# question about waterproof shingle underlayment at chimney



## ttboy (Oct 18, 2007)

Should waterproof shingle underlayment be installed beneath the step flashing or over(covering) the step flashing when flashing a chimney that extends out beyond the eaves of the house? 

I was under the impression that the underlayment should go beneath the step flashing, but I recently read somewhere that it should go over the step flashing. Any input would be greatly appreciated.


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## Ed the Roofer (Dec 12, 2006)

It sounds like the flashing and the chimney extend beyond the decking.

If that is the case, then the step flashingsa and counter flashings would be purely decorative.

Can you post a photo?

Are you the contractor for a job or just looking for further information about your own home?

Ed


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## tinner666 (Nov 3, 2004)

Underlay goes 'under'. Not that I bother with it at penetrations. On a case by case basis, I use it or leave it out.


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## dennis (Nov 17, 2004)

Though it does make a nice temporary seal over the step flashing if you are not going to get the counter flashing on before it rains.


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## ttboy (Oct 18, 2007)

The homeowner has requested that I use the waterproof underlayment at the chimney flashing. The homeowner reports occasional leakage around the chimney that is visible as water stains on the interior drywall. The chimney is a brick veneer and faces east. The chimney is located at the edge of the eave and extends slightly beyond the eave (so you can't really use a base flashing). The homeowner says that under normal circumstances there's no leak around the chimney. However, when the rain blows out of the east the leak occurs. My impression is that the rain is blowing beneath the step flashing at the gap between the step flashing and the brick veneer.

I will post a picture as soon as possible. The chimney now has the standard step flashing and counter flashing with a cricket on the back that is flashed as well. The homeowner has asked me to use the waterproof underlayment to cover the cricket and cricket valleys as well as the sides of the chimney to hopefully prevent any future leaks. I can't really argue with them on this one so I want to make sure I get this right the first time since there's already a leakage problem (although it's only intermittent). Thanks again for the input.


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## tinner666 (Nov 3, 2004)

Sounds like water wicking through the brick. If everything else is correct, a brick sealer might be the answer. 
You're profiled as a roofer. Why consider underlay as a top layer?


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## tinner666 (Nov 3, 2004)

How's the cap piece?


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## ttboy (Oct 18, 2007)

Thanks for the input. The waterproof underlayment would not be used as a top layer. It would be used over the step flashing, but under the shingles. Again, this is not something I've done. This is based on something I read recently regarding chimney waterproofing.


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## Ed the Roofer (Dec 12, 2006)

ttboy said:


> *The chimney is a brick veneer and faces east.* The chimney is located at the edge of the eave and extends slightly beyond the eave (so you can't really use a base flashing). The homeowner says that under normal circumstances there's no leak around the chimney. However, when the rain blows out of the east the leak occurs. *My impression is that the rain is blowing beneath the step flashing at the gap between the step flashing and the brick veneer.*
> 
> quote]
> 
> ...


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## ttboy (Oct 18, 2007)

The cap appears to be intact best I can tell from a visual inspection. 

The drwall stains are at the sides of the chimney where the wall drywall joins the ceiling drywall. This area is located immediately beneath the chimney flashing which makes me suspect the flashing as the culprit.


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## ttboy (Oct 18, 2007)

Ed,

My thought is exactly like yours that the rain is blowing between the step flashing and brick veneer. Since the chimney protrudes slightly through the eave you can't put a base flashing around the chimney to seal the small gap.

What would do to try to seal this that would give long term results? I've never had this problem before and frankly haven't given it much consideration until now. Thanks again.


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## tinner666 (Nov 3, 2004)

I hadn't commented on the gap equation yet. Still puzzling over 'how/why/where exactly/ and huh'.


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## Ed the Roofer (Dec 12, 2006)

I would have installed the lower counter flashing on the bottom side of this chimney with a counterflashing first, and make sure the tabs get folded at least 3" past the 2 corners.

Then the side counter-flashings abd then the pan/cricket/saddle side.

If ther would be even a minor gap where the base apron CF intersects with the side CF's, then I would install either NP-1, Quad, or Vulkem to match the sheet metal color and seal the minor gap.

Wait! Actually I would install the sealant around the corner prioe to installing the side CF's, so that the sealant was embedded between the 2 seperate sheets of sheet metal and would not dry out from the UV and deteriorate.

Ed


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## tinner666 (Nov 3, 2004)

I like my lower corner pieces like this:









After the apron is on, I put a bit of sealant on the corner, then put these in. Sealant is protected from UV, and NO water coming down the side will hit the apex of the corner. Then counterflash.

I found out many years ago that tight, neat corners are in reality relying on the sealant as the first line of defense. My way, it's only a 'backup' plannin case of strong winds.


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## ttboy (Oct 18, 2007)

I greatly appreciate the input guys. I will get some pictures for you guys to take a look at tomorrow. The problem with this chimney location is that an apron cannot be used on the front because the chimney protrudes beyond the eave.


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## tinner666 (Nov 3, 2004)

OH. That step is not cut at that angle. It's folded. The fold will cover the sealant in the corner.


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## tinner666 (Nov 3, 2004)

Does the flashing extend past the corner of the brick? If it's cut flush, it could be directing water onto the brick. A simple extension could alleviate the issue. Just a thought.


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## Ed the Roofer (Dec 12, 2006)

In progress photos.

Ed


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## tinner666 (Nov 3, 2004)

"chimney protrudes beyond the eave." How much? Maybe the steps do stop a bit short. Please take several pics. Close-ups will be appreciated.


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## Ed the Roofer (Dec 12, 2006)

More.

Ed


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