The Strawbale House Project at Swarthmore College (1994-1998)

This building was an environmentally innovative structure, constructed mainly out of load-bearing strawbales. It was built by student volunteers, and by undergraduate student members of the 1995 Environmental Studies Capstone Seminar. The building was designed by students in this seminar under the direction of Professor E. Carr Everbach (Engineering Department). The course is open to senior Environmental Studies concentrators, and in 1995 it focused on the various ways people can live in the world while minimizing damage to their natural environment.

The house was dismantled during the summer of 1998. For a detailed description of what we learned as we took it down, click here.

The straw bale house simulated a dwelling for a small family, possibly one living in a rural area or Indian reservation. The floor plan consisted of a circular living room, a kitchen, bathroom, utility room, and bedroom; the interior spaces (other than the circular living room) were never implemented. Feasibility studies were performed for several subsystems and designs were produced, but after the building envelope was completed, interest in "finishing" the house waned. The main purpose of the project was for the students in the Environmental Studies Capstone Seminar to learn about straw bale construction by actually building one, and more generally to investigate the tradeoffs between environmental benefits and practical considerations. The house was not built to serve a need for housing on campus, and ended up serving as a laboratory for analyzing straw bale construction in the northeastern U.S.

If you'd like to know how we built the structure, click here.

As we were preparting to dismantle the house, we undertook an experiment to see if bales could be replaced in-situ, as the walls were still intact. This process simulates what would have to occur if bales were damaged by moisture in a strawbale residence.

During the four years that the house stood, we measured temperature and humidity using data loggers implanted in the bale walls. We are compiling the data into meaningful measurements of the performance of our structure.

If you would like to know exactly where the site was on Swarthmore's campus, see this map.

Frequently Asked Questions about our project:

Why straw?

Building from straw is an ancient technique recently rediscovered by environmentalists. The bales are relatively inexpensive and very thermally insulating (about R=2.1 per inch of wall thickness). There are few other uses for straw, since, unlike hay, it cannot be used by animals for feed. Furthermore, because it decomposes very slowly, it isn't often used for composting. Every year, millions of tons of straw are discarded or burned in the U.S.

How long will it last?

The same things that make straw hard to use for other purposes make it ideal for building. When kept dry, straw is very sturdy. Straw has been found, completely intact, in ancient Egyptian tombs. Properly taken care of, a straw house could conceivably last as long. The biggest enemy of our house is moisture, and the walls have already suffered slight damage when the bales were wetted for several months during construction. On the positive side, however, the straw has already proved able to hold up well to extreme weather conditions, even in an unfinished state. Mildew on the wetted portions of the bales dried and became dormant, with no measurable degradation in strength or insulating ability of the bales.

Does it burn easily?

Because the straw is packed so tightly together (our 46 in. by 22 in. by 16 in. two-string bales weigh about 54 lbs. each, double the density of regular bales), oxygen cannot get into the middle of the bales, and so they do not burn easily. Exposed to enough heat, they will, of course, burn, but less easily than a comparable house built of conventional construction materials.

Additional Environmental Costs and Benefits

Although far superior to traditional building methods, the house was far from perfect, environmentally speaking.. The foundation used concrete and polyethylene foam, environmentally costly substances. However, the foundation was designed to use less concrete than conventional buildings do (see Technical Details, below). There was also a small amount of concrete mixed into the stucco placed on the walls. On the positive side, our straw walls had an average insulation value of R45, which means that it took very little energy to heat or cool the house.

The Future of the Project

The Straw Bale House was begun in late Summer, 1994, and the building envelope complete in late Summer, 1995. Prof. Everbach and his students measured temperature, humidity, moisture content of the walls, and other relevant parameters continuously since November, 1995. Our goal was to conduct an extended research project on the performance of such structures and on related techniques that promote a more "sustainable" use of resources. Since there are few straw bale houses in areas with cold wet winters, we hope that the information gathered will be very useful to anyone in interested in building a straw house on the East Coast. When the House was dismantled, the building materials were recycled.

How we built it

The foundation was poured, and steel rods (#4 rebar) were embedded into it.
Bales were impaled on the rebar, and stacked upwards in staggered rows like bricks. At each level two stakes of bamboo (grown on campus), wood dowels, or steel rebar were pounded in and through at least the course below to give the wall strength and stability.
A plywood frame called a bond beam was placed on the top course of bales upon which the roof beams bear. The bond beam provides extra stiffness in the walls, especially in the direction perpendicular to the plane of the wall.
Galvanized steel diamond mesh was pinned around the outside of the walls using "Robert pins" (big Bobby pins), and stucco (a plaster made from of 7 parts common bar sand, 2 parts lime, and 1/2 part Portland cement) was applied to protect the walls from moisture.
The roof was constructed using new and recycled wood. First a "bond beam" was laid on top of the walls for additional support. Then "I-beams" (14" TGI) were laid over the entire top of the structure. Next boards (3/8" OSB) were placed on top of the I-beams, and asphalt roll roofing applied to the roof. The roof was then attached firmly to the foundation with a series of long rods (#3 rebar with zinc-plated allthread rod welded to the upper end). Finally, the roof was insulated with 14 in. blown cellulose insulation made from recycled newspaper (R = 45). The final building was quite strong, and would have lasted decades had we not had to remove it.

Technical Details

The concrete foundation of the straw bale house is a variation of a design used by Frank Lloyd Wright: a beam of reinforced concrete cast on a shallow gravel-filled footer with external insulation. Straw bales were used as forms during the casting process, as shown in the accompanying diagram. The (pink) extruded polyethylene insulation, though not a very environmentally-friendly material, allows the internal heat of the building to keep the ground from freezing under the foundation and obviates the need for a deep concrete footing. This shallow frost-protected foundation design has been in use in Scandinavian countries and performed excellently in our application. There was no measureable frost-heaving, despite solid 4-foot-deep freezes of the ground outside the house.

The bales, which were harvested from a field near Allentown, were laid like bricks in courses around the concrete foundation. The lowest courses were impaled upon the vertical reinforcing bar of the foundation; higher courses were pierced with bamboo rods harvested from Swarthmore College's own bamboo groves, as well as with wood and steel rebar spikes. Wire lath holding sand-and-lime stucco covered the exterior, and minimizes flammability. Conventional doors and windows were built into the strawbale walls, and a flat shed roof in two oppositely-pitched sections rested on the bondbeams of the uppermost course of wall bales. Twin telephone poles provided stabilization at the juncture of the circular and rectangular sections, and served to support the upper windows of the clearstory.

The Environmental Studies Straw Bale House Project was funded by a generous grant from the Educational Foundation of America, as well as the Roberts Engineering Fund of Swarthmore College. Special thanks are due the Swarthmore administration, Athletics department, Rainbow Awnings, and Scott Arboretum, for allowing temporary use of the site and other College resources. If you wish more information about the project, please contact Prof. Carr Everbach .