How to Install Chimney Flashing

In this video I’m gonna show you how to properly install flashing around your chimney. Chimneys tend to be one of those places that leak a lot. We’re the Roof Repair Specialist, and we repair a lot of chimneys. So if done properly, chimney flashings should last for years. Pretty much as long as your roof lasts, the flashing should last just as long. You should not be relying on asphalt, mastic, sealants to keep your roof waterproof. You should be relying on proper flashing. I’m gonna show you the steps how to do that.

Now in this demo we’ve got a mock chimney build. We don’t have a chimney wall up but it’s the same concept. Just imagine this wall going straight up. The flashing’s gonna be the same. We’re just working here because it’s easier to show you and video the process. Let’s get into it.


Now, we’ve already got our shingle installed all the way up to this wall right here. We install our shingles all the way up, and whether it’s perfectly flush or we’ve got two inches that needs to be covered, our metal here will cover this up.
So we call this a 110 metal. It’s bent prefabricated to 110 degrees from the factory. This side is four inches and the step up is two inches. So this is gonna be installed right here. Now, we’ve got a little bit of fabrication to do at these corners ’cause really the corners are what matters and that’s where we have to pay special attention to. So we wanna push this snug up, and Marco’s gonna demonstrate on how to properly cut it and where to make our markings. So he’s actually using his tin snips right now to make a line at a 45-degree angle. Now, you can see here, this flange will get bent down and this flange will slide over to the side. And this is the basic theory of it.

Another thing we like to do as always is round these corners off and bend these in, and we wanna do that on both sides. Now, for this demonstration, we’ve got a piece of flashing that’s prefabricated. This is the same 110 metal, 4 inches and 2 inches, that’s precut. You can see here, the corners are rounded, all that’s left to do is to bend this flashing nice and tight to this corner, and we’re gonna do the same thing on this side. So that’s pretty much it. This is our 110 metal installed. The next thing is gonna be to install step flashing here on this side.


Alright, now that we have our headwall flashing installed, the next thing to do is to install our step flashing going up the side. Step flashing is essentially a piece of flashing bent to a 90-degree angle and we actually install one piece of step flashing then install a shingle, and this steps up like so. What we use to make step flashing is actually what we call tin shingles. These are just essentially 8-inch by 12-inch square pieces of metal. They come pre-painted as well as just galvanized. Now, generally, we like to go with the pre-painted step flashing just to match the roof as close as possible. So you can see we’ve got like a darker gray charcoal color roof we’re installing, so we’re installing a dark gray roof. These are pretty easy to bend by hand and don’t need to be a perfect bend ’cause this is gonna be all covered up. So we’ll mark this here, and that’s all you need to do. And now you’re ready to start installing.

Now, the first piece of tin shingle we wanna fabricate slightly to improve our flow of water. What you wanna do is bring it down to this point right here, past the shingle’s nailing tab. Then what we wanna do is make a mark like this. And actually, you wanna cut this down, and I’ll show you the purpose of this shortly here. And as always, we always wanna round off these corners here. Just for aesthetics and safety purposes, just round it off slightly. Now, the purpose of this is when we install it, it’s actually gonna help the water flow down as we don’t want water to get into this corner here, ’cause this is our vulnerable corner right here. So when we install this first piece, we’re gonna install some adhesive back here, some caulking. Install this and any water flowing down here is gonna catch this lip and flow down onto our shingle roof. So this corner is what we really wanna protect with some adhesive caulking. You can see what’s gonna happen now as we press this down. This joint is fully sealed. So any water that tries to get in here is not gonna be able to. And I’m gonna lift this up. Generally, we wouldn’t lift it up. You can see that that corner is fully sealed now.

So we’ve got our first shingle, tin shingle. Now, we can install our first shingle up to it. We wanna make sure that it’s aligned here. And we wanna leave a slight gap between the shingle and the step flashing to allow for drainage in this area right here. Now, the only difference is, similar to what we did around our pipe flashings– if you haven’t seen that video, you can refer to that– around any penetration, we don’t wanna nail right here, and you’ll see why shortly. When we install our next tin shingle step flashing, we wanna make sure that this corner right here is not vulnerable. So when we install this, this is gonna allow the water to flow on top of here and will also hold the shingle down.

