Honest ,reliabel,compitent contractors ALWAYS make provision in EVERY contract for bad deck exposed at tear-off. Normaly the contract states each 4x8 section/sheet or fraction of will be replaced for $xx per section/sheet additional to contract amount. Without a provision,you are open to change orders which you have no cost control of. Only a shysters and fools tell the customer prior to tear-off how much deck needs replaced.
80% of places that rely on sealant to prevent leaks will fail. Sealant is ok for temporary emergency repair but good installers use little or non on new 3 tab roofs. What you have looks like thousands of other chase chimney surrounds installed every day. I can't say exactly what kind simply from looking at a picture but the chimney surround would be flashed were it mine.
Bottom line,hire a reputable contractor then alow him to decide what is best or hire one of us as a paid consultant to advise you in person and on site..

You don't flash the prefab in the conventional way. This would throw up a red flag on the contractor who said he would flash it that way. You do not have mortar joints in a prefab, which would ground out for counter flashing in the normal setting. I would opt to forget about that contractor who wanted to step and counter flash it.

Word of caution about sealing the prefab. "Normally" they have about a 4-6" flange. Most of the time the flange looks like Swiss cheese with pin holes everywhere. Several options are usually available. I'm assuming this chimney is used for the hot water and or furnace flue. If so, you may want to eliminate the chimney look for cost savings, and put a standard flue. However, depending where you live, the city/county may require a licensed HVAC installer to install it. In this case, it would require coordinating with the roofer so he could flash the penetration around the chimney or typical flue pipe instead of the HVAC installer doing their thing afterwards.

Either way, if there is rotted wood around the chimney, make sure they pull the chimney off and replace the wood. Even removing the chimney may require a licensed HVAC installer do it, depending on what your local code is.

I shouldn't have assumed. Is this a gas fp?

I was going to comment, but klem 1 said it all.

did either mention building a cricket?
you have a slope into the flat side of a chimney..what's made from is only
part of the problem..divert the water away from the chimney..then the flashing
is the easier part of the problem

Thanks for your help! The fireplace is a metal prefab woodburner.

I have received 4 bids so far (out of 6 roofers I contacted), and none has mentioned a cricket.

Here's a couple pictures of jobs I've done. I was taught you don't build a saddle if the chimney is under 21". The one picture is just 21". I wouldn't even think about putting a saddle behind something you couldn't step and counter flash correctly.

I stand by you don't try to counter flash a prefab when it's not brick or don't have appropriate siding etc to be used as the counter flashing. Simply you can't grind out the mortar joints, which the custom bent flashing is inserted. Since you can't grind out the joints, you will have sealant for the barrier. Take for instance the 22 ft chimney picture. Some "expert" decided for counter flashing, they would run the counter with the roof line instead of grinding out the joints, custom bending the flashing with a brake, and doing it right. They slapped sealant on top of the counter for their first line of defense against element intrusion. You do not want to do this on your prefab. Sure it takes longer to do things right, but you have to know when to try to do the right thing AND if it's possible to do what you want to do.

The prefab "should" have a flange, which is used for securing the fake chimney to the decking, but is also a flashing flange. If it doesn't I would opt out of using the fake look, and get a HVAC installer to put in a regular vent.

I've done hundreds if not thousands of flashing of junctures. I used to make a very good living on other's mistakes, then I reached the age of wanting to keep my feet on the ground.

Hi Roof35, that's some handsome looking work there.

According to the one (and as far as I can tell, the only) roofer who's looked at the chimney up close, yes, it has a flange. He is proposing that he seal the flange (I don't know whether he means seal it to the decking, or to the shingles, or to what) with Geocel.

My first inclination was to give this guy the job, if only because he cared enough to actually get up on the roof and look it over. But Klem said "80% of places that rely on sealant to prevent leaks will fail." You said "most of the time the flange looks like Swiss cheese with pin holes everywhere." So maybe he's not the right person for the job.

OTOH, I don't know if any of the other roofers bidding on the job realize what that chimney is. For sure they haven't told me what they'd do with it, other than the one who said (when I asked him) "Metal or not, I can seal it up the proper way."

I haven't measured the chimney surround, so I have no idea whether it's 21" or larger. Thus I can't say whether your idea of building a saddle (same as a cricket???) would work here.

Klem seems to be saying "pick somebody experienced and trust him to do the job right." Over the years, I've had 4 roof jobs done on various houses, had problems with 2 of them. "Trust but verify" seems like a better strategy.

Early this week I'll get on the phone again with these various roofers and see if I can get any more thoughts out of them about how they'd expect to treat that chimney and/or surround.

Thanks again to all.

ROOF 35 SAID "I reached the age of wanting to keep my feet on the ground. "

Isn't it amazing how something can be so obivous for so long before you finally see it one day? It dawned on me when I noticed I had gone from holding on with one hand to holding on with two then I noticed everything that climbed around on buildings had tails,,,,,besides me.
Hello David. Don't read things into a contractors actions or in this case,lack of action (explaining how and what he intends doing) if you din;t ask. He may plan doing everything correct but just isn't tooting his horn about it, I often write things such as "chase chimney to be inspected , flashed and water proofed to assure life span equeal to roof cover". Take my word,that is far better than verbably explaining guage,width and style of flashing along with nail size and pattern to a consumer that hasn't a clue what I'm talking about. Don't get me wrong,it might look intirely different if addressing a GC,engineer or sub-contract situation. IMO,where consumers cut their own throat is neglecting to pay roof35 or other consultants to hold their hand. With no intent to offende, it's obivous you are unprepared to make roofers give down the milk. It's also fact that talking to expert A will never prepare a person for dealing with B if B is inept or intent on swindeling their customers. Please understand,there are contractors just as deficient in understanding and comunicating as their customers are. If and when you know all there is to flashing chimneies,drip edges, valleys,end walls,side walls and dormers are each equaly interesting. If all that fails giving you hives from fretting about it,there is the matter of damage caused by improper handling of material before it's even installed.

klem1- You are so right!

davidr- Sorry it took me so long to get back. Been working those 16 hr days fighting that white stuff that fell out of the sky. The State isn't too kind when you tell them no.

It wasn't I who said about a saddle behind your chimney. Since my contention is you can't flash & counter flash the fake chimney, you couldn't put a saddle behind it. Because the saddle would get normal flashing and counter flashing.

I have never been a fan of the flange for flashing on those things. Klem is correct about sealing is good for a temporary solution. I have seen my share of shingles sealed at a juncture. This solution is not a permanent solution, or the correct way to solve the problem. I'm very familiar with Geoseal, it's the only sealant I ever used. However, it is not meant to seal where the shingles are butted to the chimney. Myself, I liked to leave a water way (unobstructed gap) between the shingles and flashing. Guess I could write a book on how I used to do it, but books have already been written on the subject.

An important thing to remember. The fake chimney must come off in order to install new sheathing. In the cities I was licensed, the removal & installation for a woodburner could be done by the roofer. If it were gas, that was a different story. An inspection of the flashing for the chimney should be made, to see _if_ it should be reused. Honestly, I don't see how someone can tell you how they are going to proceed with the unknowns involved.

Good luck with the project.

I had a roofing company in my area come out to install the red brick metal decorative chimney surround with a cage. I was thrilled it was going to get done. After a half hour, the worker said to me that it cannot be installed with the kind of chimney I have. He told me that my chimney is concrete inside. And that it will not fit etc etc etc. I was livid and so disappointed. Have you ever heard of this before. What can I do to resolve this. Or is there something else out there to make your chimney look nice.

Karen P Lizzano