Accepted Answer

Hi XXXXXXXXX
If the brickwork and existing flashing is still in good shape the best option would be to use the existing flashing as counter flashing. To do this you would cut the existing (I'm assuming lead) flashing ~1" above the top of the shingles then bend it up. Form new lead flashing so that it runs up the brickwork and stops 1/2" from where the existing flashing is mortared in. Then bend the old flashing back down so it laps over the new stuff and holds it in place.
If the old flashing is brittle then the next best thing is to dig out the old flashing where it is mortared into the brickwork then replace it with new lead and re-mortar the joint. It is best to use a latex additive in your mortar mix if you use this method.
If the brickwork is bad and you have some masonry skills then you should strip (and save the bricks) the chimney down to just below the roof line then re-lay the bricks. Of course this will entail setting up staging on the roof which is no big deal if the chimney is near the ridge. If it emerges from the middle of the roof then your stainless option will probably be the best option. The stainless option is the most expensive but if it is a steep roof and the chimney isn't near the ridge then it is worth the added expense.

Expert:	Rick
Pos. Feedback:	100.0 %
Accepts:	652
Answered:	8/18/2009

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Licensed Construction Supervisor & Remodeling Contractor 35+ years experience