Overlapping of new/old roofing felt on an extension
 

I've recently had the house extended lengthways (in line with the ridge)
and just noticed that, where the new roof joins the old, the builders
haven't overlapped the felt very far; are there any standards or regs
that cover this?
The old felt goes to the edge of the first new rafter and the new felt
goes to the edge of the first old rafter, so both hang down. The builder
is proposing to fix-up some battens to stop them drooping but I would
have expected that the new felt should at least have gone over the first
old rafter. Any roofers out there?
--
Dave S
(The return email address is a dummy)