Leak-Proof Flashing: Fixing Leaks Around Chimneys
Exterior, Repairs and Installation, Roofing 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.
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.