Equally as extensive green roofs, the maximum expected payback period, with only personal costs and benefits, is 10.4 years (124 months) with 90% of confidence. However, payback period is most likely to be 4.6 years (55.2 months). Similarly, with 90% confidence, costs and benefits for both social and personal sector, results in a maximum payback period of 9.7 years (116 months). Nonetheless, the return period is most likely to be 4 years (48
months).