The Natural Philosopher wrote:

Bloody obvious.

You have a flat roof and **** all flashing on the stack.,


Go up and prise up the lead. Bet you its all wet underneath.


You need to take roofing felt an carry it up the sides of the stack,
to where the flashing starts, and probably mastic it in, then put in
new flashing and dress it several inches out along and over the
roofing felt. So that driving rain under the flashing has to go a
long way and then UP to the flashing top, before it meets the brick.

Who's to say the felt doesn't already go up behind the lead? - my bet is
that it does, but this isn't the problem.


Yu might also, as others have suggested, at the same time repoint the
stack and remortar the cowl top.


Personally I would scaffold up, or whatever, and demolish the stack
top, and start again and build a new top, done properly.

I take it the flat roof is part of the new conversion? If so its been
badly done.

It should be redone in conjunction with the chimney.

IME you can't seal a chimney with lead on a flat roof - where they've took
the felt up the chimney sides and then flashed over it, they can't seal the
corners and this is where it's getting in, that is to say, the felt is split
at each corner and doesn't go 'around' the corner in one piece, and as you
say, the lead is just covering brickwork at this point.

I wouldn't flash a chimney like this with lead onto a flat roof - it needs
something completely different, torch-on would probably be best but not very
permanent

--
Phil L
RSRL Tipster Of The Year 2008