Dwell Magazine Special Issue Materials Sourcebook Features Rammed Earth Works by Alex Wright

Dwell Magazine included Rammed Earth Works (as well as Watershed Materials) in their recent Special Issue - Materials Sourcebook 2016. We're so honored!

The letter from the Editor-in-Chief, Amanda Dameron, entitled In the Material World speaks to our mission in more ways than one :

"Over the past 16 years, we've amassed a deep archive of architectural projects that convey modern values through conscious design decisions. This special issue celebrates the way that architects and residents alike have engaged bold material palettes as a vehicle for communicating their ideals.

In the pages that follow, we honor the artistry of the build through the lens of material exploration. We acknowledge that when architects experiment with material properties, they push their own power of expression.

While the wheel need not be reinvented with each use of stone, wood, concrete, metal, glass, and even recycled goods - surely we can chart modern architectural progress through technological innovation and ceaseless iteration. What would 'modern architecture' mean today if Alvar Aalto hadn't spent years experimenting with wood, if Louis Kahn hadn't embraced brick, or if Frank Gehry hadn't explored the limits of metal?

It's inconceivable to conjure the work without the materials, not to mention the tireless minds that dared to recast the mundane."

We couldn't agree more!

This feature is a reissue of a larger Dwell Magazine story on Rammed Earth Worksoriginally published in April, 2009.

Open House - Saturday February 13th 2016 by Alex Wright

Rammed Earth Works and Watershed Materials are hosting an Open House on Saturday, February 13th from 10am to 3pm at our production shop / pilot factory / research lab. RSVP on the Facebook event page. Stop by to get an in-person tour of :

Rammed Earth Works' curved demonstration wall designed by Andy Goldsworthy

- Pre-cast rammed earth

Watershed Materials' new prototype high compression concrete block machine

Zero cement block mix design made with lime, slag and aluminosilicates

Zero cement geopolymer block

Black block made with rice husk ash

If you're attending the BuildWell conference, this is a perfect finale. Our factory is located at 11 Basalt Road, Napa CA 94558. Call (707) 224-2532 if you need help finding the shop.

Pre-Cast Rammed Earth by Alex Wright

The Rammed Earth Works team has been ramping up production of our pre-cast rammed earth panels, made in our factory in Napa then transported to and installed on job sites.

These pre-cast rammed earth panels are 3-4 inches thick and are ideal for non-structural applications for projects that don't have the available footprint for traditional on-site rammed earth walls that can often range from 18-24 inches thick. Rammed Earth Works is able to produce these panels at our factory at much higher volume than on-site installations with custom one-off formwork. Rammed Earth Works is able to take advantage of re-using formwork as well as the factory environment to speed production time.

Measuring five feet high by twenty-four feet long, each of the 3” thick panels weighs 4,200 pounds when fresh out of the mold - 3,850 once the hydration water is converted. What keeps them together? Ultra high compression.

Measuring five feet high by twenty-four feet long, each of the 3” thick panels weighs 4,200 pounds when fresh out of the mold - 3,850 once the hydration water is converted. What keeps them together? Ultra high compression.

Working with panels this thin, delivering the soil mix into the formwork at a uniform depth is essential. The team at Rammed Earth Works continues to develop equipment specifically suited to the task at hand. Here we’re using a linear traveling delivery conveyor dropping mix through the feeding box - three linear feet every fifteen seconds; 2.4 cubic feet per lift.

Working with panels this thin, delivering the soil mix into the formwork at a uniform depth is essential. The team at Rammed Earth Works continues to develop equipment specifically suited to the task at hand. Here we’re using a linear traveling delivery conveyor dropping mix through the feeding box - three linear feet every fifteen seconds; 2.4 cubic feet per lift.

Each five-inch loose lift takes one minute twenty seconds to deposit into the formwork. Target density is 136 pounds per cubic foot. A Jet 2-T rammer has a tool weight of twenty-one pounds, works on 90 psi of air pressure, and has a strike rate of 700 blows per minute. To reach 97% compaction rate, the rammer travels along the twenty-four foot long wall at the same rate as the delivery conveyor - three linear feet every fifteen seconds.

Each five-inch loose lift takes one minute twenty seconds to deposit into the formwork. Target density is 136 pounds per cubic foot. A Jet 2-T rammer has a tool weight of twenty-one pounds, works on 90 psi of air pressure, and has a strike rate of 700 blows per minute. To reach 97% compaction rate, the rammer travels along the twenty-four foot long wall at the same rate as the delivery conveyor - three linear feet every fifteen seconds.

Here's an installation of pre-cast rammed earth panels at a job site in the South Bay Area. We look forward to producing more pre-cast rammed earth and reporting back on the progress.

BuildWell Conference 2016 by Alex Wright

Are you attending BuildWell 2016? We're excited to be involved in our second BuildWell conference. This year, David Easton will be speaking in two panels:

Ultra Low Carbon Materials : Natural building goes mainstream from 11:15a to 12:30p on Wednesday, February 10 

Going Big League : getting to scale - the good, the bad, and the ugly from 11:15a to 12:30p on Friday, February 12

We're also hosting an Open House following the BuildWell conference at our shop / factory / research lab in Napa - a great way to end a week discussing the future of sustainable building materials.


Rammed Earth, A Historical Perspective And a Solution to Modern Day Challenges by Dr. Rongrong Hu

Vernacular rammed earth structures common in China.

