Originally Posted by
Chad Fabry
The metal roofing industry might take offense at that statement. Screws with captive neoprene washers are the preferred method of attachment for all face secured metal.
When used with metal roofing attached to the roof sheathing or purlins, I agree.
When used at pictured in the photo, there will be movement and the fasteners will loosen against the metal, creating a leak at the fastener.
The difference is that metal roofing 'is not' "water tight", there is a slip sheet and underlayment beneath it which is like the dry-in under singles, whereas flashing *IS* the watertight 'flashing' between two surfaces meeting at an angle, two dissimilar surfaces, etc..
Flashing is designed 'to make it' watertight. At least, as water tight as possible.