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Question DetailsAsked on 7/23/2016

Repair and replace small chimney flashing

Chimney flashing and roof are without good flashing from roof replacement, chimney is of vinyl. May need to remove and replace with cement board.

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6 Answers


Here are some prior somewhat similar questions with some responses including some very general cost info -


Below clearance info assumes International Residential Building Code applies in your area (most states have adopted it with minor local revisions) - Uniform Building Code used in a few areas is similar but rules are more complex - as I read it vinyl could only be used on a brick/stone chimney if it was at least the above distances from the stone or brick AND at least 12 inches from the inner face of the nearest flue.

Not sure why you are talking about replacing the vinyl with cement board - I presume you mean a siding sheet or plank material like HardiBoard or hardiPlank ?. If the reason you are considering replacing the vinyl (siding, I presume you mean) due to fire risk, with a bare flue (brick or clay pipe or steel liner but NOT internal independent double-wall Class A liner), generally any combustible siding or sheathing would have to have 2" clearance from the chimney (assuming true brick or stone construction) within the house proper, or 1" clear to combustible materials outside the house and its siding - so if the vinyl is part of house siding 2" clear, if a separate vinyl sheathing with fire break from house (presumably at roofline) then 1" clear to combustible material - meaning presumably steel mounting straps or unistrut or such to provide the clearance under the vinyl.

With Class A double-wall stainless pipe flue (commonly used on factory stoves and fireplaces which use metal flue rather than brick or stone), you need 2" clearance to combustible materials throughout the "chimney" chase.

Whatever you do, if you change the sheathing, you need to be sure the crown still sheds the water and melting snow off the chimney and uses a dripedge to drop it well OUTSIDE the sheathing so water can't get down inside the sheathing or chimney - and just a raincap on the flue pipe will NOT do this - needs to be a proper crown cap (my preference by far) or mortar crown.

Source: International Residential Building Code R1003.18

Answered 4 years ago by LCD


how much does it cost to flash a small chimney

Answered 3 years ago by rocketfire1



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Answered 3 years ago by Member Services


Rocketfire1 - in response to your question answer below. Note that instead of asking a new question tacked onto another (unless asking for clarification to an answer given to that question or as the original poster adding info or replying to an answer), to get a better response to your new question post a new question using the Ask button - otherwise the only people who will see it are those who previously posted to that question thread you tacked onto.

This work should have been done by the roofer unless you specifically said not to redo the flashing - so if a recent reroofing you may have recourse there. This is standard with reroofing.

Below are some prior questions about that with answers FYI - though they are for real chimneys.

In your case instead of cutting a reglet (a slot in the brick for the top edge of the flashing to be grouted into) the flashing would have to fastened to the chimney another way - perhaps with riveting through a backing strip (OK actually facing strip in this case) to hold it tightly into a caulk bedding, then maybe ice and water shield or a fiberglass wrap around the top edge of the flashing to keep water from getting between the flashing and the chimney.

I have never seen a vinyl chimney - I can't imagine that being legal because chimneys are supposed to be built of non-combustible material. Unless you mean the chimney is brick (or metal) but has been wrapped with vinyl siding, in which case normal step flashing (google for images of that) slipped up under the siding typically 4-6 inches would be the normal solution for that.

Either way, for a normal maybe 3x4' or so single-flue chimney, about $400-600 would be my guesstimate for the flashing only (no vinyl replacement) - perhaps 25-50% more in a very few very high cost areas like NYC or SFO high-density urban areas - also if difficult access or steeper than about 5:12 or 6:12 roof slope.

Note when you were talking cement board replacement possibly, that normal cement backer board is NOT suitable for exterior use - you would need to use an exterior siding concrete board like Hardiplank or Hardiboard.

Answered 3 years ago by LCD


Rocketfire1 - if you meant roof in general wasnot flashed properly, then that is going to take some shingle or tile or whatever removal and installation of flashing - and ice and water shield if that was not done propearly either.

Answered 3 years ago by LCD


Rocketfire1 - if you meant roof in general wasnot flashed properly, then that is going to take some shingle or tile or whatever removal and installation of flashing - and ice and water shield if that was not done propearly either.

Answered 3 years ago by LCD

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