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Leak-Proof Flashing: Fixing Leaks Around Chimneys
By: Danny Lipford 
My firm gets more calls about leaks around chimneys than about any other problem. And more often than not, the culprit is the flashing — the sheet metal that keeps the intersection between the chimney and roof watertight. When water gets behind faulty flashing, it can do a lot of damage to the roof sheathing and framing and to the ceiling below, so you need to deal with this problem immediately.
Proper flashing around a chimney includes two layers. The first is called step flashing: Sections of L-shaped sheet metal are woven into the shingle courses and lapped up the side of the chimney. Next comes the counterflashing: A second layer of metal is embedded in the chimney mortar joints and folded down to cover the top of the step flashing.
The corners are especially vulnerable. We cut and bend the metal around the corner. Even in a quality installation, this leaves one small spot that should be sealed with a high-quality urethane caulk. This caulk can work itself loose over time. If the flashing looks to be in good condition, recaulking should take care of the problem. However, caulk is not a substitute for properly overlapped flashing materials.
The type of metal used for flashing depends on where you live. Aluminum and galvanized steel are the usual choices in the South where I live. Copper is the longest-lived, but because it’s expensive, we see it only on high-end jobs here. Another advantage to copper is that the corners can be soldered for a watertight connection. In the Northeast, masons are partial to lead flashing, which is soft and easy to bend to shape. But no matter which material is used, it must be layered correctly if water is to be kept out.
When the chimney is at the bottom of a roof slope, we always install a cricket, a small diversion roof that prevents water from pounding the up-roof part of the chimney. We frame and sheathe crickets just like the rest of the roof, and then completely cover them with a modified bitumen membrane, which is folded up under the chimney flashing. We install asphalt shingles over the membrane to blend the cricket with the rest of the roof.
Because chimneys are such a potential trouble spot, inspect them once every year or two for loose or missing flashing and cracks in the masonry. Small cracks can be sealed with caulk designed to repair masonry. I also recommend that my customers waterproof their brick chimneys every few years with a silicone-based sealer that can be applied with a garden sprayer. Not all builders agree, but this is a great way to keep water from seeping into the brick.
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28 Comments on “Leak-Proof Flashing: Fixing Leaks Around Chimneys”
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June 30th, 2007 at 9:56 pm
Can you show pictures of how to build a cricket or is there already a place to find one that shows it. Thanks
Nicholas Roussos Says:July 2nd, 2007 at 10:31 am
I don’t have anything readily available, but I did find this rather brief how to build a chimney cricket (scroll down to chimney section).
August 5th, 2008 at 3:38 pm
I have noticed water coming in around the chimney (the house is only 6yrs old), but I don,t want to use any products which will look unsightly. I have a (forest green)roof and if possible, I would like to know if there is any product which is transparent, or green which will help with the water leak. Thank You.
August 24th, 2008 at 9:16 am
I had a new roof put on about two years ago. I noticed the last time it rained, it started dripping inside the chimney (between the rock facing in the house and the opening of the fireplace. Today it rained again and it is leaking down the front of the rockface. What could be causing this? How do I fix it?
August 26th, 2008 at 11:06 am
I also like Wmberly on your comment page had my roof done 2 years ago. The tiles were put on October and by December I had water come down like there was (is!) a hole on the roof; $30,000.00 later! The roofer did not respond to our call. We then hired a chimney person to replace the cap & put a marine seal (10 year warranty). I called him when I had the fireplace full of water and his reply to me was “And what do you want me to do? Are you asking me to re-visit the job?”. Well, he never showed up either. I home with pots gathering water. Can you recomend someone in the south Florida area that knows what they are doing?
P.S. I had replaced the ceiling & wall sheetrock, redone the popcorn ceiling, wallpaper & more…it’s ALL going to waste.
September 2nd, 2008 at 12:00 am
Roofer installed new roof 4 yrs ago . Aluminum flashing is perforating away . Chimney is cultured stone with lots of morter showing. He will replace with product of my choice . What are my options on products, price and life span.I think he is expecting me to pay for materials.What are your thoughts I have a written 5 yr warranty.
October 27th, 2008 at 1:48 pm
I have a rocked chimney and wanted to know of flashing options for this. The one installed looks horrible, and was told it had to be like that because it is rocked not bricked.
