During a trip through southeast Idaho, Dietmar and fellow architect Martin Hammer happened upon a rural archetype of straw covered barns, or cellars to be more precise, as they are typically built over an excavated pit. Marty and Dietmar wrote up an article for the "The Last Straw" (http://www.thelaststraw.org/), the International Journal of Straw Bale and Natural Building. Here is the complete story with a few extra pictures, for those who are not TLS subscribers (yet).

Brooks Buxton's potato cellar near Arco, ID, is covered with a the straw bale roof.

Idaho Potato Cellars 
By Martin Hammer 

In the spring of 2002, Dietmar Lorenz and I visited Idaho to climb its highest peak, and along the way discovered a regional archetype which uses straw bales in an unusual way.  While driving through central Idaho near the town of Arco (“The First City in the World to be Lit by Atomic Power”), we spotted a rustic farm building with a triangular profile and a soil covered roof.  It spoke to us and we decided to investigate.  With some respectful trespassing we looked through the building’s large front opening to see a vast space which was partly excavated into the ground.  Opposing rafters of round timbers spanned over 30 feet.  When we looked outside the building and examined the roof, we were amazed to find baled straw, exposed in places where the soil covering had worn thin.  A closer look revealed the composition of the roof assembly to be soil and gravel over straw bales, over 1” thick skip sheathing, over peeled tree trunk rafters. (See Drawing).

 

 

Before long, we were visited by the building’s owner, Brooks Buxton.  Both gruff and gregarious, he willingly answered all of our questions about the building, as well as many we didn’t ask. Recently retired at age 72, Brooks had been a potato farmer all of his working life.  And this building, which he built some 50 years ago, was used to store his potato crop after each October harvest.  It was a potato cellar.  By being built partly into the ground, and with a roof insulated with straw bales, the building is able to keep potatoes from freezing in the winter, and keep them cool enough into May so they won’t sprout or deteriorate.

 
The 6 foot pit of  Brooks Buxton's potato cellar covers some 30 by 90 feet and is covered by a round timber roof structure. Even though the building has been decommissioned a decade ago, the straw and gravel roof shows only moderate disrepair.
 

Brooks talked about the modern buildings used to store potatoes, which we had noticed along the way.  They are made of sheet metal and built entirely above ground, so they can’t accurately be called cellars, though they often have earth berms along both sides.  The interiors are mechanically controlled for temperature and humidity.  In addition, they often use an ozone system as a sprout inhibitor and to control bacteria.  “It’s supposed to be a cheaper, better way to store spuds, but it’s more complicated.”, says Brooks.  “With all that equipment, it’s more expensive.”  Subsequent talks with other potato farmers shed more light on this unusual building type.

 
The contemporary Idaho potato cellar keeps the earth bermed geometry but relies on mechanical systems, including ozone treatment, to extend the availability of "fresh potatoes" all year round. An earth bermed potato "cellar" with a sheet metal exterior, applying the typical geometry without using straw bales on the roof. (We don't know, if straw bale or other insulation is used inside the metal skin.)
 

The old style potato cellars have been utilized since the early 1900’s, and evolved from the practice of simply digging a pit, and burying the potatoes under straw and soil, to keep them from freezing during the winter.  Creating a roof structure over the pit allowed greater access, and greater quantities to be stored.  The cellars have been used throughout southeastern Idaho, wherever seed potatoes or commercial (food) potatoes were grown.  Seed potatoes need to be stored until the next spring’s planting, so the simple potato cellars work very well because the potatoes will keep until May.  With commercial potatoes there is a glut at harvest time, so the market price is usually at its lowest.  Farmers like to store much of their crop to sell later at a higher price, and potato cellars were used for that purpose until as late as May of each year.  But beyond May the potatoes become too warm and will sprout or deteriorate.  So until the advent of the modern storage buildings in the 1970’s, fresh potatoes were available only from October to May.  Today, commercial potatoes are stored almost exclusively in modern, climate controlled buildings, and are available “fresh”, all year round.  Because the old style potato cellars are inexpensive to build and operate, and work well for the purpose, seed potato farmers still sometimes utilize them, or something in between the modern and the old style buildings.  Lynn Rothwell uses one he built in 1985 which is fully above ground, with 8 foot high compacted earth walls and earth berms. It employs simple climate control with warm, cool, or moist air driven by fans through perforated steel culverts buried in the pile of potatoes.  The roof, with bales, is the same as the below ground cellars.

 
This straw covered potato "cellar" in southeast Idaho is not excavated but earth bermed.

