How to Fix a Leaking Chimney: Pro’s Guide

How to Fix a Leaking Chimney: Pro’s Guide

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How to Fix a Leaking Chimney: Pro’s Guide

how to fix a leaking chimney

So you have a pesky roof leak, and it’s coming from your chimney. Try not to stress it because this can be fixed pretty quickly by a professional roofing company or yourself if you have what it takes to climb up onto your roof (although I don’t suggest that). 

A chimney leak on an asphalt shingle roof is pretty common. I’d say it’s number 2 on the list of most common places for a roof leak, right after a vent pipe boot. Below I’ve listed a few reasons your chimney could be leaking and how to properly repair it. 

Bad Counter Flashing

The chimney’s counter flashing must be done right, or it will leak. Either it will leak right away, or it will leak years down the road, but we know for sure it’s going to leak. The main problem I’ve seen throughout the years of doing roofing repairs is that the counter flashing simply isn’t installed correctly.  

The proper way to do it is to grind into the chimney about a quarter-inch and slide a piece of custom bent counter flashing into the grind. Most of the time, roofers will just nail a piece of flat metal to the chimney, caulk it, and pray it doesn’t leak before collecting the check from their customer. That’s obviously not how to do things.   

Steps for Fixing Counter Flashing

I like using a battery-powered DeWalt grinder, so I don’t have to worry about an extension cord reaching two stories up in the air on an extensive roof or what if the home is older and doesn’t have an outside power outlet. 

Step 1: I bend my new counter flashing out of aluminum stock coil. We usually match the fascia color with whatever color we will use for the counter flashing. 

Step 2: Once I have it bent, I head up to the roof with my clear silicone, pencil, caulk gun, hand brake, battery-powered air blower, hammer, and tin snips. Notice I didn’t mention nails; you should NEVER have to use nails when installing chimney counter flashing properly! 

Step 3: Once I’m up on the roof, I take my already bent piece of counter flashing and hold it up against the chimney, I mark a cut line with my pencil, move the bent metal out of the way, and I start grinding. I want to grind about ¾ of an inch into the chimney making sure I have an even grind all the way down. 

Step 4: Once that is done, I check to make sure my metal fits in nice and snug. If it does, I remove it and blow out all of the excess dust to make sure the area is as clean as possible. 

Step 5: Take my caulk gun and I run a bead of clear silicone into the grind and slide the pre-bent metal back into the grind. The silicone will dry over time and act as a glue. 

Step 6: Clean it off with a cloth, and I’m done with that side of the chimney. You want to use that hand brake I mentioned before to go around the chimney corners. When tracing your piece to cut on the chimney, give yourself an extra inch or two and bend that around each corner. 

Note: Start at the bottom and work your way to the top. Remember, what runs downhill, or down roof in this case!

Below is a diagram to show you kind of what I mean:


Chimney Cricket

A lot of the leaks we see are from the chimney not having a cricket behind it. The picture below shows what a chimney cricket looks like. 

chimney cricket

Now, not all chimneys need a chimney cricket. The ones that need one are when they are set in the middle of the roof. Most chimneys are on the side of a roof or at the very top; those don’t need one.  

They do need it because water and snow cause significant problems when the water has nowhere to go. If snow and ice are sitting back there, they eventually leak then re-freeze at night, causing big problems. The water needs to be directed away from the back of the chimney. Most of the time when we see this it’s already too late.  

When removing the old shingles we find that the wood is more than likely rotted away and it’s a big mess.  Sometimes the rafters have some rot too. So having a cricket installed on your chimney is pretty important and you should do it asap, don’t wait until it’s time to do the entire new roof.  

Steps for Fixing Chimney Crickets

Well, this kind of plays into the chimney counter flashing as we talked about before. If you’re doing a new cricket then you’re 100% of the time doing new counter flashing as well. The way to build it is pretty simple.

Tools Required: 

You just need a tape measure, a 2×4, 1 sheet of plywood, pencil,  speed square,  a circular saw, hammer, and nails.  Or you could do a drill and screws. 

Step 1: You first want to build the “ridge” piece by measure from the chimney over to the roof.  I’d say go up about 6 to 8 inches, depending on how steep the roof is. 

Step 2: Cut your 2×4 at the angle of the roof pitch. You can find your roof pitch angle by using your speed square. Side note, teaching someone how to read a speed square needs to be an entirely different lesson on its own. Let’s just assume you know how to read one. 

Step 3: The next step is to install that 2×4 ridge piece, make sure it’s directly in the center of the chimney.  

Step 4: Next step is to cut the plywood. Use your tape measure to measure from the ridge down to the edge of the chimney and from the chimney to the end of your ridge piece.  

Step 5: Once you’re done cutting, it should look like a weird triangle. Install that with nails or screws, whichever is easier for you. After that, you’re done! 

Note: You’ll need to install some ice and water shield and once you shingle and step flash it you’ll need to install counter flashing.  

Still can’t figure it out? Well, those two reasons above are the most common but most expensive ways to fix your chimney. They’re the most expensive because they’re the proper way to do it, but there are cheaper avenues to explore before spending the big bucks.  

  1. Grad some silicone and a caulk gun and head up to your chimney. Spread the silicone all over the corners and tops of the existing counter flashing. I recommend using silicone because it’s much easier to spread. If you use a window or bath caulking, that stuff gets messy and sticks to your fingers. With silicone, all you have to do is use the tip of your finger, and you can spread it easily. 
  2. There are products out there that you can use to coat your chimney. There are many different products you can get at Home Depot or Lowe’s that say they can seal up your chimney. Go ahead and give them a try, but please don’t use roof cement! It creates bigger problems in the long run. In my opinion and from experience, it just traps moisture and creates a big mess and more damage than it saves. 
  3. If you get to your chimney and notice that the existing counter flashing is loose, just tape it back in with a hammer and seal it up with silicone. 

Those three things won’t last long, but they will help you in the short term so you can prepare for a chimney repair or a new roof. Make sure that the roofers install a new chimney counter flashing every time if you’re getting a new roof!  

Why have a new roof with some old counter flashing? 

I hope my tips help save you some time and money and remember, it’s always best to leave this stuff to the professionals.  Plenty of local professional roofing contractors are happy to help and make sure you have a roof that will protect your home for years to come. 

steve dreamworx

Steve Snyder
"It is our goal to treat your project as if it were our own home with unmatched workmanship and communication" -Dreamworx COO and Co-Owner, Steve Snyder

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