The following is a guest post by Dr. Rongrong Hu, professor at Xi'an University of Architecture + Technology and an expert on rammed earth in China. She visited Rammed Earth Works and gave a talk at the Hamel Winery called “Rammed Earth, A Historical Perspective And a Solution to Modern Day Challenges”. We enjoyed her visit, learned tremendously from her international experience, and are proud to share the report of her trip :

When I step on the thousand year old Great Wall of China built with rammed earth or when I see the old and beautiful vernacular rammed earth houses in China, a question about rammed earth construction always comes to my mind: what is the future of this disappearing ancient construction technique with such a long history in China?

To help me find the answers, David Easton, founder of Watershed Materials and Rammed Earth Works arranged a trip to Napa where his companies are headquartered. Arguably, Napa is California’s rammed earth country. Going to Napa, I really did not know what to expect. I knew David is very passionate about rammed earth construction, after all he has devoted most of his career to this technology and specifically to creating a new construction block made with technology that evolved from rammed earth. However, I did not know I was about to meet so many enthusiastic people from different walks of life, all with the common goal of furthering the progress of this technology.

Dr. Rongrong Hu and David Easton at the Watershed Materials headquarters, standing in front of a building made with rammed earth Watershed Block below rammed earth PISE.

I drove to Napa valley on Saturday, August 21st. Arriving early afternoon, first on the agenda was a tour of David’s extensive laboratory on rammed earth. As I walked around David’s lab, he explained to me how he has built this state of the art lab with the aid of National Science Foundation (NSF). I was encouraged to see that the United States’ government is supportive of the sustainable building technology. David had built a truly magnificent laboratory equipped with all sorts of machinery to measure everything that could potentially be measured on his new technological marvel, the Watershed Block. In the front portion of his lab, he was conducting tests on strength, drop testing, water absorption, contraction, expansion and many other tests which we did not have time to delve into.

His lab was well equipped beyond any other lab I had seen. He explained his vision of how he thought the Watershed Block could be built with little or no cement, yet capable of meeting the needs of our modern day construction practices. His Watershed Block resembled an ordinary concrete block, but the cement content is substantially reduced. I was amazed at the strength of David’s Watershed Block. The natural question was how was he able to get such amazing strength? Then David explained how he had to invent a kind of rammed earth pressing machine, capable of putting tremendous amount of force on these blocks and this force was key to creating the strength needed. As we walked together to the back of his lab, he showed me his machine connected to conveyor belts and motors powering it. This second generation machine was capable of producing 4 blocks every minute. Connected to the machine were long conveyor belts carrying the blocks away from the pressing machine. It was easy to get impressed by all the technology in David’s laboratory.

Rammed earth home in Northern California built by Easton's Rammed Earth Works

After visiting David’s lab, it was time to visit some of the houses built using David’s technology. David drove me to visit some modern rammed earth homes and their owners. They graciously welcomed us into their homes and shared their stories, opinions and passion of rammed earth with me. They told me the reasons they chose and love their rammed earth homes. Thanks to all the modern rammed earth home owners for their encouraging words. Their stories, their opinions, their love of rammed earth will contribute to the rammed earth construction development in China.

On the evening of August 22, 2015, an event was hosted by Mr. Hamel in the beautiful Hamel Family Winery to showcase rammed earth construction. I was the invited speaker. I was impressed by the amazingly beautiful new winery which was built with massive rammed earth walls perfectly becoming a part of natural landscape. It is an obvious masterpiece of modern architecture. I am not a wine expert, but I was told the wine was excellent. Wonderful hospitality, great wines, beautiful view from inside and outside, what an unforgettable experience! The Hamel family were such gracious hosts. They had paid attention to every detail. I will always remember their hospitality. Many thanks to the Hamel family!

Dr. Rongrong Hu at the Hamel Family Winery before her presentation on the history and future of rammed earth in China.

There were guests from every walk of life. Some were architects and engineers, some had their homes built with rammed earth, yet others were just intrigued with the technology and were considering construction projects. I had prepared a presentation on rammed earth history in China and how we have started to use this technology again to solve our modern day pollution problems.

My presentation was full of colorful pictures on China’s popular rammed earth monuments. It probably went longer than I expected. After the presentation, I expected most guests to dash out of auditorium given I went over my allotted time.

However to my surprise, many of the audience came to the podium after the presentation to ask about rammed earth construction today in China. They were all hopeful that rammed earth becomes mainstream in Chinese construction, especially in rural China. The guests also shared their stories and opinions on rammed earth construction. They all believed rammed earth construction has a bright future because of its history, light carbon footprint, beauty, and comfort.

After the event I wanted to do a more thorough survey. I was wondering how the guests really felt about rammed earth. The responses were overwhelmingly positive on rammed earth. I took the liberty of compiling some of the guest responses at the end of this note.

I had a great time in the beautiful Napa Valley. And I owe gratitude to many. Specially, I like to thank David any Cindy Easton for inviting me to Napa and hosting me at their beautiful home. Their inviting hospitality made me feel right at home. I also like to thank the Hamel family again for the wonderful event they hosted. I am grateful for all their hospitality.

Last but not least, I like to thank all the guests came to the event who shared their valuable opinions with me and thank the home owners who welcomed me to their homes. Their valuable opinions will guide me and others in the Chinese academia in shaping the future of rammed earth construction.

I truly believe rammed earth construction has a future, especially as we try to change our construction methods/techniques to protect the planet and ensure a healthier environment for future generations.
I think that’s the key to the future of rammed earth - it’s past. History has proven it’s beauty, functionality, and resiliency.

