"Tubular" Concrete House
Simple 8ft by 8ft cement home made from sewn tarps and concrete. The tarps act as forms when concrete is pour providing a simple cost effective \$300 house.

Solution

Before I get too far into the description of the design, I think this proposed design is an excellent design or at least a design that should be given to Engineering Universities in India or other countries to give to their engineering students to continue to work on the concept.  I think improving and optimizing my proposed design would be interesting design project for engineering students.  If you have connections to these universities please forward my design information.

I believe I can produce this house for under \$300.   I would have to spend some time doing an in depth structural analysis to verify optimal dimensions to get exact dimensions numbers, but I think my cost estimates are close.  Rebar is sold by the pound (\$740 per ton) or kilogram so I was able to get reasonable costs estimates for the rebar.  I used the actual cost I paid for the tarp material to figure the cost per square foot.  Concrete is made from cement, sand and gravel.  I found the cost of cement in India and estimated the cost of sand and gravel to be approximately \$10 per yard.  I have estimated the cost of concrete per yard is \$28 per yard.

My vision in creating this \$300 house design was to build 1,000�s of houses simultaneously without costly concrete forms.  The proposed design starts with building four corner posts approximately 6 ft high.  This is done by supporting a tarp post bag using the internal rebar structure and pouring only a foot of concrete at a time and allowing it to harden before another foot is poured.  The tarp bag is not lifting the concrete it is only holding from flowing outward.  I estimate the tarp I used could hold 1 vertical foot of concrete without damage in the corner post tarp.  This might seem like a slow process, it would take six days to pour the post but I this processes does not  require forms.  Now imagine creating a small village and in approximately six days I would have all the corner posts created for every house in that village.  Think of this design concept of building houses in parallel and if you designed using forms you build in series.  The more houses you build simultaneously the more you want to build in parallel.

When the concrete in the corner post reaches the bottom of the header beam rebar, the concrete should be allowed to cure until desired strength compressive strength in the concrete is achieved.  Now it is time to hang the wall tarp onto the header rebar beam.  (The wall tarp could easily be mass produced.)  The upper edges of the wall tarp should have a reinforced hem that a 12mm diameter rebar slid into the hem loop.  Brackets made from rest on the header rebar beam and raise the top of the hem(rebar) above the header rebar beam.  Rebar would be inserted at the footer location thru the wall tarp to tie the bottom of the posts together with rebar.  Remember to put duct tape or something at the end of the rebar so you do not damage the tarp during inserting.  Rebar would be inserted at the window location and where needed in the wall for additional strength.  Concrete can now be poured into the wall tarp. The length of the wall tarp is designed so the footer rests on the ground so the wall tarp does not hold up the concrete but only keeps concrete from traveling outward.   There are some issues that the footer does not shrink in size as the tube part of the wall, but I believe this can easily be solved by sewing the footer to a smaller length.  Because the diameter of the wall tubes are smaller than the diameter of the corner posts the stresses in the wall tarp are less and higher vertical amount of concrete can be poured.  I was able to pour six feet at one time on my prototype. I would use strong enough tarp material to pour to the height of the bottom of the header rebar beam.  Fill window tubes with wet sand and gravel mixture at the window location.  I would then allow the concrete in the wall tube to harden.  This would then allow you to readjust the wall tarp at the header beam to fill concrete completely around the header rebar beam to the top of the wall tarp.  The roof could be finished a variety of ways.  I have proposed creating concrete tubes on the ground and then lifting them onto the roof and concreting the tubes together.  The house is now livable after cutting openings in the wall tarp for the window and installing the door.  The tarp can be left on until if the tarp falls apart or the tarp can be removed and the joints between the tubes filled with mortar.

Update...  The 2nd generation header design will increase the estimated cost to \$332 due to the more rebar.  However if I use a cheaper door, eliminate foundation and either leave the tarp or mud the wall joints I estimate the cost to be \$296.

I performed a simple test using to simulate how the post will fill with concrete using water (See video below).   Polyethylene bag or sheet like material could also be used with heat welded seams if ithe material can be designed to withstand the applied forces and induced stress.

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