GEIGER RESEARCH INSTITUTE of SUSTAINABLE BUILDING
- Promoting natural building, and sustainable design and development, through research, training, education and consulting services.
|Kelly Hart's Earthbag/Papercrete House|
An Earthbag/Papercrete House
Kelly and Rosana Hart are good friends of mine who allowed me to stay in their home this past winter while I managed their business - Hartworks, Inc.
As leaders in the sustainable building movement, their house has been featured in The Art of Natural Building, edited by Joseph Kennedy, Catherine Wanek and Michael Smith; Homeworks: Handbuilt Shelter, by Loyd Kahn; Building with Earth, by Paulina Wojciechowska; videos by Hartworks, Inc. including Building With Bags and Sampler of Alternative Homes (one of my favorite videos), and Living Homes calendar by Dead Red Crab Publishing, among others. Even their dog Larry is famous, having been included in many of these books and videos. I enjoy telling him he is a movie star dog (he loves hearing this).
Here then, is their story:
In 1997 my wife and I decided to build the most ecologically sensitive house we could, given our available economic and material resources. I had just produced a video program about sustainable architecture, featuring a wide range of building techniques and designs, and was eager to try out some the ideas expressed in the program. One concept that particularly intrigued me was building structures with earthbags (or sandbags), as Nader Khalili has popularized, by making corbelled domes with bags filled with earth.
Domed structures eliminate much of the need for tensile roof materials, such as wood and steel. Since I wanted to avoid these materials for environmental reasons, we decided to build our house as a combination of domes. Instead of filling the earthbags with soil from the building site, we decided to use lightweight crushed volcanic rock to increase the level of insulation. We live at over 8,000 feet (2,500 meters), where the winters are very cold, so a well insulated house is essential for comfort.
As a plaster over the bags to protect them from the deterioration of sunlight, we decided to use papercrete, made from pulped junk paper, sand, and a bit of Portland cement. In the United States , waste paper often ends up in the landfill, so it is very satisfying to find a beneficial use for it. This has allowed for a completely breathable wall that is comparable to a straw bale wall in insulation, but is not subject to the potential for rot or rodent infestation. We decided to leave the papercrete plaster breathable, without applying a moisture barrier in the entire wall system. Even though the papercrete absorbs a considerable amount of water when it rains, this moisture is retained like a sponge and then released to the atmosphere later. We have not had a drop of water come through to the inside of the domes.
To test our ideas, we first made a 14 foot diameter experimental dome. We placed two strands of four-point barbed wire between each course of bags to help hold them together. We also tied polypropylene twine around the bags to help unify the wall and give the plaster something to grip onto.
The house is designed with a 16 foot (5 meters) diameter bedroom dome at one end and a 20 X 30 foot (7 X 10 meters) elliptical dome at the other end, for kitchen and living room. In between them is a central space that serves as bathroom, greenhouse and utility room. Above each of these spaces are lofts for offices and storage. The area between the domes was created with a partially spherical bag wall on the north that leans against the two domes and is braced into place by wood framing. It has a flat, south-facing roof to accommodate the solar electric and water heating panels.
In addition to these primary domes, there is a partial, mini dome on the north wall next to the kitchen that is entirely underground, where it stays nice and cool for produce and other food supplies. This is our walk-in pantry, a favorite feature of our home. We also built a vaulted mudroom entryway with a bell tower for visitors to ring. This vault spans eight feet at the base and required massive, double bag walls to be self-supporting.
The building site is a south-facing sand dune that we dug into. Because the sand drains so well, we decided to start laying the bags directly on volcanic rock laid down as a pad to insulate the entire floor. There is no other foundation. [This technique can save thousands of dollars on foundation costs. Consult with an engineer in your area, because this house was built in an area with no structural building codes. Most building jurisdictions will require a foundation.]
Because the design is passive solar, we needed a large expanse of south-facing glass, and this meant creating earthbag arches that span 6 feet (2 meters). This proved to be difficult to accomplish, until we found a way of stacking two adjacent bags, in a cross-hatch pattern, over a wooden arch form.
We found that putting in a loft with joists that span across the dome and are supported right on the bags themselves would stabilize the structure considerably. Even so, the large elliptical dome proved to be a huge building challenge. I soon realized that it would require a permanent, rigid interior framework to be self-supporting. My advice to other earthbag dome builders is to stay with circular shapes, where the forces are equally distributed in all directions.
For floors, we used a combination of local flagstone and poured adobe (a mixture of sand, clay and chopped straw). These materials have a natural beautiful appearance and are surprisingly durable. As the adobe was drying, I troweled it until it was very hard and smooth, then eventually applied several coats of linseed oil to darken the color and provide a water-tight surface. Both the stone and the adobe are thermal mass materials that absorb heat during a sunny day, and then give it off at night. During the summer, these same materials help keep it cool inside, thus stabilizing the interior temperature.
To keep the heat in on cold nights, we use thermal curtains or insulated panels to cover the windows. This keeps us comfortable at night without any additional heat, even when the temperature outside drops to below freezing.
The original wood stove was replaced with a more convenient gas heater. This gives us much more control over the temperatures, since the solar heated house only needs a little bit of auxiliary heat for short periods of time.
The walk-in pantry has proven extremely functional. It stays between 38 and 65 degrees Fahrenheit year-round. Rosana likes the feeling of connection with the earth that the earth-berming provides. She often feels that when she walks into the pantry, which is half underground.
Some things we would do differently time: Try to design in more storage in the original plans, design the kitchen to be more user-friendly, and get the hot tub functional right off the bat!
The most difficult part of building our home was designing and building the elliptical dome. It was also challenging figuring out how to make arches with earthbags that span 6 feet. Some of the most physically taxing work was applying the layer of lime plaster in the cathedral of the large elliptical dome... lots of overhead plastering while standing on a ladder! Finishing an adobe floor is also a tremendous amount of labor.
A few more facts about our house:
- Natural materials: Sand, adobe, flagstone, rock, lime, scoria, small diameter poles
- Recycled materials: Glass, wagon wheels, culvert couplers, misprinted rice bags, recycled lumber, doors, paper, sink
- New materials: Barbed wire, Portland cement, some milled lumber, polyethylene sheeting, fasteners, paint, linseed oil, tile, chicken wire
- Number of bags used: About 5,000 altogether, including for the small guest cabin
- Square footage: House, 1300 approximately; cabin, 150 approximately
- Time to build: About 3 years of owner/builder time at about 30 hours a week. No hired labor. Occasional friends’ help.
- Cost of basic house total: $23,232 or $16/per square foot
- Overall cost including solar system and appliances: $34,969 or $24/per square foot
- Grand total including land and site preparation: $49,969
For more information about our house, and other aspects of natural or sustainable building, you might check out our website www.GreenHomeBuilding.com, where you will find many educational resources, links to other related sites, and free advice from a panel of experts. The earthbag page has many more photographs of the process of building our unique earthbag/papercrete home.
Dr. Geiger’s comments after living in the home for one winter:
GEIGER RESEARCH INSTITUTE OF SUSTAINABLE BUILDING