Flat Roof Scupper Drain Installation

In this video, I wanna show you how to properly install a scupper flashing on a torch down roof. Let’s get into it.

Intro & Explanation

A scupper is a piece of flashing that is bent in such a way to allow water to enter and exit through the parapet wall. A scupper generally allows water drainage for a large area of water, so it’s super important that we get the details done correctly. If you can imagine like a 1000 or a 2000 square foot roof might have just one scupper drain. That means if there’s one small hole on the scupper, if there’s one small failure, it can lead to huge leaks. The other reason that’s important to pay special attention to the scuppers is because we’re trying to bond a bitumen asphalt surface to a sheet metal surface, and that’s always difficult to do any time we have incompatible or different materials bonding together. So we wanna make sure that we take a few extra steps to make sure we get this critical area of the roof done correctly. There’s multiple different ways of doing this one area. The way we’ve developed with our manufacturer, I think, is a really solid and bulletproof way of doing it, and we have done other systems in the past, which has worked, but really, I think we’ve fined tuned it to a great place, and I wanna show you all those details today. Let’s get into it.

Install a Target Piece

The first step in the process is gonna be installing our target piece. Now, similar to our video on how to install drains, when we’re installing scuppers, what we wanna do is install the scupper first, then bring our field and burn on top of that. So we’re gonna be starting with our self-adhered base layer. This is Polyglass’ mid-ply. The way you wanna measure this is put your scupper down. You wanna make sure you have at least six inches past each side of your scupper here. So this is gonna be sufficient to get a good sandwich between your torch and your smooth mid-ply. And keeping half the field on, we’re gonna fold it back, remove the adhesive backing, and then slowly put this on, getting a nice tight corner there.

Now, you can see here, this is kind of what we’re trying to avoid. If we didn’t install this target patch, we would be installing our scupper on top of this joint, but we wanna make sure that we have a nice uniform finish, to have a nice smooth transition.

How to Prep Scupper For Installation

So we’ve got our base layer installed. This is probably the simplest step in the process. The next step is going to be install our scupper flashing. Any time we’re bonding an asphalt bitumen-based product to a metal, a sheet metal that’s galvanized, we wanna make sure that we prep that metal to ensure optimal adhesion because opposite materials don’t really like to bond together. Any time galvanized metal comes out of the factory, it’s coated with an oil and has some residue on it, which doesn’t allow for good bonding. So the first thing we wanna do is actually wash this off with some vinegar or metal etching solution. Let me show you how to do that. So in order to prep our scupper and actually any flashing for that matter, whether it’s low-rise pipe flashing, T-tops or scuppers, what we wanna do is first of all, scuff it up with an abrasive brush, and you can either do it by hand, and we like these cup… I don’t know what they’re called, but they’re essentially a bristle brush, and you just wanna give it a light scratch. Now we wanna do it on both sides.

You can see the reflectivity here as opposed to kind of the matte finish on the bottom. We wanna have that roughness in order to have a better adhesion between our torch and our flashing. Alright. So we’ve got the front done. Now, this doesn’t mean that we’re actually complete. What we wanna do is actually do the back. I’m gonna show you why later on, but we wanna prep the back, similar to what we did in the front.

Now we’ve got the back brushed up. Our last step in this prep work is actually to apply a vinegar solution. All this is is a regular white vinegar you can buy over the counter. You can also use a metal etching solution. Vinegar does the same exact thing. It’s organic, cheaper, easier to find, and it’s not as rough on your hand when you’re working with it all day. Make sure we have a decent coverage over the entire thing, and what this is gonna do is really eat away at those chemicals, the left over residue from the factory. So now that you’ve got the whole thing wet, you just wanna leave this.

You can either tap it dry or just put it to one side. We like to do all our metal prep work prior to starting the project, get all your metal flashing prepped, put it to one side and you’ll be ready to go. Now that our metal is dry, before we do anything else, what we wanna do is take these corners and round these off. What this is gonna do is it’s gonna give us a smoother transition between our torch and our metal, and what this will do is protect the torch down material throughout the years, preventing these corners to poke through the material itself. So that’s it. Again, you can see they’re all done a little bit differently, but the important thing is to take that sharp corner off. Now we’re ready to prime. Again, we’re gonna be using an asphalt primer. What this is gonna do is give it a coat of asphalt prior to us torching on top of it, which will ensure a good adhesion, and you wanna make sure you get that scuffing and that vinegar etching done before you do this. Again, you wanna make sure you get a nice solid coat similar to this, and we’re gonna be doing the front and the back. Alright. Now that we have this all primed, we’re gonna leave this to one side and let it dry before we start installing it.

