I can give you a data point on one. I used to work in a factory/office building that had a water-retaining roof like the one described in the article. I'm won

I can give you a data point on one. I used to work in a factory/office building that had a water-retaining roof like the one described in the article. I'm wondering if the architect was reading this magazine - the structure was built around the same time. Suffice to say, having hundreds of thousands of gallons of standing water on the roof was not a good thing in the long term. Nor was it good in the short term. The extra weight. Algae. Mold. Icing. Leaks everywhere. Just awful. The new way is to plant a garden up there, which seems a lot more reasonable and probably gives a similar thermal load.