Dave is absolutely right.
Two of the great benefits of Insulated Concrete Form construction are the energy efficiency and strength.
ICF construction gets its energy efficiency from a combination of a total of 5" of rigid styrofoam insulation Trapping the reinforced concrete in the insulation "sandwich" allows the concrete to become part of the thermal mass.
The next is strength. All ICF construction requires both vertical and horizontal re-bar embedded in the pour creating what is known as reinforced concrete. This step is not required in conventional residential foundations (with some exceptions). It is the same method as is used in building bridges and buildings!
Fantastic strength can be achieved...just remember this if you decide to change a window opening or renovate later, you made need a missle to create the new opening!
As Dave mentioned, quiet is an understated benefit. It cannot be truly appreciated until you are standing inside one but because there is virtually no vibration and no hollow cavities in the wall to transmit sounds, it can be eerily silent in an ICF home.
We built a 12,000 square foot ICF bungalow on a rural property west of Toronto a few years back. The construction took place during a particularly cold winter and this property was quite exposed and subject to high winds. With no drywall or finishes up and the last window installed, you could not hear a whisper inside that building, even with a wild winter storm raging outside. They are quiet!
Lastly is value. ICF construction costs more than conventional building, but when you compare foundations, more of your construction dollars are being spent on the actual structure as opposed to the "renting" of forms and boom trucks, etc. that are stripped away a few days later. Once installed, all of the form stays in place and is integral to the system, therefore more of your dollars go towards the actual structure and efficiency of the home.
Another combination type construction that is also super energy efficient is an ICF foundation and a Structural Insulated Panel (SIP) framed structure above grade.
You can get some great information on ICF's here: http://www.forms.org/
Structural Insulated Panel information can be found here: http://www.sips.org/
The supplier I use for SIPS has great information on their website here: http://www.thermapan.com
Best of luck.
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