> The results indicate that the energy savings ratios of the rooms with the sedum-tray garden roof and with the white roof were 25.0% and 20.5%, respectively, as compared with the black-roofed room, in the summer; by contrast, the energy savings ratios were −9.9% and −2.7%, respectively, in the winter.
It seems that covering the building with a green garden is better than painting the roof white, but the heating costs were higher in the winter for both designs.
I guess that changing the roof could work in climates where the winter is not too cold.
On a side note, I wonder if it would be better to work on better insulation (both roof and sidings) rather than re-roofing a house.
Note: I am not a civil engineer so I have no clue if the paper is good or not.