Dr. Rongrong Hu speaking about the history and future of rammed earth in China to a group of rammed earth advocates knowledgeable about rammed earth in the United States.

Rammed earth is usually reserved for those US projects with a healthy budget. It will be interesting to see if the Chinese can do it affordably and safely. I am even more excited about the future of your rammed earth CMU as it is a valuable tool for Architects. Since the price is similar to concrete CMU, the real advantage is that you achieve an extremely attractive interior and exterior finish, that’s the REAL savings.

Dr. Rongrong Hu speaking with attendees of her presentation asking them their feelings on the future of rammed earth.

The answer is ‘absolutely yes, rammed earth has a big future.’ In a century where population growth and rising standard of living demands more and better housing - at the same time as our most precious resources of clean air and pure water are diminished - it is imperative and inevitable that we find ways to build that have a lighter carbon footprint, and less impact in general on resources. The efficiency of rammed earth, from the perspective of its very small carbon output, its ease of manufacture, and assembly, and its reduction in operating costs for the resident, all make it a certain winner in the race for better building techniques. In the words of a great Hollywood film, Back to the Future!!
Do I think rammed earth has a future? Absolutely, having enjoyed lived in a rammed earth home for 15 years it is hard for me to imagine not living with the beauty, sustainability, convenience and comfort of living in this earth home.

What I enjoy most about rammed earth is the beauty and solid structure. I also feel a sense of stability and strength from the home, having experienced a 6.0 earthquake close to the epicenter without an item out of place. Education for architects, building contractors, and building departments to familiarize with the design and engineering techniques and developing a cost structure to compete with traditional building methods will hopefully change this in the future.

The work that David Easton and his colleagues in the industry are spearheading, including the availability of techniques like the rammed earth blocks, may be key to the future of rammed earth. I certainly hope that this method will bring the wonderful lifestyle of this building to many around the world.

Windhover Contemplative Center wins Best of Competition in the 2015 International Interior Design Association's interior design competition. by Alex Wright

We're thrilled to hear the news that the rammed earth Windhover Contemplative Center was just awarded the Best of Competition in the 2015 International Interior Design Association's Interior Design Competition. The award was given at the annual Award Gala in Chicago.

In addition to the Honor Award, the rammed earth project was bestowed the Best of Competition award, top among over 450 entrees from around the world.

The rammed earth Windhover Contemplative Center featured on the front and back cover of the awards catalog for the 2015 International Interior Design Association's Interior Design Competition.

The rammed earth Windhover Contemplative Center featured on the front and back cover of the awards catalog for the 2015 International Interior Design Association's Interior Design Competition.

Windhover Contemplative Center award page detailing the Best of Competition award.

Windhover Contemplative Center award page detailing the Best of Competition award.


David Easton Keynotes the First International Conference on Rammed Earth Construction - Perth, Australia - February 10th to 13th 2015 by Watershed Materials

David Easton is thrilled to keynote the First International Conference on Rammed Earth Construction in Perth, Australia from 10 to 13 February 2015. The conference is hosted hosted by The University of Western Australia and will bring together researchers, engineers and practitioners in order to communicate the latest developments in the design and analysis of rammed earth structures.

David's keynote will focus on themes of creating unified definitions and standards for rammed earth construction as well as increasing the sustainability profile of rammed earth by limiting or eliminating Portland cement from mix designs.

Here are a few select quotes from the keynote :

“Who in his right mind would believe that you could simply pound dirt into durable shelter - that walls built this way could stand up to wind, weather, and gravity? Who in his right mind would think you could make a business out of such a thing, that people would actually pay for it? What were we thinking? That here was an opportunity to support our families and put our kids through college? That we would get rich and successful and launch a global renaissance? Mark Twain once said, ‘it takes two things to be successful in life - ignorance and confidence.’ Look at us old timers today. What in the world made us stick with the idea of rammed earth? Was it ignorance, or confidence?”

“Is rammed earth only pure compacted soil or is it any aggregate pounded into a monolithic wall, whether or not blended with stabilizer? Is it the act of ramming, or the composition of the earth? Is a poured earth wall rammed earth? Is a shot earth wall rammed earth? Is a wall of compressed earth blocks rammed earth? What defines rammed earth? The material, the method, or it’s monolithic character? Does cement stabilization change the character of the wall so much that we can no longer call it rammed earth?”

“Why do the world’s codes differ so radically on the perception of what is safe rammed earth - 0.25 MPa (30psi) in some countries, 17 MPa in others? In soils, it takes a minimum of 10% Portland cement to achieve strengths of 17 MPa, less cement in crushed aggregate. What this means, distressingly, is that there is nearly twice the cement in a 400 mm stabilized earth wall than there is in a typical concrete wall, and every pound of cement calcined generates nearly a pound of CO2.”

“What is it that makes rammed earth so attractive, so alluring, so captivating? What exactly is the magic? Is it simply the hygroscopic ability of raw earth to maintain optimum humidity levels within a space? Or is it the way thick earth walls can soften sounds and provoke a sense of calm? Perhaps they capture the essence of biophilic design, that the earth walls provide a source and sense of connection to the natural world, distilling natural materials to their elegant simplicity and rightness of fit.”

“The recent interest in biophilia - architecture to connect people with nature - could not find a better mascot, a better poster child than rammed earth. A thick, strong earth wall acts like a filter, excluding the noise and the stress that is outside, creating a positive, beneficial environment within. It’s pure and simple.”

