We've got various jobs to be done on our roof. One of which was to renew the valleys as the existing mortar is crumbling. The roofer we planned to use wants to wait until the risk of frost has passed which is fair enough. We've already got dry verges and he will be doing a dry ridge. He originally quoted to just replace the mortar on the valleys but I'm tempted to push for him for dry valleys. Is there a disadvantage to dry valleys? I just wonder why he never suggested it?