How to Cut and Fold an End Dam for Drip Caps

In this short how-to video, Dave from Northview Carpentry walks through how to cut and fold an end dam for a drip cap—the metal flashing that goes above a window or door. He covers measuring the opening, marking and cutting the end dam, pre-bending on a 45-degree line, clamping and folding the tab, closing the dam with vice grips, and finishing the sharp corner with a hem. It's a practical, hands-on tutorial for anyone doing exterior trim or window flashing work.

TRANSCRIPT:

Hey folks, I wanted to give you a rundown of how to cut an end dam for the end of a drip cap—the drip cap that goes above your window or door. You can see how this end dam looks here, and we're going to replicate that.

Measuring and marking

The first thing we need to do is measure our opening where the drip cap is going to go. We need to measure from outside of trim to outside of trim, or from wherever we want the drip cap to terminate. After we do that, we're going to add an extra inch on both sides of the drip cap, and that's going to give us the height we need for the end dam.

So here I'm going to come in one inch and mark it there, and mark it here. Now I'm going to square this up across the bottom, and then connect the dots between these two points. You're not going to be able to see me draw this very well, but I'll show you the end result.

Cutting the 45-degree corner

You can see I drew a 45-degree corner going up there. The idea is that this is where the bend is going to be—that's how we're going to make it fold around the corner. What I need to do first is trim off the very end of the drip cap—the actual drip part—and nip that off entirely.

Pre-bending and folding the end dam

Now we're going to grab our vice grips and pre-bend on that 45-degree line, just to give it a little direction for where we want it to go. I'm just giving it a little crimp so that it's already starting to bend on that line.

Now we can come down to our one-inch mark, which is the height of the end dam. We clamp down on that, and when we bend up, it will fold right on that line. You can see how it folded on that line there.

Closing and finishing the end dam

Right now the end dam is pretty open—you can see it's not very tight. What we can do is grab our vice grips and pinch that closed to help prevent any water from backing up in there. You could also grab a hammer, lay it flat on the table, and tap that in.

One thing to notice is that this end dam is quite sharp at the very tip. You could just take scissors and nip that off, or you could crimp it as well. What we can do is called a hem—take your vice grips, grab the corner, and bend it over. You can see I've got it started there, and then we can finish that off. Now that corner is much less sharp to the touch, and because it's doubled up, it's also more robust.

I hope you guys find this helpful.