Read the full keynote here.

Artist Andy Goldsworthy Uses Rammed Earth Works for Newest Art Installation by Watershed Materials

Rammed Earth Works is thrilled to have worked with renowned artist Andy Goldsworthy on his most recent installation in the Presidio, called Earth Wall. The piece is Andy's fourth for the For Site Foundation, following “Spire” (2008), “Wood Line” (2011), and “Tree Fall” (2013).

“We’re looking at a wall made from earth from the Presidio and embedded in the wall is a ball of branches and earth that appears to have been excavated out of the wall,” Andy says. “The branches have the appearance of having been there for an awful long time, and that was a very strange thing because you’re always trying to see your work outside yourself, and it looks like I dug something up from a long time ago that I hadn’t even put there, so it was a real process of discovery for me, as I hope it will be for other people.”

Andy digs out a ball of gnarled eucalyptus branches embedded inside a rammed earth wall.

Andy digs out a ball of gnarled eucalyptus branches embedded inside a rammed earth wall.

Andy selected rammed earth as the medium around the twisted branches to give the appearance of the eucalyptus having been buried under layers of earth deposited and compacted over a long period of time. The rammed earth “simulated layers of earth laid down over time, as if the layers were made as sedimentary layers. We did in a day what nature would have deposited and compacted over thousands of years” says Khyber Easton of Rammed Earth Works.

“Prior to this Andy Goldsworthy project, Rammed Earth Works had always been building structural walls. Now artists are asking to build aesthetic, conceptual projects. This Goldsworthy project highlights conceptual aspects of rammed earth and legitimizes rammed earth as a medium of art, not just structure.”

Rammed Earth Works is thrilled to have worked with Andy on such a timeless piece. Below is a short video via The Presidio of San Francisco followed by a series of production images detailing the installation of Andy Goldsworthy's Earth Wall at The Presidio.

Eucalyptus branches from the Presidio installed before the formwork for the rammed earth wall is installed.

Eucalyptus branches from the Presidio installed before the formwork for the rammed earth wall is installed.

Formwork for the rammed earth walls installed, locally sourced Presidio earth mixed and poured into the forms, and ramming begins. Rammers carefully compact earth around the twisted ball of  Eucalyptus branches.

Formwork for the rammed earth walls installed, locally sourced Presidio earth mixed and poured into the forms, and ramming begins. Rammers carefully compact earth around the twisted ball of  Eucalyptus branches.

Some passion filled earth ramming.

Some passion filled earth ramming.

Rammers have reached the top of the rammed earth wall that surrounds the now buried eucalyptus branches.

Rammers have reached the top of the rammed earth wall that surrounds the now buried eucalyptus branches.

Formwork is removed revealing a freshly packed rammed earth wall and the center point of the ball of gnarled eucalyptus branches. Both the raw earth for the rammed earth wall and the eucalyptus wood was sourced from the surrounding Presidio.

Formwork is removed revealing a freshly packed rammed earth wall and the center point of the ball of gnarled eucalyptus branches. Both the raw earth for the rammed earth wall and the eucalyptus wood was sourced from the surrounding Presidio.

Artist Andy Goldsworthy poses with the installation before beginning to dig out the earth surrounding the encased eucalyptus wood.

Artist Andy Goldsworthy poses with the installation before beginning to dig out the earth surrounding the encased eucalyptus wood.

Detail of the rammed earth wall.

Detail of the rammed earth wall.

Artist Andy Goldsworthy poses with the installation before beginning to dig out the earth surrounding the encased eucalyptus wood.

Artist Andy Goldsworthy poses with the installation before beginning to dig out the earth surrounding the encased eucalyptus wood.

Detail of the rammed earth wall.

Detail of the rammed earth wall.

Artist Andy Goldsworthy excavates the rammed earth from around the gnarled eucalyptus wood.

Artist Andy Goldsworthy excavates the rammed earth from around the gnarled eucalyptus wood.

Detail of the buried then revealed eucalyptus branches surrounded by a rammed earth wall.

Detail of the buried then revealed eucalyptus branches surrounded by a rammed earth wall.

Rammed Earth Works' Khyber Easton and artist Andy Goldsworthy.

Rammed Earth Works' Khyber Easton and artist Andy Goldsworthy.

Artist's quotes sourced from this SF Gate article.

Indoor Comfort Isn’t Just About R-value: Addressing the Relationship Between Insulation and Thermal Mass by Watershed Materials

This post was originally published by our sister company Watershed Materials

People often ask us about the R-value of a Watershed Block, or of a wall built of Watershed Block, or of a rammed earth wall built by our sister company Rammed Earth Works. For many good reasons, the building industry is highly interested in insulation. Reducing heating and cooling costs is paramount in reducing the overall embodied energy of our built environment. However, focusing on insulation alone (R-value) as a mechanism to ensure indoor comfort with lowered heating and cooling costs overlooks another key element of the equation - thermal mass.

The relationship between insulation and thermal mass is nuanced. Insulation reduces the movement of heat, while thermal mass has the effect of storing heat. Insulation, while very good at slowing the movement of heat, generally has little to no capacity to store heat. By contrast, thermal mass, while very good at storing heat, generally has a relatively poor ability to slow the movement of heat. Despite these differences, the comfort of indoor environments can be efficiently maintained by employing either insulation or thermal mass, or a combination of both.

