Tuesday, April 15, 2014

Earth Bag House

By Michelle Harris

This semester has been one of exploring alternative building types.  I have had the privilege of observing the construction of an earth bag house and assisting with a cobb house. I am currently drafting a finished pole framed house. In each incidence, the natural resources and means of construction were easily accessible. However, the technique and construction management is lacking. While this may seem a harsh judgment, the amount of preparation to effectively build is why you have a contractor, architect and engineer. The accessibility to design and construction professionals who are adept in alternative construction is rarer than not. After studying the alternatives, I am not sure if they are what I want to do professionally. I love the concept: a building made from local supplies that ideally will be inexpensive to construct, own and operate.
Even though I am not a hundred percent sold on these methods as feasible for mainstream construction, I’d like to recommend what I have learned to you!
This week, I’d like to talk about my observation of earth bag construction. The example I studied is of a house on a local farm. In this example seed bags were filled with earth dug from a hillside. The bags are stapled shut. Then these filled bags were laid end to end in a circle to be tamped. Tamping is done with a heavy solid object, ideally a tamping rod. This particular building is one that has structural issues due to the imbalance of the bags. If the bags are not solidly tamped they can shift due to the weight distribution. In this case, the forces push the bags inwards. The exterior has buttressing to relieve some of this stress. However, all in all, it is not enough to sustain the amount of force distributed vertically from the building materials.

The reason for the issues with weight distribution is that this earth bag house is a dome. Domes and arches require special attention to vector forces. If the forces are not properly directed into the buttressing the dome will begin to collapse as you see here.
This is mendable. More buttressing and support can be provided. However, the structure is intrinsically flawed and will continue to need maintenance for the rest of its life.  This isn’t to say that earthbag construction is not a good technique. If properly managed there are phenomenal opportunities for this method.
I was not an active participant in this construction however I thoroughly appreciate the work contributed to the creation of this earth bag house. Each layer has hand filled bags. These bags are then ‘velcroed’ to the next layer with barbed wire. Incorporating the two by four framing needed for windows and doors does not appear easy. The exterior of an earth bag house is covered in adobe. This hides much of the work that goes into the construction. Adobe is an excellent material for cooling in the summer and heating in the winter. However due to Southern Illinois’ climate, the amount of rain, adobe is not an ideal building material for this region.
Earth bag construction has flourished in dryer Southern Climates as have other alternative construction practices that rely on adobe as an exterior finish.
If you are interested in learning more an excellent resource of which I am willing to loan is ‘Earth Bag Building’. You can browse the book here through Google Books: https://play.google.com/store/books/details?id=jEYWaBdyoHcC&source=productsearch&utm_source=HA_Desktop_US&utm_medium=SEM&utm_campaign=PLA&pcampaignid=MKTAD0930BO1)

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