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Minisode 12 - Cob Cabin Update - Beginning Roof and Rainwater Harvesting Tank

7/16/2017

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This Minisode shows the progress on the roof of the cob cabin, the porch support poles and the cob wall integrated ferrocement rainwater harvesting tank.

The roof will be ferrocement, like our water tanks, consisting of 3 layers of steel lath encapsulated in cement for a total thickness of 3/8 inch (click here to see our page about ferrocement). Because the roof will be a patio we need to make it extra strong to support a lot of weight in case a lot of people go up there. To do so we are using 24 foot 2x12 rafters laid into the top of the cob walls which to the cob wall on the other side, about 18 feet. These are spaced 1 foot oc on 1 side on 16 inches oc on the other. We will pulace plywood on top of the rafters and apply the ferrocement roof on top of that. The ferrocement roof will be floating to compensate for different expansion and contraction of the wood versus cement. Small gutter-like devises will be custom integrated in the roof to convey water towards a downspout on one corner of the roof that leads to the water tank.

The water tank is made out of ferrocement (click link to be directed to more information about our ferrocement water tanks) and will be integrated into one of the cob walls. This will save time and materials because we will not have to build a cob wall there while also providing a ton of thermal mass. A rocket mass heater will be built between the water tank and large integrated granite boulder inside the cob cabin. Overflow from the water thank will be directed to our food forest (click link to see blog and video about food forest).

The roof will overhang approximately 12 feet to the south in a semi-circle to provide a large covered patio. This will provide passive heating and cooling including shade and shelter from the rain. We sunk 2 sections of telephone polls into the ground to support this patio roof. The poles were free from the electric company who was replacing them on our land. An additional horizontal pole will be placed on top the two vertical poles sunk in the ground to support the roof rafters.

For the vertical telephone poles we dug down until we hit solid rock, about 2 feet in those 2 spots, then made a level spot in the bottom of the hole with concrete, placed a pole on that, then filled in around the poles with recycled road-base (basically crushed concrete of various sizes) ensuring it was well compacted.

Please enjoy the video below.

You can click the "Cob" category on the right hand side of this page to see all previous posts about the cob cabin building project.

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Ferrocement - a simple, cheap, long lasting building medium

10/31/2016

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Ferro means iron, and although we do not use iron in ferrocement, we do use steel, an iron alloy.
The cement we use is Portland cement, a form of limestone.
Cement is used to encapsulate the steel mesh in thin layers forming the walls of the tanks. This method utilizes the compressive strength of cement and tensile strength for a marriage of unequal quality.

Ferrocement was first used back in the 1850s, by the great French architect Henri Labrouste, a Boulogne gardener Joseph Monier and a country gentleman named Jean-Louis Lambot. They made plaster vaults, flower pots, doors and boats. In 1876 mechanical engineer W.E. Ward built a ferrocement house in Port Chester, New York which is still in good condition!


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Ferrocement boat built in 1887 and still afloat today.
The building of our tanks is modeled off that of Martin Iorns and Lou Watson who invented and patented this building process in the 1960s called laminated ferrocement - the use of a mold to accurately reproduce super strong and long-lasting boats. And their boats are still in great condition today! We took their idea a step further to make water tanks and integrate a modular system for off-site manufacturing of the tank sections.
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A ferrocement boat built by Fibersteel, Iorns' and Watson's company, in 1978.
We make pre-cast modular water tanks in 2 foot tall sections. Currently we make a 3 foot diameter water tank, but will have other sizes available in the future. The bottom section (seen in below photo) includes the 2 foot tall sidewalls and a bottom, then we can stack additional 2 foot tall sidewall sections on top of the using a male-female compression lip. This allows the sections to nest snugly against each other. Then we seal the seal with a super-strong industrial polyurethane sealant which is potable grade so it does not affect water quality.
The short modular sections allow for an easier casting/curing process and make it much easier to move the sections around. Once cured, we roll them on our trailer and right into your yard where we stack them together, then add a lid. This way we don't need big cranes or a lot of space for installation.
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Bottom section being placed on gravel frame, ready for second section.
Our laminated ferrocement building process uses approximately 80 percent less cement that conventional reinforced concrete and is far stronger and does not crack as is often seen in foundations, bridges, other cement structures. The walls of our tanks are only 3/8" thick but super strong and will hold your water for decades to come!
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