The thick earth walls of China Fujian Tulou, here shown in the Hekeng cluster, have been providing their inhabitants with cool daytime temperatures and warm nighttime temperatures for hundreds of years. Image credit Fon Zhou, used with permission of Creative Commons Attribution-NonCommercial 2.0 license. 

The thick earth walls of China Fujian Tulou, here shown in the Hekeng cluster, have been providing their inhabitants with cool daytime temperatures and warm nighttime temperatures for hundreds of years. Image credit Fon Zhou, used with permission of Creative Commons Attribution-NonCommercial 2.0 license. 

These two mechanisms inform two distinctive strategies for maintaining stable indoor temperature and comfort. The first strategy uses thorough insulation and vapor barriers to effectively separate indoor air from outdoor air. A complex heating and air-conditioning system then circulates indoor air. Efficiency is gained through using as little heating and cooling as possible, with the HVAC unit often drawing on the exhaust air to pre-heat (or pre-cool) intake air in a sort of temperature exchange. The second strategy instead relies on a concept of a thermal flywheel to naturally heat or cool thick masonry or earthen walls that store this temperature and naturally regulate indoor air temperature, often with little to no heating or cooling.

Exterior walls of homes that embrace modern construction concepts including Passive House and Net Zero often seal off exterior air from interior air with impermeable vapor barriers and high amounts of insulation. Heat exchanging ventilation systems circulate air. Image credit NBT used with permission of Creative Commons Attribution No Derivitives 2.0 license.

Exterior walls of homes that embrace modern construction concepts including Passive House and Net Zero often seal off exterior air from interior air with impermeable vapor barriers and high amounts of insulation. Heat exchanging ventilation systems circulate air. Image credit NBT used with permission of Creative Commons Attribution No Derivitives 2.0 license.

Each strategy has its merits and downsides. The first strategy relies on complex heating and cooling systems that may not function during power outages or after mechanical failures. Additionally, a fully insulated and vapor sealed building does not “breathe” naturally, raising concerns of air quality. The indoor air quality of sealed buildings is such an issue the California Building Code now requires additional mechanical ventilation to bring in fresh air in all new construction.

The second strategy, while relying less on complex heating and cooling systems, relies instead on fluctuations between the nighttime and daytime temperatures, known as diurnal swing. Without these temperature fluctuations, the thermal flywheel mechanism doesn’t function and little energy savings are achieved.

With the above as background to the discussion, how do we answer the question when asked to put a number on the R-value of a Watershed Block or a Watershed Block wall, or a rammed earth wall? A Watershed Block, like rammed earth, has a relatively low R-value. That’s the point, after all, of materials with a high thermal mass. A Watershed Block, like a rammed earth wall, has to move heat in order to store heat. Even with a low R-value, a Watershed Block wall, like any earthen wall, can still contribute to maintaining a comfortable indoor air temperature. And, a low R-value does not mean that a Watershed Block or rammed earth wall needs to be insulated.

Let’s examine the two questions separately - how can a Watershed Block wall, like a rammed earth wall, provide insulative properties while having a low R-value, and, what is the effect of adding insulation to a Watershed Block wall or a rammed earth wall?

The first question - how can a Watershed Block wall, or  a rammed earth wall, provide insulative properties while having a low R-value -  examines the idea of “effective R-value”, otherwise (and more accurately) known as “mass enhanced R-value.” The difference between R-value and “effective R-value” / “mass enhanced R-value” can be understood by examining the difference between the lab environments in which R-value is measured versus the real world environments in which building materials are used.

R-value is measured technically in a lab, specifically in a machine called a guarded hot box. One side of a material - whether fiberglass, a Watershed Block, or a sheet of drywall - is maintained at a constant temperature. The other side of the material is kept at a different constant temperature. The amount of energy required to maintain this temperature difference is measured, and an R-value is determined.

This specific R-value is a “steady-state” R-value and reflects the material’s ability (or lack thereof) to insulate against two constantly different temperatures. What about the real world in which temperature differences are dynamic, not steady?

In much of the United States, the outside air temperature changes greatly over a 24 hour period, a situation referred to as diurnal swing. In the desert environments and Mediterranean climates that dominate the West and Southwest, the temperature outdoors changes greatly during the day, rising above a comfortable indoor temperature in the afternoon then falling far below a comfortable indoor temperature at night. Over a course of 8-12 hours, the temperatures on two sides of an exterior wall can change dramatically. So the steady state R-value determined in a lab is no longer so valuable in determining how the indoor temperature can be best maintained when applied to a dynamically changing outdoor temperature.

From this more dynamic and changing environment, the concept of “effective R-value” / “mass enhanced R-value” has emerged and relates to the idea of high mass exterior walls functioning as a thermal flywheel. Warm daytime temperatures and direct sun slowly warm exterior walls but this heat does not reach interior spaces until after the sun has set. The latent daytime heat in the exterior walls warms interior spaces during the evening, at which point the process reverses and the walls slowly begin to expel the daytime heat through the thick exterior walls into the now cooler nighttime air. By morning, the thick exterior walls have cooled again, and the process continues, offsetting the daytime heat to the evening and the evening cool to the daytime.

The thick exterior walls of a rammed earth house can provide insulative properties above the measured steady state R-value when used in climates where the daytime and nighttime temperatures swing above and below the desired indoor air temperature, also known as high diurnal swing.

The thick exterior walls of a rammed earth house can provide insulative properties above the measured steady state R-value when used in climates where the daytime and nighttime temperatures swing above and below the desired indoor air temperature, also known as high diurnal swing.

