Chimney Flashing: To replace (or not) when re-roofing

My original shingle roof has lasted 24 years, problem free. Now, I am planning to have a new roof installed (after tearing off the old) and I am learning there is way more to this than meets the eye! One issue is flashing around my brick chimney .
The current flashing is galvanized steel. There has been no leakage. About 15 years ago I went up there and painted it because it showed some unsightly rust. The paint job still looks good.
Most re-roofing bids I've received have included new chimney flashing and I've never questioned that until I got the latest bid from a reputable contractor. He told me that he would be glad to reflash the chimney (for $450), but that it didn't need to be done. He said a good galvanized flash job would last forever, if painted.
Further, he commented that the dormer up on the roof (75% of chimney is inset in the dormer) was built around the chimney, and it would be difficult to do as good a flashing job as the original effort. (He did indicate that he could do a good job. It's just that he didn't think it was necessary.)
I've done a fair amount of Google research on flashing. Many folks have suggested replacing valley flashing when re-roofing, but I've found no discussion on the pros and cons of reflashing a chimney versus keeping the old, problem-free existing flashing. I get particularly concerned when I read all the horror stories of flashing jobs gone bad.
All I want is a good job, and the piece of mind that comes from knowing that the new roof and related work will last, and be problem-free. What do you think? Tom
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The roofer told me the same thing. He said the flashing is in excellent shape and didn't need it done. It was done back in the day when everything was done with quality work. You have to wonder what material is available today - aluminum foil? He's a reputable roofer so I followed his advice and kept the same flashing.
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If you saw rust it is deteriorating even with paint sealing it. Have it redone but be sure they cut into mortar joints and mortar it in. Copper is best. Lead and copper last a lifetime not galvanised steel. Many roofers don`t know how to flash or will cut corners, hire someone who knows . The guy that said galvanised lasts a lifetime does not.
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Really it is a job for a mason to cut in the flashing but it will be hard to find a guy to do the small job unless he specializes in repairs.

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I can't see your chimney from here but based on the mention of the dormer I will assume that at least one side of your roof has a rising grade to the chimney. Ask the contractor how he plans to deal with the step flashing along those sides.
A properly flashed wall or chimney in this situation has step flashing and over flashing. The step flashing prevents water on the roof from getting into a crevice and the over flashing prevents water on the chimney from getting behind a crevice in the step flashing. As illustrated by the crude ANSI drawing below. This drawing assumes that the chimney is on the left of the page.
| = overflashing is mortared into the chimney |__ = step flashing forms an L between the chimney and the roof. One piece is installed for every course of shingles. How you could remove the shingles without destroying the flashing is beyond my ability to understand.
Even if they just butt the shingle up to the chimney with no flashing and add a little caulk, it will be few years before you have a problem. If they leave the overflashing in place and add some caulk it will be longer before you have a problem but you will before your shingles wear out.
If you are just doing a nail-over, you should do a bit more research before you sign a contract for this option.
I do agree with the statement that the old may be better than the average sold on today's jobs IF it properly utilized. The quality goods are still sold. Most people are to cheap to pay for them.
Colbyt
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It is easy to cut in the mortar joints with a grinder. All roof pros in my area do it, the hacks dont. I would not hire anyone that would not cut it in.
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But I've seen cut ins of just a quarter inch which is worthless.

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Just curious... how would a hack do it?
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Hacks use tar or caulk - sealant, when that fails water bypasses the flashing on the chimney.
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On 15 Mar 2005 11:18:00 -0800, "Milwaukee Tom"

You've had some suggestions, and I'll add a little bit more to it.
Chimney's often leak. We all know that. Why do they leak? Because they were either not flashed or not flashed properly. How do you do that? One reply gave pretty good details on that so I won't go into it any more than to say that oftentimes it is a good suggestion to seal between the shingles and the step-flashing you install with every course of shingles just as an added precaution (which is oftentimes warranted.) Really, though, it is usually not the straight edges of the chimney where the leaks develop, although that happens sometimes, rather it is at the corners where the ability of the installer is most important and how he works the metal in these locations will either give you a headache or you will be blissfully unaware of how good a job he did since you've never had any problems at all.
As to the question of should the existing flashing that is installed in the mortar be replaced? I can't answer that question from here...no one can. Good, heavy gauge galvanized steel will last decades in this application. Thin galvanized will rot in a few years. I've seen some that are in almost new condition after decades of service and don't warrant replacement and to do so would gain the homeowner nothing but a lighter pocket-those we don't replace. If it is at all questionable, and many are, then they get replaced. How? We use a worm drive Skil saw with an abrasive blade to cut a groove into the mortar, fashion a new piece of metalwork, and install it using a urethane sealer made for sealing this kind of exterior joint. I've never seen a good installation using this method fail. In North Texas sun and extremes of weather. Sure, if you could find a mason to do such a small job, you could mortar it in, maybe the new mortar would match the old (the sealer we use comes in a wide variety of colors and one will match most any mortar), but maybe not, and in my opinion, the added expense of the mason isn't warranted since the urethane sealer does such a good job in and of itself. I've seen bad mason repairs not last as long as this stuff will.
In short, you need to ask yourself a question...Do you trust the roofer who said, in effect, sure I could charge you more money (thereby making more money for myself) and change it out, but the materials in place are in fine shape and you don't need to spend that money and I'm going to tell you this straight up.
And yes, with proper painting it will last as long as your new roof...if the condition it really is in is as good as I believe it to be sight unseen. You can even treat that rust with some products on the market today that will stop it in its tracks and it won't spread any more...if you want to go to that much trouble. And I'm not talking about Naval Jelly or Red Lead. There are some great products out there that will stop rust dead in its tracks.
Use your best judgment. If you, and your roofer, are wrong, later it is perfectly possible to replace the flashing. But I suspect it won't be needed.
Good luck and I hope this helps.
-- John Willis (Remove the Primes before e-mailing me)
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