Chimney flashing and condensation

Can you guys verify something for me? I was told that a chimney needs to be tarred before flashing to provide a barrier for moisture. Otherwise, during winter, the moisture from a warm chimney will work its way to the metal flashing and condense on the inside of the cold flashing, causing long term moisture problems under the flashing.

Has anybody heard of this?

That would be a new one for me but funnier things have happened. Who told you that. I have installed i cant count how many and never had a problem.

Oh yea if you want to chat email me your number and it would be nice to talk to a local roofer that is not my comp. Just a thought.

Kestas, who told you this?

Thats sounds like an old wives tale to me. It is a good idea to always wrap your chimeny with ice & watershield before you tie in the flashing though.

I have seen moisture/condensation on the inside of chimney flashings in cold weather, either caused by warm air from the attic or chimney. But it usually does not cause a problem.
I suppose if the chimney and flashing is large and there is a lot of warm air escaping the attic, it could cause some masonry damage long term.


Is this mositure from the chimney exhuast? If so the chimney lining is shot or if there is no liner the brick have become porus and the chimney needs a liner.

Gas deterioates brick faster then oil.

If this is the case. Roof cement will save the flashing. It will cause more moisture problems else where.

Setting the chimney flashing in roofing cement has been a method I have used from time to time over the last 35 years .It has been around before ice and water sheild came out.You will never have to worry about the flashing becoming loose and if they cement it well enough you will never have to worry about any leaks.I still use this method when reflashing a chimney,never had a leak on one I flashed.

This is one I haven’t heard before, kinda makes sense…
Thinking back I guess I have removed flashings with moisture behind them, on masonry chimneys.
With no dicernable leak…
Masonry chimneys tend to leak and not show themselves in the home.
There may be a little puddle on the floor in the basement by the chimney foundation…

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snow and ice piled up on roof, chimney goin, makes sence to me that the warmth of that area could melt some snow and come in through metal flashing joints,
maybe even the brick it self.

if not tar, then ice and water sheild.
something solid behind metal flashing.

maybe paint the brick too.

good luck.


Dennis, without context I have no idea how to undestand that photo.

Obviously it’s an “after”, i.e. other work being performed & this is part of it.

But what was the overall diagnosis?

Dosen’t look like apron,wall,and counter flashing.It looks like they wrapped the whole wall in a flashing.

Sorry, got busy, should have added something.

Brick parapet wall over living space.

Just shows the moisture that was present between the wall and the flashing.

I’m not sure, but the original brick may have been exposed and later covered with tar and then copper.

Notice how the worst of the discoloration conforms to the open brick and mortar.

I figured the brick wall should be left exposed, so I cleaned off the loose tar and replaced the copper. But left a gap at the top and counter flashed a short piece into the mortar under the stone.

Thinking about it further, I would expect any water seepage through mortar and brick to be slow enough so it wouldn’t be a problem. The slight gap between bottom flashing and counter flashing should shed the water vapor fast enough.

Also, shouldn’t any vapor barrier be placed on the warm side?.. meaning that if this problem was true, the inside of the chimney would need the tar.

My buddy is not a roofer and he was talking in general terms. We were discussing my roof and all the fine points of my DIY job.

On my chimneys, I removed the 46-year-old flashing and ran I&WS up the sides from the roof, then reflashed (using good roofing techniques) with galvanized steel. I don’t like aluminum because of excessive thermal cycling associated with it. I cut into the mortar and filled the cut with roofing tar before setting the top lip of the counterflashing.

gtp, I’m not a roofer, but for some reason roofing fascinates me as a hobby. I have a lot of respect for the experience people have on this board.

Kestas,roofing cement or tar works fine between two surfaces but will only crack and separate after a year or two if applied exposed to the weather.At least use a polyurathane sealer such as MP-1 when sealing counter flashings, nail heads,or anything that is exposed to the weather.A layer of fiberglass membrane works well with roofing cement on larger areas and keeps it from cracking when it dries out.I never use silacone.Good luck with your hobby.

i have seen this before but the reason for the tar is not for a moisture barrier its to fill air space.

if you flashing is neat and tight than there is no air space.if there is no room for moist air than theres no condensation.
its like the space between your front door and your storm door. when it gets cold the inside of the door is wet the water runs down the glass.

i have also seen it on skylights where the flashings were replaced and not kept tight to the frame.

if a chimney has masonry or flue problems no amount of flashing can help it. only pointing water proofing and a new thick cement crown will stop the water.

Couldn’t imagine a scenario where I’d need cement, or fabric and cement on any sloped roof. Other than pointing slate ridges. If my felt or I&W doesn’t go tight to a chimney or wall, and stay there, I just cut it out of the way.
Neither is critical to a good install.

[quote=“tinner666”]Couldn’t imagine a scenario where I’d need cement, or fabric and cement on any sloped roof. Other than pointing slate ridges. If my felt or I&W doesn’t go tight to a chimney or wall, and stay there, I just cut it out of the way.
Neither is critical to a good install.[/quote]

I wasn’t around 75 to a 100 years ago but it seems like none of the older chimneys had ever had flashing,most are deteriating and need to be torn down.They dont want their chimney flashed,they want the leak stopped.

glad your enjoyin your self kestas,
just one questions.
what the hell is excessive thermal cycling

is that a fancy name for condinsatin alot…