply 10/bag 7
Quickcrete 60lb bag Hensels Ace 7/bag 7
Fire Bricks 50 Mill in Samoa, Ca 1.25/brick 40
Lime 40lb bag Hensels Ace 18 18
Tile and colored clay pieces As needed Arround CCAT, Aidan's house Donation 0
Refractory Cement 1 gallon Hensels Ace 23/gal 23
Total Cost $156

Stove & Conveyance Materials

Material Quantity Source Cost ($) Total ($)
6" Steel Stove Pipe 12 ft (5 sections of 4ft) Hensels Ace 28 per 4 ft 96
6" 90 Degree Stove Pipe Elbow 3 Hensels Ace 20 60
6" Stove Pipe Cap/Rain Guard 1 Hensels Ace 9 9
6" Stove Pipe T-fitting w/Cap 1 Hensels Ace 35 35
8 foot exhaust pipe 1 Craigslist Donation 0
Total Cost $200

Total Budget Cost: $356


Proposed Timeline[edit]

Due to the fact that cobb is very time intensive process it is very important that we proactive in preparing for the building process. Our proposed timeline projects the team to test cobb mixtures as well as plaster recipes well before construction commences.

Date Action Details
2/28- 3/3 Create and secure budget Generate multiple designs of stove and bench orientation:
3/4- 3/8 Contact Risk Management. CCAT directed us to RM for project approval. Risk mitigation techniques with different alternatives concerning safety.
3/5- 3/8 Present multiple designs to client Record feedback
3/6- 3/13 Design Prototyping and Material Prototyping Create sample cobb mixtures and allow for drying
3/15- 3/22 Material Sourcing 55-Gallon drum from Scrapyard, fire brick from decommissioned Samoa Mill, stove pipe, concrete, and lime from Hensels Ace, river sand from Wes-Green Landscaping, clay sourced on-site, urbanite/filler-brick from Craigslist,
3/22- 3/29 Preparation of site Clear/clean space of debris. Place some of collected materials in their respective spaces.
4/1 - 4/7 Mitigation of Final design Addressing possible risks (exhaust, asbestos, temp and evolving structure). Usage and Maintenance manual + future cover proposal
4/8 - 4/14 PROTOTYPE Assemble test stove on site using 50 gallon schematics, test burn and observations, adjustment of airflow measurements, lastly place stove at finalized location
4/15 - 4/21 Bench Foundation and Straw Slip Mortar red bricks into framework for the outline of the bench. Apply insulating buffer layer against existing structure and ground exposure (clay-straw slip mixture).
4/21 - 5/5 Cobb Mixing and Application Shape the oven and combustion chamber covering to desired design, trimming and edging, allow a few days for cobb to dry and set between applications, most LABOR INTENSIVE section of project
5/6 - 5/13 Final Shaping and Completing Cobb Applications Artistic Design Proposals, collecting clay tiles and other aesthetic inputs, collaborations with individual designs of VF 5/10. Plaster Application Week, testing direct ratios of lime plaster wash on finished design, every other day applications of 2 coats of plaster. Exhaust chimney and securing stove pipe.
5/14 - 5/17 Clean and Organize Working Area Finishing touches on plaster. Completing Operations Manual and documentation.


Operation[edit]

Our RMH cobb bench takes a little bit of love to maintain and operate sustainably. This stove is MUCH different than starting your typical wood stove and there are key characteristics you need to know. Please carefully read and consider the following step-by-step manual of how to get her nice and warm for your bum and hopefully lots of bums.

Instructions[edit]

How to efficiently fire-up the RMH cobb bench. This video offers a more visual and in-depth description of how to properly start and maintain the rocket stove fire: >>>>CCAT Rocket Stove Mass Heated Cobb Bench 2019<<<<

How to Get Warm Butts
ImageStep
Feed Chamber Step 1 : Remove Feed chamber cover. Check to make sure feed chamber is free of debris and any leftover ash. (The cover keeps rodents and moisture out. It also assures the feed chamber is prepped for next use.
Sizes of fuel Step 2: Always keep the tinder fuel stored in a dry place. The first wood you will want to add is pencil-sized split wood.
Vertical Fuel Feeding Step 3: All Fuel will be added vertically once the fire is started and the draft is going through the whole system
Crumpled Newspaper Step 4: Only use newspaper to start the draft and to ignite kindling. Other paper has chemicals and additives that will add creosote buildup on the internals of the combustion chamber
first kindling size Step 5: This is the size of the first kindling you will want to use to get a fire going
Loading fuel Step 6: As the burn progresses and gets hotter, add larger pieces vertically
Monitoring Temperature Step 7 : Keep a feel to how hot the bench will be getting as the fire warms up the thermal mass. As the whole bench reaches desired temperature for butt warming stop adding fuel and let the fire die out.
Invite Friends Step 8: Invite your friends to all sit on the bench and enjoy the warmth. Have conversations on thermal mass and R-values. Enjoy warm butts together. Admire how radical CCAT is while interacting with the coolest (or warmest ;) bench in the county. Do your thang...