Now, that we’ve got our flashing primed, etched and prepped, we’re ready to install it. Now, the reason we want to prep the back similar to what we do in the front is you can see this smooth actually has a film of torch down on it. So when we install this and this gets heated up, this is actually gonna melt and bond to the back of this flashing right here and create an amazing bond. So essentially what we’ll have is the back of this bonded, the front of it bonded, so that metal is sandwiched between two layers of asphalt torch down material, and we’ll get a real nice bond going.

What Type of Nails to Use When Installing Scuppers

What we wanna do is install it using round cap roofing nails. These nails are a little bit shorter for our demo, but we usually like to use inch and quarter nails. These are electro galvanized. You wanna make sure that you’re using the same material. So if your scupper flashing is galvanized, make sure your nails are also galvanized. And we’re gonna be installing nails every two to three inches on center. This may seem like a lot, but what it actually does, it prevents excessive expansion and contraction in the metal. Your metal’s gonna want to expand and contract faster than the asphalt material itself. So nailing it down every two to three inches is gonna prevent excessive expansion and contraction, and will ensure that those metals do not separate over time.

Now that we’re done nailing this, you can see that we installed it using a staggered pattern, every three inches, that way we’ll get a nice tight scupper going, and once we have a torch installed on top, we won’t have too much expansion.

Installing Torch Down Over the Scupper Drain Opening

We’re ready to start installing our first layer of torch down. So we’re gonna be doing this in two sections. The first one’s gonna be installed on the roof base, going up the parapet wall. The second one will be coming down the parapet wall, covering this and coming down on the roof field. Similar to any time we install the roofing along our parapets, our base layer is gonna be coming up past this cant strip, about two to three inches, then the layer on top will be coming down. So we’re gonna be using the same pattern here while installing the scupper.

Now that we’ve got this back half torch down already, what we wanna do is cut this opening for our scupper before we torch this side on. You don’t need to worry about keeping this top strip because when we install our torch down from the top, it’s gonna be covering this area and coming down onto our roof. Anytime you’re torching, like I always say, it’s just as much of an art as it is a science. You can watch our other videos on how to properly heat up the membrane. You wanna make sure you don’t overheat it or under heat it. You have to get it hot to the correct temperature to make sure you have good adhesion and at the same time you’re not damaging or burning through the membrane.

All right. So we’ve got our base installed on our roof. The next step is we’re gonna be installing our torch down cap sheet on top of our parapet wall and coming onto our field. We’ve marked out these areas, six inches past our cant strip. So this is how far we’re actually gonna be coming out.

So what we need to do right now is actually make what we call relief cuts. So we have a cant strip here and no cant strip here because scuppers come at a 90 degree angle, but the rest of our roof, we have this 45 degree angled cant strip that’s installed. We’re gonna be making relief cut in opposite directions in order to make this transition from this 45 down to this 90 degree angle, and while making sure that we’re still waterproof. So this is a trickier transition. Again, just make sure your cuts are opposite. So if you’ve got one cut at the bottom, the other cut needs to be on the top so that they overlap properly.

Alright. So we’ve got our relief cuts made here for our cant strip transitions. We also have our cut made for the scupper. What we like to do is cut it at a 45-degree angle, roughly. This allows proper water drainage here and stops water from building up back here. You can imagine if we didn’t cut this out, water would kinda pull right here and would create a lip. We don’t wanna do that. We wanna create a clear path for the water to flow. So this is gonna be cut at a 45-degree angle. Now, in reality, this piece right here is not as important as you may think, because even if water were to get underneath here, it will be stopped right here. However, doing this gives us a solid bullet-proof way of roofing where we’re not only relying on one layer of roofing, but we have multiple layers in our most vulnerable area of our roof, giving us double, triple protection where it really counts. Let’s start torching.

Finish It Off With PolyFlash 1C

The last step in the process to finish our scupper off, being that this is a very vulnerable area, there’s a lot of water traveling here and we’re doing a lot of repairs throughout the years, we’ve realized that scuppers tend to leak the most. We do one last step to really ensure that this area does not leak for years to come. That’s applying a coat of PolyFlash 1C. This is a Polyglass product, and we’ve found great success using it. So we’re gonna be using PolyFlash 1C coupled with a layer of polyester mesh. So we wanna first measure off our polyester about three inches bigger on each side than the scupper opening itself. So we like to cut it at a 45-degree angle, so that way, when we do install it, it will look something like this, and we’re protecting this corner. So we’ve got this cut, prepped, ready to go. What we wanna do is apply a base layer first, embed this on top, then apply a second coat of the PolyFlash 1C on top of that.

So now that we’ve got our first layer of PolyFlash 1C applied, what we wanna do is install a polyester mesh. We found the easiest way to do so is using plastic gloves and just setting this in with your hand to align it properly. Now that we’ve got this set, we just wanna apply another light coat of PolyFlash 1C on top of that and call it a day. Now that we’ve got PolyFlash 1C applied and embedded in the polyester, this is a detail and flashing that’s gonna last for years to come. Thanks for watching, tune in to the next one.