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Archive for February, 2010

Roofing hold-downs resist uplift

Roofing hold-downs resist uplift

Here’s a simple way to help prevent metal roofing from being blown away. Roofs are typically quite vulnerable to uplift in windy areas. There are commercially available roof hold-downs that bolt trusses and rafters to walls, but I’ve never seen the system described here. It was inspired by hearing all the stories about metal roofing blowing off in Haiti. (Apparently it’s routine to reattach metal roofing after major wind storms.)

This hold-down system is low cost and simple. It consists of 1/4″ x 3/4” flat galvanized steel bars bolted to purlins. Drill bolt holes at the top of corrugations. Use rubber washers to prevent roof leaks. (Insert rubber washers below the bars.) The drawing shows hold-downs located at the top, bottom and middle of each 8’ long sheet of roofing. Adjust the spacing between hold-downs for your region. The higher the wind speeds, the closer the spacing.

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Enviro Dome

Enviro Dome

I’m gradually converting my basic hand-drawn plans to AutoCAD and SketchUp, starting with the most popular designs at Earthbag House Plans. I think you’ll agree there is much improvement. And it isn’t just visual effects. Plans are being tweaked based on reader input. The Enviro Dome, for instance, now has a small (optional) pool in front that collects and stores rainwater.

Computer generated plans currently available through Dream Green Homes:
Enviro Dome
Native Spirit
3 Pod
U-Shape

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How do you keep a high vertical earthbag wall that is straight from toppling over? This is always a concern when designing and building standard rectilinear buildings with earthbags. The conventional solution generally relies on periodic buttresses and/or heavy-duty reinforced concrete bond beams at the top of the wall.

I have come up with a simpler solution that is much easier to install, requires no concrete or buttresses, and also provides hurricane and earthquake protection for the walls and the roof framing.  At the same time this method will automatically provide strong lintels over doors and windows.

The idea is that during construction, once you have arrived at the height where you are at the level of the top of any door or window (presuming that these are the same height), you lay down a piece of hollow, rectangular-section steel tubing right on top of that last row of earthbags.  It is also possible to do this pieces of wood by using somewhat larger dimensions, but I prefer metal because it is stronger and more reliable in its characteristics.  It should be as long as the wall is, going from the center of one corner to the center of the other corner. In most localities you can purchase such tubing up to 6 meters (20 feet) long, and two pieces can be strapped together if necessary, using connection plates that are either welded or bolted in place. This tubing can be various sizes, depending on how long the wall is, but I recommend about 1 1/2″ X 4″ in general.

For a complete description of this concept and step-by-step instructions for installation see earthbagbuilding.com.

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The most common size bag for earthbag (sand bag) building measures about 18”x30” measured when empty. This is often called a 50 pound bag, since these bags are used to store 50 lb. of grain and feed. When filled, this size creates walls about 15”-16” wide. This is a good size for earthbag building because they create stable walls with sufficient mass, and yet they’re not too heavy to handle. Even though earthbags are typically filled on the wall to reduce labor, there’s still a fair amount of sliding and aligning involved. Using bags larger than 18”x30” will require a lot more effort to construct your home. Even a small difference in size adds up. For example, I decided not to use some bags that measured about 19”x30” because I realized these bags would be more difficult to work with but not provide any appreciable added value.

There’s a larger size called 100 lb. bags that measure about 22”x36” measured when empty. Using larger bags will greatly slow construction, although they are very useful for specialized applications such as basement walls, rootcellars and earth sheltering. Larger bags are also more expensive and take extra fill material – more material than necessary for typical above-grade walls. Each additional cubic foot of fill material has to be shoveled, moved, put in bags and tamped. The larger size will work, but they’re much more difficult to build with since they’re much heavier. Plus, they take up additional space.

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Michael Janzen's Emergency Earthbag Shelter

Michael Janzen's Emergency Earthbag Shelter

A hybrid earthbag and pallet building would provide excellent protection from the weather and would be virtually free to build with debris and discarded shipping pallets. The addition of rain water collection, humanure composting, and simple solar oven(s) would provide fresh water and help keep human waste safely out of the way. Any additional materials would only enhance this basic earthquake resistant structure.

Be sure to visit Michael Janzen’s Tiny House Design website for many more sustainable building ideas.

[Note: this project was part of a design competition at Core77]

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Emergency Earthbag Shelter

Emergency Earthbag Shelter

This emergency shelter was deemed a failure and rejected for use in relief efforts. Those involved with the design and evaluation of the shelter all failed to realize one simple point. Pure sand in sandbags (earthbags) will slump and shift as shown. But tamped soil consisting of an appropriate sandy soil/clay mix will compact into solid walls much like rammed earth. Also note how a running bond was not used. Full bags should overlap joints below; half bags should start alternate courses. So here’s an example of perfectly good shelter design, in my opinion, that didn’t pass grade due to lack of understanding.

The same is true of crude sandbag walls built by the military. These hastily built, temporary walls and structures are typically just bags of sand stacked on top of each other. If you add about 25% clay with sand or sandy soil, mix thoroughly and tamp the bags in level courses you will have a vastly superior wall system. This simple point makes a big difference in wall stability. That’s one reason I prefer the term earthbag building over sandbag building.

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From time to time we’ll post answers to reader’s questions.
Q: What methods can be used to close the ends of earthbags?

A: Most people fold the bag ends over and then butt the folded end tight against the previous bag. (This keeps the contents intact and prevents spillage.) That’s the fastest way. If money is tight or you just want to minimize the number of bags required, you can sew the bags closed with cord or 15-20 gauge galvanized wire, or pin them closed with nails. These methods use fewer bags because you can fill them more completely. This simple step can reduce the total number of bags required by about 17% when using 18″x30″ bags: folded ends 20″ long; sewn ends 24″ long.

Kelly Hart’s Earthbag FAQ provides answers to all the most common questions about earthbag building.
(Note: the Q and A above is by me, not Kelly.)

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