May 6th, 2009 at 11:23 am
Emily, did you ever receive any advice on flashing around your rocked chimney? I have one as well and I am getting ready to re-shingle.
July 31st, 2009 at 8:26 am
We’re 3 years now working on this problem around the chimney. 2 roofers have tried to fix the leak to no avail. We have installed a ventless gas thing in the fireplace so I’m considering just wacking the chimney off. Any concerns with that?
Ben Erickson Says:August 4th, 2009 at 10:00 am
Hi Julie,
If your fireplace insert is a true ventless model that isn’t using the chimney to remove combustion gases, and nothing else vents into the chimney, you should be able to take it down below the roof and roof over it. You might want to check the building codes in your area first to see if there are any concerns. You can find out more about ventless fireplaces in our Family Room Addition: The “Hunt” for More Room episode and article.
October 30th, 2009 at 12:32 am
I have noticed water coming in around the chimney and leaking into my attic. We currently will be installing a new roof. To be specific, we hired a contractor who will be removing the old shingles and tar paper and installing new shingles and what ever else is required. Is this sufficient, or is this a far more serious problem than that? What should we have the contractor do? or rather ask of the contractor?
December 5th, 2009 at 12:32 pm
I am now in the process of rocking my chimney, but it has rained, and I can see where the cender blocks are wet in spots and at the bottom (floor)traces of water is seen. Is this from the chimney liner?, or what? What can be done to fix this problem? This chimney is of age.
March 14th, 2010 at 12:59 pm
I have water dripping from under the fireplace lentle onto the hearth.Do to the size of the fireplace it sits on a slab outside of the building with only a small portion coming through the outside wall into the house. The chimney has a liner,but was constructed out of cinder block and then painted.When the chimney was constucted,the portion against the outside wall lays against T-11 paneling. Only part of the chimney goes through the roof and a cricket was installed in this area. Step flashing was installed.Flashing appears to be OK, do you feel that the water may be penetrating through the cinder block and finding its wat to the area above the lentle and dripping onto the hearth and this is where the leak is coming from ?
August 5th, 2010 at 2:15 pm
I have a cricket against a chimney. The house is only used in the summer. Every spring the plaster has to be repaired near hearth (interior). Water appears to be getting in somewhere. House has a new roof. Please advise. CHEERS!!!!!!
August 24th, 2010 at 9:27 am
I have a leaky flashing. It was caulked and resealed about a year and a half ago. The sealant went over all of the (lead?) flashing and is made of a black tar-like material. This seemed to hold the leak for about 18 months, but now it is leaking into the house again. The company that sealed the flashing previously is planning to go over it again with a similar product. Do you recommend this course of action? How good are these “flashseal” products?
Ben Erickson Says:August 26th, 2010 at 10:16 am
Hi Lynda,
Roofing cement works well for sealing a small hole or minor gap in or around flashing, but if the flashing wasn’t installed correctly or has bigger problems, you’re better off fixing it rather than applying more roof cement every year or two. Good luck with your project!
September 8th, 2010 at 2:53 pm
I had a horrible leak a few weeks ago along the chimney line but I could not find any problem with the roof flashing. My house is about 60 years old and the chimney is made of concrete bricks. I noticed it was totally soaked with water after rain. After reading your advice, I waterproofed the brick chimney with a silicone-based sealer. (One gallon sealer. Applied in two layers.) Yesterday, it rained heavily all night but I did not have any leak. Thank you so much!!
Ben Erickson Says:September 9th, 2010 at 10:18 am
Hi Yuming,
Glad our article helped, and your chimney is no longer leaking!
April 18th, 2011 at 5:59 pm
We have a metal roof and THEN had a fireplace put in w/a stone chimney. The mason had not worked with metal roofs prior and did not admit this——we now have a leak at the chimney! We believe that he did not put in a long enough piece of flashing, he tried to do a “quick fix” w/caulking but it is already out. We have pictures of the leak when it is raining——-how should the flashing have been installed since the metal roof was already in place?
Thank you, we just want it fixed but neither the mason nor the builder wants to take the responsibility to fix it!
June 20th, 2011 at 9:12 am
Rain water runs down the inside of thin stone over cinder block chimney. I think a replacement masonary cap on chimney (not flue cap) would help. Old concret cap has chipped away. Would you please recommend a masonary product for a not very thick cap? Also is “Flex Seal” advertised on TV a good product?
