Is it unusal for roof flashing to leak?

[Mopsy]

I noticed a small damp patch in the corner of my hallway. It is annex type ceiling (while outside it is porch like adjoing the roof, if you know what I mean) so the builder decided to look at the problem and has established that part of the flashing has failed. House is 10 years old. Is this unusal? I thought that flashing work never failed. It now has to be replaced. Would it be wise for me to get an accessor to look at the damage? It looks like the flashing has to be replaced on both sides of the ` annex`. That part of the roof is not very big, like a little bigger than porch size so I am now worried about the cost!

Has anybody any ideas why and how this happened?

 

[Lak]

The lead thart makes up the flashing has certainly not failed which is how I would ineterpret your question.
The workmanship in installing it may have been poor, most likely and very simple to address is the weak point between wall and lead, where the edge of the lead is tucked into the wall. The lead needs to be held tight in place with small wedges of lead and be pointed with mortar to make it impervious to wet weather. Replacing rather than repairing seems a little drastic.