How "green " is polystyrene when used in construction walls ?

I am not the right person to provide you with the result of a research (I have not done such) about the polystyrene as a panel core but at least I can tell that I've used the material for wall/roof construction. For an official statement regarding its use in concrete building construction please go to:

http://www.structurtech.com/cms_pages/3dp_benefits.php

Hope this will be a good start.

I think you may be thinking of the term "embodied energy".......

See this page for more information:

http://en.wikipedia.org/wiki/Embodied_energy

Also of interest, the Union of Concerned Scientists turned a study of the environmental impact of a household into a book titled "The Consumer's Guide To Effective Environmental Choices." They looked at a typical (U.S.) household's environmental impact in different categories of impact (for example global warming gases versus toxic air pollution) resulting from household activities. Included is the environmental impact of construction relative to household operations (which includes gas and electric utilities). Chapter one of the book can be seen here:

http://www.ucsusa.org/publications/

For example, have you ever wondered about the relative environmental impact of home construction vs home energy use? The impact of our garbage/recycling relative to a household's transportation impact? How about simple things like "paper vs plastic bags" at the supermarket or "cloth vs disposable diapers"? For me, the Consumer's Guide was a huge eye-opener. It shatters a number of preconceived notions I believe most people have about which household activities do the most harm (and the least). It's very informative and highly recommended for anyone concerned about REAL environmental impacts........it should be required reading for anyone characterizing themselves as an environmentalist!

Many thanks to you both (energy guy and second and kind technician)for the informative reponse. I will follow up the webb sites you have nominated and will revert soon thereafter.

NB where I am: " embodied energy" is usually referred as "contained energy" but I accept your definition

Do of course remember that at least here in Europe, bricks are not always "bricks". Some of them have either been made of material with a lot of trapped air, or are of a shape that makes it more difficult for heat to pass through them or both in one brick.....

I would expect that you have the same or similar where you are.

Also there are available very modern prefabricated wooden houses with incredible sound and heat insulation, that come up very very competitive in price and come already built (mostly) on a few big lorries, instead of months of building, it reduces to a couple of weeks in most cases! Thats the direction I would take if I was 40 years younger.....

A friend of mine, who lives high up in the Taunus mountains with such a prefabricated house, only needs to open the curtains when it is sunny but sometimes down to -15°C outside and his house warms up and the heating stays off during the sunny time!!

As to how green the insulation is, does it matter if it will not every have to be disposed of, does not leach out poisons into the atmosphere and gives good insulation, therefore reducing energy costs....that is "Green" enough for me!

If energy prices continue to rise, we will all be very happy in the future if our houses are so well insulated that a lot less energy is needed to warm or cool them!!