What does everyone think of the idea of building a composite wall of concrete and solid Geofoam expanded polystyrene blocks?  Here is my idea that I may want to try:
Use concrete block, placed concrete or ICF's for the outside wall.  This masonry wall of nominal thickness would serve as structure to support the roof and protect the house in a storm.  And then use large Geofoam blocks to build the inner wall.  (Geofoam is available in various densities, thickness and depths.  See http://www.geofoam.com/)  The two walls do not have to be tied together since the Geofoam could be anchored to the slab.  The Geofoam wall inside the house would not need a footer since it is so light and non-structural.  Route out the Geofoam wall for the electrical and other utilities.  Then use stucco or a synthetic stucco such as Sealmark (acrylic - no cement) on the outside face of the concrete and the inside face of the Geofoam wall for the finish.  By using this system of two dis-similar walls, we have the insulation and the massive walls.  In fact, we can dial in the thickness of the combined walls.  In some coded areas, all of the expanded polystyrene would have to be protected from fire with real stucco or drywall.  The outside could be Sealmark to avoid water intrusion problems.

Although Geofoam is available with termite resistant Perform Guard, there should not be any termite problems - no structural wood in the walls.

The above method of building a composite wall would be a takeoff on the SAB system without the engineering or special admixtures and glass-fiber reinforced concrete coating.

I am posting here for everyone to comment.  Be honest in your critique.  Other than the extra cost for the two walls, what else is wrong with this method?  I thank the posters in jelston's topic for making me think of this system.

I am currently consulting with a homeowner that wants two-story ICF walls and a flat concrete roof.  He plans to use the roof as a deck for parties.  The flat roof will actually have a slope of 1/4" per foot for drainage to the rear.  We are considering various systems to support the flat concrete roof.  Looking at pre-stressed pre-cast hollow-core concrete planks versus bar joist/structural metal pans versus structural pans supported by shoring.  It will be interesting when the quotes are in on the various systems.

Jelston,

You may need temporary shoring in the middle of the wide spans to prevent sags in the roof.  I have seen sags in ceilings caused by the wet concrete and the extra weight of the workers standing in the middle of the span.  The temporary shoring should be able to be removed after about 14 days of curing.  I prefer to leave the shoring in longer if it is not rented. 

Bruce,
I am considering using 4" foam + 6" reinforced concrete + 4" foam.   I think it will take a minimum of 4" of expanded polystyrene on both sides to have enough strength to hold the wet concrete.  My goal is to superinsulate and build a home that will withstand storms.  The concrete wall would be used as the necessary structure only.

I like the idea of stucco or the look of stucco inside and outside.  I admit that I have done only one home (Insteel forms with shotcrete) where the inside and outside facades were stucco.  The interior partitions were steel studs covered with drywall.  After the drywall was finished, the only way we could tell which wall was real stucco and which wall was drywall was by knocking on the walls.  Drywall walls sounded somewhat hollow.

I have used vertical ICF's (homemade) with 2.5" of foam on both sides with great results.  With through-the-wall ties it took minimum bracing.  The bracing also allowed myself and another person to walk around on while placing the concrete.  By the way, Geofoam has an application that uses their foam for foundations.  My concept just extends it up to the full height of the wall.

After thinking about it, I agree that ties would be necessary to keep the wet concrete from separating the two walls of Geofoam.