Maintenance[edit]

For CCAT employees and facilitators on site, this is a detailed schedule of what Team Rocket Power believes to be necessary maintenance. Key problems commonly seen in RMH stoves are as follows (ordered in probability):

*trouble starting and maintaining a fire in the burn chamber, *back-firing and improper draft, the build-up of ash inside stove ducting, *ash removal inside burn chamber, *animals nesting inside of combustion chamber and/or ducts, *rusting of stove pipe and exhaust chimney,

Maintenance of the Rocket Stove and Cob bench will entail checking for water build up on a weekly basis. The stove top will collect water and which will start to erode at the plaster and cob. Another potential area that could collect water in heavy rain is the feed chamber, cupholders, and the area behind the backrest underneath the steel barbecue. It is recommended to check this area to soak up any excess water build up. Monthly checking of the cleanout cap to see if excess ash is building up inside system is recommended. On a yearly basis, a shop-vac should be used to suck out ash from the barrel. Maintenance of lime plaster is necessary when cracks and erosion are apparent. A yearly practice of lime generous lime wash coats is necessary to keep water from soaking the interior cob.


T-fitting clean out is recommended at least every 6 months to ensure no rodent inhabitants, ash/creosote buildup, and a clean exhaust ducting. We recommend both a chimney brush and a Shop-Vac with a 12ft hose extension to reach all the way into the barrel chamber

Schedule[edit]

Follow routine check-ups on the entire RMH system to ensure the maintenance problems listed above do not happen.


Daily

*Check for built up water in cupholders, behind the bench, and on top of the stove. *Make sure feed chamber cap and chimney cap are in place.

Weekly

*Clean outfeed chamber of any ash and debris. *Check cleanout cap and stove piping for any blockage.

Monthly

*Use shop-vac and clean out the cap to suck out excess ash and debris. *test fire to ensure the system is working properly.

Yearly

*Use a chimney scrub to clean the stovepipes of ash and debris. *Repaint exhaust and stove top with stove pipe as needed. *Apply generous coats of lime wash to maintain waterproof coat and plaster strength.

Every other year

*Fix plaster if cracking. replace tiles if falling out. *Replace flashing on exhaust, or replace exhaust if rusting.

Reference to how the stove pipe is laid out to understand the process of cleaning with either a shop-vac or chimney brush

References[edit]

  1. Evans, I., and Jackson, L. (2006). Rocket Mass Heaters: Superefficient Woodstoves YOU Can Build.
  2. Wisner, E. (n.d.). “Rocket stove efficiency/certification .” Permies.com, <https://permies.com/t/3249/Rocket-stove-efficiency-certification> (Feb. 21, 2019).
  3. Bryden, Mark, D. Still, D. Ogle, and N. MacCarty. "Designing improved wood-burning heating stoves." Aprovecho Research Center (2005).
  4. Evans, I., and Jackson, L. (2006). Rocket Mass Heaters: Superefficient Woodstoves YOU Can Build.
  5. Still, D., Kness, J., Billesten, B., Cox, G., Espenan, M., Nael, J. B., Nicholas, D., Subramanian, M., and Zettler, D. F. (1996). “Efficiency of combustion, Operator Expertise, and Heat Transfer Efficiency.” Fuel Efficient Wood Stoves and Hayboxes.
  6. Solunit Rocket Stove (2008) I love cob!, Green Web Hosting [online]. http://ilovecob.com/archive/solunit-rocket
  7. Hazeltine, B., and Bull, C. (2003). A field guide to appropriate technology. Academic Press, Amsterdam.
  8. Elizabeth, L., and Adams, C. (2000). Alternative construction: contemporary natural building methods. Wiley, New York.
  9. Elizabeth, L., and Adams, C. (2000). Alternative construction: contemporary natural building methods. Wiley, New York.
  10. O. A., ., C. J., ., A. O., ., O. D.-S., and ., A. E. (2006). “Engineering Properties of Cob as a Building Material.” Journal of Applied Sciences, 6(8), 1882–1885.
  11. “Climate-Data.org.” (2015). Climate Sahara: Temperature, Climograph, Climate table for Sahara - Climate-Data.org, Climate-Data.org, <https://en.climate-data.org/north-america/united-states-of-america/california/arcata-15733/> (Feb. 20, 2019).
  12. O. A., ., C. J., ., A. O., ., O. D.-S., and ., A. E. (2006). “Engineering Properties of Cob as a Building Material.” Journal of Applied Sciences, 6(8), 1882–1885.
  13. “Where Does Cob Work?” (n.d.). Green Home Building: Earthships, <http://www.greenhomebuilding.com/QandA/cob/where.htm>(Feb. 19, 2019).
  14. "R-values of Insulation and Other Building Materials." Archtoolbox.com. Accessed February 21, 2019. https://www.archtoolbox.com/materials-systems/thermal-moisture-protection/rvalues.html.
  15. Inspectapedia.com. (2018). R-Values of Materials: Table of Insulation R-Values and Properties for Various Insulation Materials & Building Materials (brick, block, wood, soil, air gaps, etc). https://inspectapedia.com/insulation/Insulation-Values-Table.php [Accessed 21 Feb. 2019].
  16. Knight, R. d. (n.d.). Physics for scientists and engineers: a strategic approach.
  17. Still, D., Kness, J., Billesten, B., Cox, G., Espenan, M., Nael, J. B., Nicholas, D., Subramanian, M., and Zettler, D. F. (1996). “Efficiency of combustion, Operator Expertise, and Heat Transfer Efficiency.” Fuel Efficient Wood Stoves and Hayboxes. .
  18. Evans, I., and Jackson, L. (2006). Rocket Mass Heaters: Superefficient Woodstoves YOU Can Build.