In this way, thick earthen exterior walls can have a higher “effective R-value” that is determined by via computer modeling to determine what a similar steady state wall R-value would need to be to offer the same performance.

However, key to the concept of “effective R-value” / “mass enhanced R-value” is where and how the material is used. A thick exterior earthen wall will have a higher effective R-value, but only in certain climates where the diurnal temperature swing allows for this thermal flywheel performance. That same wall in a consistently cold climate - one where the exterior temperature is always below a comfortable indoor temperature - will have no effective R-value improvement. So the answer to the first question - how can a Watershed Block wall, like a rammed earth wall, provide insulative properties while having a low R-value -  has to do with the environment where the wall is used. In an environment where the diurnal temperature swing allows for a thermal flywheel performance, a thick earthen wall can provide insulative properties, and a higher effective R-value despite having a low measured steady state R-value. However, in an environment without a diurnal temperature swing, a thick earthen wall does not provide significant insulative properties beyond its measured steady state R-value.

The second question - what is the effect of adding insulation to a Watershed Block wall or a rammed earth wall - follows much of the above discussion and examines how thick earth walls, either exterior or interior, can be used effectively in climates in which the temperature is consistently above or below a desired indoor temperature. Additionally, new building regulations like California’s Title 24 virtually mandate insulation, regardless of a wall system's thermal storage capacity. So what is the effect of insulating thick exterior earth walls? Again, location and local climate conditions are key to the answer.

In an ongoing study to determine the most effective use of structure and energy performance, this wall assembly of double block provides one set of hollow cells to receive reinforcing steel and concrete grout to support roof loads and provide earthquake safety, with one set of cells left open to capture dead air space to improve thermal resistance. This wall assembly will have a different thermal response depending on which side of the house it's located. The north side will tend to be much cooler than the south and west because it never sees direct sunlight.

In an ongoing study to determine the most effective use of structure and energy performance, this wall assembly of double block provides one set of hollow cells to receive reinforcing steel and concrete grout to support roof loads and provide earthquake safety, with one set of cells left open to capture dead air space to improve thermal resistance. This wall assembly will have a different thermal response depending on which side of the house it's located. The north side will tend to be much cooler than the south and west because it never sees direct sunlight.

In a Mediterranean / desert climate like the American West and Southwest with relatively high diurnal temperature swings, adding insulation to thick exterior earthen walls halts the functionality of the thermal flywheel described above. Warm daytime temperatures cannot reach indoor spaces to warm the interior space at night. And the cool night air cannot expel the home’s heat in the pre-sunrise night. Insulation added to exterior walls will do exactly what insulation does best - stop heat transfer.

In climates with long periods of consistent cold or consistent heat, insulation is necessary even in thick exterior earthen walls. However, the mass-effect of using materials with high thermal storage capacity can still provide noticeable benefits to indoor air comfort. High mass earthen walls used inside the insulation envelope will slow indoor temperature swings and regulate indoor humidity. Used outside the insulation envelope, high mass earthen walls can delay intense heating from direct sun by shifting the time that heat reaches the insulation envelope to the evening when cooling systems are more efficient.

The effect of adding insulation to a Watershed Block wall or a rammed earth wall is highly debated, especially in environments most appropriate to thermal flywheel heating and cooling. Recent energy code changes in California further amplify the debate. The role of high thermal mass wall structures has not been consistently integrated into concepts of highly insulated net-zero construction.

So to answer a question with another question, how are you incorporating insulation with thermal mass, and in what climate?

Further reading :

http://www2.buildinggreen.com/article/thermal-mass-what-it-and-when-it-improves-comfort

http://www2.buildinggreen.com/article/thermal-mass-and-r-value-making-sense-confusing-issue (requires a paid account to BuildingGreen.com / Environmental Building News)

http://www.passivebuildings.ca/resources/Documents/RammedEarthForAColdClimate-StuFix.pdf

http://ceramics.org/wp-content/uploads/2013/05/sanders.pdf

http://www.crockerltd.net/adobe_thermalmass.htm

Building From The Watershed by Watershed Materials

One of the primal attractions to building with earth is harvesting raw materials from the construction site itself. In the old days (pre-industrial revolution), that was always the case. Soil dug from the foundation trenches or from a nearby borrow pit was either molded into sun dried bricks and laid up into block walls or rammed between wooden form boards into monolithic walls. Man converting raw local resources into shelter is truly sustainable building.

During the past decade or two, the earthbuilding industry has drifted away from this core precept, settling into the comfort zone that comes from using familiar and consistent quarry-processed aggregates. This quest for comfort has come at an environmental cost.

Don’t get me wrong, I am all in favor of consistency and dependable results, but I’ve also become more aware of the carbon consequence of putting trucks on the road, burning diesel fuel, wearing out rubber, and pounding asphalt. I trucked quarry materials to our rammed earth and pise jobsites for years, but I now believe the right path is to improve our understanding of local geology and our skills at formulating mix designs to allow us to incorporate even more of each site’s unique resources.

I think of it as the construction industry’s version of the slow food and locavore movements - better quality, closer to home. I want to call it “building from the watershed”. The goal is to develop a series of protocols that allow us to evaluate any found soil and predict how it will perform in a structural capacity. When we complete the assembly of this soils library, we will then have the ability to reproduce consistent results from site to site, using fewer quarry amendments and thereby reducing the number of trucks on the road and CO2 in the atmosphere. Carbon offset construction.