So that’s it. Essentially, with each layer of shingle, we install a new piece of step flashing. We’ve installed our step flashing and shingles all the way up, and now, we’re at the back wall. We wanna cut this and bend it over. Similar to the bottom, we wanna make sure we have a good joint and good flashing between here and this back wall right here. So let’s make a slight notch here. And then fold it over. So you can see here is what we came up with. Now this is going to be the first piece. We’re gonna install one more to make sure we have a greater overlap. So we’ve already installed this. As I mentioned there’s a small overlap here, just an inch. We want to install one more piece to provide more protection, especially in this corner right here. So what we’re gonna do is since we already have this, we’re gonna overlap this about two inches. I’m gonna mark my corner right here. And what I’m gonna do is starting here.

So all I did was make a 45 degree cut from right here to this corner. Now what that allows me to do is bend this top here, and bend the bottom here. When I install adhesive at this corner then install my saddle on top, it’s gonna provide for great protection in this area right here. So that’s our last piece of step flashing. What we’re gonna do is install one more shingle right here, then we’ll show you how to install the saddle right here.

So we’ve finished the step flashing on this side. You can see we’ve got our shingles, we’ve got our step flashing. We still need to install a piece of counter flashing on top of this. Now one thing I wanna show you in the meanwhile is how water acts when we’re pouring it down here. So during a rain what’s gonna happen is as water comes along here, it’s gonna constantly come off, roll off each one, so it has no chance of getting underneath each shingle. That’s exactly what we wanna see. And you can also see here that this lip helps water not come here. My fingers here are completely dry. So that’s the reason we install step flashing here, as opposed to a long piece of L metal, is to allow the water to constantly come off here and step onto the shingle below it.


So we’ve installed our step flashing on each side. We’ve installed our 110 metal roof to wall connection on this side. Now we’re gonna go to the topside and install our saddle flashing here. I’ll show you how to fabricate it, install it, and how to caulk the corners to make sure we’re properly waterproofed. So we’ve precut our saddle flashing. We want it to stick out four inches from each side, from each end of the wall. And what we’re gonna do is mark this back right here. So what we did here is just drew a mark, and what that’s going to allow us to do is to cut and fabricate based off this end right here.

Anytime when you’re working with sheet metal, make sure to wear gloves. For this demonstration, I’m not, but these can be razor sharp corners, so be careful. As always we wanna round off these corners right here both for aesthetics and for safety. So you can see we’ve already cut this down to size. These corners here are flush.
We’ve got this wrapped around. What these channels are gonna allow us to do is it will help divert the water around it. So the majority of the water is actually gonna go around and stay away from this corner. We want to protect this corner as much as possible. So prior to installing this, we’re gonna apply a nice heavy bead of adhesive caulking. And we actually want to come up this wall here. So we can see here what this adhesive has done is fully seal this corner. So as we’re pressing it in, that’s coming out the sides. If you want, you can give it a quick wipe. And that’s going to make sure that no water ever gets in there. So you can see what Marco did was not install any nails here. We wanna make sure this area is free of nails because as the water comes down, it’s gonna be diverted. We don’t want any nails to have nail holes to allow the water to get through.

Alright, now that we’ve installed the saddle flashing, we are ready to install the rest of the flashings. As I’ve mentioned in our video before on how to properly install shingles, it’s gonna be the same nailing pattern just right on top here. We’re gonna line it with this shingle here. So we’ve installed our shingles and we’re all set to go. You can see our saddle is four inches up and actually goes 14 inches high. So what that means is, underneath here, we’ve got full solid flashing that has no nail holes. So we’re not worried about this joint. Literally, we can have this open. It still wouldn’t leak because we’ve got solid flashing here. Now, keep in mind, if your penetrations are wider than 30 inches, you’re gonna wanna put a cricket. And we’ll discuss that in a different video on how to install a cricket. But in our case, we’re under 30 inches, so we’re not installing a cricket. Another thing I want to note is the gap between the saddle and the shingles. Whenever possible, you want to leave a little bit of a channel here to allow water to flow. If we had our shingles butted up all the way, it would prohibit the proper water flow. So now in this case, we’ve got 3-4 inches exposed. It’s gonna allow our water to go around and properly drain.