So what do you do when you have a flat roof that holds a lot of water? The most common result of this ponding water is granule loss. It is an unfortunate occurrence that will reduce the life expectancy of the roof system as granules provide UV protection and those areas that become exposed will deteriorate at a faster rate than those still protected by original granules. I had such a case today in Vancouver and I did not have a definitive answer. I recommended Strata contact the local office of Soprema torch on membranes and request a site visitation from their Technical Representative. I have no doubt this guy will have the answers. I too look forward to the recommendation. I never stop learning.