Btw, the issueis not whether green roofs are a nice idea or have benefits — I am in full agreement they are attractive and probably have many excellent qualities.

The issue as I see it is but whether green roofs are the most cost-effective way to achieve the goals which they are supposed to fulfill:
storm water quality and detention,
energy use/building insulation,
‘urban heat island’ effect,
natural habitat,
general urban livability.

Any others?

I suspect — and we need the studies to say one way or another — that techniques other than green roofs will be more cost-effective.

But my surmise (and it is only my own guess right now) is that the benefits of green roofs can be achieved as or more effectively and at lower cost by more prosaic methods. If you are willing to give it a fair hearing I will elaborate.

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

I have not researched this thoroughly and don’t have a paper to cite for you, but maybe someone else could chime in. My educated guess is that if you factor in all the benefits, including all the externalized costs, that it would make sense for us to be doing a lot more green roofs than we are doing now.

And likewise, do you have any studies you could share that say green roofs are not worth doing?

@12, you should probably get on the phone to Germany right away and let them know that we don’t know if green roofs make sense, since they’ve already put them on 10 percent of their buildings. Do you really believe that lack of knowing what to do is holding us back, as opposed to not implementing effective policy?