A Modern Rammed Earth Home in Silicon Valley by Watershed Materials

David Easton has directed the construction of hundreds of homes around the country and the world, but began taking on a special job over the past few years - building homes for his children. With decades of experience, David had the perfect opportunity to apply the best of his techniques, including stacking modular formwork, to help his step-son, Jack, construct a modern rammed earth home Silicon Valley.

The entire construction process has been thoroughly documented here. And below find a series of highlight images from the build.

Keeping the Costs Down by Watershed Materials

One of the challenges facing the popularization of rammed earth is it’s installed cost.  It’s ironic that what might be viewed as a free raw material has evolved into an expensive finished product. In the past, probably the greatest appeal to building with rammed earth was its low cost. 

Soil was harvested on site, the forms were simple, and the work was done by hand.  Buildings served basic needs, with walls that were rough and only more or less plumb.  This practice remained the norm for a very long time, from early civilization through the middle of the twentieth century.  It still is the norm in rural China, the Middle East, and Africa.

When rammed earth began to re-emerge in the mid 1970’s, it was still considered an inexpensive wall system.  Soil was predominantly sourced on site, formwork was relatively simple, the architecture was linear, and unskilled labor could be used for most of the work.  Walls were a little ragged and unrefined.  Plaster was a common finish treatment.

Over the past few decades, rammed earth has grown in popularity, with an increasing number of professional builders developing the requisite skills.  Contrary to the law of supply and demand, however, in which competition reduces prices, rammed earth has become more expensive. 

Why is this?  The answer is complex, or rather complexity.  Rammed earth began as a simple system that recognized, even celebrated, the inherent flaws and unpredictability of raw earth. Over time, as builders improved their skills and the marketplace grew to appreciate the unique beauty of rammed earth, architects began to push the material to applications and expectations that were extremely difficult to fulfill. They were difficult but not impossible, only time consuming and expensive.  Gone were the days of simple forms, unskilled labor, and site-sourced materials.  In their place were elaborate formwork built and set by highly skilled carpenters, and imported screened soil and processed aggregates stabilized with 10% cement. Each course of soil in the forms must be carefully placed and conscientiously compacted, with the whole installation under the watchful eye of a paid special inspector.  Add color blending, strata lines, curves, rakes, niches, lintels, chamfered bond beams and watch the square foot cost approach Carrara marble. 

What can we do?  There are two solutions, and the good news is that they can co-exist.  On one hand we can continue to refine our skills and produce rammed earth with the look, feel, and price tag of art.  On the other hand, we can provide clients and architects with value engineering feedback on how to design efficiently for the material.

Rammed Earth is massive so keep it simple.  Rammed Earth is regional so source materials locally.  Appreciating the unpredictable character of finished wall surface celebrates the authenticity of natural materials and showcases its hand built qualities.

Rammed earth doesn’t have to be expensive.  Designed with the system in mind, it can be one of the best values in the building industry today.

A Contemporary Rammed Earth Home in the Mountains by Watershed Materials

David Easton has directed the construction of hundreds of homes around the country and the world, but began taking on a special job over the past few years - building homes for his children. With decades of experience, David had the perfect opportunity to apply the best of his techniques, including economic re-use of formwork and site sourced resources to help his daughter, Terra, construct a modern rammed earth home high in the California mountains.

The entire construction process has been thoroughly documented here. And below find a series of highlight images from the build.

Why Not Concrete by Watershed Materials

Although I’ve been asked this question a hundred times, by engineers, building officials, concrete contractors, and other skeptics, I’m always a bit unprepared for it.

I first started building with rammed earth nearly forty years ago in a quest for low-cost construction solutions and with a certainty that sourcing “free” material from the site had to be economical.  Over the years, as code compliance and client preference compelled us to achieve higher strengths and more uniform wall quality, we found ourselves forced to import quarry products and stabilize with higher cement ratios.  In effect we were pulled by market forces towards a product that was indeed akin to concrete.

Hence my difficulty with the question.  Is rammed earth less expensive than concrete?  Does it represent a reduction in carbon footprint?  Is it stronger or more durable?  Is it less expensive to heat and cool?  Does it improve indoor air quality?  Is it healthier?  Is it more attractive?  Is it better for the planet?

First, rammed earth is not necessarily less expensive than concrete.  Even though the forming systems for the two materials are similar and take more or less the same man-hours to erect, layering and compacting rammed earth into the form takes considerably more labor and equipment than pouring and vibrating concrete.  The only savings possible are a reduction in aggregate and cement costs.  To achieve these savings a mix design must be developed that utilizes a major portion of either on-site or other free mineral soil and a minimum rate of stabilization. 

Rammed earth can represent a much lower carbon footprint than concrete.  If the soil for the walls is close to the project, then transportation fuel consumption will be low.  If careful formulation allows design strengths to be met with 7% or less cement, then a big savings in CO2 will accrue.  The question of design strength is another challenge altogether.  Where some structural engineers are comfortable designing one and two-story rammed earth walls with an f’c of 600 psi, other engineers specify strengths as high as 1500 psi.  A design strength of 600 psi can be attained in an ideal soil blend with 1-1/2 sacks of cement per yard, but it can take up to 3-1/2 sacks to get 1500 psi.  What this shows is that engineering design plays a big role in carbon reduction.