August 12th, 2011 at 3:38 am
does theflue liner go on the inside of the up stand of the lead tray or out side
September 27th, 2011 at 3:10 pm
I have a question. I had a guy from a chimney company come out and he was here for 55 minutes. All he did was put flashing cement around all three vent pipes and around chimney. Then he charged me $650.00. He didnt replace anything. Did he rip me off?
October 17th, 2011 at 5:22 pm
I had a new roof 2008.
Before that ….no leaks for the 3 years I had lived here.
Since that..leaks around the chimney.
My contractor says…I need a new “hat” for the chimney and that will fix everything.
Is this true? The chimney is NOT used…decorative purposes only.
October 27th, 2011 at 8:23 am
My wife and I bought a 20 year old home last year and recently we had a chimney professional out to clean the chimney. While cleaning he indicated that a few things should be done and took some photos of the chimney to illustrate. The damper and grate was rusty so it seemed evident that rain had been getting in – some mortar in the firebox also needed repair due to water damage. In addition, he recommended a new crown (old was cracked) and flue liner. He also recommended a roofer redo the flashing and some overhanging limbs be removed.
We had all of this work done and then we had heavy rains for a few days. At that point I noticed that there was rain leaking into the firebox. It only appears to be leaking down the inside front and dripping onto floor of firebox.
I had the chimney guy come back out and put a new cap on and remove the old damper. I also asked him to look at the flashing that the roofer had done – he said it looked OK. It rained again and we still had the same problem.
So I had the roofer come back out to inspect his own work and also the work of the chimney guy to see if there was anything that looked like a problem. He indicated that everything looked fine.
It rained again last night and of course it is still leaking. So now the roofer and the chimney guy stand by their own work and claim that it is something that the other person did or did not do correctly. I don’t want to pay a 3rd person to come out and look at it. I just want it fixed.
By process of elimination I would like to determine what the most likely cause of the problem is so that the correct person fixes it. How likely is bad flashing to cause a leak inside of the firebox? It seems more likely that it is a chimney issue.
This is really frustrating.
November 10th, 2011 at 6:12 pm
My wife have a 2 year old house with a boxed in flue prmnetrating the roof. The exposed portion of the chimney is wrapped with brick. This brick starts just below the roof line. The builder attempted to fix this problem several times and even went so far as removing the brick and attempting to install flashing and drainage but with recent heavy rains there were numerous places where water was leaking in and saturating wood, the foam insulation and the ceiling below. The builder wants to spray waterproffing on the bricks and is assuring me that it will take care of the problem. What do you think?
I was hoping that you might have a detail showing the proper techniques addressing flashing / waterproofing / drainage associated with brick chimneys passing through the roof. The brick façade on the chimney starts just below the roofline except for the outside wall where it goes to the ground. I am trying to find specific details that I can show my builder. I am of the impression that he should have designed in adequate drainage to move the water away from the inside of the bricks to the outside. Everything I have read indicates that gravity and proper overlapping of impenetrable materials should take care of this and that coating the bricks with weatherproofing sprays is NOT the solution.
March 20th, 2012 at 10:10 am
I have a ventless fireplace. Water is coming in underneath the fireplace were the ignite button is. It also starts leaking at the bottom of the mantle on both sides.
We are totally dumb founder on how its coming in. Any ideas?
April 4th, 2012 at 2:13 pm
During rainstorms, we had a continuous drip around our stone fireplace which we could not locate. We did everything we could think of…mastic around the chimney, replaced flashing, etc, with no success. Finally we called the man who replaced the roof five years ago. He arrived with a bucket of sealer and a paint brush. He explained that sometimes with older stone chimneys, the cement grouting becomes old with time and seeps. He brushed the sealer on the whole chimney, and presto…no more leak problems!
April 30th, 2012 at 6:16 pm
Water drips directly below our fireplace (onto the basement floor) during a rainstorm. There is no visibile rain actually coming into the fireplace but leaks directly under it??? The roof (and flashing) were replaced six months ago and I just had a new chimney cap installed 2 weeks ago. In addition to that we had sealant brushed onto the chimney. Still leaking. Any ideas???