Depending on the quality of manufacture and simply according to their age, tiles can lose their water repellency over time. They become porous and begin to gorge with moisture; This will eventually cause the appearance of foam and weakens especially during periods of frost.
Changing the roof is a major investment, if you want to save time without your house falling apart, here is a useful little tip.
With a sulfator (spray), apply a water-repellent solution to all of your tiles. If you do not have a sprayer, use a long-haired roller.Suggest a tip for this theme