Is rammed earth stronger or more durable than concrete?  The answer is clearly no, but the question should be: is rammed earth strong and durable enough for its intended purpose?  If the soil is selected correctly and the wall built properly, then rammed earth meets all the required performance standards and will provide decades of serviceability with little or no maintenance.  Rammed earth has an inherent beauty that transmits a warmth and natural character very different from concrete. 

Rammed earth walls are typically much thicker than a concrete wall, which makes them much more effective at controlling indoor temperature fluctuations.  An 18” wide wall creates a 12-hour thermal flywheel - outside temperatures take half a day to migrate through the wall to the inside face.  This means a mass wall balances out diurnal temperature swings.  In most climates and with proper exterior shading, this makes for no cooling loads.  Heating loads vary considerably based on orientation and building design.  Heating and cooling efficiency are big contributors to energy consumption and carbon footprint reduction. 

Finally, the questions about whether rammed earth is healthier for the occupants or for the planet.  Many people, especially in Europe, believe that clay in an interior wall works to maintain optimum indoor humidity, which in turn results in improved indoor air quality.  Certainly, natural earth walls are more healthy than materials that may be off-gassing glues, paints, resins, or other chemicals.  There are no factories exposing workers to toxins.  Rammed earth walls create quiet spaces that resonate solidness, which can be perceived of as an increased sense of comfort and well-being.  As for the impact on the planet, rammed earth uses fewer resources, both in construction and over the life-span of the house. 

 

Finding the Right Soil by Watershed Materials

Clay/sand ratio has the greatest contributing effect on how well an earth wall will perform.  Traditionally, for raw rammed earth, that ratio has been established as 30% clay and 70% sand. 

When using cement as a stabilizer, clay content can be reduced, in some cases and with high stabilization rates, clay (and other fines) can be as low as 8% to 10%, depending on numerous factors (uniformity of gradation, plasticity, particle shape, and parent rock).
Unlike earlier times, when the building material was nearly always harvested on or near the construction site, today we have access to a wide range of importable mineral soils and admixtures.  Formulating a blend of soils capable of achieving optimum structural performance is our objective.


To do this, we begin by looking at the underlying soil on the building site itself.  A review of the boring logs from the geotechnical report will yield valuable data:  gradation, USCS soil type, and in some cases a plasticity index.  We have found that most site soils can be used in some proportion to create a useable formulation.  Using site soil has several advantages:  reduced cost of importing materials, increased LEEDs points, color continuity with the local geology, reduced off-haul costs, and reduced carbon emissions from construction.


The gradation report (also called a sieve analysis) identifies how much of a given soil is fine particles, those passing the 200 mesh screen.  The Plasticity Index is an indicator of how much of those fine particles are “clayey”.  Clay particles help to bind together the soil matrix.  If the gradation indicates more than 25% passing 200, the addition of sand will likely be required.  High clay soils also benefit from small gravel as supplemental amendments.  


If boring logs and site investigation indicate utter unsuitability, or if there is no excavation planned for the site, it is possible to source a portion of the wall building material in other ways.  Excavating contractors, pool contractors, or other general contractors frequently have excess material they need to move off site.  Phone calls or scouting trips can be productive, as is the old “Clean Fill Wanted” sign.  


For the required amendments to site or other free material, you can start the search for a suitable sand or gravel amendment at the local masonry or landscape supply yards.  Coarse sands with a good distribution of particle sizes are usually better than fine or uniform sand.  Cracked or crushed gravel is better than “pea” or river gravel because of its angularity.  Color and cost are also important considerations. 


For a small project and for all of the required pre-construction testing, the search can end at the supply yard.  For larger projects where several truck loads of amendment will be required, you will be able to negotiate a better price dealing directly with the quarry.  


Finally, if site soil is unsuitable and free clean fill is unavailable, or if screening and processing is impractical, then purchasing and importing all of the wall building material from a quarry is the logical choice.  Cost, travel distance, color, wall density, required stabilization and geo-regionalism will dictate which quarry to use.

Delivery Systems - Spring 2010 by Watershed Materials

The challenge for spring 2010 is all about delivery systems.  We abandoned shovels for conveyors several years ago, but somehow every job seems to warrant a different configuration of belts, trolleys, and rails.

In March we were in Glendale, California.  The owner and general contractor gave us a monumental challenge:  800 linear feet of stratified earth wall to be completed in eighteen days.  The wall was to be comprised of 19 individual strata, four different colors, each lift a different thickness and a different color.  We had to design and build two new delivery conveyors to fit the staging areas we were assigned; one an elevating conveyor that would lift material from the mix rig to a height of 15’ and the other a pivoting/tracking conveyor that would travel along the top of the forms and distribute material for the varying lift depths.  The first photo in this post shows the set up.  As is always the case with prototype equipment, there were hitches at the start.  The first few days were really long ones in order to meet our required quota.  We redesigned and rebuilt the elevating conveyor, adding a powered head pulley, and we modified both the track and the trolley.  The first week it took us nine hours to meet the daily production schedule.  By the second week we were down to seven hours; the third week we were down to six, and the final four days we were placing eight yards an hour, finishing before lunch.
In May we mobilized to a single family residential project in the Los Altos hills above San Francisco Bay.  Here we had to fill a curving form, 120 feet long, two feet thick and in some cases twenty feet deep.  Each of the three set-ups required a different conveyor configuration.  One photo in the post shows our gas powered three-way conveyor.  The other photo shows how we chained four conveyors together to get across the basement excavation and into the 12-foot tall forms.