 

There are numerous variations of the old style cellars.  Some had both sloped and flat roofs with supporting poles in the middle, and were as much as 50 ft. wide by 350 ft. long.  Sometimes concrete sidewalls or slabs were used, but more often just exposed earth, because concrete takes moisture out of the potatoes.  Retaining the potato’s moisture is important for both quality and because potatoes are sold by weight.  A potato can lose 20% of it moisture and weight during winter storage. Before balers were available, loose straw was used instead of bales.  Either way, the straw was usually barley or wheat straw.  Sometimes only wire mesh was used over the log rafters to hold up the straw.  Arvella Rothwell relates that theirs never leaked.  “It was a good system.”, she says.  “Not real modern, but it worked.”  Marjorie Leischner, whose father built their first potato cellar in 1910, described how the winter’s snow provided additional insulation when it was needed most, and that the sloping roof and snow provided an unintended benefit.  “We kids would climb up on top and ride sleds down in the winter.”, she says.


Round timbers support the skip sheathing and straw bale roof. The perforated culverts at the base get assembled and put in under the spuds, a means to control moisture and temperature of the potato pile through ventilation.

 

Fortunately, buildings as rugged, simple, functional, and elegant as these are still used, and have resisted an often unnecessary march toward higher technology.  They have life spans, including bales, of 40 years or more, though one must consider the high arid climate of southeastern Idaho and its 4-5 month winter which arrests any deterioration of the straw or wood during that time.  Still, these buildings, especially those without concrete, stand as a wonderful testament to appropriate use of available resources to create buildings that perform nobly through their lives and then return fully to the earth.  

 

Right: A group of straw covered potato cellars near Atomic City, ID. The seemingly archaic scene shares the vast plain with dozens of nuclear test- reactors, among them the oldest reactor in the United States.

 

Some Thoughts on Unplastered Bales
By Dietmar Lorenz 

 A striking characteristic of the Idaho potato cellars is the straightforward use of the building materials, not driven by style, but practical concerns. The straw bales are not plastered, because they don’t have to be. The roof structure is made of round timber, because that’s how trees grow. One gets a strong sense of what a building is made of and how it’s put together.

 
For architects and builders, mimicking the boldness of a farmer may end up in formal mannerisms, if it’s primarily about achieving the looks of rural archetypes. Still, there is a lot to be learned by studying what’s driving those vernaculars. The methods may not be appropriate everywhere, but the general thinking tends to be universal. For us, seeing those structures was inspiring and refreshing.

Brooks Buxton,  Idaho Farmer
 

Returning to the drafting boards, we’re left with the question how to get some of that fresh vernacular breeze into our design. In residential projects, straw bale houses typically get plastered. Practical concerns and building codes call for it (do they really?) and it usually makes a lot of sense. But honestly, who has never felt a sense of disappointment once a bale wall got plastered, with none of the golden straw left to be seen, touched and smelled?  Truth windows don’t count. In most of the Potato Cellars, the straw can be seen through the skip sheathing on the interior. Here are a few thoughts on how we can make the straw show.

 
It has been suggested to use baled hay to wrap Mongolian gers (yurts) in the fall and use the hay to feed the life stock as winter recedes. For a nomadic culture it sounds like a good idea to turn the extra insulation into future food before the next move. That seasonal approach is not so different from stacking firewood around a cabin in the winter to provide another layer against the winter chill. Straw and other annually renewable materials lend themselves for seasonal approaches. How about a north wall of a greenhouse that gets used for mulching in the summer and re-stacked with fresh bales after the fall harvest?  

 
Unplastered bales might also be an option for temporary structures, like at county fairs, carnivals, summer camps and other gatherings. In that type of use, fire safety is likely to become an issue, notably flame spread. Structural concerns need to be addressed, too. We don’t want bale walls falling on people. How about jumbo bales? They are way too heavy to be tipped over. The downside is the need for a tractor or forklift. Two courses provide a nice ceiling height and a wall only twice as tall than wide, a very stable geometry. 
Chapel-shaped pile of jumbo bales somewhere in Germany, Old Europe.

 

On the other side of the spectrum, straw and other agricultural waste products are gaining popularity in industrial building products, like straw based MDF (Medium Density Fiberboard) or compressed straw building blocks. Some of those show off their alternative nature, others just take advantage of an abundant resource and are hard to distinguish from timber based products. In either case, there are strong ecological benefits in taking straw building to an industrial level, especially by penetrating larger markets and widening the applicability of the material to finishes, cabinetry etc. But that’s a different story and probably won’t take away from the popularity of straw bale construction, but complement it. Somehow, there are nice associations that come along with just the regular straw bale. It’s a familiar sight on the fields at the end of summer, comfortable to sit on, not too heavy to drag around and overall a fairly benign thing. So, show it, when you can!

  
Martin Hammer is an architect in Berkeley, California.  Dietmar Lorenz is an architect with Dan Smith and Associates in Berkeley. Their offices are about 600 bale lengths apart. 

All photographs by the authors, unless otherwise noted.

Above: Sliding down a winter slope on a hay bale. (Picture from a gingerbread  jar)